THE OCCURRENCE OF LIVING AND SUB-FOSSIL REMAINS OF BETULA NAN A L. IN UPPER TEESDALE

Transcription

1 THE OCCURRENCE OF LVNG AND SUB-FOSSL REMANS OF BETULA NAN A L. N UPPER TEESDALE BY T. C. HUTCHNSON Department of Botany, The University, Neiocastle-upon-Tyne (^Received 6 January 1966) SUMMARY A small colony of the arctic-alpine dwarf birch, Betula nana, has been discovered in Upper Teesdale, this being the only English station for the species. t is elsewhere in Britain confined to the Scottish Highlands. The plant associations with which the species occurs throughout its range are of two t\'pes, tundra vegetation in the north, and sub-alpine dwarf shrub vegetation in the south of its range. n Teesdale the species is confined to the sub-alpine dwarf shrub type although an open tundra type is also present. Sub-fossil leaf remains of B. nana have been found in Teesdale close to the living colony, in a fen peat. The leaf remains are associated with deposits later than the commencement of Zone Vila, thus indicating that the species has probably been continuously present in Teesdale since Atlantic times. The Late-glacial finding of the species in Lower Teesdale suggests that the present colony may have a continuity in Upper Teesdale from Late-glacial times to the present day (approximately 1,000 years). NTRODUCTON During May 1965, a small colony of the arctic-alpine dwarf birch, Betula nana, was found growing on blanket bog in Upper Teesdale. The colony, which is at an altitude of 1700 ft (548 m), consists of a small number of individuals. No further colonies have yet been found in the neighbourhood, neither has the age of the plants been ascertained. Several of the larger ones are approximately 15 cm high and much branched, perhaps due to grazing. None of the plants flowered in 1965 and the viability of the colony is clearly in question. t seems unlikely that the lack of flowering is due to the plants being juvenile. Within the British sles the present distribution of the species w as thought to be confined to the central and northern highlands of Scotland, and it was previously unknown from England. The distance between the Teesdale site and the nearest Scottish colony in Perthshire is approximately 10 miles (1 km) (see Fig. i). There are, however, a number of old records which would partially bridge this gap but, with one exception, these are all considered dubious and are not mapped in the Atlas of the British Flora (196). Baker and Tate (1869) mention a herbarium specimen reputedly collected near Wooler, Northumberland, but they cast grave doubts on its site of origin. Druce (19) mentions B. nana from lists for Berwickshire, Peeblesshire and Lanarkshire, covering records fori777andi85i. Outside of the British sles the distribution of the species is north and central European, extending north to latitude 78" in Spitzbergen, east to the Carpathians and Central Russia, and south to the Jura mountains of France and Switzerland. t is absent from Denmark and Holland. n the south of its range it is local and alpine. 51

2 5 T. C. HUTCHNSON ASSOCATED SPECES N TEESDALE AND ELSEWHERE Before considