On the vegetation of former river beds in the Netherlands

Transcription

1 On the vegetation of former river beds in the Netherlands J van onselaar (Botanical useum and Herbarium Utrecht) (in collaboration with G Kop and E E van der oo) (R0N-Communication nr 9) (received January 6th 96) CONTENTS ntroduction 3 The former river beds as habitatsfor plants Some important aspects of the larger rivers Water household 2 Alluvial and marine deposits 6 3 Chlorine content 7 2 evelopment and properties of the former river beds 7 2 Upper course ower course 8 ethods 9 Survey of the habitat 9 Age and development 9 2 Water household 9 3 Chemical factors 9 Soil type 0 2 Survey ofthe vegetation 0 3 etermination of the relations between plant communities and habitats Classification of the former river beds The PANT COUNTES Cl ittorelletea 2 Ord ittorelletalia 2 All ittorellionuniflorae 2 Eleocharetum multicaulis 2 2 Cl Potametea 2 2 Ord Potametalia 2 2 All Potamion eurosibiricum 2 2 Potametum lucentis yriophylleto-nupharetum 2 3 Polygoneto-Nymphoidetum 2 Hydrochareto-Stratiotetum 20 2 Community of Ranunculus circinatus and Elodea canadensis egetations in oligo- to mesohalinic water 22 3 Cl Phragmitetea 22 3 Ord Phragmitetalia 22 3 All Glycerieto-Sparganion 23 3 Sparganieto-Glycerietum fluitantis of the Community tidal area 26

2 2 J AN ONSEAAR 3 2 All Phragmition Scirpeto-Phragmitetum medio-europaeum Cicuteto-Caricetumpseudocyperus Scirpetum triquetri et maritimi All agnocaricionelatae Caricetum elatae Caricetum acutiformo-paniculatae Caricetum gracilis-vesicariae Comparison between various subdivisions that have been proposed for the agnocaricion Thelypterideto-Phragmitetum 9 Cl olinieto-arrhenatheretea 0 Ord olinietalia coeruleae 0 All Filipendulo-Petasition 0 alerianeto-filipenduletum 2 Association of Sonchus paluster 6 3 Community of Epilobium hirsutum and Phalaris arundinacea 7 Phragmites-consociation 9 Wet meadow vegetations 9 6 Cl Scheuchzerio-Caricetea fuscae 62 6 Ord Caricetalia fuscae 63 6 All Caricion fuscae 63 6 Caricetum lasiocarpae Caricetum canescentis-fuscae Juncetum acutiflori 68 7 Cl Oxycocco-Sphagnetea 69 7 Ord Ericeto-Sphagnetalia 69 7 All Sphagnion europaeum 69 8 Carrs 69 The typesof former river beds andtheir distribution 69 Characterization of the types 69 Type Zwart Water 70 2 Type eerlo 7 3 Type Spui 72 Type Tuil 72 a Subtype Tuil 73 b Subtype Ossermeer 73 Type Hurwenen 7 6 Type Kekerdom 7 6 a Subtype Kekerdom 7 6 b Subtype Zandkolk 7 6 c Subtype Bovenstrang 7 7 Type Krook 7 8 Type Bloemstrang 7 2 istribution of the types 76 Summary 77 ist of former river beds includedin this study 78 References 8

3 EGETATON OF FORER RER BES 3 NTROUCTON A considerable part of the Netherlands consists of the deltas formed by the great rivers euse and Rhine and by some smaller ones These rivers played an important part in the geological evolution of the country uring the whole of the Quaternary period oxbow lakes and other types of former river beds came into existence Originally they resulted from spontaneous diversions of the streams later on mainly from artificial cut-offs n this paper every expanse of water which once formed part of the summer bed of a river but which now at least in summer no longer functions as such is considered to be a former river bed Up till 9 little attention has been given to the scientific investigation of these former river beds Of course their presence is mentioned in handbooks of geology geography and soil science (eg Faber 97/8; Schuiling cs 93; Edelman 90 a and b) but only a few papers enter into details (Boissevain 9; Pannekoek van Rheden 92; Hoeksema 97) The flora and the vegetation of the former river beds in the Netherlands have been never systematically investigated oreattention than to other aspects has been given to hydrobiological problems ery valuable is an investigation of the planctonic organisms by eentvaar (9 9 97) Boer (92) is the only author who gives some information with regard to the communities formed by the higher plants There is very little literature on the vegetation that is found in former river beds occurring outside the Netherlands but comparable with ours on itis (939) classifies and denominates on purely geographical grounds the Altwasser (former beds) of the river anube For the rest here too hydrobiological papers dominate (eg on itis ; Grohs 93) Some information with regard to the communities of higher plants can be found in papers by auterborn (96-98 Rhine inswitzerland and Germany) Oberdorfer (97 Rhine in S Germany) Allorge (922 Seine in and France) Koch (926 inth in Switzerland) This publication deals with the plant communities of the former river beds and their habitats except the carrs ie the humid woods consisting of small trees such as willows and alders r G Kop (96) wrote a paper on the carrs and as the latter are here left out of consideration it may be regarded as supplementary to this one W A E van onselaar-ten Bokkel Huinink (96) gave special attention to the ecology of some communities in a restricted number of former river beds and published her results separately an der oo published descriptions of some of the former river beds (96 a and b 97) Other papers are concerned with the ecology of some plant species (an der oo and Westhoff 96) with the importance of the work from the point of view of nature preservation and with the geological and geographical of the former river aspects beds (an onselaar 96 97a)

4 J AN ONSEAAR THE FORER RER BES AS HABTATS FOR PANTS (See Fig ) Origin and development of former river beds have been described comprehensively by anonselaar (97 a) Here it will be sufficient to mention the main lines ore attention will be given to those properties of the former river beds which may influence plant life now Fig Schema of a great river in the Netherlands with its former river beds and adjoining deposits

5 EGETATON OF FORER RER BES SOE PORTANT ASPECTS OF THE ARGER RERS Water household The larger rivers have a summer bed and a winter bed uring the greater part of the year the water is carried off by the summer bed As a rule it is bordered by small summer dikes The winter bed comprises the summer bed and the low grounds (forelands) on both sides of it Along the euse in the province of imburg and along some minor parts of the Rhine and the Jsel the bounderies of the winter bed are formed by the edge of higher grounds; for the rest the winter bed is enclosed by the heavy winter dikes Nearly every year either late in winter or early in spring floods inundate the forelands and thus bring the winter bed into function Apart from local factors (eg the height of the summer the dikes) frequency of the inundation of the foreland areas increases with the distance from the mouth of the river Near the utch frontier nearly every year inundation occurs whereas at a certain distance from the mouth the forelands are never inundated as a consequence of the annual floods ) There inundations result only infrequently and irregularly from the stowing of high water by storm (Edelman 90) A special feature of the rivers in winter is the drift of ice This simple picture completely fits for the Jsel which debouches in the tideless Jselmeer With the other rivers we must distinguish between an upper and a lower course The upper course shows the phenomena just described The lower or tidal course is influenced by the tide of the North Sea Here it is better to speak of a low tide bed and a high tide bed instead of the terms summer using bed and winter bed The amplitude of the tidal fluctuations in the river declines with the increase of the distance from the mouth The same relation holds for the width of the foreland strip which is inundated during high tide Here too at a certain distance from the mouth the amplitude becomes zero and this point nearly coincides with the point where the influence of the annual floods ends So the border line between the upper and the lower course is rather sharply marked the by effect of two different causes There are differences between the upper courses of the individual rivers Jsel that is to say of the euse the the Waal Rhine-ek and the The other river branches eg the erwede the Heusdense aas and the Oude aas only form their lower courses Since the comprihensive canalization of the euse ( ) this river hardly ever inundates its forelands (Pons 99) f an inundation occurs it lasts only for a very short period: by the opening of the sluices the surplus of water is immediately disposed of The forelands of the Jsel lie relatively high and consequently they are less frequently inundated than the forelands of the Rhine-ek and the Waal rl r J W Tops (afd Studiedienst van de irectie Bovenrivieren van de Rijkswaterstaat) kindly gave household this and other valuable information about the water

6 6 J AN ONSEAAR 2 Alluvial and marine deposits (see Edelman 90 a and b) uring the last part of the Pleistocene the alluvial deposits of the larger rivers consisted of river loam (rivierleem) ) Originally the properties of these soils will not have differed much from the younger river n clay the greater part of the river area the loams have been covered by clays but along the euse in the province of imburg outside the present winter bed the river loam is still found at the surface (Schelling 9; Pons 9 a) The soil type however has degenerated under the continuous influence of climatic factors t is now in contrast with the river clay soils poor in mineral nutrients All rivers are at least along their upper course bordered by forelands which consist of river-foreland clay (uiterwaardgronden) This clay is very fertile The soils inside the dikes which are no longer inundated are called river-levee soils (stroomruggronden) n the Netherlands till now no degeneration of these soils has been observed The river-foreland soils and the river-levee soils are calcareous except those of the euse up to Heerewaarden (Pons There 99) is no satisfactory explanation for this fact uring the Roman period the lower courses of the rivers crossed an extensive peat area By later incursions of the sea the lowermost part of the rivers obtained the character of estuaries and many islands were formed Part of the peat landscape was completely destroyed elsewhere the peat was covered with a layer of marine clay or silt The peat became soaked with sea water and ever after kept a high salt content n places where the clay cover is thin the soil is called salty peat soil with clay cover (poelgrond) completely under the marine deposits Where the peat disappeared we must make a distinction between the inner and the outer part of the flooded area viz deeper inland in fresh water the estuary silt-soils (gorsgronden) and nearer to the coast in brackish or salt water the marsh silt-soils (schorgronden) were deposited All areas consisting of these three soil types have been embanked long ago Against the dikes the sea deposited new washes which mostly were embanked later on thus adding new parts of marsh silt soil to the existing land area The soils from which the lower courses of the rivers are for the greater part separated by their dikes belong to these three types The forelands mainly consist of silty washes; those soils are not considered in the soil classification of Edelman The uppermost part of the lower courses however is bordered by soils of a different Here type they are the continuation of those found along the upper courses: inside the dikes river-levee soils outside the dikes river-foreland soils A *) soil map is added both to the utch and to the English edition of Edelman s handbook Some of the English soil-type names on this map differ from those used in the English text The names on the map are used here

7 EGETATON OF FORER RER BES 7 3 Chlorine content n the upper course the water is fresh n the lower courses the average chlorine content increases with the decrease of the distance from the mouth There is a freshwater a brackish and a saltish tidal zone (see an eeuwen 9) For a more precise classification the following scale of Redeke (932) will be used fresh water 0-00 mg Cl/ ( oligohalinic mg Cl/ brackish water < mesohalinic mg Cl/ ( polyhalinic mg Cl/ saltish water >7000 mg Cl/ 2 EEOPENT AN PROPERTES OF THE FORER RER BES 2 Upper course When under natural circumstances a river leaves a part of its bed whatever the cause may be the former river bed as a rule remains at one side in connection with the new summer bed (Fig : 2 and ; see also Pannekoek van Rheden 92) n this stage the water of the former river bed has for this reason many properties in common with that in the river itself Along the upper course this means that it is eutrophic and fresh with a Ph of 7 to 8 that it remains in motion during the greater part of the year and that it will flood the banks with a certain n frequency this the stage depth may be considerable t depends on the frequency and the durationof the flooding and on the force of the current during that time whether the former bed will remain open or will be silted up gradually Under natural conditions the high water of a lowland river floods a very extensive area and therefore the force of the current during the inundation period is only weak f there is a narrow bed naturally or as a result of dike building the force of the current will be much greater and consequently the silting up slower or even wholly lacking (on itis 939) n the Netherlands where the beds are relatively narrow an important factor influencing the speed ofthe silting up is the position of the former river bed with regard to the edge of the present winter bed n a former river bed which follows thebend of a dike during a period ofinundation only a sluggish stream or none at all will be found (Fig :2) whereas in a similar one parallel to the stream a strong current may be present (Fig : ) n every instance however the possible deposit of plant remains is inconsiderable in comparison with the deposit of alluvium n the next stage the former river bed has totally lost contact with the summer bed (Fig : 3 and ) This means that there is during the greater part of the year no movement in the water This may aid the silting up but for the rest all properties remain the same Under natural conditions the frequency of inundation in a certain place decreases with the progress of the silting up of its surroundings At last the high water does not reach the place any more and the former river bed if not completely silted up becomes a pool with

8 8 J AN ONSEAAR permanently stagnant water (Fig :; see on itis 939) This however may also result from a sudden diversion of the stream Anyhow the properties in this stage are quite different from those in the former two nundation and silting up have come to a stop Now the bottom is raised only by the accumulation of plant remains At first the whole environment (soil and water) remains eutrophic and slightly alkaline n the long run however the properties change The plants take up nutritive salts from their environment and when they die off part of these nutrients is deposited in the peat layer so that it is no longer available As long as a sufficient amount of new nutrients is supplied by the surrounding soil the only important change is a decrease in depth of the pool The surrounding soil however degenerates and the peat layer grows continuously thicker so that at last the vanished minerals can no longer be replaced Consequently the habitatbecomes mesotrophic or even oligotrophic and the alkalinity changes into a slight acidity (see Ruttner 92) ndeed in the Netherlands the former river beds in the river- loam soils along the euse are meso- to oligotrophic They are however no longer in their natural condition and that they still can be recognised in the landscape is due to the fact that the peat has been dug out by former generations (Schelling 9) n the river-clay area too there is a number ofisolated former river beds (Fig :6) The greater part of them came into existence as a result of dike building and is much younger than the just discussed group (see ibbits 90) As a rule peat formation has not advanced very far and the habitat is still eutrophic and slightly alkaline This is caused by the properties of the surrounding river-levee soil (see under 2) A fluctuation of the water level parallel to that in the river itself was found in some former river beds of this type along the anube (Grohs 93) and in a number of wash-outs (wielen) in the Netherlands (an Heusden 9) t will certainly be present also in the isolated former river beds tbat are situated in the vicinity of the dikes 22 ower course Along the upper part of the lower course too the first two stages mentioned under 22 are present (Fig : 7 and 8) However compared with these stages along the upper course and mutually their properties are rather different n the first stage there is a permanent tidal movement Though this has only a small it amplitude is sufficient to keep the former river bed in connection with the river and to prevent the development of peat f it happens to pass into the next stage the water becomes stagnant n both stages the water is fresh or slightly oligohalinic (up to 0 mg Cl/) and slightly alkaline Nearer to the mouth of the rivers former river beds still staying in the first stage are found in the washes (Fig : 9 and 3) They consist of long narrow stretches of water With every high tide the whole high tide bed is flooded with slightly oligohalinic water (up to about 30 mg Cl/)

9 J AN ONSEAAR: On the vegetation of former river beds in the Netherlands ap showing all former river beds included in this study

10 The EGETATON OF FORER RER BES 9 Since the floods mentioned great in 2 many of the new islands have been united by dikes to bigger ones and the latter have continually been enlarged by reclamation n this way quite a number of isolated former river beds came into existence all have They stagnant eutrophic water and a peat layer of a certain thickness There is some variety in the chlorine content of the water in accordance with the properties of the surrounding soil types: those in contact with the estuary silt soils have fresh water (Fig : 0) those in contact with the marsh silt-soils (Fig :) and the salty peat soils with clay cover (Fig : 2) have oligo- to mesohalinic water (20 to 2000 mg Cl/) ETHOS The former river beds were visited in the months ay up to and including August The investigators worked individually or in groups of two or three The examination of the greater part of the objects took one day SUREY OF THE HABTAT Age and development ata with regard to age and development of the individual objects were obtained mainly from the literature and from old maps The most important sources were the publications of Beekman (93-930) and Teixeira de attos (92) the map collections of the Topographical Service at elft and of the aarten van Rossumhuis at Zaltbommel 2 Water household At the day of our visit the actual water depth was measured wherever necessary and possible with a stone on a rope with an oar or with a similar device ata about low and high (tidal) water level were obtained mostly from indirect observations (eg drift line) from the literature or by information from inhabitants of the region The position of the former river bed with regard to the bounderies of the winter bed and the relations to the summer bed were observed directly in the field and studied on maps 3 Chemical factors The degree of acidity expressed of indicator paper (from erck) as Ph was measured with strips results of this rough method should not be compared with those obtained by means of more accurate methods of investigation They only have a relative value within the scope of the present investigation The chlorine content was measured with a simple but reliable field method A solution of silver nitrate was used for titration with potassium bichromate as indicator n order to obtain a general idea of the content of nutritive salts

11 0 J AN ONSEAAR only indirect observations have been used As a rule the food supply was deduced from other environmental factors (eg soil type and relation to the n river) some cases the data of eentvaar (9) could be used Soil type n the field only casual observations were made with regard to the soil ost information was obtained from the literature and from maps The main sources were the maps of the Geological Service the soil map in the handbook of Edelman (90 a and b) and several publications of the Soil Survey Service (Stichting voor Bodemkartering) eg Edelman cs (90) Schelling (9) an iepen (9) and Pons ( a and b) 2 SUREY OF THE EGETATON n principle the vegetation was investigated according to the concepts and methods of the Braun-Blanquet school (Braun-Blanquet 932 9; Becking 97) n recent years this system ofclassification has been the subject of many critical discussions among its followers (see oing Kraft 9) t became evident that a number of new ideas had to be incorporated as necessary supplements Some of the new views generally practised in the Netherlands and in this investigation in particular will briefly be mentioned n the first place it must be stated that our starting-point was the idea that it must be possible to distinguish vegetational units as abstractions the on ground of a certain discontinuity in the vegetation itself which would already be at recognisable the level of the association This conception has its most convinced opponents among the US investigators especially J T Curtis and his collaborators (see Curtis eg and cntosh 9) n the Netherlands this matter was discussed in 9 (see eijer and Westhoff 97) and in 97 (eijer Zonneveld an onselaar) Our working-method was based on the view that vegetational classification should be typifying not dividing (see also Tuxen 9; oing Kraft 96) So far the classification of the communities has most often been based on the presence of characteristic species (ie faithful taxa) These however are now considered to be a case special of the more generally useful differential species ifferential species often were used to discriminate between vegetational units and also to indicate a certain differentiation within the limits of a definite unit n the latter case variants may be distinguished Another case special of differential species are the characteristic species within the formation (See Ellenberg 9; Schwickerath 92; oing Kraft 96) There were a number of units poor in species which could not be described as associations but better as sociations in the sense of the Scandinavian investigators (u Rietz 930) t is possible to incorporate these communities in the existing classifications eg by uniting a number of associations and sociations in an alliance (see Ellenberg 9; Westhoff 99; Zonneveld 960)

12 EGETATON OF FORER RER BES n conformity with the generally accepted practice in the Braun- Blanquet school no highly specialised statistical methods were applied This point will not be discussed here 3 ETERNATON OF THE REATONS BETWEEN PANT CO- UNTES AN HABTATS First the vegetational units were determined Then a correlation of such a unit with a definite constitution of the environmental factors that is to say with a certain habitat was established As eg Westhoff (9 b) and Tuxen (9) pointed out this does not permit us to draw definite conclusions with regard to the causal relations between the communities and their habitat The composition of a community does not only depend on the habitat but also on historical and other factors which are not included in this investigation n particular the interrelations between the plant species (eg their power of competition) be mentioned (see also Heybroek must 9) CASSFCATON OF THE FORER RER BES As a rule in every former river bed the communities were found to be situated concentrically Within the scope of this investigation it was not possible to determine the succession experimentally or by the use of permanent quadrats Nevertheless in many instances succession could be established Sometimes by comparing our data with the results of the quadrat method (see lieger and an Zinderen Barker 9) sometimes by the use of a new method (see an onselaar-ten Bokkel Huinink 96) n other instances it was only possible to speak of zonation (n considering the succession Tansley s terms autogenic and allogenic succession proved to be very useful) Anyhow it was evident that former river beds with the same or nearly the same set of communities also possessed quantitatively similar environmental factors Thus types could be established characterized by special sets of communities and by correlated abiotical properties THE PANT COUNTES Though the communities were determined without any preconceived notion a great part of the results proves to be in accordance with the Synopsis of Plant Communities generally used in the Netherlands (Westhoff cs 96) To simplify the description of the results this Synopsis will be used as our starting-point n cases where our results are in accordance with it this will generally not be mentioned separately

13 2 J AN ONSEAAR Class TTOREETEA Braun-Blanquet et Tüxen 93 Order ittorelletalia Koch 926 Alliance ittorellion Koch 926 Eleocharetum multicaulis Allorge 922 (Table ) A few records were made of the Eleocharetum multicaulis The vegetation was everywhere rather fragmentary consisting mainly of a few characteristic species of the association and of the alliance n other places than those of the records Scirpus fluitans (ch of the association) and uronium natans (ch of the alliance) were observed too TABE ) Eleocharetum multicaulis nr of record 2 nr of former river bed nr 2 2 river water depth (cm) area (sqm) 0 0 cover (%) 00 Ch Ass Hypericum elodes 2 3 Ch All Potamogeton polygonifolius Pourr Juncus bulbosus 23 Acc Phragmites communis Trin Hydrocharis morsus-ranae 2 Sphagnum palustre ) See explanation on p 8 The community was found in a part of the former river beds along the euse viz in those with stagnant oligo- to mesotrophic fresh water and a Ph of 9 to 6 The soil on the bottom consisted of loose peaty material resting on firmer and peat river loam The community formed narrow zones between vegetations belonging to the Potamion and to the Caricion fuscae 2 Class POTAETEA (Narayanayga 928) Tüxen 92 2 Order Potametalia Koch Alliance Potamion eurosibiricum Koch 926 n the former river beds quite a number of communities occurred belonging to the Potamion Some of these are generally accepted associations; some other ones will be introduced here n this connection we wish to draw attention to the fact that Polygonum amphibium fo natans must be eliminated as characteristic species of the alliance (see under 2 3) n accordance with Westhoff (99) the same will have to be done with Utricularia vulgaris (see under 2 )

14 < < 2 EGETATON OF FORER RER BES 3 2 Potametnm lucentis Hueck 93 (Table 2) This association is not mentioned in the Synopsis but it is nevertheless widespread in the Netherlands n older literature it is generally called Potametum perfoliati potametosum lucentis (eg Sghwickerath TABE 2 Potametum lucentis nr of record 2 3 nr of former river bed o -S river W W J U o water depth (cm) «o area (sqm) cn CT) cover (%) total 9 c floating layer 0 pu submersed layer 60 Ch Ass Potamogeton lucens Ch All Nuphar luteum () Sm -f2 32 emna minor 2 in trisulca emna 2 ii Nymphaea alba 2 ii Nymphoides peltata (Gmel) O Kuntze 2 i Ch Cl Ceratophyllum demersum 2 ii a Acc filiformous algae 3 3 ii Equisetum fluviatile i Supplement to the table Ch All: Potamogeton natans Elodea canadensis ichx Spirodela polyrhiza () Schleiden Hydrocharis morsus-ranae ; Ch Cl: Potamogeton pectinatus ; Acc: Phragmites communis Trin Scirpus lacustris ssp lacustris ; lieger 937; an Zinderen Barker 92 97) Under this name the community is according to Koch (926) and a former edition of the Synopsis (92) considered to be a subassociation of the Potameto perfoliati-ranunculetum fluitantis ater on the community has been identified with the Potametum lucentis of Hueck first in Germany (see Tuxen 9) and recently also in the Netherlands (an ijk and Westhoff 9) n the utch broads large sheets of water which in the Netherlands have been formed by the removal of peat ) the association consists mainly of submersed Potamogeta especially Potamogeton lucens and P perfoliatus but the former is the only one which evidently has its optimum init t always occurs on a more or less peaty soil in deep stagnant eutrophic fresh water and is occasionally preceded by a vegetation of Characeae The association was found in those former river beds which are t) On account of their slight depths they are best comparable to the broads of East Anglia and for this reasonin this paper they will be called by the same name

15 0 0 < AN J ONSEAAR situated in the forelands without tidal influence generally on mineral soil t forms a narrow zone on the outer side of the other Potamion communities (yriophylleto-nupharetum and Polygoneto-Nymphoidetum ) and is therefore the vegetation occurring on the deepest spots ( to 3 m) This river foreland variant is poorer in species than the variant found in the broads; especially the absence of Potamogeton perfoliatus must be mentioned The scarcity of the other submersed species may be ascribed the to density of the stratum formed by Potamogeton lucens t is true that this species is itself but submersed it produces the greater part of its leaves just below the and in surface consequence catches most of the light This however does not explain the nearly total absence of Potamogeton perfoliatus for this species grows in the same way 22 yriophylleto-nupharetum Koch 926 (Table 3) This association is very common in the Netherlands t has its optimum development in those fens in which the water is deeper than m and which are sheltered from the wind (see eg Clason 928; lieger 937; an Zinderen Barker 92 97; Bennema 93; eijer 9; an ijk and Westhoff 9; Westhoff cs 96) t consists mainly of species with floating leaves viz Nymphaea alba (ch) Nuphar luteum and Potamogeton natans but Potamogeton lucens and TABE 3 yriophylleto-nupharetum A B A B nr of record nr of former river bed b 79b 9 river J W W R J -S T3-3 a water depth (cm) >7 > oo 0 S üg v Ph water open area (sq m) cover (%) {%) total s floating layer h P* Oh submersed layer < ö Ch Ass Nymphaea alba B Ch All emna trisulca 2 2 ll emna minor 2 Spirodela polyrhiza () Schleiden 2 Nuphar luteum () Sm Potamogeton Nymphoides peltata (Gmel) O Kuntze 2 Ch Cl Ceratophyllumdemersum Acc filiformous algae K BH BH-B

16 EGETATON OF FORER RER BES yriophyllum spicatum are also frequently present n the Synopsis the last two are mentioned as characteristic species However if we include the Potametum lucentis in the list of Potamion-communities occurring in the Netherlands Potamogeton lucens can no longer be regarded as a characteristic species of the yriophylleto-nupharetum n the former river beds the association shows a certain variability to corresponding variations in the habitat n isolated fen waters the association answers the n general the river forelands it description occurs only on a muddy soil in those former river bed which have no connection with the summer bed and are situated in parts that are not often inundated or that if they are inundated are not exposed to a strong current during inundation time Here the composition of the vegetation is rather poor (see rec 2-6) Even Nuphar luteum d es not occur very frequently This species has in the former river beds found in the forelands its optimum in the Polygoneto-Nymphoidetum There are however many transitions between the two associations Theeutraphentous variants oftheassociation occur at a depth of to 2 m The vegetation may be preceded by the Potametum lucentis and is bordered at the land side by the Hydrochareto-Stratiotetum or by a community belonging to the Phragmition A very poor variant of the association occurs in the oligo- to mesotrophic former river beds with a Ph of 6 to 7 at a depth of about m Nymphaea alba is usually the only species (rec ) This is mentioned also by orzer Bruijns and Westhoff (9) Perhaps this variant is similar to the Association ofnymphaea alba-minor ollmar 97 Passarge (9 a) describes it as loose colonies of Nymphaea alba fo minor and Potamogeton natans in water with a Ph of 62 ndeed the colonies of Nymphaea alba (the forma was not determined) sometimes are accompanied by colonies of Potamogeton natans 23 Polygoneto-Nymphoidetum ass nov (Table see p 6) A new association is established here: the Polygoneto-Nymphoidetum Comparison of our results and of data from the literature leads to the establishment of the following characteristic species: Nymphoides peltata Polygonum amphibium fo natans Potamogeton pectinatus fo vulgaris and P perfoliatus The association occurs on mineral soils in eutrophic slightly alkaline (Ph 7 to 8) fresh water with a depth ranging from to 300 cm Some water movement caused by wind current or tide is essential Two subassociations can be distinguished viz P-N typicum and P-N These potametosum pectinati have differential species partly identical with characteristic species as is demonstrated in the table on p 7 Subass typicum The optimum habitat for the subass typicum is formed by those former river beds occurring along the upper courses in the forelands in permanent connection with the summer bed The more the former river bed is exposed to the current in times of inundation the greater

17 Polygoneto-Nymphoidetum typicum nr of record nr of former river bed 8 9 a g river W J W R W W W W W W g water depth (cm) 22-0 > area (sq m) cover (%) total g floating layer p* submersed layer < Ch Ass Nymphoides peltata (Gmel) O Kuntze ( subass) Polygonum amphibium fo natans nch Potamogeton pectinatus fo vulgaris Cham et Schlecht 2 2 Ch All Nuphar luteum () Sm Potamogeton lucens ll emna trisulca ll emna minor ll Spirodela polychiza () Schleiden 2 2 -j--2 Potamogeton natans Elodea canadensis ichx 2 2 Ranunculus circinatus Sibth 2 2 Hydrocharis morsus ranae 2 Ch Cl Ceratophyllum demersum Acc filiformous algae Supplement to the table Ch All: Potamogeton crispus Potamogeton compressus Riccia fluitans ; Acc: Potamogeton cf trichoides Cham et Schld (8: ) Phalaris arundinacea (9:!) Rorippa amphibia () Besser (0: ) Butomus umbellatus (0: 2) Alisma plantago-aquatica Oenanthe aquatica () Poir QB-S B-QB-S TABE Polygoneto-Nymphoidetum typicum nr of record nr of former river bed 8 9 a W river W u W R W W W W W W U O water depth (cm) 22-0 > ^0 u area (sq m) cover (%) total G floating layer h submersed layer < Ch Ass Nymphoides peltata (Gmel) O Kuntze ( subass) Polygonum amphibium fo natans nch Potamogeton pectinatus fo vulgaris Cham et Schlecht 2 2 Ch All Nuphar luteum () Sm Potamogeton lucens emna trisulca emna minor Spirodela polychiza () Schleiden Potamogeton natans Elodea canadensis ichx 2 2 Ranunculus circinatus Sibth 2 2 Hydrocharis morsus ranae 2 Ch Cl Ceratophyllum demersum Acc filiformous algae

18 X EGETATON OF FORER RER BES 7 Subassociation typicum potametosum pectinati Ch and species Ch Nymphoides peltata tot est to tot est to 2 Ch Polygonum amphibium fo natans x Ch Potamogeton pectinatus fo vulgaris vulgaris xx Ch Potamogeton perfoliatus Potamogeton crispus Potamogeton pusillus Elodea canadensis xx xx xx xx the chance that the soil remains purely mineral and the better accordingly the community is developed Only here where the current during the floods and maybe the drifting ice floes prevent the development of a herb vegetation the occurs community also in shallow water t consists mainly ofextensive and close vegetations in which as a rule Nymphoides peltata and sometimes Polygonum amphibium or Nuphar luteum dominate t is remarkable that Nuphar luteum in the former river beds with which we are dealing here has its optimum in the Polygoneto- Nymphoidetum and not in the yriophylleto-nupharetum On the deeper side the community is generally bordered by the Potametum lucentis on the land side by the community of Ranunculus circinatus and Elodea canadensis or by the Scirpeto-Phragmitetum oenanthetosum n the utch literature there are some indications that this subassociation or at least transitions of the latter to the yriophylleto- Nupharetum are found also outside the river area See an Zinderen Barker (92) and Kuiper and Segal (9) Subass potametosum pectinati The subass is potametosum pectinati identical with the imnanthemo- Potametum pectinati Allorge 922 in the (wrong) interpretation of the latter given in the Synopsis t is the so-called canal-side-community of the utch literature and it does not occur in the former river beds t arises from the subass typicum on spots where either a too lively water movement or else cleaning during the vegetational period reduce the extent of the floating layer Polygonum amphibium is probably more sensitive to this influence than Nymphoides peltata: the former vanishes the latter totally remains with low total estimates Consequently the light supply for the submersed species increases considerable and causes the extension of eg the differential species of the subassociation The optimal habitat of this community are the canal sides These are periodically cleaned and have now and then water movement caused by wind boats or sluicing The community also occurs in large exposed broads (see lieger 937; Bennema 93; Westhoff cs 96; orzer Bruijns and Westhoff 9)

19 8 J AN ONSEAAR Occurence of this and allied communities outside the Netherlands n some papers dealing with the vegetation of Europe indications of the occurrence of the Polygoneto-Nymphoidetum are to be found Allorge (922) established for a part ofthe Seine valley the Association of imnanthemum peltatum and Potamogeton pectinatus The description of this community shows elements of the Polygoneto-Nymphoidetum of the yriophylleto-nupharetum and even of the Hydrochareto-Stratiotetum Allorge mentions vegetations consisting mainly of Nymphoides peltata especially in the active former river beds These probably belong to the subass typicum ebrun cs (99) mention under the name imnanthemo-potametum pectinati vegetations of Nymphoides peltata especially in former river beds which are influenced by high water n NW Germany the association has not been recorded; it has probably been considered to be a part of the yriophylleto-nupharetum (see Tuxen 937 9) auterborn (97) certainly found the subass typicum in a number of active former river beds situated along the Rhine between Bingen and Bonn in W Germany: the only species in the floating layer were Nymphoides peltata and Polygonum amphibium auterborn s data from the Rhine between Basel and are more Bingen difficult to translate in terms plant-sociological Anyhow it is obvious that in the communities of hydrophytes in the latter area the characteristic species of the Polygoneto-Nymphoidetum are but in addition present; Trapa occurs here natans n 97 Oberdorfer proposed the Trapo-Nymphoidetum and indicated Nymphoides peltata and Trapa natans as characteristic species Polygonum amphibium fo natans considered to be a characteristic species of the alliance v (the Nympheion infra) does not occur in this community The habitat of the community are the former river beds in the valley of the Rhine in S Germany The bottom must be humic and muddy Oberdorfer has divided the Potamion into two alliances the Eu- Potamion and the Nympheion To the latter belongs ao an associationgroup consisting of associations which are dominated by Nymphoides peltata These associations resemble one another but on the otherhand they present floristic differences depending on geographical factors and are called for this reason geographical vicariants This principle is also explained by Westhoff (90) According to Oberdorfer the Trapo-Nymphoidetum the imnanthemo-potametum pectinati and a similar community occurring on the Balkan peninsula are geographical vicariants On account ofwhat we have said above on the imnanthemo- Potametum it will be clear that the Trapo-Nymphoidetum and the Polygoneto-Nymphoidetum are to be regarded as geographical vicariants The border line between the areas in which they occur may lie somewhere in the vicinity of Bingen (see auterborn)

20 A B stag Hydrochareto-Stratiotetum stagnant water river foreland A B tot mesotrophic eutrophic nr of record _ nr of former river bed 2 3 0c d 93 -t) river J H J W g g Q water depth (cm) >7 >7 30 <00 30 >60 > E «S Ph open water eo o> area (sq m) _ cover (%) total S 3 floating layer 00 7 < 9 < Pi d submersed layer 2 Ch Ass Hydrocharis morsus-ranae ( B) Stratiotes aloides Utricularia vulgaris Ch All ( B) emna trisulca 2 2 ( A) Potamogeton natans emna minor Nuphar luteum () Sm 2 Elodea canadensis ichx 3 ll Spirodela polyrhiza () Schleiden 2 Hottonia palustris 2 Ch Cl Ceratophyllum demersum 23 Acc filiformous algae 3 2' Agrostis stolonifera -f3 2 Supplement to the table Acc; Comarum palustre 2: 2 Equisetum nuviatile 3: Sagittaria sagittifolia 3: Slum erectum Huds : 2 Cicuta virosa : 2 Typha latifolia : 2 Glyceria maxima (Hartm) Holmb : 2 entha aquatica : Cardamine pratensis ; yosotis scorpioides : Rorippa amphibia () Besser 7: Oenanthe aquatica () Poir 8: Sium latifolium 8: 2 ythrum salicaria 8: 2 Typha angustifolia 8: 2 Poa palustris 8: 2 7 QB-S QB-S QB-S K QB-S TABE A B Hydrochareto-Stratiotetum stagnant water river foreland A B tot mesotrophic eutrophic nr of record u nr of former river bed 2 3 0c d 93 -S "S river J H J W o O O ü water depth (cm) >7 >7 30 <00 30 >60 > u Ph open water CO 0 area (sq m) cover {%) total floating layer submersed layer < < Ph C Oh G Ph Ch Ass Hydrocharis morsus-ranae ( B) Stratiotes aloides Utricularia vulgaris i Ch All ( B) emna trisulca 2 2 in ( A) Potamogeton natans ii emna minor 2 2 # ii Nuphar luteum () Sm 2 # Elodea canadensis ichx # 3 i Spirodela polyrhiza () Schleiden a 2 i Hottonia palustris 2 i Ch Cl Ceratophyllum demersum 23 i Acc filiformous algae Agrostis stolonifera 3 -f3 2 2 ii i

21 20 AN ONSEAAR J 2 Hydrochareto-Stratiotetum (an angendock 93) Kruseman et lieger 937 (Table ) egetations belonging to the Hydrochareto-Stratioteum mainly consist of the two characteristic species mentioned in the Synopsis viz Hydrocharis morsus-ranae and Stratiotes aloides However sometimes Utricularia vulgaris becomes dominant and according to Westhoff (99) this species too should be included among the characteristic species (see also an ijk and Westhoff n this 9) connection it must be mentioned that Oberdorfer proposed in 97 the Hydrocharetum rhenanum an association with Hydrocharis and Utricularia vulgaris but without Stratiotes aloides and considered it to be a geographical vicariant of the n Hydrochareto-Stratiotetum the Netherlands the community mostly occurs in stagnant shallow fresh water on shaltered to spots which the plants possibly may have been blown the by wind t is generally succeeded by a floating-mat See vegetation eg lieger (937) an Zinderen Barker (92 97) Bennema(93) Westhoff cs (96) orzer Bruijns and Westhoff (9) eijer Kuiper (9) and Segal (9) n the Synopsis two subassociations are distinguished though not named The first is the most typical one with closed vegetations of Hydrocharis and/or Stratiotes The second presents more open vegetations and comprises Ranunculus circinatus and Potamogeton compressus differential species as A variant of the association corresponding with the general description and without Ranunculus circinatus and Potamogeton compressus was found in the former river beds with eutrophic fresh water either inside the winter dikes or in the forelands in a sheltered position and without contact with the summer bed (Table: B) t occurs as a rule at a depth of 7 to 00 cm; it is preceded by the yriophylleto- Nupharetum and succeeded either by the Scirpeto-Phragmitetum typicum or by the the Cicuteto-Caricetum pseudocyperus typicum On less sheltered spots it appears sometimes in the form of a long and narrow zone of Hydrocharis with few very or without Stratiotes in just front of the swamp vegetation (see rec nr 8) n the oligo- to mesotrophic former river beds a special variant can be distinguished (Table: A) This community has no Stratiotes and no emna trisulca n this habitat Hydrocharis is generally accompanied by Potamogeton natans whereas in eutrophic water the latter shows preference for the yriophylleto-nypharetum Thus it is a differential species which distinguishes the mesotraphentous variant of the Hydrochareto-Stratiotetum from the eutraphentous one n the table Nuphar luteum seems to be in the same position The literature however proves that this species may occur also in the eutraphentous variant (see eg Bennema 93) This community may be preceded by the mesotraphentous variant of the yriophylleto-nupharetum; on the land side it is bordered either by the Eleocharetum multicaulis the Caricetum lasiocarpae the Cicuteto- Caricetum pseudocyperus comaretosum or the Caricetum elatae comaretosum

22 EGETATON OF FORER RER BES 2 2 Community of Ranunculus circinatus and Elodea canadensis (Table 6) n 93 Bennema and Westhoff proposed an association with the name Ranunculeto-Potametum compressi (Bennema 93) The characteristic species should be Ranunculus circinatus and Potamogeton compressus The community was said to occur in ditches where the water was in contact with a mineral soil Floristically it resembled the Hydrochareto-Stratiotetum but it differed from the latter ecologically; it required a habitat with more or less moving water The Synopsis drops the association but divides the Hydrochareto- Stratiotetum into two subassociations for which no names are proposed The one differs floristically from the other by two differential species viz Ranunculus circinatus and Potamogeton This subassociation compressus obviously corresponds with the Ranunculeto-Potametum compressi TABE 6 Community of Ranunculus circinatus and Elodea canadensis nr of record 2 3 of former river bed nr T3 -S river W J T J T O water depth (cm) JJ area (sq m) cover (%) total c S floating layer 20 < < ph submersed layer 9 9 cn Oi Ch All Ranunculus circinatus Sibth Elodea canadensis ichx Potamogeton natans H emna trisulca 32 -j H Potamogeton lucens 32 Nuphar luteum () Sm 32 3 H emna minor yriophyllum spicatum Stratiotes aloides 2 2 Hydrocharis morsus-ranae Spirodela polyrhiza () Schleiden 2 Hottonia palustris 2 Potamogeton pusillus 3 Acc filiformous algae Sagittaria sagittifolia 2 Sparganium erectum ssp polyedrum (A et Sch et Th G) 2 Supplement to the table Ch All: Nymphaeaalba Polygonum amphibium fo natans nch Hippuris vulgaris ; Acc: Rorippa amphibia () Besser (3: ) Alisma plantago-aquatica (3: ) Phragmites communis Trin (: 2) Glyceria maxima (Hartm) Holmb (: 2) Sparganium simplex Huds Acorus calamus (: 2) Oenanthe aquatica () Poir yosotis scorpioides K K

23 22 J AN ONSEAAR n the former river beds a community was found characterized by Ranunculus circinatus and high total estimates of Elodea canadensis t has many features in common with the Ranunculeto-Potametum compressi in which Elodea also may have high total estimates The only striking difference is the absence of Potamogeton compressus Though Hydrocharis and Stratiotes are present with low abundances the community does not resemble the Hydrochareto-Stratiotetum very much t was mainly found on mineral soils in slightly moving water in one case even under some tidal influence (rec nr ) The optimum habitat seems to be the former river beds in the forelands in contact with the summer bed and exposed to the current during the period of inundation There at a depth up to m Ranunculus circinatus is in present extensive but loose with Elodea and other submersed colonies species in big patches under the surface t must be mentioned that Elodea decreases in the presence of Potamogeton lucens (compare rec nrs 2 and with nrs 3 and ) Probably the community takes the place of a swamp vegetation whose was development prevented in some way Under these circumstances it is bordered its on deeper side by the Polygoneto- Nymphoidetum (often forming transitions with it) and is on the other side in contact with the edge of the meadows n accordance with advice received from r Westhoff this community is not described as a new association n view of the facts mentioned above its ecological position can not be regarded as sufficiently clear 26 egetations in oligo- to mesohalinic water Our observations of the vegetation in the stagnant oligo- to mesohalinic former river beds (20 to 2000 mg Cl/) are not sufficient to justify any conclusion with regard to the communities to which they should be referred ery few species are present and the differences between the single vegetations are too considerable n the deepest spots Chara div sp and aucheria sp may occur n less deep water were found eg emna trisulca emna minor Potamogeton pectinatus Zanni- (div formae) Enteromorpha intestinalis and in one case chellia palustris The following record gives an example Fieldnr 6-22 ate Spui near Brielle (nr 7) Water depth cm 20 mg Cl/ Total cover 00 % floating layer 8 % submersed layer % Ceratophyllum demersum Enteromorpha intestinalis ink aucheria sp 3 2 yriophyllum spicatum 2 emna minor 2 Ranunculus circinatus Sibth 2 3 Class PHRAGTETEA Tüxen 92 3 Order Phragmitetaliaeurosibirica Tüxen (Koch 926) 92 The order has many characteristic species Generally our results are in accordance with the Synopsis but some differences must be mentioned

24 EGETATON OF FORER RER BES 23 Rumex hydrolapathum in the Synopsis mentioned as a characteristic species of the Phragmition occurs also in the agnocaricion n both alliances its frequency is about 30 % n the Caricetum acutiformopaniculatae an association of the agnocaricion its frequency 2 % This is in accordance with Boer (92) who gives is even in this connection % The species is better considered to be characteristic for the order Equisetum fluviatile according to the Synopsis a characteristic species of the order does not deserve this position ts occurs frequently and with rather high abundances in the Caricetum lasiocarpae and allied associations anden Berghen (92 b) regards it even as a characteristic species of the Caricetum lasiocarpae Oenanthefustulosa can in our opinion not be regarded as a species of the Phragmitetalia though it is mentioned as such in the Synopsis Tuxen and Freising (9) call it a characteristic species of the Caricetum vulpinae ( agnocaricion ) We doubt however whether the Caricetum vulpinae belongs to the agnocaricion (see p 8) Oenanthe fistulosa was frequently found in wet meadows along the former river beds 3 Alliance Glycerieto-Sparganion Braun-Blanquet et Sissingh 92 The Synopsis distinguishes two associations of the alliance Glycerieto- Sparganion viz the Glycerieto-Sparganietum neglecti Koch 926 and the Helosciadietum modiflori Braun-Blanquet 930 Recently however difficulties arose with regard to the characteristic species t appeared that in these communities not only Glyceria fluitans but also G plicata and G declinata are present which sometimes have been confused may with the former one and that apart from Nasturtium officinale also N microphyllum is present oreover Scrophularia alata has been divided into S neesii and S balbisii Another difficulty is that several utch investigators may have confused Apium nodiflorum and Sium erectum As a result of this increase in our knowledge the subdivision of the alliance had to be changed For the Netherlands a first step was taken by aas (99) According to this author characteristic species of the alliance are: Sium erectum Sparganium erectum ssp neglectum Nasturtium officinale N microphyllum eronica beccabunga and anagallisaquatica n our opinion Callitriche stagnalis must be added to this list (see p 2) ore or less in accordance with Oberdorfer (97) aas distinguished the following associations; Scrophularieto-Glycerietum plicatae Sparganieto-Glycerietum fluitantis and Helosciadietum nodiflori A community of the alliance occurring in the tidal area (Zonneveld 960) is not comprised in this revision 3 Sparganieto-Glycerietum fluitantis Oberdorfer 97 aas mentions in his text as characteristic species Glyceria fluitans Agrostis stolonifera var natans and Callitriche sp (mainly C hamulata and C stagnalis) n his table however it says that the Callitriche sp

25 2 J AN ONSEAAR is mainly C hamulata n this respect it must be mentioned that the community of Zonneveld (960) which is probably different from this association (see p 26) comprises a species indicated as Callitriche cf stagnalis consider C Therefore we think that for the moment it is better to stagnalis to be a characteristic species of the alliance According to aas the association in the Netherlands is a community occurring in acid to neutral water rather in minerals poor and lime He distinguishes three subassociations viz: ) Subass typicum The records given by aas of this subassociation are all made in and along springs and brooks who accord with his description of the habitat The subassociation however occurs also in ditches as can be seen from the records in Boer (92) Undoubtedly these ditches had alkaline water rich in plant nutrients 2) Subass bidentosum ifferential species: Bidens tripartitus B cernuus Polygonum hydropiper and imulus moschatus Habitat: small shallow brooks; transition to Bidention 3) Subass ranunculetosum aquatilis ifferential species: Ranunculus aquatilis Potamogeton natans Elodea canadensis and Ceratophyllum demersum; transition to Potamion n the river forelands a fourth subassociation can be distinguished (Table 7): Subass polygonetosum subass nov ifferential species: Oenanthe aquatica Rorippa amphibia Polygonum amphibium (both formae) and Eleocharis palustris only characteristic species present Glycerin fluitans is the This subassociation was in the forelands especially found in the former river beds occurring in those of the Rhine and the Waal The mineral soil clay as a rule may be either solid or weak and muddy These forelands are calciferous except those of the aas upstream from Heerewaarden (see p 6) The water is fresh and eutrophic and its depth varies from to 0 cm aybe in cases the water many is polluted by grazing and paddling cattle The former river beds in which this community was found are not in communication with the summer bed Therefore the greater part of the year the water is practically stagnant Only during the short-lasting inundations in winter and spring the vegetation is more or less influenced by the current This is in contrast with the habitat of the three other subassociations where the water is moving either permanently (brooks) or at least now and then (ditches) The community may be rich in species of the Potamion especially in places where the deeper side of its habitat is in contact with that of a Potamion-community Therefore it is no longer possible to use most of the Potamion-species as differential species of the subass ranunculetosum aquatilis Ranunculus aquatilis however can be maintained as this species does not occur in the river forelands n many cases this community was found bordering a vegetation

26 f EGETATON OF FORER RER BES 2 TABE 7 Sparganieto-Glycerietum fluitantis polygonetosum nr of record nr nr of former river bed b 8 river W R R W R R U g water depth (cm) O g \ 2 area (sq m) _Ca total (%) cover herb layer Ph floating layer 2 0 ( > )nn 00 < <0 submersed layer 0 < 0 * Ch Ass Glyceria fluitans () R Br Ch All eronica anagallis-aquatica Callitriche stagnalis Scop # Ch Ord t> ( subass) Oenanthe aquatica () Poir ( subass) Rorippa amphibia () Besser Glyceria (Hartm) Holmb Alisma pantago-aquatica a H # 2 Sium latifolium Galiumpalustre 2 2 Typha latifolia 2 Scirpus lacustris ssp lacustris Ch Potamion emna minor ll emna trisulca ll Hydrocharis morsus-ranae filiformous algae Elodea canadensis ichx Potamogeton lucens 3 Ranunculus circinatus Sibth s s Ceratophyllum CeratophyHum demersum Spirodela polyrhiza () Schleiden 2 2 Acc ( subass) Polygonum amphibium yosotis scorpioides -j-l ( subass) Eleocharis palustris R et () Sch Poa palustris 2 2 entha aquatica 2 2 Supplement to the table Acc: Potamogetonpectinatus ; 2 Rumex maritimus : Juncus articulatus : 2 Ranunculus sceleratus 2: 2 entha arvensis : 2 Rumex acetosa : 2 Rumex crispus 6: 2 Ranunculus repens 6:

27 -i J AN ONSEAAR belonging to the Scirpeto-Phragmitetum oenanthetosum On the land side it is always bordered by foreland meadows 32 Community in the tidal area (Table 8) n two former river beds of the freshwater tidal area records were made who certainly indicate a community belonging to the Glycerieto- Sparganion On the slight slopes on which these vegetations were found clay was deposited At low tide the zone rose above the water Apium nodiflorum which occurs in one of the records is generally considered to be a characteristic species of the Helosciadietum nodiflori n the Netherlands the last mentioned association is found along rivulets in the province of imburg and in some polder and fen areas (Westhoff 93; id cs 96) t does not seem to be correct to (incorporate one or all of our records into this association for there are several differences both in fioristic composition and in habitat Zonneveld (960) describes a of the community freshwater tidal area which he does not know how to classify t contains ao Apium nodiflorum and differs from all other communities of the alliance by the occurrence of Scirpus lacustris ssp lacustris ythrum salicaria Bidens frondosus and aucheria div sp Our records more or less resemble this TABE 8 Glycerieto-Sparganion community in the tidal area of record 2 3 nr of former river bed river H H area (sqm) cover (%) 9 0 Ch All Nasturtium officinale R Br eronica beccabunga 2 eronica anagallis-aquatica Apium nodiflorum () ag 22 Ch Ord Glyceria maxima (Hartm) Holmb 2 3 Phalaris arundinacea 2 2 Rorippa amphibia () Besser 2 Alisma plantago-aquatica 2 Carex acuta 2 2 Sium latifolium 2 Acorus calamus 3 2 Acc Caltha palustris 2 2 yosotis scorpioides -\-2 2 entha aquatica 2 ythrum salicaria 2 Agrostis stolonifera 32 Equisetum fluviatile Polygonum Stachys palustris

28 EGETATON OF FORER RER BES 27 community Only after further investigations and after a total revision of the Glycerieto-Sparganion it will be possible to give these communities of the tidal area a place in this alliance 32 Alliance Phragmition eurosibiricum (Koch 926) Tüxen 92 em Braun-Blanquet et Sissingh 92 The Synopsis mentions five characteristic species for the alliance Phragmition n our opinion some alternations must be made Rumex hydrolapathum has to be transferred to the order (see p 23) n the Synopsis Typha latifolia is claimed as a characteristic species of the Scirpeto-Phragmitetum ts abundance however may be equally high in the Cicuteto-Caricetum especially in the subass comaretosum (see p 3) The presence in the two associations is according to our results resp 8 % and 3 % according to Boer (92) 20 % and 27 % n our opinion the species is characteristic for the alliance f we take the preceding remarks into account we may say that in the Netherlands the Phragmition has the following characteristic species: Scirpus lacustris ssp lacustris Butomus umbellatus Typha angustifolia T latifolia and Ranunculus lingua n the Netherlands the alliance includes three associations viz the Scirpeto-Phragmitetum the Cicuteto-Caricetum pseudocyperus and the Scirpetum triquetri et maritimi A number of associations which for one reason or another are not accepted here will also be dealt with viz the Glycerietum maximae the Association of Oenanthe aquatica and Rorippa amphibia the Calletum palustris and the Scirpetum maritimi 32 Scirpeto-Phragmitetum medio-europaeum (Koch 926) Tüxen 9 (Table 9) The Synopsis gives four characteristic species for the Scirpeto- Phragmitetum viz Sparganium erectum ssp polyedrum Sagittaria sagittifolia Acorus calamus and Typha latifolia The latter is better transferred to the alliance (v supra) The community is known from many European countries and in the Netherlands it is common very See eg Havinga (99) Koch (926) Clason (928) Sghwickerath (933) an angendonck (93) an ZinderenBarker (92 97) Boer (92) an ijk and Westhoff (9) Kuiper and Segal (9) an onselaar- Ten Bokkel Huinink (96) According to these descriptions the association has its optimum development in eutrophic stagnant fresh water on a more or less peaty soil Sometimes it is represented by a mixed vegetation rich in but species more often by various facies which are rather poor in species Pioneering facies (into vegetations of the Potamion) or at least facies in relatively deep water may consist of Scirpus lacustris ssp lacustris Sparganium erectum ssp polyedrum Typha angustifolia and T latifolia The two Typha-species prefer a more muddy soil than the other ones Also on a muddy soil but in more shallow water a facies of Glyceria maxima may occur Phragmites communis forms facies in shallow

29 < 3 -fl -fl -fl -f fl # -f2 2 -j- -f2 2 -f2 -f f fl fl 2 * * TABE Scirpeto-Phragmitetum medio-europaeum stagnant water typicum river foreland of record nr nr 8 9 nr of former river bed 7b a 32 0 river W J U W W J u H W water depth (cm) <0 7 area (sq m) cover (%) total herb layer floating layer < Ch Ass Sparganium erectum ssp lyedrum(a etg)sch etth po- -fl Sagittaria sagittifolia t Ch All Ranunculus lingua 2 to t-fo Equisetum fluviatile t-fc c Ch All Typha angustifolia Typha latifolia 2 22 o Ch Ord Oenanthe aquatica () Poir o-fc oc Ch Ord Phalaris arundinacea c Acc Caltha palustris aucheria sp Ch All Scirpuslacustrisssplacustris ssp 2 22 Ch Ord Glyc max (Hartm) Holmb Rorippa amphibia () Besser -f2 2 -f2 2 -fl -fl Phragmites communis Trin Alisma plantago-aquatica Sium latifolium fl -f2 -fl Rumex hydrolapathum Huds -fl s 2 -fl 2 # Galium palustre 2 2 Carex acuta -f f -f2 -h*2 t-fo Acc emna minor -f -f f 2 emna trisulca -fl Spirodela polyrhiza () Schl -f f2 2 Hydrocharis morsus-ranae Nuphar luteum () Sm 2 -f aquatica -fl f2 2 yosotis scorpioides -fl! -f2 Polyg amph fo terr eyss 2 -f2 Stachys palustris -f2 -fl K -fl ycopus europaeus -fl Solanum dulcamara ris pseudacorus 2 Symphytum officinale Supplement to the table Ch Ass: Acorus calamus : ; Ch All: Butomus umbellatus : 0; Scirpus maritimus 0; 2 2: 2 Cicuta virosa 3: ; Ch Ord; Glyceria fluitans () R Br 0: 2 Carex acutiformis Ehrh 6: 2; Acc: Riccia fluitans 3: 9: 3 Cardamine pratensis ; 6: 2 Senecio paludosus 6: 2 20: 2 Bidens tripartitus 8: 20: 2 Urtica dioica 20: 2 2; 2 ythrum salicaria 3: Epilobium palustre 3: Ricciocarpus natans () Corda 3; yriophyllum spicatum :l Nymphaea alba 6: 2 Ranunculus acer 0: Polygonum persicaria 0: Ranunculus sceleratus 0: Scutellaria galericulata 2: 2 Poa palustris : 2 Polygonum amphibium : 2 Elodea canadensis ichx ; 2 ysimachia vulgaris 6: 2 Rumex crispus 6; 2 iburnum opulus 6: 2 Polygonum nodosum Pers 7: Poa pratensis 8: 2 Cardamine amara 8: Polygonum mite Schrank 8: Ranunculus repens 8: Equisetum palustre 20: 2 Polygonum hydropiper 20: 32 Achillea ptarmica 2: 2

30 * 22 2 i j j * : 9 i oenanthetosum t o c tot calthetosum t O C tot no tidal influence tidal influence 0 ii T3 3 77b a 2a 'S -S "S! "H 'H U WRRWWR W R R W W R o o JWWR W W 8 O 8 }J >70 >70 *J « C cn - ic S S 30 < < u C 8 U ) " u X Ph X X ll H ill H 22 :!! 2 ll -2 2 i i! i Z # # i sl 32! ll H H # ii ll in ii ii ii i : ; 2 2: * * S QB BH BH S BH QB-S QB-S--B QB

31 30 J AN ONSEAAR and in deep water usually on a firm soil The actual depth of the water in which the various facies occur depends on other factors like water movement One may ask whether the community can be rich in species if it occurs under natural conditions in shallow water Tuxen (97) found that a richly developed vegetation belonging to this association which occurred in a spot that was regularly mowed developed into a uniform Phragmites- field after the mowing was stopped As a rule in the Netherlands the shallower side of the reed swamps is exploited! (See also Westhoff 9 this b) Anyhow does not hold for the tidal Scirpeto-Phragmitetum (see p 32) The association occurs in the greater part of the former river beds that is to say in all those with eutrophic fresh water Our results concerning the various facies and their are ecology in accordance with the facts known from the literature oreover we found facies of Equisetum fluviatile and of Oenanthe The aquatica first occurs both in water and in stagnant the forelands and be may pioneering The second is characteristic for former river beds in connection open with the summer bed and/or often inundated to and/or exposed the current during the periods of flood aybe it is also favoured by the treading of cattle örzer Bruijns and Westhoff (9) state that fragments of the Scirpeto-Phragmitetum consisting of Oenanthe aquatica and some other species come into existence on spots which are regularly dredged This species can survive the effect of this treatment by its short life cycle Probably the influences mentioned above have a corresponding effect on the vegetation n 92 Tuxen and Freising (see also Tuxen 9) divided the association into two subassociations viz ) Subass typhetosum angustifoliae (the Teichrdhricht is pool reed-swamp ) occurring in stagnant water ifferential species: Typha angustifolia and Ranunculus lingua 2) Subass phalaridetosum arundinaceae (the Flussrdhricht is river reed-swamp ) occurring along streaming water ifferential species: Phalaris arundinacea and Oenanthe aquatica Zonneveld described in 960 a new subassociation viz S-P calthetosum (see also This 92) community is often dominated by Typha latifolia and Sparganium erectum as well as Glyceria maxima may be abundant t further comprises Typha angustifolia and Phalaris arundinacea but lacks Ranunculus lingua and Equisetum fluviatile ifferential species are Caltha palustris and aucheria div sp The subassociation has an enormous extension in the Biesbosch a freshwater tidal delta but occurs also in the rest of the freshwater tidal area of the rivers (see an eeuwen 9) Zonneveld also gives subdivision a new of the association Apart from his own observations he disposed of the table of Boer (92) and of 27 of our own descriptions (with plot records) of the former river beds His idea was that all records made in the former river beds occurring in the forelands respresent the subass phalaridetosum Starting from this idea he concluded that the subass typhetosum does

32 X EGETATON OF FORER RER BES 3 not have any differential species for Ranunculus lingua and Typha angustifolia occur in the forelands t would only be possible to determine the subass typhetosum by the absence of the differential species of the other two subassociations He proposes to change the names of the two first subassociations into resp S-P typicum and S-P oenanthetosum With due consideration of the literature mentioned above we propose to subdivide the as Scirpeto-Phragmitetum it occurs in the Netherlands with the aid of differential species in the way indicated in the following table Subassociation typicum oenanthetosum calthetosum ifferential species Ranunculus lingua Equisetum fluviatile X X X Typha angustifolia X X Typha latifolia X X Oenanthe aquatica Phalaris arundinacea Caltha palustris X X X aucheria div sp X Subass typicum Zonneveld 960 This community is identical with the subass typhetosum of Tuxen and Freising (92) This name however is no longer adequate as the subass calthetosum also contains the two Typha- species The name ranunculetosum linguae would be acceptable but typicum seems preferable Of it must not course be confused with the variant typicum ofkoch (926) The original description given by this author probably includes the subass oenanthetosum as well but the subass typicum of Zonneveld is doubtless the most typical utch literature deals with this form form of the association ost This subassociation does not only occur in stagnant water but also in a number or former river beds in the river forelands (see table) As to the water household these former river beds occupy an intermediary position between the summer bed of the river itself and a pool with permanently stagnant water This applies to their soils too Thus the former river beds in the forelands which are not frequently inundated and/or have a sheltered position with regard to the current during high water normally have a swamp vegetation resembling the Scirpeto-Phragmitetum of stagnant pools This result is in accordance with the data of Tuxen and Freising (92) The subassociation shows a number of facies but also magnificent mixtures occur n one of the former river beds the Kil near Hurwenen it (nr 62) forms very extensive floatingmat vegetations (rec nr see also an onselaar-ten Bokkel Huinink 96) According to the literature and as confirmed by our own observations the zone occupied by the community is bordered by the yriophylleto-nupharetum or by the Hydrochareto-Stratiotetum on the deeper

33 32 J AN ONSEAAR side and by the Caricetum gracilis-vesicariae or by the Caricetum acutiformo-paniculatae on the land side Subass oenanthetosum Zonneveld 960 This community is identical with the subass phalaridetosum of Tuxen and Freising (92) Here too the authors unhappily chose a wrong name for afterwards it turned out that Phalaris arundinacea is a constant species in the subass calthetosum t occurs in former river beds which are frequently inundated and/or are exposed to the current during high water n a few cases there is some tidal movement n contrast to those of the subass typicum the aspect of the vegetation is determined by lower herbs Phalaris arundinacea in this subassociation prefers shallow water The most common facies are those of Oenanthe aquatica and of Glyceria maxima According to our results Typha atifolia is absent This however is not in accordance with the records of Tuxen and Freising (92) and of Tuxen (9) The vegetations are situated between the Polygoneto-Nymphoidetum typicum on the one side and the Sparganieto-Glycerietum fluitantis polygonetosum or the Caricetum gracilis-vesicariae on the other side Subass calthetosum Zonneveld 960 This subassociation was found in a few former river beds in the freshwater tidal area n some cases as a result of mowing (see p 9) its place is taken by a sociation of the Phragmites-consociation ll comparison with the Biesbosch our vegetations are poor in species (see Zonneveld) As the characteristic species of the association are absent in our records the community can be referred to the Scirpeto- Phragmitetum only because other possiblities can be excluded f the differential species are absent the subassociation is indicated by the combination of Phalaris arundinacea and Typha latifolia n contrast with the two other subassociations hydrophytes are in consequence of the tidal movement completely absent The community is bordered by the Scirpetum triquetri et maritimi on the deeper side and by the Caricetum gracilis-vesicariae or by the above mentioned Glycerieto-Sparganion-community on the land side Special attention must be given to record nr 6 t was made along a former river bed of the Jsel which up to 932 has been under the influence of the tides of the Zuiderzee Then the dam was completed and the Zuiderzee became a lake the Jselmeer We may suppose that the subass calthetosum was a common community near the mouths of the rivers debouching into the Zuiderzee t is rather astonishing that after 2 of river foreland life the years community still can be recognised Recently two associations have been introduced which must be dealt with in connection with the Scirpeto-Phragmitetum Both have

34 EGETATON OF FORER RER BES 33 been observed in NW Germany (see Tuxen and Freising 9; Tuxen 9) and in S Germany (see Oberdorfer 97) ohmeyer (90) described the Association of Oenanthe aquatica and This Rorippa amphibia association resembles much very (and may be identical with) the Oenanthe aquatica- facies; of the Scirpeto-Phragmitetum oenanthetosum t has no Typha sp and no Ranunculus lingua but Glyceria maxima Oenantheaquatica and Phalaris arundinacea (P =!) are present The main differences with our facies of Oenanthe are the presence () and the high total estimates (2-) of Rorippa amphibia The community is a characteristic association of the valleys of the great rivers in N and W Germany As in summer its habitat mostly runs dry its position is probably on a higher level than our Oenanthe-facies Nevertheless we have the impression that we better leave this association out of consideration and stick to the Scirpeto-Phragmitetum oenanthetosum f the Oenanthe-facies would be set apart from this subassociation there would not be left very much of the latter Tuxen (9) revived the Glycerietum maximae Hueck 93 ts only floristical characterization is that Glyceria maxima is dominating The habitat of the community runs periodically dry We observed facies of Glyceria maxima which thrive in deeper water than the Glycerietum maximae of Tuxen seems to do However there is no more reason for us to separate this facies from the Scirpeto-Phragmitetum then to do so with any of the other facies Therefore we prefer to leave the Glycerietum maximae out of consideration here 322 Cicuteto-Caricetum pseudocyperus Boer et Sissingh 92 (Table 0) n the Synopsis three characteristic species are mentioned for this association viz Cicuta virosa Carex pseudocyperus and Caltha palustris The community consists of vegetations floating on water or on a soft organic mud Before its description it was included in the Scirpeto- Phragmitetum ( typicum) r) but afterwards it appeared to occur in all utch broads and in many other fenlike habitats also in Germany See Schwickerath (933) an Zinderen Bakker (92) Westhoek (99) Tüxen and Freising (9) eijer (9) Kuiper and Segal (9) Especially Boer (92) an Zinderen Bakker (97) and an ijk and Westhoek (9) give interesting details concerning the origin of the floating-mat vegetations There is some difference of opinion with regard to the position of the association in the order Phragmitetalia Originally Boer (92) included it in the Phragmition and all utch authors agreed to that Tuxen and Freising (9) however transferred it to the agnocaricion Although we never found an argumentation for this transfer we can see some reason for accepting it The floating vegetations produce a mat of rhizomes with organic remains in between found somewhere between the bottom and the water surface or even at the surface Thus they form substrate for a a number of species which usually occur in less deep water Among these be characteristic may and differential species ofthe agnocaricion Our results that the prove

35 comaretosum typicum com typ tot Cicuteto-Caricetum pseudocyperus ( stagnant water river forel mesotrophic eutrophic w «"f "f s nr of record nr of former river bed 8 0b 0c 26 6a a river J O W J J g g Ph open water d area (sq m) cover (%) Ch Ass Cicuta virosa Carex pseudocyperus Calla palustris com Acc Comarum palustre 2 2 Carex rostrata Stokeṡ 2 2 Carex lasiocarpa Ehrh 2 typ Ch Phron Typha angustifolia Ch Phra Rorippa amphibia () Besser Acc Stachys palustris yosotis scorpioides Ch Phra Sium latifolium ll Ch Phron Scirpus lacustris ssp lacustris - Typha latifolia 2 2 Ranunculus lingua 2 2 Ch g Galium palustre ysimachia thyrsiflora g ysimachia vulgaris 2 TABE 0 comaretosum typicum com typ tot Cicuteto-Caricetum pseudocyperus stagnant water river forel meso trophic eutrophic to -3 3 th nr of record Ou Oo C J nr of former river river bed 8 0b 0c 26 u 6a O W 2 U 6a J u CO fi h fi < c Ph open water H ph Ph area (sq m) cover (%) Ch Ass Cicuta virosa # 22 ill Carex pseudocyperus in Calla palustris * ii com Acc Comarum palustre Carex rostrata Stokes li Carex lasiocarpa Ehrh 2 typ Ch Phron Typha angustifolia Ch Phra Rorippa amphibia () Besser ii Acc Stachys palustris yosotis scorpioides * ii Ch Phra Sium latifolium ii Ch Phron Scirpus lacustris ssp lacustris ii Typha latifolia 2 2 ii Ranunculus lingua 2 2 Ch g Galium palustre 2 m # 2 2 in ysimachia thyrsiflora g ysimachia vulgaris 2 ii

36 TTnTTnra! Kumex hydrolapathum Huds ll Sparganium erectum 22 2 Phragmites communis Trim Glyceria maxima (Hartm) Holmb 2 22 Alisma plantago-aquatica 2 2 Acc ycopus europaeus entha aquatica Equisetum fluviatile 2 ll Solanum dulcamara emna minor Spirodela polyrhiza () Schleiden ll Supplement to the table Ch Phron: Acorus calamus 9; 2; Ch g: Carex hudsonii A Benn 2: 2 Carex acutiformis Ehrh : 2 Carex riparia Curt 7: 2; Ch Phra: Slum erectum Huds 3: 2 7: 2 eronica beccabunga : Oenanthe aquatica () Poir 6: ; Acc; Peucedanum palustre () oench : 2: 2 Salix cinerea 2: 2 : 2 Equisetum palustre 3: 0: Bidens tripartitus : 2 : 2 Salix triandra : 2 9: 2 Hydrocharis morsus-ranae 6; 9; -2 Alnus glutinosae () Gaertn 2; enyanthes trifoliata 3: 3 Bidens cernuus : 2 Epilobium hirsutum ; 22 Epilobium parviflorum Schreb 6: Nuphar luteum 6: emna trisulca 8: 2 filiformous algae 8: Cardamine pratensis 9: 2 Ranunculus repens 9: 2 Stellaria palustris Retz 0: BH S QB-S QB-S K Ch l'hra Kumex hydrolapathum Huds Sparganium erectum 22 2 Phragmites communis Trin Glyceria maxima (Hartm) Holmb 2 22 Alisma plantago-aquatica 2 2 Acc ycopus europaeus entha aquatica * Equisetum fluviatile 2 Solanum dulcamara emna minor Spirodela polyrhiza () Schleiden 2 2 2

37 36 J AN ONSEAAR Cicuteto-Caricetum is indeed rather rich in species belonging to the agnocaricion (see table) and this is also obvious in the table of Boer in most records Nevertheless the Phragmition- species retain their Another dominating position argument to put the association in the Phragmition may be found in its position in the succession As a rule vegetations of the Phragmition are preceded by a vegetation of the Potamion and succeeded by a vegetation of the agnocaricion This as a applies rule also to the Cicuteto-Caricetum t mostly comes into existence in a mass of floating Stratiotes aloides plants belonging to the Hydrochareto-Stratiotetum After the floating mat has become firmer the association develops into the Caricetum acutiformo-paniculatae On the base of our own results the literature (especially the table of Boer) and some unpublished records of r Westhoff we propose to divide the association into two subassociations These are indicated on the table with their differential species Subass typicum subass nov Nearly all utch literature deals with this subassociation t presents all three characteristic species although Calla palustris lacks in our table The optimum habitat of the community is found in sheltered spots in eutrophic stagnant fresh water Nevertheless we made one record (nr 7) in water with 200 mg t was Cl/ also found in a few former river beds in the forelands Of course these are not inundated very often and they occupy a sheltered position with regard to the current Stratiotes aloides although not in present the table may also be considered to be a differential species The position ofthe community in the succession has been dealt with above Subass comaretosum subass nov This community was found in nearly all mesotrophic former river beds along the euse t occurs above a peat soil n many cases Calla palustris determines the aspect of the vegetation The community presents less characteristic species of the order and the alliance than the subass typicum The vegetation is preceded by one belonging to the Hydrochareto-Stratiotetum (mesotraphentous variant) anden Berghen (92 b) described the Calletum palustris with Calla as the only characteristic species He reckons it together with the Caricetum lasiocarpae to an alliance called Caricion lasiocarpae Characteristic species of this alliance are enyanthes trifoliata Comarum palustre and Carex rostrata A floristic and ecological comparison of the Calletum palustris with the Cicuteto-Caricetum pseudocyperus comaretosum leads to the conclusion that the two communities are identical n this connection it must be mentioned that the C-C p typicum does not occur in Belgium at least was not noticed by ebrun cs (99) 323 Scirpetum triquetri et maritimi Zonneveld 960 (Table ) n 933 Tuxen described the Scirpetum maritimi an association with Scirpus maritimus and Scirpus lacustris ssp glaucus as characteristic species t was mentioned from brackish water along the coast and near the

38 EGETATON OF FORER RER BES 37 mouths of the rivers in NW Germany Since then this association has been recognised also in Belgium (ebrun cs 99) and in the Netherlands (Synopsis) Boer (92) described the association for the Netherlands and divided it into a number of subassociations The of greater part his records were however made along the Jselmeer the former Zuiderzee which at that time was desalinating gradually Therefore his conclusions concerning this community are of little value Zonneveld (960 see also 92) described the communities of the Biesbosch a freshwater tidal delta One of these communities resembled the Scirpetum maritimi However Zonneveld s community had its optimum development in the area covered by his investigation and moreover it differed from the association of Tuxen ao by the enormous extension ofscirpus triqueter This species was accepted already as a characteristic species of the Scirpetum maritimi by Boer and in consequence also by the Synopsis Zonneveld however wanted to leave the account ofboer out of consideration for the reasons mentioned above Therefore he described his community as a new association the Scirpetum triquetri et maritimi We fully agree with his argumentation Characteristic species of the new association are Scirpus triqueter Scirpus lacustris ssp glaucus fo major and Scirpus maritimus fo maritimus Subass Zonneveld 960 typicum phalaridetosum and senecietosum Zonneveld divides the association into three subassociations viz typicum phalaridetosum and senecietosum The main difference from an ecological point of view is their position with regard to the flutuating water level The three subassociations were found along a few former river beds that were in open connection with the lower course of the river The water may be fresh or slightly oligohalinic (see rec nrs The -3) vegetations are not very representative and only a few records were made They are bordered on the land side by one of the Caricetum gracilis-vesicariae the Phragmites-consociation or the Scirpeto-Phragmitetum calthetosum Subass typhetosum subass nov n the former river beds with stagnant oligo- to slightly mesohalinic water we found a community which is more or less intermediary between the Scirpetum triquetri et maritimi and the Scirpeto-Phragmitetum typicum The main species ofit occurring either in combination or as a facies are Scirpus maritimus Scirpus lacustris glaucus ssp (the formae of these two were not determined) Typha angustifolia Phragmites communis and Glyceria maxima A number of hydrophytes too are This present community probably also occurs in other oligoto mesohalinic territories in the Netherlands viz Botshol (Westhoff 99) lperveld (an Zinderen Barker 97) Waterland (see Waterland 9) e iede (Reynders 92) Zwet (eijer 93) n these cases in accordance with our results it is bordered by a halobious Potamion-

39 typ sen typhetosum maritimi et Scirpetum triquetri tidal influence stagnant water nr of record nr of former river bed river e e U mg Cl/ water depth (cm) Ü area (sq m) cover (%) total c herb layer a floating/moss layer 0 < submersed layer 0 0 Ch Ass Scirpus triqueter 22 Scirpus lacustris ssp glaucus (Smith) Hartman Scirpus maritimus sen Acc Cardamine amara 2 typh Ch All Typha angustifolia j Ch Pot emna minor ll Ceratophyllum demersum 2 2 emna trisulca 2 Spirodela polyrhiza () Schleiden 2 Enteromorpha intestinalis ink 2 Potamogeton pectinatus 2 Ch All Scirpus lacustris ssp lacustris 2 Ch Ord Phragmites communis Trin Rumex hydrolapathum Huds 2 2 Carex riparia Curt 2 2 Sium erectum Huds Glyceria maxima (Hartm) Holmb Acc yosotis scorpioides ll ris pseudacorus aucheria sp Ranunculus sceleratus 2 2 TABE Scirpelum triquetri et maritimi typ sen typhetosum tidal influence stagnant water nr of record i nr of former river bed river e e T3 J- mg Cl/ O O water depth (cm) u area (sq m) 't' cover (%) total c herb layer floating/moss layer 0 < Ph submersed layer ~ 0 0 Ch Ass Scirpus triqueter 22 # # # # Scirpus lacustris ssp glaucus (Smith) Hartman Scirpus maritimus sen Acc Cardamine amara 2 typh Ch All Typha angustifolia a Ch Pot emna minor H Ceratophyllum demersum 2 2 emna trisulca 2 Spirodela polyrhiza () Schleiden 2 Enteromorpha intestinalis ink 2 Potamogeton pectinatus 2 * * Ch All Scirpus lacustris ssp lacustris 2 Ch Ord Phragmites communis Trin Rumex hydrolapathum Huds 2 2 Carex riparia Curt 2 2 Sium erectum Huds Glyceria maxima (Hartm) Holmb Acc yosotis scorpioides ris pseudacorus aucheria sp Ranunculus sceleratus 2 2

40 A B _ C A B i C tot Ph water e2-6 9 eutrophic P H open water 72-7 eutrophic Caricetum acutiformo-paniculatae open water fresh <0 mg Cl/ mg Cl/ " j bri h * stagnant water river foreland stagnant water _ ü > O ' "h h Jh Jh nr of record o t-~ o - nr of former river bed lie 2 0a a d a Z Z a c a river W J J O O H W J J J - - area (sq m) cover (%) herb layer floating layer < < < 0 Ch Ass Carex paniculata Juslen ll Carex acutiformis Ehrh Carex riparia Curt A Comarum palustre 2 2 ll AB ycopus europaeus Eupatorium cannabinum 2 2 -j-l 2 Peucedanum palustre () oench 22-2 ll ABC Solanum dulcamara ll (Ch Ord) Glyceria maxima (Hartm) Holmb ythrum salicaria 2 2! ysimachia vulgar is 2 ( 2 2 (Ch Ord) Typha latifolia ll Equisetum fluviatile B Angelica sylvestris 2 BC Stachys palustris (Ch Ord) Rorippa amphibia () Besser 2 2 ( (Ch All) Carex acuta 2 2 { BC entha aquatica (Ch Ord) Slum latifolium (Ch Ord) Scirpus lacustris ssp lacustris -j-l 2 C Polygonum amphibium fo terrestre eyss -2 (Ch Ord) Alisma plantago-aquatica 2 2 j j Festuca arundinacea Schreb 2 22 (Ch All) Galium palustre H Ch Ord Phragmites communis Trin Rumex hydrolapathum Huds 2! H H Sparganium erectum )-l 2 2 Typha angustifolia H Sium erectum Huds j Acc ris pseudacorus Epilobium hirsutum 2 2 -) j Calystegia sepium () R Br -j-l 32 yosotis scorpioides Agrostis stolonifera -j j ychnis flos-cuculi S H emna minor H -K QB -30 A K BH K QB-S ranae : 6: 2 Galium aparine ; 22 Galeopsis tetrahit : 2 Stellaria palustris Retz 2: 2 Juncus effusus 3: 2 Bidens tripartitus 3; 2 Alnus glutinosa () Gaertn : Rubus caesius ;! Rumex crispus 8: 2 Cardamine pratensis 9: Glechoma hederacea 9: Symphytum officinale 2: 2 Pedicularis palustris 2: 2 aleriana dioica 2: 2 Hottonia palustris 3: Equisetum palustre : Urtica dioica 9: 2 Carex otrubae Podp 9: 2 Oenanthe fistulosa 20: 32 Calliergon stramineum (Brid) Kindb 3; 2 nium affine Schwaegr 2: 22 repanocladus fluitans (Hedw) Warnst 7: 22 20; 32 Supplement to the table Ch Ord; Sparganium simplex Huds 2: 2 Calla palustris 3: 2 Oenanthe aquatica () Poir 6: Nasturtium officinale R Br 6: 2 Phalaris arundinacea 9: 2 Acorus calamus 2: 22 Scirpus lacustris ssp glaucus (Smith) Hartman 7: 2 Scirpus maritimus 7; 2; Ace: Epilobium palustre 3: 2 6: 2 Scutellaria galericulata 6: 7; 2 Epilobium parviflorum Schreb 6: 2 9: 2 Poa trivialis 7: 2 20: 2 ysimachia nummularia 7: -f2 2: 2 Spirodela polyrhiza () Schleiden 8: 2 6: 2 Poa palustris 9: 2 9: 2 Salix triandra : : Caltha palustris 2: 2 6: 2 Hydrocharis morsus- TABE 3 A B C A B c tot Cariceüm acutiformo-paniculatae Ph mesotrophic open water eutrophic Ph open water 72-7 eutrophic open water fresh <0 mg Cl/ mg Cl/ CO CO CO CO CO T3 stagnant water river foreland stagnant water Ou O o ou Oo) O O U i-> u u nr of record o o nr of former river bed lie 2 0a a d a W J J O O H W J J J area (sq m) Ph Ph Ph Ph cover (%) herb layer floating layer < < < 0 Ch Ass Carex paniculata Juslen ii ii Carex acutiformis Ehrh 3 s # 2 2 ll ii ii in Carex riparia Curt in in A Comarum palustre 2 2 AB ycopus europaeus in Eupatorium cannabinum ii Peucedanum palustre () oench 22 2 i ABC Solanum dulcamara in ii (Ch Ord) Glyceria maxima (Hartm) Holmb i ii ythrum salicaria # i ysimachia vulgaris # i (Ch Ord) Typha latifolia i Equisetum fluviatile i B Angelica sylvestris 2 ii BC Stachys palustris ii i (Ch Ord) Rorippa amphibia () Besser 2 2 i i (Ch All) Carex acuta 2 2 i BC entha aquatica in in in (Ch Ord) Sium latifolium 2 2 # # 2 2 ii i i (Ch Ord) Scirpus lacustris ssp lacustris 2 i i i C Polygonum amphibium fo terrestre eyss 2 (Ch Ord) Alisma plantago-aquatica 2 2 Festuca arundinacea Schreb 2 22 ii (Ch All) Galium palustre ii i ii Ch Ord Phragmites communis Trin in Rumex hydrolapathum Huds ii in Sparganium erectum i ii Typha angustifolia i ii Sium erectum Huds ii Acc ris pseudacorus # 2 i Epilobium hirsutum i i Calystegia sepium () R Br 32 i yosotis scorpioides Agrostis stolonifera i ychnis flos-cuculi ii emna minor ii ii J AN ONSEAAR: On the vegetation of fromer river beds in the Netherlands

41 EGETATON OF FORER RER BES 39 or Ruppion- community at its deeper side and often by the Association of Sonchus paluster at the land side We propose to consider the community to be a subassociation of the Scirpetum triquetri et maritimi and to call it subass typhetosum t is distinguished from the other subassociations by the absence of Scirpus triqueter and by the presence of number a of differential species viz Typha angustifolia and some characteristic species of the Potametea n contrast with the other three subassociations it occurs only in oligoand mesohalinic water From the stagnant Scirpeto-Phragmitetum typicum it can be distinguished not only by the absence of Sparganium erectum ssp polyedrum but also by that of Ranunculus lingua and Typha latifolia 33 Alliance agnocaricion elatae Koch 926 The Synopsis gives three characteristic species for the agnocaricion One of these we want to exclude viz Poa palustris This species may be regarded as characteristic for the alliance so long as only natural vegetations are taken into account However it reaches its optimum in wet meadows (see p 62) The two remaining species are Galium palustre fo elongatum and ysimachia thyrsiflora The Synopsis includes four associations in the alliance but one of them the ariscetum serrati may be left out of consideration here as it does not occur in any of the former river beds The other three will be dealt with but we will not enter here in a discussion of the many differences existing between the utch the German and the Belgian subdivision of the agnocaricion These differences will be mentioned in a separate section ( 3 3 ) 33 Caricetum elatae Koch 926 A comparison of the literature and our records of the Caricetum elatae makes it clear that the association is not homogeneous The original author distinguished two characteristic species viz Carex hudsonii and Senecio paludosus The first can be maintained but the second has its optimum only in apart of the area in which the community occurs n accordance with the original conception the community every- Supplement to the subass typhetosum : Hydrochis morsus-ranae ; Ch Ord: Phalaris arundinacea (8: 2) Galium palustre (8: 2) eronica anagallis-aquatica (9: 2); Acc; repanocladus fluitans (Hedw) Warnst (7: 22) Oenanthe fistulosa (7: 2) Poa palustris (7: 2) Supplement to the rest of table Ch Ord: Alisma plantago-aquatica 3: 2 Sium latifolium 3; 2 Rorippa amphibia () Besser 3: 2; Acc: Polygonum amphibium fo terrestre eyss 2: Caltha palustris salicaria 3: 2 Rumex crispus 3: 2 3: 2 ythrum

42 0 J AN ONSEAAR where participates in the hydrosere on sand or peat and may be succeeded either by the Alnetum glutinosae or by a community belonging to the Caricion fuscae For the rest there are many following subdivision can be made: differences The Subass typicum subass nov ifferential species: Senecio paludosus Phalaris arundinacea and aleriana officinalis This subassociation corresponds with the original t is description a mainly eutraphentous type of vegetation Characteristic species of the alliance and the order are not numerous but anyhow they outnumber the representatives of other groups This subassociation was found in Switzerland (Koch 926) S Germany (Oberdorfer 97) and Belgium (anden Berghen 92 a; ebrun cs 99) n this connection it must be mentioned that in the Netherlands Senecio paludosus has its optimum in quite a different habitat viz the forelands of the upper as well as the lower courses of the larger rivers Along the lower course it occurs with total estimates of up to 2 in the Scirpetum triquetri et maritimi senecietosum and in the adjoining community of Epilobium hirsutum and Phalaris arundinacea (see Zonneveld 960) Along the upper courses Senecio paludosus has its optimum development together with Phalaris arundinacea in the transition of the Caricetum gracilis-vesicariae to the alerianeto-filipenduletum senecietosum (see p ) Subass comaretosum subass nov (Table 2) ifferential species: ysimachia thyrsiflora Calamagrostis canescens and the characteristic species of the class Scheuchzerio-Caricetea eg Comarum palustre and This Epilobium palustre subassociation is more mesotraphentous than the subass typicum n this connection an ijk and Westhoff (9) state that in the Netherlands Carex hudsonii is the mesotraphentous counterpart of the eutraphentous Carex paniculata The subassociation occurs in the Netherlands (Boer 92; amman 9) and in N Germany (Tuxen 937; Passarge 9 b) t was found in a number of former river beds along the euse with stagnant mesotrophic water with a Ph of 6 to 67 above a peat soil ts position in the hydrosere is usually between the Cicuteto-Caricetum pseudocyperus comaretosum and the Alnetum glutinosae or the Caricetum lasiocarpae 332 Caricetum acutiformo-paniculatae lieger et an Zinderen Bakker 92 (Table 3) The Caricetum acutiformo-paniculatae has been described in 92 (an Zinderen Barker 92) and since then it has been mentioned in several utch publications; see Boer (92) an Zinderen Barker (97) Westhoff cs (96) orzer Bruijns and Westhoff (9) an ijk and Westhoff (9) Kuiper and Segal (9) n Belgium an association of this name is mentioned by ebrun cs (99) but it does not correspond with the original description The community obviously has its optimum development

43 EGETATON OF FORER RER BES TABE 2 Caricetum elatae comaretosum comarelosum c n T3 -o of record 2 3 nr oo of former river bed nr river o r-- water depth (cm) area (sq m) 0 0 Cc 2 20 cover (%) 8 00 Ph Ch Ass Carex hudsonii A Benn Ch Galium palustre 22 # # ( subass) ysimachia thyrsiflora 2 Carex paniculata Juslen 2 Ch Ord Cicuta virosa 2 2 Typha latifolia Phragmites Ch S-C subass Comarum palustre Epilobium palustre Hydrocotyle vulgaris 2 2 Stellaria palustris Retz Agrostis iola palustris 2 2 Eriophorum angustifolium Peucedanum palustre () oench Acc ( subass) Calamagrostis canescens (Web) Roth ysimachia vulgaris 22 2 ycopus europaeus 22 -f2 2 2 emna minor -(-2 -j-2 2 Bidens tripartitus 2 Juncus effusus 2 2 Cardamina 2 pratensis 2 Brachythecium sp 2 2 Supplement to the table Ch Ord: Sparganium erectum Rumex hydrolapathum Huds ; Ch S-C; Carex rostrata Stokes ; Acc: Hydrocharis morsus-ranae (2: 2) Alnus glutinosa () Gaertn (2: 2) Frangula alnus ill (3: 2) Salix cinerea (3; 2) Sphagnum recurvum P de B (3: 3) Polytrichum Hedw commune (3: 3) Solanum dulcamara (; 2) Calystegia sepium () R Br (: 2) Cirsium arvense () Scop (: ) Salix triandra (: ) in the Netherlands There it is a very characteristic stage in the autogenic succession in stagnant water The habitat may be eutrophic or it may tend a little towards mesotrophic and the water even oligoto mesohalinic The soil consists of peat or peaty clay The community was found in several of the former river beds ts floristic composition shows a certain variability in correspondance with differences in the environment A subdivision of the association into subassociations however is as yet not justfied; to this end the presence of the species which might be differential ones is too low Therefore we only will distinguish some variants (see Table 3)

44 2 J AN ONSEAAR Attention must be drawn to the fact that the three characteristic species hardly ever occur together Nevertheless their actual ecological amplitudes overlap for the greater part Species which are found more frequently with one of the three than with the other two could not be detected ariant A n the mesotrophic stagnant water of the former river beds along the euse the association occurs without Carex riparia The presence of Comarum palustre and the absence of some purely eutraphentous species indicate a mesotrophic habitat The soil on which the vegetation occurs and its environment consists of peat The vegetation usually forms a floating mat with large tufts of Carex paniculata t is often a succession stage following the Cicuteto-Caricetum pseudocyperus comaretosum but sometimes it directly succeeds a Potamion-community n all cases the next stage is the Alnetum glutinosae Along some of the former river beds vegetations of Carex paniculata and of Carex hudsonii may alternate but they do not intermingle anywhere ariant B This variant corresponds with the greater part of the descriptions of the association given in the literature (eg Boer 92; an Zinderen Barker 92 97) t has its optimum development in the utch fens and broads and is rich in t is species probably in some cases hardly separable from the preceding stage the Cicuteto- Caricetum and may moreover be a combination of the variants A and B (eijer 9; Kuiper and Segal 9) Under natural conditions the community consists in the former river beds of floating mats found between either the Scirpeto-Phragmitetum typicum or the Cicuteto-Caricetum pseudocyperus typicum and the Alnetum glutinosae f by human interference the latter is absent the communi ts is usually bordered by meadows on the land side The soil consisty of peat or peaty clay but somewhere the water must be in contacc with clay ariant C This community occurs in a number of former river beds in the river forelands which during high water are not strongly influenced by the stream t is characterized here by the absence of Carex paniculata and by the preponderance of Carex riparia The floating mat retains some plant remains but the subsoil consists of clay Only in this habitat the association forms a stage in an (at least partly) allogenit succession t is preceded either by the Scirpeto-Phragmitetum typicum or by the Cicuteto-Caricetum pseudocyperus typicum and passes on the land side into the Caricetum gracilis-vesicariae or into some other community influenced by man

45 ~ EGETATON OF FORER RER BES 3 ariant Along the oligo- and mesohalinic former river beds with stagnant water sometimes a variant of the association occurs in the zone which is situated between the Scirpetum triquetri et maritimi typhetosum and the Association of Sonchus paluster or the meadow and which with regard to the water level is somewhat higher than that occupied by the other variants t consists nowhere of a floating mat The soil consists of peat or peaty clay The community lacks many of the common species and is characterized by the presence offestuca arundunacea and possibly also by that ofsium erectum n the table ofboer (92) one record made by Weevers on the island of Goeree belongs to this variant Perhaps this variant will turn out to be the most clearly definable one and to deserve the status of a subassociation 333 Caricetum gracilis-vesicariae Westhoff 99 (Table ) The Caricetum gracilis-vesicariae not mentioned in the Synopsis was described by Westhoff (99) ts characteristic species are Carex acuta and C vesicaria The association occurs in the Netherlands and in Belgium but has usually been described under the name Caricetum inflato-vesicariae Koch 926 (see eg lieger 937; eijer 97 a; an angendonck 93) andenberghen (92 a) uses this name too but his records do not correspond with the original concept n the literature the vegetations include the two characteristic species many species of the Phragmitetalia but also a few species belonging to the class Scheuchzerio-Caricetea The community occurs on a humic clay soil on the banks of stagnant water The association was found along many former river beds n all cases Carex acuta dominates; Carex vesicaria has a low abundance or is absent and this applies to all species of the Scheuchzerio-Caricetea The soil is mineral and consists mainly of clay; the water is eutrophic and fresh or slightly oligohalinic The vegetations are preceded by one of a Phragmition- association and on the deeper side they may be rich in Phragmites communis Under natural conditions the succeeding stage would be a Salicion-community but in most cases this is replaced either by the alerianeto-filipenduletum or by a meadow community Along former river beds with tidal influence Carex vesicaria is absent There the community is situated between the Scirpetum triquetri et maritimi the Scirpeto-Phragmitetum oenanthetosum or the S-P calthetosum on the outside and a tidal Salicion-community or the alerianeto- Filipenduletum subass of Heracleum At every high water the vegetation is submerged n the forelands without tidal influence the community occupies a zone where the water height in summer varies from next to nothing to 0 cm Here it is an important partner in the allogenic succession ts position is between the Scirpeto-Phragmitetum typicum or the S-P oenanthetosum and a foreland S'a&zon-community Where the latter is replaced by the alerianeto-filipenduletum senecietosum the transition is marked by a high abundance of Phalaris arundinacea and Senecio

46 Carex disticha Huds J AN ONSEAAR TAB Caricetum gracilis-vesicariae tidal influence of record i 2 3 nr of former river bed river W water depth (cm) area (sq m)! 9 cover (%) herb layer floating and submersed layer Ch Ass Carex acuta 2 Carex vesicaria Ch All Galium palustre 2 2 Ch Ord Phalaris arundinacea 22 Glyceria maxima (Hartm) Holmb 2 Sium latifolium 2 Rorippa amphibia () Besser 2 Phragmites communis Trin 2 2 Rumex hydrolapathum Huds Alisma plantago-aquatica Scirpus lacustris ssp lacustris Acc Equisetum fluviatile Senecio paludosus 2 2 Polygonum amphibium terrestre eyss 22 ris pseudacorus ythrum emna minor Equisetum palustre Supplement to the table Ch Ord: Typha latifolia 7: Oenanthe aquatica () Poir 0; Slum erectum Huds 3: 2 Ranunculus lingua 3: 2; Acc: Agrostis stolonifera : 2 7: 2 Rumex crispus 2: 0: Cardamine pratensis 2: 2 2: Calamagrostis canescens (Web) Roth : 2 9: -2 aleriana officinalis 6: 9: entha arvensis 7; : 2 Filipendula ulmaria () axim 8: 9: -2 Solanum dulcamara 0: 2 : 2 Hydrocharis morsus-ranae 3: 2 : 2 ycopus europaeus : 2 Galium aparine : 2 Ranunculus repens 2: 3 Cirsium arvense () Scop 6: Epilobium hirsutum 7: Scirpus sylvaticus 7; yosotis caespitosa K F Schultz 7: 2 Stellaria palustris Retz 7; 2 Poa trivialis 0; 2 Polygonummite Schrank 0: 2 Scutellaria galericulata : icia cracca 2: -- Amblystegia cf kochii Br et Schimp 2:

47 f-l i EGETATON OF FORER RER BES stagnant water river j foreland no tidal influence j n T3 su 02b b 0 J U R uj H WWWWW W W W W W J U J U i SO u C -S ^ Oh ll a # Potamogeton pusillus : 2 Utricularia : sp Spirodela polyrhiza () Schleiden : 2 Ricciocarpus natans () Corda 6: QB-S QB S QB-S K BH BH BH K S

48 6 J AN ONSEAAR paludosus Sometimes a record can be made with mainly these two species but usually they are accompanied by species of the preceding and the succeeding stage Along the stagnant former river beds the community usually occurs in less deep water There it is sometimes in contact or mixed with the Caricetum acutiformo-paniculatae (see p 8) At the land side it may be bordered by the acrophorbieto-alnetum or the alerianeto-filipenduletum Possibly in this habitat the community can maintain itself only is mowed regularly if it 33 Comparison between various subdivisions that have been proposed for the agnocarcion n Table some of the agnocaricion- associations that have been accepted in Belgium Germany and the Netherlands are compared The Caricetum inflato-vesicariae introduced by Koch (926) is a unit that has no value in the Netherlands The habitat of Carex rostrata and the other so-called characteristic species differ too widely This has been argumented sufficiently by Westhoff (99) The subass of Carex rostrata may better be regarded as a of the Caricion community TAB Comparison of some associations belonging ebrun Tiixen cs (99) Tlixen (937) Tiixen Caricetum inflato-vesicariae Ch Carex disticha subass of Carex disticha (Ch All) Caricetum inflat (Ch All) Ch ysimachia thyrsiflora Ch Pcucedanum palustre Ch Carex rostrata subass of Carex rostrata Ch Carex rostrata subass typicum Ch Carex vesicaria var of Carex vesicaria var Ch Carex vesicaria Caricetu Ch Carex acuta Ch Carex acuta (Ch All) var of Carex acutiformis Ch Carex acutiformis Ch Carex riparia Ch Carex riparia Caricetum acutiformo-paniculatae Caricetu Ch Carex paniculata Ch Carex paniculata

49 EGETATON OF FORER RER BES 7 fuscae or as a transition to this alliance A record answering the description of this community is given here as an example: Fieldnr -77 ate Cover 20 % Wychense Yen (nr 7) Area sq m Carex rostrata Stokes 22; Ch Phragmitetea: Phragmites communis Trin ysimachia thyrsiflora Galium palustre Acorus calamus Ranunculus lingua Typha latifolia Carex pseudocyperus 2; Ch Caricion fuscae:comarum palustre Stellaria palustris Retz 2; Acc: Oenanthefistulosa 2 etnha aquatica Stachys palustris 2 yosotis scorpioides ycopus europaeus Peucedanum palustre oench Cardamine pratensis The (Belgian) subass of Carex disticha was found along several of the former river beds The vegetations border the Carex acuta- zone on places grazed by cattle The community consists mainly of Carex disticha and contains also several typical meadow species with often high total estimates and very few species of the Phragmitetea Therefore it is regarded here as a wet meadow community (see p 62 and Table 22 nrs and 9) The subass (or variant) of Carex vesicaria probably corresponds with most utch descriptions of the Caricetum inflato-vesicariae The ne agnocaricion proposed by different authors and Freising (9) Westhoff cs (96) Westhoff (99) SO (wet meadow vegetation) esicariae (Ch All) subass of Carex rostrata (Caricion fuscae community) Caricetum gracilis-vesicariae subass of Carex vesicaria Ch Carex vesicaria racilis Ch Carex acuta Caricetum acutiformo-paniculatae Ch Carex acutiformis Ch Carex riparia aniculatae Ch Carex paniculata variants A and B

50 8 J AN ONSEAAR community should be mesotraphentous and this is more or less in accordance with its floristic composition in the Netherlands (see p 3) The Caricetum gracilis of Tuxen seems to show a strong resemblance to the variant ofcarex acutiformis of ebrun cs Some records answering the description of this community were made along some former river beds See the following example: Fieldnr K 6078 ate Scherpenzeelse Hank (nr ) Area 9 Water depth 20 cm Cover 9 % sqm Carex riparia Curt 32 Carex acuta 22; Ch All: Galium palustre 22; Ch Ord Phragmites communis Trin 22 Rorippa amphibia Besser () 2 Phalaris arundinacea 2; Acc: Hydrocharis morsus-ranae 2 Polygonum amphibium fo terrestre eyss 2 ris pseudacorus 2 Poa palustris 2 entha aquatica x entha arvensis 2 Carex disticha 2 Senecio paludosus 2 The occurrence of the combination of Carex acuta and Carex riparia can in our opinion be explained in the two following ways: On ) some places in the forelands the silting up and the accumulation of plant remains exercise an equally important function in the succession Then a habitat comes into existence where both species flourish 2) f a former river bed is isolated from the river by a dike the succession in the water changes from allogenic into autogenic The soil on the deeper side of the Carex acuta-vegetation will gradually be covered by plant remains and possibly even a floating mat vegetation will try to take its place n consequence temporarily a mixture can of the old and the new community will be present and this mixture will maintain itself for some time especially if the vegetation is mowed We regularly nowhere found the combination of Carex acuta and C acutiformis The German Caricetum paniculatae and the Belgian Caricetum acutiformo-paniculatae correspond probably with our variants A and B in so far as they consist mainly of Carex paniculata or (in the latter case only) of Carex acutiformis (table 3 eg nrs 2 7-8) The Cicuteto-Caricetum in our pseudocyperus opinion a Phragmitionassociation is included by Tuxen and Freising (9) in the agnocaricion This has been discussed on p 33 Tuxen and Freising also mention a Caricetum vulpinae Tuxen (9) a gives description of the association accompanied by one record t should be less wet than the other associations of the alliance and occur in river valleys with great fluctuations in the ground water level Carex vulpina should be the only characteristic species An example of this community was found along one of the former river beds t is given here: Fieldnr -K ate Former river bed in the Banwaard (nr 29) Area 8 sqm Soil; wet grey-brown clay Water level - m Cover 9 % Carex vulpina 22; Ch Phragmitetea: Glyceria maxima (Hartm) Holmb 32 Phalaris arundinacea 2 Carex acuta 2 Galium palustre ; Ch ~ ' olinieto-arrhenatheretea: Poa trivialis 32 Equiselum palustre 2 Taraxacum officinale Weber Rumex acetosa Cardamine pratensis 2; Ch Agropyro-Rumicion: Ranunculus repens 2 Alopecurus geniculatus 2 Potentilla anserina 2; Acc: Polygonum amphibium

51 EGETATON OF FORER RER BES 9 fo terrestre eyss 2 Eleocharis palustris () R et Sch 2 Stellaria palustris Retz 2 yosotis scorpioides 2 Caltha palustris 2 Trifolium sp n our opinion this record can not be regarded as representing a community belonging to the agnocaricion The part played by species belonging to other units is too large This also applies to Tuxen s own record Our own subdivision of the agnocaricion has some important advantages By excluding the communities which form transitions to the wet meadows (vegetations of Carex disticha and of Carex vulpina) we obtain an alliance consisting of swamp associations only n the hydrosere they are generally preceded by a Phragmition-community and succeeded by some carr or by a Caricion fuscae-community The autogenic succession in stagnant water comprises the Caricetum elatae comaretosum (mesotraphentous) or the Caricetum acutiformo-paniculatae (slightly meso- to eutraphentous) The Caricetum gracilis-vesicariae is the community growing on firm mineral soils along the border of pools Possibly it must be divided into two subassociations The first is more mesotraphentous with Carex vesicaria and species of the Caricion fuscae and occurs along stagnant water on a humic clay soil The second is purely eutraphentous dominated by Carex acuta and occurs especially in the forelands on a purely mineral soil The system ofebrun cs has the advantahe that frequently occurring combinations by others considered as transitions all may be included in the large Caricetum The inflato-vesicariae of Tuxen system and Freising makes a clear division between a mesotraphentous Caricetum inflato-vesicariae and an eutraphentous Caricetum gracilis aybe both systems are appropriate in their respective regions n the Netherlands however the Caricetum acutiformo-paniculatae with three characteristic Carices can not be neglected and this fact determines the main differences between our system and the other two 33 Thelypterideto-Phragmitetum Kuiper 97 (Table 6) Kuiper (97 see also 98) introduced a new association of the Phragmitetalia: the Thelypterideto-Phragmitetum Up till now he himself did not describe the community but he refers to a table of eijer (9) indicated as vegetations of rypteris thelypteris The only characteristic species is ryopteris thelypteris The community may participate in the hydrosere of stagnant eutrophic fresh water on exposed and is found behind spots the Scirpeto-Phragmitetum typicum Kuiper is not yet sure whether the association belongs to the Phragmition the or to agnocaricion n three former river beds a vegetation with much ryopteris thelypteris was found t is however relatively poor in species The place of the vegetations is more or less in accordance with Kuiper s data All three records are given in the table Characteristic species of the Phragmition the agnocaricion and the (meso-oligotrapentous) Scheuchzerio-Caricetea are mentioned separately

52 0 AN ONSEAAR J TABE 6 Thelypterideto-Phragmitetum 2 3 nr of record nr nr of former river bed river J T area (sq m m) ) cover (%) 2 Ch Ass ryopteris thelypteris () A Gray Ch Phron Typha angustifolia 2 Typha latifolia 2 2 Carex pseudocyperus Ch g ysimachia thyrsiflora 22 Galium palustre 2 Carex hudsonii A Benn 2 *2 Ch Ord Phragmites communis Trin 32 Sparganium erectum A 2 Rumex hydrolapathum Huds!l Ch S-C enyanthes trifoliata 22 Comarum palustre Epilobium palustre E2 2 l Carex rostrata Stokes Acc ycopus europaeus entha aquatica 2 Scutellaria galericulata - Equisetum fluviatile E2 2 Calamagrostis canescens (Web) Roth 22 Supplement to the table Acc: emna minor : Peucedanum palustre () oench 2: ysimachia vulgaris 2; 2 Solanum dulcamara 2: Stachys palustris 2: 2 ryopteris cristata () A Gray 3: 2 Cirsium palustre () Scop 3: archantia 3: sp Brachythecium 3: sp K Class ONETO-ARRHENATHERETEA Tüxen 937 Order olinietalia coeruleae Koch 926 Alliance Filipendulo-Petasition Braun-Blanquet 97 n 97 Braun-Blanquet separated the Filipendulo-Petasition from the alliance olinion coeruleae Koch 926 The new alliance observed in NW and S Germany (see Tuxen 9; Oberdorfer 97) and also mentioned by uvigneaud (99) seems to be acceptable in the Netherlands too (see Segal and Westhoff 99) n the Netherlands the olinion four associations After comprises a complete revision of the classes olinieto-arrhenatheretea and Scheuchzerio-Caricetea fuscae (which certianly is necessary see ebrun cs

53 EGETATON OF FORER RER BES 99; uvigneaud 99) none of these four would be left in it According to Segal and Westhoff the (99) Cirsieto-olinietum might be transferred to the Eriophorion latifolii This probably holds for the Juncetum acutiflori too The two other communities the alerianeto-filipenduletum and the Association of Sonchus paluster be may regarded belonging to the Filipendulo-Petasition (see also uvigneaud 99) f this is accepted the alliance would merely consist of replacingcommunities of carrs (A lneturn glutinosae Salicion and Alnion glutinosoincanae) Their habitat generally would come into existence by the cutting down of the trees or else by an artificial heightening of the substrate See e g Westhoff (99) and Waterland (9) A natural factor which prevents the growth drift (Zonneveld 960) of trees and shrubs may be ice Although future changes are not excluded we propose for the moment the following species as characteristic (within the formation) of the Filipendulo-Petasition in the Netherlands: aleriana officinalis Epilobium hirsutum Eupatorium cannabinum and Angelica sylvestris alerianeto-filipenduietum Westhoff 99 (Table 7) According to the Synopsis and Westhoff (99) the characteristic species of the association are: aleriana officinalis Hypericum maculatum Euphorbia palustris Stachys palustris Crepis paludosa eronica longifolia athyrus paluster and Festuca arundinacea Some alterations are recommendable aleriana officinalis also occurs in the Association of Sonchus paluster and must be regarded as a characteristic species of the alliance Supplement to table 7 Ch A: Eupatorium cannabinum : ; Ch C: Holcus lanatus : -)-2 3: 2 actylis glomerata 2: 2 : 2 athyrus pratensis 8: 2; Acc: iburnum opulus : 2 : ychnis flos-cuculi : 8: 2 Ranunculus repens : : 32 Rubus idaeus 2: 2 3: 2 otus uliginosus Schkuhr 2: 2 : Galium aparine 3: 2 2: Epilobium parviflorum Schreb : 8: 2 entha arvensis : 7: 22 Stellaria palustris Retz ; 2 7: 2 entha aquatica 6: 0: 2 Potentilla reptans 0: 2 : Rubus sp 3: 2 Scirpus sylvaticus 3: 2 ycopus europaeus 3; 2 Galeopsis tetrahit 3: 2 Cirsium palustre () Scop : 2 Carex pseudocyperus : 22 Carex elongata : Salix cinerea : Alnus glutinosa () Gaertn ; Sambucus nigra : Athyrium filix-femina () Roth : 2 Stellaria alsine Grimm ; Rorippa amphibia () Besser : Sium latifolium : Scirpus lacustris ssp lacustrisg: Rumex hydrolapathum Huds 6: 2 Trifolium repens 7: Achillea ptarmica 8: 2 Rumex obtusifolius 9: yosotis caespitosa K F Schultz 0: 2 Salix triandra 0: 2 Artemisia vulgaris 2: Tanacetum vulgare 2: 2 Cirsium arvense () Scop 3: yosotis scorpioides 3: Rumex conglomeratus urr 3: Typha latifolia 3: 2 Plantago major ; 2 Festuca gigantea () ill : 2 olium perenne : 2 Senecio jacobaea : K QB-S BH K QB-S QB-S

54 # 2 J AN ONSEAAR TAB jvincetosum juncetosum alerianeto-filipenduletum mesotrophic stagnant water nr of record nr of former river river 2 3 bed 2 a llh 7 area area (sq m) cover (%) 00 9 Gh Ch Ass Filipendula ulmaria () axim Thalictrum flavum June Juncus effusus Juncus conglomeratus 2 sen Senecio paludosus Polygonum amphibium fo terrestre eyss ysimachia nummularia her (Ch Cl) Heracleum sphondylium (Ch All) Epilobium hirsutum Anthriscus sylvestris Hoffm Agrostis stolonifera not June (Ch Cl) Phalaris arundinacea Phragmites communis Trin Symphytum officinale icia cracca j Glyceria maxima (Hartm) Holmb not All) sen (Ch Angelica sylvestris j not her ysimachia vulgaris 2 Calamagrostis canescens Roth 33 2 alerianaofficinalis Ch All 32 3 Ch Cl Poa trivialis 22 Cardamine pratensis Acc Rubus caesius i 22 j ythrum salicaria 2 2 ris pseudacorus 2 Stachys palustris 2 2 Calystegia sepium R Br 22 Urtica dioica 22 Carex acuta Galium palustre 2 Glechoma hederarcea Equisetum palustre 2 Solanum dulcamara Rumex crispus Equisetum fluviatile * 'i 2

55 -2 2 s EGETATON OF FORER RER BES 3 7 senecietosum subass of Heracleum sen her tot June eutrophic stagnant water or river foreland no tidal influence o records tidal influence o J J y in= S in R W W W W u o v e « Ph Pto P records records in records S in P \ ~2! TT 2J\ # # !! T H H ll ll 22 # H H 2 a # 2 2 H

56 J AN ONSEAAR Stachys palustris must be eliminated; it is as just important in the Phragmitetea Thalictrum flavum and Filipendula ulmaria occur in the Cirsieto-olinietum but undoubtedly have their optimum in the alerianeto-filipenduletum oreover it seems better to transfer the Cirsieto-olinietum to the Eriophorion latifolii and if this is done they may be accepted ascharacteristic species of the alerianeto-filipenduletum The association shows a remarkable variability which corresponds more or less with the differences in the undergrowth of the replaced carrs Along the former river beds we found three communities which must be regarded as subassociations n the utch literature moreover the presence of two other subassociations (though not described as such; see also Westhoff 9 a) is viz one indicated along the broads in the Haf district and one along brooks n table 8 are listed all species which in one way or another are useful as differential species The characteristic species are indicated Remarks separately in the literature concerning the occurrence of Crepis paludosa and Hypericum maculatum are not clear Anyhow these species do not occur in the subassociations juncetosum and senecietosum and the subass of Heracleum The subassociations of the broads and the brooks will be left out of consideration now They are not found along the former river beds See the publications and tables dealing with the broads: an Zinderen Barker (92 97) e Jong (93) Westhoff (99) Reynders (92) an ijk and Westhoff (9) eijer (9); dealing with the brooks: Klinkenberg (93) n Belgium where the association occurs also Heinemann (see ebrun cs 99) distinguishes four subassociations viz ) with Carex disticha 2) typicum with 3) Holcus lanatus ) with Urtica dioica This subdivision corresponds in no way with ours aybe it can be applied in the Netherlands too but for the moment our subdivision seems better founded Subass juncetosum subass nov This subassociation was found along the mesotrophic former river beds soil t on a peaty replaces the mesotraphentous variant of the Alnetum and glutinosae may border the Caricetum acutiformo-paniculatae amman (93) gives two records of this community made in the same region as ours Subass senecietosum subass nov Outside the tidal area the forelands have their own subassociation of the alerianeto-filipenduletum There it replaces a foreland Salicioncommunity n some cases not the cutting down of the trees but the ice drift in winter may the prevent development of a marsh-carr any of the former river beds with stagnant and eutrophic fresh water found inside the dikes have this community along their borders There it is a relic from the situation before the dike was constructed and usually is preserved by mowing t corresponds with

57 otus uliginosus X X Heracleum sphondylium X EGETATON OF FORER RER BES TABE 8 junce- senecie- Sub association tosum broads of Herabrooks tosum cleum Characteristic and differential species Ch Crepis paludosus Ch Hypericum maculatum Juncus effusus X Juncus conglomeratus X Calamagrostis canescens X X X X ysimachia vulgarisia X X X X Ch Filipendula ulmaria X X X X X Angelica sylvestris X X X X Scutellaria galericulata X X X icia cracca X X X X Ch Thalictrum flavum X X X X Symphytum officinale X X X X Phragmites communis X X X X Glyceria maxima X X X X Phalaris arundinacea X X X Ch Euphorbia palustris X Ch athyrus paluster X Succisa pratensis X Ch eronica longifolia X Achillea ptarmica X Polygonum amphibium fo terrestre X Senecio paludosus X ysimachia nummularia X Rubus caesius X X X Anthriscus sylvestris Ch Festuca arundinacea X X Cardamine amara Agrostis stolonifera X X Epilobium hisutum X carrs belonging to the Salicion or to the Alton glutinoso-incanae and usually borders the Caricetum gracilis-vesicariae Along former river beds which have been isolated very long ago from the river and which are foundin places where in the surrounding soil the profile-formation has reached an advanced stage Angelica sylvestris and Eupatorium cannabinum (both lacking in the subass

58 6 J AN ONSEAAR senecietosum) may occur Eight records with these species were left out of account in the subdivision of the association Subass of Heracleum Zonneveld 960 Zonneveld described a provisional subassociation occurring in the tidal area t has quite a number of differential species and its habitat totally differs from that of the other subassociations Therefore we propose to accept it as a distinct subassociation The community was found along a number of former river beds with tidal influence There it replaces a tidal variant of the Salicion Only three records were made which are all three included in the table The differential species and the species not in occurring this community have not been taken from our own records but from Zonneveld s table 2 Association of Sonchus paluster lieger et an Zinderen Bakker 92 (Table 9) lieger and an Zinderen Barker (see an Zinderen Barker 92) described a community of Sonchus paluster which they did not (yet) propose as an association n our opinion two ofthe three records which are given by them must be referred to the alerianeto-filipenduletum but the third represents a community which afterwards was mentioned by others under the name community of Sonchus paluster See an Zinderen Barker (97) Westhoff (99) Reynders (92) eijer (93) Waterland (9) This same community was found along the halinic former river beds with stagnant water n our opinion the community deserves the status of an association t is sufficiently distinct from the the community which it resembles most by characteristic species of its own alerianeto-filipenduletum and by the very particular character of its habitat There is however a transition between the two Sonchus paluster is a characteristic species and this applies also to Althaea officinalis as suggested by the Synopsis Epilobium hirsutum (also suggested) however is much more common in the subass of Heracleum of the alerianeto-filipenduletum Eupatorium cannabinum may be used as a differential species to distinguish it fromthe subassociations of the alerianeto-filipenduletum occurring along stagnant waters Two differential species by which it differs from the whole of the alerianeto- Filipenduletum are Sium erectum and Carex riparia; it differs from this association also by the absence of Calamagrostis canescens ysimachia vulgaris icia cracca and Glyceria maxima from Apart Eupatorium cannabinum a high presence is also shown by Poa trivialis Angelica sylvestris Phragmites communis and entha aquatica The association has its optimum development along mesohalinic water stagnant Only there Althaea officinalis is present whereas aleriana officinalis is lacking The community also occurs along oligohalinic waters There it be mixed with the alerianetomay Filipenduletum or it be may bordered by this community on the land side

59 2 EGETATON OF FORER RER BES 7 TABE 9 Association of Sonchus paluster nr of record 2 3 nr of former river bed river mg Cl/ in open water area (sq m) cover (%) Ch Ass Sonchus paluster Ch All Eupatorium cannabinum 2 aleriana officinalis Epilobium hirsutum 2 Filipendula () Ass Carex riparia Curt Symphytum officinale 2 Urtica dioica 2 Rumex conglomeratus urray 2 Pulicaria dysenterica () Bernh 2 Rubus caesius The association is generally preceded by the Scirpetum triquetri el maritimi typhelosum According to our data however the Caricetum acutiformo-paniculatae (variant ) may be interposed between them A similar zonation was also observed in some broads an by Zinderen Barker (97) Possibly this zonation will be found only along oligohalinic waters The drier side of the community may replace a eutraphentous variant of the Alnetum glutinosae 3 Community of Epilobium hirsutum and Phalaris arundinacea Zonneveld 960 (Table 20) Zonneveld (960) distinguishes a community of Epilobium hirsutum and Phalaris arundinacea found in the Biesbosch t is situated between the Scirpetum triquetri et maritimi senecietosum and the alerianeto-filipenduletum subass of Heracleum The community has no characteristic species of its own whereas characteristic species of the Phragmition and the olinion (Filipendulo-Petasition) are equally important Without

60 C/ J AN ONSEAAR TABE 20 Community of Epilobium hirsutum and Phalaris arundinacea nr of record 2 T3 "2 u nr of former river bed u river W <u 2h m) 6 area area (sq cover (%) 00 -S CO Ph Phalaris arundinacea 22 Stachys palustris 2 Phragmites communis Trin - -l Senecio paludosus 2 Urtica dioica 2 Calystegia sepium () R Br 2 Rorippa amphibia () 2 Sium latifolium S TABE 2 Phragmites-consociation nr of record nr of former river bed river e O O O e area (sq m) cover (%) Species of the Phragmites-consociation Phragmites communis Trin 3 palustris Cardamina amara Ranunculus ficaria 2 22 Other species Polygonum amphibium fo terrestre eyss 2 22 aleriana officinalis -f-2 Calystegia sepium () R Br - Phalaris arundinacea 2 22 Galium aparine 2 -j-2 2 Urtica dioica 2 Equisetum arvense K K K K

61 EGETATON OF FORER RER BES 9 taking a definite decision Zonneveld is inclined to reckon it to the Phragmition n two of the former river beds with tidal influence a community was found resembling the just mentioned one not only in composition but also with regard to its position Two records are given as examples Phragmites-consociation Zonneveld 960 (Table 2) n the reed swamps and in the adjacent communities in the tidal area Phragmites communis may come to absolute dominance This is caused either by its enormous competing force or by human interference mainly regular mowing The few species occurring in these very dense Phragmites- fields have their flowering period early in spring or do not flower at all in this habitat Zonneveld (960) describes the dominance of Phragmites in the Biesbosch There the Phragmites- fields may occupy jhe place of the Scirpeto-Phragmitetum calthetosum the community of Epilobium hirsutum and Phalaris arundinacea and the alerianeto-filipenduletum subass of Heracleum The floristic differentiation of the Phragmites- fields does not correspond with the various communities which they replace Therefore it is not allowed to designate it as the Phragmites- facies of a special community oreover the character of these vegetations hardly permits to describe them as vegetation units in the sense of Braun- Blanquet Therefore Zonneveld designates the whole group of Phragmites- fields as the Phragmites-consociation and divides it in sociationgroups and sociations in the sense of u Rietz (930) egetations representing this consociation play an important part in a number of former river beds in the tidal area As in the Biesbosch they occupy in the first place the basins The records nrs 2 and 3 represent the Phragmites-Caltha-sociation respectively in its normal form in one that is poorer in Caltha and in one that is richer in Caltha These sociations replace parts of the Scirpeto-Phragmitetum calthetosum the Scirpetum triquetri et maritimi senecietosum and even transitions to the community of Epilobium hirsutum and Phalaris arundinacea The records nrs and 6 are probably more or less transitional between one of Zonneveld s sociations and the communities they replace n only one of the former river beds viz the Kooigat near Rhoonse eer (nr 7) eucojum aestivum was found This species which is very rare in the Netherlands occurs also in other places along the Oude aas (an eeuwen 9) but is absent in the Biesbosch Along the Kooigat its occurrence is restricted to the vegetations of the Phragmites-consociation Though not numerous the had plants flowers and and made fruits a healthy impression WET EAOW EGETATONS (Table 22) any former river beds are meadows surroundedby Thesemeadows may occur in places which under natural conditions would be fully occupied either by a carr or by a vegetation of the alerianeto-filipenduletum or one of the Caricetum gracilis-vesicariae

62 wet meadow vegetations nr of record nr of former river bed d b -o river J R J J J J eg area (sq m) A* S cover (%) Alopecurus geniculatus and Rumex crispus Ch Ass of ysimachia nummularia 2 2 Carex hirta 2 22 Potentilla reptans 2 Rorippa sylvestris () Besser Cl Plantaginetea majoris and Agropyro-Rumicion crispi Ch All Ranunculus repens Agrostis stolonifera ll Potentilla anserina Rumex crispus 2 2 olium perenne 22 eontodon autumnalis Plantago major 2 Sagina procumbens 2 Cl Phragmitetea and agnocaricion elatae Ch All Galium palustre Phalaris arundinacca ll Glyceria maxima (Hartm) Holmb 32 ll Carex acuta 2 2 olinieto-arrhenatheretea Ch Cl Equisetum palustre 2 2 ll Cardamine pratensis 2 2 ll TABE 22 wet meadow vegetations nr of record nr of former river bed d b o ««U R U u U J S 8 area (sq m) a S cover (%) Ch Ass of Rumex crispus and Alopecurus geniculatus ysimachia nummularia Carex hirta 2 22 Potentilla reptans 2 Rorippa sylvestris () Besser Ch All Agropyro-Rumicion crispi and Cl Plantaginetea majoris Ranunculus repens Agrostis stolonifera Potentilla anserina Rumex crispus 2 2 olium perenne 22 eontodon autumnalis Plantago major 2 Sagina procumbens 2 Ch All agnocaricion elatae and Cl Phragmitetea Galium palustre Phalaris arundinacea Glyceria maxima (Hartm) Holmb 32 Carex acuta 2 2 Ch Cl olinieto-arrhenatheretea Equisetum palustre 2 2 Cardamine pratensis 2 2

63 Poa trivialis Rumex acetosa 2 Taraxacum officinale Weber Thalictrum flavum 2 icia cracca 2 Other species Carex disticha Huds Polygonum amphibium fo terrestre eyss j entha aquatica! ll Eleocharis palustris () R et Sch ll yosotis scorpioides 2 ll Trifolium repens Juncus articulatus Oenanthe fistulosa Stellaria palustris Retz 2 Equisetum fluviatile 2 2 Caltha palustris 2 Poa palustris 2 Poa pratensis Supplement to the table Ch Phragmitetea: Phragmites communis Trin 6; 7: 2 Rorippa amphibia () Besser : Typha latifolia 3: Glyceria fluitans () R Br ; Rumex hydrolapathum Huds 6: 2; Ch olinieto-arrhenatheretea: Prunella vulgaris 2: -fl 8: 2 Juncus conglomeratus 2: 2 : 2 Cerastium caespitosum Gilib 3: 8: 2 ysimachia vulgaris 7: 8: 23 Festuca pratensis Huds 8: 2 9: athyrus pratensis 8: 9; aleriana officinalis : 2 Chrysanthemum leucanthemum 2; 2 otus uliginosus Schkuhr 2: Ranunculus acer 2; Achillea ptarmica 2: Cynosurus cristatus 2: Filipendula ulmaria () axim 8: 2 Alopecurus pratensis 9: Holcus lanatus 9: ; other species: eschampsia caespitosa () P B : 2 7: 2 ycopus europaeus : 8: entha arvensis : 2 2; Carex otrubae Podp 2: : 2 Euphrasia odontites 3: 2 : 2 ythrum salicaria : 7: Glechoma hederacea : 2 Stellaria graminea : Carex nigra () Reichard : Plantago lanceolata 2; Senecio jacobaea 2: Scutellaria galericulata 3: Calliergonella cuspidata (Hedw) oeske : Juncus compressus Jacq : 2 Senecio paludosus 7: 2 Symphytum officinale 7: 2 ychnis flos-cuculi 7: 2 Rhinanthes glaber am 7: Equisetum arvense 7: ris pseudacorus 8: K K S QB-S S QB-S Poa trivialis 22 a 2 3 Rumex acetosa 2 Taraxacum officinale Weber Thalictrum flavum 2 icia cracca 2 Other species Carex disticha Huds Polygonum amphibium fo terrestre eyss entha aquatica Eleocharis palustris () R et Sch yosotis scorpioides 2 Trifolium repens Juncus articulatus Oenanthe fistulosa Stellaria palustris Retz 2 Equisetum fluviatile 2 2 Caltha palustris 2 Poa palustris 2 Poa pratensis 22 22

64 62 J AN ONSEAAR Though a number of species of the replaced communities may be present the flora of the wet meadows has a specific composition this connection three species deserve our special attention viz Oenanthe fistulosa Poa palustris and Carex disticha n the Synopsis papers too they are considered to be characteristic species n and in other of the Phragmitetalia or of one of its lower units n our opinion these species have their optimum development in wet meadow communities not belonging to the Phragmitetalia (see also p and 7) Constant species which may reach high abundances are Carex disticha Agrostis stolonifera and Eleocharis palustris t can be seen from the table that there are other species which may reach high abundances t also appears which are either constant or that there is a great variability in the floristic composition t is not possible to find any correlation between the presence or absence of a species or a group of species and one of the environmental factors that could be studied at the time the records were made This is not surprising for there are a number of other factors dominate the effect of the latter Tuxen (90) (97) state that in river forelands the composition which may influence or even communities may vary greatly from year to year according and Oberdorfer of some meadow to differences in the length of the inundation period Other factors of great importance that were not investigated are grazing and mowing (see an Woerdt and e ries 98) t is not possible to identify all records with one of the vegetation units that so far have been described and that are acceptable to us Certainly a number of our records agree with the Caricetum inflatovesicariae subass Carex disticha (see a record by anden Berghen 92 a) but we prefer to exclude this The possibility (see p 7) greater part of the records however shows to affinity the Association of Rumex crispus and Alopecurus geniculatus This association belongs to the Agropyro-Rumicion crispi an alliance of the Plantaginetalia majoris which is the only order of the class Plantaginetea majoris Before Tuxen (90) proposed this classification the Association of Rumex crispus and Alopecurus geniculatus was known under the name Association of Ranunculus repens and and Alopecurus geniculatus included in the Arrhenatherion elatioris (Tuxen 937; Westhoff cs 96) orzer Bruijns (97) is the only author who described the in community the Netherlands viz in the valley of the Jsel n our opinion the new classification of Tuxen (90) may be useful in the Netherlands too We therefore include the characteristic species of the Association of Rumex crispus and Alopecurus geniculatus in the table; some corrections given by Tuxen (9) in a later publication are taken into account 6 Class SCHEUCHZERO-CARCETEA FUSCAE (Nordhagen) Tüxen 937 n different countries the class Scheuchzerio-Caricetea fuscae has been subdivided in very different ways A review of the various systems will not be given here because the class is represented in the former

65 EGETATON OF FORER RER BES 63 river beds by three associations only Attention must be drawn however to the main Belgian literature dealing with this class viz uvigneaud (99) uvigneaud and anden Berghen (9) ebrun cs ( 99) and andenberghen (92 The b) first-mentioned author gives a complete revision of the classification of all plant communities occurring in Europe on a more or less peaty soil He unites them in a new class the Sphagno-Caricetea fuscae which comprises the Scheuchzerio-Caricetea the Oxycocco-Sphagnetea and parts of the olinieto-arrhenatheretea Though it is not sure that the subdivision given in the Synopsis the best one for the Netherlands it will be used here is 6 Order Caricetalia fuscae Koch Alliance Caricion fuscae Koch 926 The position of Carex rostrata in the Synopsis a characteristic species of the Caricetum inflato-vesicariae has been discussed by Westhoff (99; see also p 6) We add it to the characteristic species Caricion fuscae a possibility already suggested by Westhoff of the 6 Caricetum lasiocarpae Koch 926 (Table 23) n the Synopsis the Caricetum lasiocarpae is given with three characteristic species viz Carex lasiocarpa C diandra and Eriophorum gracile n the Netherlands this association occurs along pools and broads and participates in the hydrosere starting in mesotrophic water ts composition is very variable; and this variability is related with its stage of development and with the properties of the water t may be preceded by a community of the Potamion of the ittorellion or by the community of Juncus subnodulosus and enyanthes trifoliata Sometimes it succeeds a agnocaricion-community t is itself succeeded either by the Caricetum canescentis-fuscae mowed and the soil drained) by by a carr or (if the vegetation is the Cirsieto-olinietum See an Zinderen Barker (92) orzer Bruijns and Westhoff (9) Kuiper (97) Kuiper and Segal (9) an ijk (9) e Wit (9 9) and Westhoff The association occurs in a number of isolated former river beds n this habitat it is however very poor in species in comparison with those given in the utch literature quoted above Two of the three characteristic species Carex diandra and Eriophorum gracile are absent and this applies also to several other species eg to the greater part of the mosses There are different opinions with regard to the question in which way the great variability of the Caricetum lasiocarpae should be dealt with Schwickerath (92) uses this association as a good example to demonstrate the way in which differential species may be used He lets the association intact but introduces many differential species to indicate its eg imperceptibly changing character from eutraphentous to obligotraphentous The Synopsis places itself on the same standpoint Other authors divide the association into two parts:

66 Caricetum lasiocarpae oligomesotrophicum nr of record nr of former river bed 2 3b 3 3c river g water depth (cm) u area (sq m) * cover (%) total c herb layer floating layer < < < moss layer 60 9 " i Ch Ass Carex lasiocarpa Ehrh Ch All Carex rostrata Stokes Epilobium palustre -2 repanocladus exannulatus (Giimb) Warnst 3 Calliergon cordifolium (Hedw) Kind Sphagnum platyphyllum Warnst Carex curta Good -2 Ch Ord Comarum palustre Campylium polygamum (Br eur) Bryhn 3 Ch Cl enyanthes trifoliata Eriophorum angustifolium Honckeny 2 Agrostis canina 2-2 Acc Hypericum elodes 2 2 Hydrocharis morsus-ranae TABE 23 Caricetum lasiocarpae oligomesotrophicum nr of record nr of former river bed 2 3b 3 3c CO U O water depth (cm) Q u area (sq m) cover (%) total herb layer C floating layer < < < moss layer 60 9 Ch Ass Carex lasiocarpa Ehrh Ch All Carex rostrata Stokes Epilobium palustre 2 repanocladus exannulatus (Gümb) Warnst 3 Calliergon cordifolium (Hedw) Kind Sphagnum platyphyllum Warnst Carex curta Good * * 2 Ch Ord Comarum palustre Campylium polygamum (Br eur) Bryhn ' 3 Ch Cl enyanthes trifoliata Eriophorum angustifolium Honckeny 2 Agrostis canina 2 * 2 Acc Hypericum elodes 2 2 Hydrocharis morsus-ranae *

67 i m : ; : : ; ; ; ; [ r emna minor ll Nymphaea alba Potamogeton polygonifolius Pourr Equisetum fluviatile j -f Typha latifolia 2 2 -(- Phragmites communis Trin 22 2 Cicuta virosa 2 -(- ycopus europaeus ysimachia vulgaris ll Peucedanum palustre () oench Galium palustre ll Ranunculus lingua 22 ysimachia thyrsiflora 2 2 Carex hudsonii A Benn -)-2 2 Salix cinerea (juv) -)-l _ _i _ _ 2 Sium erectum Huds _ _2 2 ris pseudacorus _j_l _ _ 2 H yrica gale 2 Calamagrostis canescens (Web) Roth _ _ 2 -f2 Poly trichum commune Hedw 22 Sphagnum recurvum P de B j Supplement to the table Acc; algae : 2 Juncus articulatus : 2 Betula pubescens Ehrh (juv) 2; Sparganium erectum 2: 2-2 Typha angustifolia 2: 2 Solatium dulcamara 2: 2 Scutellaria galericulata : yosotis scorpioides : 2 Potamogeton natans : 2 Sparganium simplex Huds ; 2 Alnus glutinosa () Gaertn (juv) 6: Utricularia minor 6: Juncus acutiflorus Ehrh 7: 2 Equisetum palustre 7: 2 Calla palustris 7; 2 Rumex hydrolapathum Huds 7: Cardamine pratensis 7: Carex pseudocyperus 8: Sium latifolium 8: ythrum salicaria 9: Agrostis stolonifera 9: olinia caerulea () oench 9: 2 Nostoc sp 9: -f Frangula alnus ill 0: 2 9 QB-S QB-S emna minor - 2 T-t 2 2 Nymphaea alba Potamogeton polygonifolius Pourr Equisetum fluviatile Typha latifolia 2 2 Phragmites communis Trin * 22 2 Cicuta virosa 2 ycopus europaeus 2 2 ysimachia vulgaris Peucedanum palustre () oench Galium palustre Ranunculus lingua 22 ysimachia thyrsiflora 2 2 Carex hudsonii A Benn 2 # 2 Salix cinerea (juv) 2 Sium erectum Huds 2 2 ris pseudacorus # 2 yrica gale # 2 Calamagrostis canescens (Web) Roth # 2 2 Polytrichum commune Hedw a 22 Sphagnum recurvum P de B

68 66 J AN ONSEAAR one part corresponding with the variant occurring in our former river beds and the other one with the variant described in most utch literature (this is also the one to which the original description by Koch applies) ebrun cs (99) call the parts respectively variant with Sphagnum ( Sphagnum cuspidatum and S recurvum ) and variant with Scorpidium scorpioides ( Carex diandra Eriophorum gracile and These two Scorpidium scorpioides) variants correspond with two subassociations described by uvigneaud and anden Berghen (9) viz subass oligomesotrophicum and subass eutrophicum These subassociations are included by them in two different alliances corresponding respectively with the Caricion fuscae and the Caricion davallianae n a subsequent paper uvigneaud (99) puts the two parts once more in these two alliances but here he gives them the position of associations the Caricetum lasiocarpae acidoclinum and the Caricetum diandro-lasiocarpae basiclinum As far as we can judge our association seems to be different from the original Caricetum The lasiocarpae best solution may be to accept the two subassociations proposed by uvigneaud and anden Berghen but to keep them together in one alliance the Caricion fuscae t should be emphasized however that this is but a preliminary decision The Caricetum lasiocarpae oligomesotrophicum as we found it in the former river beds also shows a remarkable variation (see the table) n the initial stage in water up to 2 cm deep Carex lasiocarpa itself may be absent and completely replaced by Carex rostrata n this stage characteristic species of the preceding Potamion and the Eleocharetum multicaulis may be frequent The following (optimum) stage is much richer in helophytes and usually forms a floating mat t usually is succeeded by the Caricetum elatae comaretosum Record nr 0 presents a variant which was found only once behind a zone of the Caricetum elatae and passing into the Caricetum canescentis-fuscae 62 Caricetum canescentis-fuscae (Braun-Blanquet 9) lieger 937 (Table 2) n the Netherlands the Caricetum canescentis-fuscae has according to the Synopsis two characteristic species viz Carex curta and C echinata t is usually found between a agnocaricion-community and the Betuleto-Salicetum See lieger (937) an Zinderen Barker (92 97) orzer Bruijns and Westhoff (9) The community was found in some of the isolated meso- to oligotrophic former river beds of the euse n these localities its composition corresponds fairly well with the descriptions given by other utch authors (see eg the records of lieger 937 and of an Zinderen Barker 92) n one case it followed the Caricetum lasiocarpae oligomesotrophicum (with Spagnum recurvum ) in the other cases it was preceded by a floating-mat vegetation resembling or corresponding Cicuteto-Caricetum pseudocyperus comaretosum The community with the was succeeded by a vegetation of the Sphagnion or the Betuleto-Salicetum

69 2 EGETATON OF FORER RER BES 67 TABE 2 Caricetum canescentis-fuscae «cn nr nr of record 2 3 of former river bed nr (h "S p river 8 area (h u (sq m) in 0 cover cover (%) total 00 c herb layer S moss layer Ch Ass Carex curta Good Ch All Carex rostrata Stokes Carex lasiocarpa Ehrh 2 -j-l repanocladus exannulatus (Giimb) Warnst 2 Stellaria palustris Retz Ch Ord Comarum palustre 22 ll Ch Cl Agrostis canina 22 Ki enyanthes trifoliata Eriophorum angustifolium Honckeny 2 Hydrocotyle vulgaris 2 Supplement to the table Acc: Betula pendula Roth (juv) : Betula pubescens Ehrh (juv) : Salix cinerea (juv) : rosera rotundifolia : Pohlia nutans (Hedw) indb : 2 Acorus calamus 2: 2 ris pseudacorus 2: 2 Juncus effusus 2: 2 ycopus 2: europaeus Polygonum amphibium fo terrestre eyss 2: ysimachia vulgaris 2: 2 Eleocharis palustris R et Sch () 2: 2 Phragmites communis Trin 2: Calliergonella cuspidata (Hedw) oeske 2: Caltha palustris 3; otus uliginosus Schkuhr 3: 2 Juncus articulatus 3: Rumex hydrolapathum Huds 3: entha aquatica 3:

70 68 J- AN ONSEAAR 63 Juncetum acutiflori Braun-Blanquet 9 (Table 2) n the Synopsis the Juncetum acutiflori is mentioned under the alliance olinion According to the authors their material presented a majority of olinietalia species They state however that the Juncetum acutiflori sphagnetosum of uvigneaud and anden Berghen TABE 2 Juncetum acutiflori sphagnetosum nr of record 2 nr of former river bed 3 8 river area (sq m) 2 9 total 00 cover (%) herb layer 2 7 moss layer 7 Ch Ass Juncus acutiflorus Ehrh 3 32 Ch All Stellaria palustris Retz Epilobium palustre Carex curta Good 2 Ch Ord Comarum palustre 2 Ch Cl Eriophorum angustifolium Honckeny # Hydrocotyle vulgaris Acc Sphagnum recurvum P de B 3 Juncus effusus ysimachia vulgaris -fl Galium palustre 2 Carex elongata Polytrichum Hedw commune 3 Oxycoccus Pers palustris Erica tetralix -2 2 Pinus sylvestris (juv) (9) should certainly be included in the Caricion fuscae Here too a way out of this unsatisfactory situation may perhaps be found by adopting the completely revised classification of uvigneaud (99) This author removes the whole Juncetum acutiflori to a new alliance the olinio-juncion acutiflori and distinguishes some subassociations among which the oligotraphentous J a sphagnetosum recurvi Along some of the isolated meso- to oligotrophic former river beds a vegetation occurred corresponding with the Juncetum acutiflori sphagnetusum recurvi t more or less alternated with vegetations Caricion fuscae and of the Sphagnion of the

71 EGETATON OF FORER RER BES 69 7 Class OXYCOCCO-SPHAGNETEA Braun-Blanquet et Tüxen 93 7 Order Erigeto-Sphagnetalia (Braun-Blanquet 9) Schwickerath 7 Alliance Sphagnion europaeum (Braun-Blanquet 9) Schwickerath Sphagnum recurvum is mentioned in the Synopsis as a characteristic species of the Sphagnion This certainly is not correct Our tables 23 2 and 2 and the Belgian literature prove that this species is common in communities of the Scheuchzerio-Caricetea fuscae at least in the South of the Netherlands n two of the meso- to oligotrophic former river beds the Caricetum canescentis-fuscae passed into a community of the The Sphagnion vegetations usually occupying small territories could not be identified with a well-defined association An example of a well-developed vegetation is given here Fieldnr -3 ate Klopven (nr 3) Area 200 Cover sqm herb layer moss 0% layer 0% Eriophorum vaginatum 3 2 Peucedanum palustre () oench 2 2 ysimachia thyrsiflora 2 ysimachia vulgaris Comarum palustre 2 enyanthes trifoliata 2 Juncus effusus 2 Sphagnum recurvum P de B 3 8 CARRS n order to understand the next chapter it is necessary to know the classification of the carrs used by Kop (96) t is reproduced here in short Class Order Alliance Suballiance Association ariant Alnetea Alnetalia Alnion Betuleto- glutinosae glutinosae glutinosae Salicetum Alnetum glutinosae mesotraphentous eutraphentous Querceto Populetalia Alno- Salicion foreland Fagetea albae Ulmion tidal Alnion glutinoso- acrophorbieto- Alnetum (?) incanae THE TYPES OF FORER RER BES AN THER STRBUTON CHARACTERZATON OF THE TYPES The classification of the 27 former river beds investigated by us resulted in the creation of types and subtypes; only 2 examples could not be included in these and groups are classified as transitions between two of them See the list on 78- p Every type is characterized by a definite set of communities cor-

72 70 J AN ONSEAAR responding with a more or less distinct set of abiotical features All this is summarized in table 26 This table also compares the types with the numbers of the former river beds mentioned in fig All information with regard to the communities can be found in the preceding chapter and (with regard to the carrs) in the publication of Kop (96) n the table subtype b is left out of account This is explained on p 73 There is also a number of communities not included in the table viz ) some rare or rather indistinct communities; 2) the wet meadow vegetations and the Phragmites-consociation (because they are strongly influenced by man); 3) the carrs on the borders of the isolated former river beds belonging to the Salicion or the Alnion glutinosoincanae; at present they do not form a stage former river bed in the hydrosere of the The communities belonging to the same type form a succession The vegetation of a type is described (apart from Table 26) mainly by a succession diagram n the diagrams again a number of communities is left out of account for the sake of clearness However the carrs on the borders which do not participate in the hydrosere are indicated separately Type Zwart Water The type Z wart Water is very clearly defined Three classes are represented solely in this type or nearly solely For the rest the type has some communities in common with the type eerlo n the course of the succession the habitat changes from mesotrophic to oligotrophic The most oligotrophic spots are occupied by vegetations of the Sphagnion This type is the only one which shows in this case starting with the Caricetum elatae comaretosum the series agnocaricion- >Caricion fuscae- >

73 EGETATON OF FORER RER BES 7 Sphagnion which is mentioned in the literature dealing with the utch broads especially with those found in NW Overijssel (lieger 937; Boer 92; orzer Bruijns and Westhoff 9; e Wit 9; an ijk and Westhoff 9; Kuiper and Segal 9) There however a stage with Carex diandra sometimes called Caricetum diandrae (lieger 937) is interposed between the Caricetum lasiocarpae ( eutrophicum ) and the Caricetum canescentis-fuscae n the utch literature there is only one description of a habitat which corresponds with this viz type the near ttervoort Tuspeel (amman 93) This is not surprising for this locality is situated in the same region (the middle of the province of imburg) and offers the same ecological environment as five of the six representatives of the type Qwart Water On the ground of the similarity between some communities found in this and type some others found in Belgium it be may supposed that in Belgium too habitats referable to this type are present 2 Type eerlo The type eerlo is not very clearly defined by specific vegetation units t has some communities in common with the type Quart Water but on the other hand several of its communities are the mesotraphentous equivalents of more generally known eutraphentous communities The type as a whole can be characterized best as a more mesotrophic counterpart of the eutrophic subtype Tuil ( a) The character of the vegetation however does not fully justify the conclusion that the habitat is mesotrophic in the sense in which this term is generally understood Perhaps the best way to characterize is it meso- to eutrophic Table 26 does nor reveal the presence of an environmental factor which would explain the differences in mineral content and in Ph of the types Quart Water and eerlo The explanation however must be found in some incidentally effective factors This will not be described in detail here The main factor is apparently the composition of the water supply derived from the surroundings The composition of the latter depends eg on the elevation the vegetation and the exploitation of the surrounding country (alder wood pine wood manured arable land etc)

74 72 J AN ONSEAAR There are no descriptions of other territories in the Netherlands which show a strong resemblance to the type eerlo ts presence in Belgium may be supposed on the same grounds as brought up for the type Zwart Water 3 Type Spui The only community which the type Spui has in common with any other type is the Alnetum glutinosae For the rest the nature of its communities is determined by the oligo- to mesohalinic habitat The acrophorbieto-alnetum on the banks does not participate autogenic succession in the The succession diagram corresponds very well with that of the mesohalinic pools given by orzer Bruijns and Westhoff (9) The description of the Botshol by Westhoff (99) indicates that at that place locally the same succession of communities is found For the rest no other halinic broads in the Netherlands seem to correspond with the type Spui Judging from the descriptions given by an Zinderen Bakker (97) many of them must be intermediate between the types Spui and Tuil Type Tuil The Tuil all type represents isolated former river beds with stagnant fresh eutrophic water n such a water floating-mat communities may play an important part in the autogenic succession especially in small pools and in isolated The ideal spots hydrosere is demonstrated in the succession diagram of the subtype Tuil However before their isolation all former river beds of this type were situated in the forelands; in some cases they were even under the influence of the tide At that time their hydrosere was different and the succession mainly allogenic After the isolation the succession in the water changed rather rapidly and now the development of a peat layer started On the part of the bank above the water surface however no longer any silt was deposited and here no development of a peat layer took place; this part therefore changed only slowly on account of a slight increase of the humus content and by the development of the soil profile As a consequence the vegetation on

75 9-62 J AN ONSEAAR; On the vegetation of former river beds in the Netherlands TABE 26 nr of type 2 3 a 6a 6b 6c 7 8 of representatives total euse Heusdense aas Waal (and the one 6 of the erwede) Oude aas 2 rest of delta W of ordrecht Rhine 2 ek 3 3 Usel 3 2 best representatives corresponding number(s) of former river beds in fig peat layer on soil river loam various clay and/ clay and/or sand clay and/oi sand soil types or sand in river foreland relation to river isolated usually no open commun open commun or no open communication open communication inundation by annual floods no annual floods less frequent tidal movement than in 6 with an amplitude stagnant or incidentally exposed to a no and/or more frequent than in very slow current caused by sluicing strong cur- and/or strong current during rent during inundationperiod period smaller than in 8 greater than in 7 ev inund by high tide general mineral content meso- to oligotrophic ' meso- to entrophic eutrophic Ph of open water 6-70? (>70) ? (>70) Cl-content of open water in rng/? 33-0 (low) (nr 69:200) i Class Order Alliance Suball Association (or community ) Subass (or variant) (nr 2:2) -2 itt itt itt Eleocharetum multicaulis ' Pot Pot Pot Jydrochareto-Stratioteturn mesotraphentous (A) eutraphentous (B) i mmmm i i yriophylleto-nupharetum mesotraphentous (A) eutraphentous (B) halobious vegetation Potametum lucentis Polygoneto-Nymphoidetum typicum i i Comm ofran circ andel can undet vegetation i i i i i i Phr Phr Phr Cic-Caricetum pseudocyp comaretosum Scirpeto-Phragmitetum typicum typicum oenanthetosum calthetosum i i Scirpetum triquetri typhetosum other subass i i i agn Caricetum elatae comaretosum Caricetum acut-paniculatae mesotraphentous (A) halobious () eutraphentous (B) foreland (C) Caricetum grac-vesicariae Glyc-Sparg Sparg-Glyc fluitantis polygonetosum ( i friwsga i i i i ; j ' smkfsmmmim undet community Sch-C f Car f Car f Caricetum can-fuscae Juncetum acutiflori Caricetum lasiocarpae Ox-Sph Er-Sph Sph undet vegetation sphagnetosum oligomesotrophicum ' ' H i l ol-arrh ol Fil-Pet alerianeto-filipenduletum juncetosum senecietosum subass of Heracleum HHBKnH HHHn i i ' i Ass of Sonchus paluster Ain Ain Ain Betuleto-Salicetum Alnetum glutinosae mesotraphentous eutraphentous i i i Q-Fag Pop A-Ulm Sal foreland tidal i i i i i i

76 EGETATON OF FORER RER BES 73 this part of the bank changed but The drier side slowly of the Caricetum gracilis-vesicariae passed into the adjoining Salicion-commumly and this community gradually passed into a vegetation belonging to the Alnion glutinoso-incanae which probably has to be referred to the acrophorbieto-a netum (see Kop 96) any the Tuil retain type on their banks vegetations Filipenduletum senecietosum the Salicion and its transitions to the acrophorbieto-alnetum former river beds of of the alerianeto- as relics of their former condition a Subtype Tuil The succession diagram of the subtype Tuil corresponds with the description of the succession by floating-mat vegetations in most of the utch broads and in pools with fresh eutrophic water especially those in NW Overijssel (see örzer Bruijns and Westhoff 9; an Zinderen Bakker 92; lieger 937; Boer 92; an ijk and Westhoff 9; Kuiper and Segal 9) b Subtype Ossermeer The subtype Ossermeer is not included in table 26 Therefore the peculiarities are given here in so far as of the subtype Tuil they are different from those Number of representatives: 0 Best representative : nr 02 Rivers : euse 3 Waal Oude aas 2 Rhine Jsel 3 Soil : peat layer locally present and then thinner than in subtype Tuil Ph of water open : Cl-content of water open : 28-7 mg/ The former river beds belonging to this subtype are intermediate between the types from which Kekerdom and they originate (Hurwenen and Krook) the subtype Tuil t may be that under expected natural circumstances the greater part of them would develop into the latter Their actual properties and vegetation are a stage in a relatively rapid evolution However in the case of other and older former river beds anthropogenous factors disturb the development Cleaning of the water and removal of the talus along the banks prevent the development of floating-mat vegetations owing of the vegetation on the banks the formation of prevents carrs and maintains in this

77 7 J AN ONSEAAR way the Caricetum gracilis-vesicariae Especially in such a habitat vegetation units belonging to more or less different hydroseres occur together and intermingle This is the reason why this subtype is not included in table 26 Type Hurwenen ost the numerous are representatives of the type Hurwenen They form nearly one third of all investigated former river beds The type includes those former river beds in the forelands which are not very intensively influenced by inundation and by currents Whereas the nature of many of the water and swamp communities is determined mainly by the mineral content of the water and to a lesser degree by the soil type it is not surprising that the vegetation in the type Hurwenen as far as it consists of plants rooting under water corresponds fairly well with that found in the subtype Tuil The communities above the water surface however resemble or are identical with those of the other foreland types ~ The ecological and floristical description given by auterborn (97) of former river beds of the Rhine suggest that a number of those found between Basel and Bonn may resemble our type Hurwenen 6 Type Kekerdom The former river beds of the type Kekerdom are strongly influenced by inundation and currents n consequence floating-mat vegetations are absent The only community which nearly all representatives of this type have in common is the Polygoneto-Nymphoidetum typicum The Scirpeto-Phragmitetum oenanthetosum occurs in two of the three subtypes a Subtype Kekerdom n the subtype Kekerdom the hydrosere is complete from the submersed Potametum lucentis up to the Salicion-carr auterborn s (97) descriptions seem to indicate that this subtype is present along the Rhine in Germany at least below Bingen b Subtype Zandkolk The representatives of the subtype Zandkolk are bordered by meadows

78 EGETATON OF FORER RER BES 7 which reach up to the edge of the water Usually cattle can graze the vegetation Perhaps this causes the deviation noted in the succession c Subtype Bovenstrang The former river beds of the subtype Bovenstrang are situated very near to the river aybe that the strong current during the inundation time and the ice drift prevent the formation of reed swamps Subtype Kekerdom (a) Subtype Zandkolk (b) Subtype Bovenstrang (c) 7 Type Krook

79 76 J AN ONSEAAR The type Krook consists of former river beds with very little tidal movement t is more or less intermediate between the type Kekerdom with no tidal movement and the type Bloemstrang with more tidal movement t has no characteristic communities of its own 8 Type Bloemstrang The type Bloemstrang is clearly defined by some communities which are restricted to the fresh water tidal area The type corresponds completely with that of many creeks in the Biesbosch (Zonneveld 960) There however all communities are much better developed 2 THE STRBUTON OF THE TYPES The distribution of the types along the various rivers can easily be understood if one compares with the fig head of table 26 However some interesting facts in relation to the distribution of the types Hurwenen and Kekerdom may be stressed The differences between these two types are correlated with the frequency of the inundations by annual floods and with the strength of the current during the inundation n this connection the water household of the large rivers must be recalled to memory (see p ) The forelands of the euse and the Jsel are inundated less frequently than those of the Rhine-ek and the Waal oreover the forelands of the Jsel form a relatively wide zone so that in many places there is hardly any current during the inundation n corresponcende with these facts the type Kekerdom does not occur along the euse and the Jsel Along the Rhine-ek and the Waal the ofthe frequency inundations of the forelands by the annual floods decreases down the river as indicated on p As a consequence towards the West the type Kekerdom gradually disappears whereas the type Hurwenen becomes a little more frequent This can be seen from the list on p 78- where the former river beds of every river are arranged in accordance with the direction of the stream

80 characteristic species found throughout the area in which the association occurs EGETATON OF FORER RER BES 77 SUARY This study deals with the vegetation of about 2 former beds ofthe larger rivers in the Netherlands t includes all communities of higher plants except the carrs which are dealt with in a separate paper by Kop (96) The investigation of the communities aimed at a knowledge of their floristic composition as well as at a definition of their habitat The description and the classification of the units was carried out according to the concepts and methods of the Braun-Blanquet school (Braun-Blanquet 932 9; Becking 97) oreover among the former river beds types were recognized characterized by a special set of communities and by correlated abiotical properties A number of vegetation-units are described here for the first time viz The Polygoneto-Nymphoidetum (alliance Potamion) with the subass typicum and the subass potametosum pectinati According to descriptions of vegetations found in the literature the subass typicum is also present in former river beds of the Rhine in Germany about to up Bingen (AUTERBRON 97); more to the south it is replaced by the Trapo-Nymphoidetum (OBERORFER 97) The Sparganieto-Glycerietum fluitantis polygonetosum (alliance Glycerieto-Sparganion) The main difference with the habitat of the other subassociations (see AAS 99) where the water is moving either permanently (brooks) or at least now and then (ditches) is that the vegetation is influenced by the current only during the shortlasting annual floods The Cicuteto-Caricetumpseudocyperus (alliance Phragmition) is to be divided into two subassociations viz the subass typicum and the subass comaretosum The main difference between the habitats of the two subassociations appears to be that the first is eutrophic and the second more mesotrophic The Scirpetum triquetri et maritimi typhetosum (alliance Phragmition) n contrast with the other subassociations (see ZONNEE 960) this one occursonly in oligoto mesohalinic stagnant water The Caricetum elatae (alliance agnocaricion) is revised Carex hudsonii is the only The community everywhere participates in the hydrosere on sand or peat The following subdivision was made: Subass typicum; the community is eutraphentous; according to the literature it is found in Switzerland (KOCH 926) S Germany (OBERORFER 97) and Belgium (EBRUN cs 99; ANEN BERGHEN 92 a) Subass comaretosum: more mesotraphentous than the subass typicum; found in N Germany (TÜXEN 937; PASSARGE 9 b) and the Netherlands Of the alerianeto-filipenduletum(alliance Filipendulo-Petasition) two new subassocaitions are established viz: Subass juncetosum; it is the replacing-community of a mesotraphentous variant of the Alnetum glutinosae Subass senecietosum; represented in the river forelands outside the tidal area; it replaces there an eutraphentous Salicion-community and may be natural if the development of trees is prevented by ice-drift Eight types of former river beds were distinguished Two of these could be subdivided into some subtypes Their classification according to their communities and their abiotical properties is summarized in table 26 escriptions of habitats which more or less resemble oneof these types offormer river beds are known from other parts of the Netherlands and from the adjoining parts of Germany and Belgium However as far as we know of the types described by us viz those represented in the river forelands along the upper courses of the rivers seem to differ from all habitats that have been described so far

81 Wijk-Aalburg Obbicht-Papenhoven alburg 78 AN J ONSEAAR ST OF FORER RER BES NCUE N THS STUY nr former river bed{s) municipality{s) map{s) type EUSE frb (wood) in river foreland 60 C 2 frbs in Grote Beemd aasbracht 8 3 Klopven Horn 8 Houterven Horn 8 frb in Weerd Beesel-Reuver 8 E 6 Koelbroek and environs aasbree 2 G 2 7 Tangkoel near Hout-Blerick aasbree 8 E 2 8 Zwart Water Arcen-elden and enlo 2 H 9 ottummer Schuitwater Grubbenvorst 2 G 2 0 Broekhuizer Broek Broekhuizen 2 E G 2 Schuitwater between eerlo and Broekhuizervorst eerlo 2 E 2 2 Schuitwater SE of eerlo eerlo 2 E 2 3 Rozendaal Wanssum 2 B E ilt Beugen 6-2 ange Yen Bergen () 6 6 Wychense eer Wychen 6 A b 7 Wychense en Wychen F -2 8 Balgoijse eer Overasselt F b 9 Oude aas egen-haren- acharen 39 E G 20 Ossermeer egen-haren- acharen E b 2 frb E ofhedel Hedel and aasdriel A 7 22 frb W of Empel Empel-eerwijk A Hedikse aas Haarsteeg A 2 Galgenwiel oon Zand op H 2 Oude aasje near rongelen rongelen E F 7 26 Oude aasje between Haagoord and Keizersveer Capelle Waspik and Raamsdonksveer E 7 HEUSENSE AAS 27 Krook Ammerzoden A 7 28 frb in oornwaard Heusden F A 29 frb in Banwaard Wijk-Aalburg F 7 30 frb in Wijkse Waard 3 frb along Zandplaat F Brakel F 8 32 el Brakel F 33 frb in e Waarden Brakel F 3 Oude aasje near oevestein Brakel 38 G E 7 WAA 3 Oude Waal W of obith Herwen-Aerdt 0 G -6 a 36 Oude Waal near Kekerdom Ubbergen 0 6 a 37 Ooijse Graaf Ubbergen 0 b 38 Strang in Sophia s Kamp Ubbergen 0 6b 39 Strang Bemmel 0 C 6 a 0 Oude Waal Ubbergen 0 C E of Nijmegen Zeumke Nijmegen 0 C 6 a 2 Zandkolk alburg 0 C 6b 3 Strang SE of Slijk-Ewijk 0 C 6 c Strang in oenense Buitenpolder alburg 0 C 6 a

82 Echteld Ophemert Rockanje EGETATON OF FORER RER BES 79 Strang near Hien odewaard 39 H 6 Bovenstrang near Hien odewaard 39 H 6 c 7 frb near Afferden ruten 39 H 8 Strang and Weeversgat near Turksweerd ruten 39 H 6 a 9 Goudmijn ruten 39 G H 6 c 0 Hoek van de ange Krib Echteld 39 G 6 c Oude Waal E of Ochten Echteld 39 G -6 a 2 Oude Waal SW of Ochten 39 G 6 c 3 Kil near Ooy Echteld 39 G 6 a Kil E of Tiel Tiel 39 G frb in Uiterwaarderpolder Wamel and reumel 39 6 c 6 frb SW of Tiel Tiel 39 6b 7 Kil in reumelse Waard reumel 39-6 a 8 Kil in Stiftse Uiterwaarden and arik 39 6 a 9 frb W of Heerewaarden Heerewaarden 39 B 6 c 60 Weiwaardsgat Heerewaarden B 6 a 6 Kil Waardenburg 39 C -6 a 62 Kil van Hurwenen Zaltbommel and Hurwenen A 63 Wiel near Tuil Haaften 39 C a 6 Kil in Breemwaard Zuilichem 38 H 6 Bloemstrang BrakelandWoudrichem 38 H F 8 ERWEE 66 Avelingerdiep Gorinchem and Hardinxveld 38 G 8 OUE AAS 67 oordevel Heerjansdam 37H 38C b 68 Waal Heerjansdam Barendrecht Ridderkerk and Hendrik do Ambacht 37 H 38 C b 69 Binnenbedijkte aas Westmaas ijnsherenland and aasdam 3 F a 70 frb E ofheinenoord Heinenoord 37 H 8 7 Kooigat and environs Poortugaal 37 G H 8 REST OF THE ETA W OF ORRECHT 72 Grote Gat Zuid Beijerland 3 E 3 73 Oostenrijk (ierambachtenboezem) Geervliet Holle are Heenvliet Spui near Brielle Nieuwenhoorn eertje van Rockanje (Waal) 37 C 3 RHNE 77 Oude Rijn between Spijk and uiven Herwen-Aerdt 0 G 6 a 78 frb S of ooveer Huissen 0 B 6 c 79 Strang in Huissense Waarden frb SW of Renkumse eer Huissen 0 B -6 a Heteren 39 F 6b 8 frb SW of exkes eer Heteren 39 F 6b 82 frb W of Oude haven Wageningen 39 F 83 Strang in aneswaard Kesteren 39 F 6b 8 Oude Rijn Kesteren and ienden 39 E b 8 frb SÉ of Eist Rhenen 39 E 6b 86 frb in Waterschap Bovenpolder Amerongen 39 B

83 Wijhe J AN ONSEAAR 87 Kil in Polder Koornwaard Amerongen 39 B 6 a 88 Kilsloot in Polder Koornwaard Amerongen 39 B 6 a 89 frb N of Eek en Wiel aurik 39 B 6b frb near Roodvoet aurik 39 B 6 a EK 9 Kleine ek ianen 38 F 92 frb in Bolswaard (open part) exmond 38 E F 8 93 frb in Bolswaard (closed part) exmond 38 E F 9 Binnenlek opik 38 E 8 9 frb in Binnen Nes Groot Ammers 38 B 96 Kil along island Hoop ekkerkerk 38 C 8 JSE 97 Rhedense aak Rheden 0 B 98 amme Jsel oesburg 33 G 0 E 99 ierense Hank oesburg 0 E 00 frb SW of Gelderse Toren Rheden 33 G -6 a 0 reekolk and environs Steenderen 33 G b 02 Oude Jsel and Hoendernesterbeek Zutfen 33 E G b 03 Blanke Hank oorst 33 E 0 frbs near Wilp oorst 33 E -6 and eventer a 0 frb in Ossenwaard eventer 33 E -6 a near 06 frb Ter Cera oorst 27 G 07 unnikenhank iepenveen 27 G 08 frbs in Olster en Hengvorder Waarden S of Olst Olst 27 G 09 Hank S of Welsum Olst 27G 0 Barlose Kolk (Southern of the two) Olst 27 G b Olst 27 G frb in Olster Waard N of Olst 2 Hank near eessen (open part) Heerde 27 E G 3 Hank near eessen (closed part) Heerde 27 E G Scherpenzeelse Hank and Olst 27 E G frb near orchten and Heerde Wijhe 27 E 6 frbs S ofherkeloo Zwollerkerspel 27 E 7 Hankskolk Hattem 27 E -6 a 8 SchellerWade (Kolk vangreve) Zwollerkerspel 2 G27E a 9 Spoolderhank Zwollerkerspel 27 F G 20 frb near oornik Oldebroek 2 2 Hank near Zalk (open part) Jsselmuiden 2 22 Hank Zalk near (closed part) Jsselmuiden 2 23 Koeluchtergat Jsselmuiden 2 2 Hank near Wilsum (open part) Jsselmuiden 2 2 Hank near Wilsum (closed part) Jsselmuiden 2 26 Oude Jsel in Onderdijkse Polder Kampen 2 a 27 Noorderdiep Kampen 2 A a C

84 EGETATON OF FORER RER BES 8 REFERENCES Allorge P 922 es associations vegctales du exin fran$ais Paris Barker 9 iscellaneous notes on Scirpus lacustris sensu lat in the Netherlands Acta Bot Neerl 3; 2- Beekman A A Geschiedkundige atlas van Nederland The Hague 98 e wateren van Nederland (aardrijkskundig en geschiedkundig beschreven) The Hague Bennema J 93 oorlopig overzicht van de gezelschappen van het Potamionverbond n; Waterplantengemeenschappen in Nederland p -7 n archives of RON Bilthoven-Noord; not publ Bittmann E 93 as Schilf (Phragmites communistrin) und seine erwendung im Wasserbau Angewandte Pflanzensoz 7: - Blaauw A H 97 Over flora bodem enhistoric van het eertje vanrockanje erb Kon Akad Wetensch Amsterdam 2nd sect 9 3 Boer A C 92 Plantensociologische beschrijving van de orde der Phragmitetalia Ned Kruidk Arch 2: Zusammenfassung in eutsch Boissevain H 9 e riviervormen in sedimentatiegebieden Tijdschr Kon Ned Aardr Gen 2nd ser 63: Braun-Blanquet J 932 Plant sociology New York 9 Pflanzensoziologie 2nd ed ienna Clason E W Over de plantengroei van het Zuidlaarder eer en omgeving e evende Natuur 33: Curtis J T and R P cntosh 9 An upland forest continuum in the prairieforest border region of Wisconsin Ecol 32: amman T 93 erslag van het sjockampje in Belfeld van 9-3 Juli 93 Kruipnieuws : -9 ibbits H A C 90 Nederland-Waterland Een historisch-technisch overzicht Utrecht iepen 9 e van bodemgesteldheid van de aaskant ersl andbouwk Onderz 8 9 The Hague Summary in English ijk J van and Westhoff 9 e plantengroei der natuurgebieden in NW Overijsel Natuur en andschap 9: 33-7 Summary in English oing Kraft H 9 e tegenwoordige opvattingen omtrent het associatiebegrip de en systematiek de van plantengezelschappen volgens de methode van Braun-Blanquet Preliminary advice and of lecture report and discussion on meeting of the Kon Ned Bot er ec 22 9; not publ oing Kraft H 96 e tegenwoordige opvattingen omtrent het associatiebegrip en de systematiek van plantengezelschappenvolgens van Braun-Blanquet akblad v Biol 36: de methode onselaar J van 96 Het vegetatiekundige onderzoek van oude rivierlopen Natuur en andschap 0: Summary in English 97 a Het botanische onderzoek van de oude rivierlopen 9-96: Samenvatting van de geografische resultaten n archives of RON Bilthoven-Noord; not publ 97 b Een verlate reactie op het Kortenhoefboek Kruipnieuws 9 : 0- Summary in English onselaar-ten Bokkel Huinink W A E van 96 An ecological study of the vegetation in three former river beds Wentia : 2-62 u Rietz G E 930 egetationsforschung aufsoziationsanalytischer Grundlage n: Abderhalden-Handbuch der biologischen Arbeitsmethoden uvioneaud P 99 Classification phytosociologique des tourbieres de Europe Bull Soc Roy Bot Belg 8 2nd ser 3-2: 8-29 and C vanden Berohen 9: Associations tourbeuses en Campine occidentale Biol Jb odonaea (Ghent) 2; 3- Edelman C H 960 a nleiding tot de bodemkunde van Nederland Amsterdam 90 b Soils of the Netherlands Amsterdam cs 90 Een bodemkartering van de Bommelerwaard boven de eidijk ersl andbouwk Onderz 6 8 The Hague Summary in English

85 82 J AN ONSEAAR Ellenberg H 9 Zur Entwicklung der egetationssystematik in itteleuropa Festschrift Erwin Aichinger Angewandte Pflanzensoz (Sonderfolge) p 3-3 Faber F J 97/8 Geologic Gorter van Nederland H P and Westhoff 92 Behoud van 3rd ed Gorinchem natuurterreinen ten dienste van de wetenschap: wensen en mogelijkheden Natuur en andschap : 00-7 Summary in English Grohs H 93 imnologische Untersuchungen zweier onaualtwasser bei Wien Arch f Hydrobiol 39: HavingaB 99 Studien over flora enfauna van het Zuidlaarder eer Groningen Heusden G P H van Heybroek H 9 Waarnemingen in enige Tijdschr Kon Ned Aardr Gen t2: 8-9 Standplaatseisen planten Jb Kon Ned Bot er 9; 2 widen in de Betuwe en onderlinge beinvloedingen van Hoeksema K J 97 erlande stroombeddingen in het rivierkleigebied Jong B de benamingen Tijdschr Kon Ned Aardr Gen 6; 0-6 Also; Boor en Spade 2: Summary in English en haar 93 Nogmaals het Filipenduletum Kruipnieuws -; 7- Klinkenberg W 93 Hoe een sjoccer zich bezig hield met het olinion en tabellen maakte Kruipnieuws 2-3: 7- Koch W 926 ie egetationseinheiten der intebene Jb St Gallen Naturv Gesellsch 6 Kop G 96 Walder und Waldentwicklung in alten Flussbetten in denniederlanden Wentia : 86- Summary in English Kuiper P J C 97 erlandingsvegetaties in NW Overijsel Jb Kon Ned Bot er 97: erlandingsvegetaties in NW' Overijsel Kruipnieuws 20 ; -9 and S Segal 9 e natuurgebieden rondom de Belter- en Beulakkcrwijde Kruipnieuws 7 3; 9-8 angendonck H J van 93 fitude sur la flore et la vegetation des environs de Gand Bull Soc Bot veg Belg 68 2nd ser 8 : 7- auterborn R ie geographische und biologische Gliederung des Rheinstroms Sitzungsber d Heidelberger Akad d Wissensch 7B 6; -6 (96); 8B : -70 (97); 9B ; -87 (98) ebrun J A Noirfalise P Heinemann and C vanden Berghen 99 es associations de Belgique Bull Soc Roy Bot Belg 82: eentvaar P 9 Rapport betreffende het planktononderzoek van een aanta! oude rivierlopen in 9 n archives of RON Bilthoven-Noord; not publ 9 Hydrobiologisch onderzoek van oude rivierlopen Handel Hydrobiol er Amsterdam 0 Summary in English 97 Observations on the populations of plankton and microorganisms in an old branch cut off from the river Waal Beaufortia 6 eeuwen Chr G van 9 Het eltaplan enzijn consequenties voor de natuurbescherming Tegenwoordige toestand en betekenis van het eltagebied Natuur en andschap 8; 6-76 Summary in English ohmeyer W 90 Oenanthe aquatica-rorippa amphibia-ass itt Florist- soz Arbeitsgem 2: 20 aas F 99 Bronnen bronbeken en bronbossen van Nederland in het eijer W bijzonder van de eluwezoom eded andbouwhogeschool Wagcningen 9 2: -66 Summary in English Resume en frampais 97 Agelerbroek Kruipnieuws 9 2: Flora en vegetatie van het Zwetgebied bij Wormer en Jisp Wetensch eded Kon Ned Bot er 6: 2-9 Waterplanten en oevervegetaties n: Ed Kortenhoef p 22- Stichting Comm v d echt en het O en W Plassengebied Amsterdam 97 Over vegetatietypen een toelichting het Kortenhoefboek op Kruipnieuws 9 3: -3 and Westhoff 97 Continuiteit en discontinuiteit in de vegetatie Kruipnieuws 9 2: 32-39

86 EGETATON OF FORER RER BES 83 itis H von 939 as Altwasser Bin Beitrag zur Gewassersystematik Arch f Hydrobiol 3: 3-3 Oekologische Studien am usthauswasser einem Altwasser im Prater von Wien Arch f Hydrobiol 37: 26-6 orzer Bruijns F 97 Over levensgemeenschappen Utrecht Summary in English and Westhoff 9 The Netherlands as an environment for insect life Amsterdam Oberdorfer E 97 Siiddeutsche Pflanzengesellschaften Ed Bundesanstalt fur Naturschutz und andschaftspflege 0 Pannekoek van Rheden J J 92 Over de reconstructie van voormaligerivierlopen Tijdschr Kon Ned Aardr Gen 9: Passarge H 9a ie Ufervegetation des Briesener Sees itt Florist-soz Arbeitsgem : b ie Pflanzengesellschaften der Wiesenlandschaft des iibbenauer Spreewaldes Feddes Repert Beihefte : 9 Pons J 98 e bodernkartering in Groot aas enwaal Boor en Spade 2: 26-3 Summary in English 99 e uiterwaarden van de aas bij Batenburg Boor en Spade 3; Summary in English 9 a e fluviatiele laagterrassen van Rijn en aas Boor en Spade 7: 97-0 Summary in English 9 b e verkaveling vanbalgoy Boor enspade 7: Summary in English Redeke H C 932 Abriss der regionalen imnologie der Niederlande Publ Hydrobiol Club Amsterdam Reynders Th and W 92 eenterreinen aan de iede en Kruipnieuws : 3- and 3: 6-9 Ruttner Fr 92 Grundriss der imnologie 2nd ed Berlin Schelling J 9 Een bodernkartering vannoord-imburg ersl andbouwk Onderz 7 7 The Hague Summary in English Schimmel H J W and P Tideman 960 Het gebied der oude Rijnstrangen tussen obith en Zevenaar Natuur en andschap : 33-9 Summary in English Schuiling R G J ulder and H J oerman 93 Nederland handboek der 6th ed aardrijkskunde Zwolle Schwickerath 933 ie egetation des andkreises Aachen und ihre Stellung im nordlichen Westdeutschland Aachener Beitrage zur Heimatkunde 3 92 Bedeutung und Gliederung des ifferentialartenbegriffs in der Pflanzengesellschaftslehre Beihefte Bot Zentralblatt 6 B 3: Segal S and Westhoff 99 ie vegetationskundliche Stellung von Carex buxbaumii Wahlenb in besonders in den Niederlanden Europa Acta Bot Neerl 8: Summary in English Tansley A G 96 ntroduction to plant ecology ondon Teixeira de atos F 92 e waterkeringen waterschappen en polders van Zuid Holland 6 2: 7 3; 8 The Hague Tuxen R 937 ie Pflanzengesellschaften Nordwestdeutschlands itt Florist- soz Arbeitsgem in Niedersachsen 3: er Pflanzensoziologische Garten in Hannover und seine bisherige Entwicklung [ahresbericht d Naturhist Gesellsch zu Hannover 9-98; Grundriss einer Systematik der nitrophilen Unkrautgesellschaften in der Eurosiberischen Region Europas itt Florist-soz Arbeitsgem 2: Pflanzengesellschaften und Grundwasser-Ganglinien Angewandte Pflanzensoz 8: as System der nordwestdeutschen itt Pflanzengesellschaften Florist-soz Arbeitsgem : -76 and E Preising 92 Grundbegriffe und ethoden zum Studium der

87 8 J AN ONSEAAR Wasser- und Sumpfpflanzen-Gesellschaften eutsche Wasserwirtschaft 37; Erfahrungsgrundlagen fiir die pflanzensoziologische Kartierung des westdeutschen Griinlandes Angewandte Pflanzensoz : -28 anden Berohen C 97 e iereman a ieux-turnhout Bull Soc Roy Bot Belg 79: a erklarende tekst bij het kaartblad Gent ( W) van de egetatiekaart van Belgie 92 b Contribution a tude des bas-marais de Belgique (Caricetalia fuscae W Koch 926) Bull Jard Bot de fitat Brussels 22; -6 lieger J 937 Plantensociologische aantekeningen in de omgeving van Blokzijl Ned Kruidk Arch 7: and E van Zinderen Barker 9 Het botanische onderzoek van het Naardermeer Jb er Behoud Natuurmon in Ned 936-: 8-7 oo E E van der 96 a andschap en plantengroei van enkele stroomgeulen in het and van aas en Waal e evende Natuur 9; 3-96 b Een uiterwaard-bos in idden-imburg e evende Natuur 9: e Oostenrijk e evende Natuur 60: and Westhoff 96 An autecological study of some limnophytes and helophytes in the area of the large rivers Wentia : Waterland 9 Report about a botanical and hydrobiological investigation in the area of Waterland between Amsterdam onnikendam and the jsselmeer coast Ed Ned Jeugdb v Natuurst istr Amsterdam Westhoff 93 Enkele opmerkingen over verlandingsgezelschappenin Nederland in het bijzonder in Zuid-imburg eded Werkgroep Biosoc v d Ned Natuurhist er 3 99 andschap flora en vegetatie van de Botshol nabij Abcoude Ed Stichting Comm v d echt en het O en W Plassengebied Baambrugge 90 Het associatiebegrip in geografisch verband Ned Kruidk Arch 7; a Flora en vegetatie van Overijssel n: Overijssel Aspecten en Amsterdam perspectieven 9 b An analysis of some concepts and terms in vegetation study or phytocenology Synthese 8; a Some remarks on synecology egetatio -6: b e plantensociologische tuin in Hannover e Wandelaar in Weer en Wind 22: 09-6 J W ijk H Passchier and G Sissingh 96 Overzicht der plantengemeenschappen 2nd ed Amsterdam (st ed 92) in Nederland and P eentvaar 97 Onderzoek en Natuurbehoud e evende Natuur 60; Wit R J de 9 e draadzegge-gemeenschapin NW Overijssel Kruipnieuws 3-2: Het Caricetum lasiocarpae bij Kortenhoef in verband met de verspreiding en de systematische plaats der associatie n: Kortenhoef p 0-9 Ed Stichting Comm v d echt en het O en W Plassengebied Amsterdam Woerdt van and der de ries 98 e botanische samenstelling van de uiterwaarden en overeenkomstige binnendijks gelegen gronden andbouwk Tijdschr 60: 8- Zinderen Barker E 92 Het Naardermeer Amsterdam van 97 e West-Nederlandse eenplassen Amsterdam Zonneveld S 92 e Biesbosch een zoetwatergetijdendelta Natuur en andschap 6: Summary in English - 9 Over natuurreservaten in de Biesbosch en het eltaplan Natuur en andschap 9; 3-28 Summary in English 97 Continu of discontinu Kruipnieuws 9 2: e Brabantse Biesbosch een studie van bodem en vegetatie van een zoetwatergetijdendelta Wageningen Part A: Summary in English

88 J AN ONSEAAR 8 EXPANATON TO THE TABES AN THER SUPPEENTS The species are arranged in groups These groups consist of characteristic and differential species of units of various ranks and of accompanying species Sometimes a characteristic species of a unit is also present in another unit Then the species is listed in the table of the latter as characteristic of the unit of the next higher rank to which both units belong Eg Carex acuta is a characteristic species of the Caricetum gracilis-vesicariae and this association belongs to the alliance agnocaricion However the species is present also in the Scirpeto-Phragmitetum which is an association belonging to the Phragmition agnocaricion and Phragmition both belong to the order Phragmitetalia; consequently Carex acuta is listed in the table of the Scirpeto-Phragmitetum as a characteristic species of the order Phragmitetalia The abbreviated indications placed in front of the species refer to the whole of a group or to a part of a group An indication between brackets however refers only to the species in front of which it is placed As a rule the records on the table of a unit are selected from the total number of records which are available of that unit The presence (P) of a species which is placed at the end of its line does not refer to the number of records present in the table but to the total number available; the latter number is mentioned above the line of Roman figures which indicate the presence of the species Some tables represent a unit which is subdivided in a number of units of lower rank n this case the number of records availablefor the whole unit may be somewhat higher than the sum of the available records of its lower units This is caused by the circumstance that not every record could be identified with one of the lower units f less than records of a unit are available the presence of a species is not indicated by a Roman figure but by an Arabic figure which indicates the real number of records in which the species is present ABBREATONS USE N THE TABES AN THER SUPPEENTS Acc accompanying species B brzer Bruijns All alliance e river erwede Ass association g agnocaricion Ch characteristic species O river Oude aas Cl class Ord order c subass calthetosum subass comaretosum com ) differentialspecies 2) rest ofdelta area W of ordrecht 3) J van onselaar BH W A E van onselaar-ten Bokkel Huinink forel foreland river Heusdense aas H her subass ofheracleum June subass juncetosum K G Kop o subass oenanthetosum P presence Phra Phragmitetalia Phron Phragmition QB A J Quen^-Boterenbrood R river Rhine S P J Schroevers S-C Scheuchzerio-Caricetea fuscae sen subass senecietosum t(yp) subass typicum typh subass typhetosum E E van der oo W river Waal river ek river aas J river Jsel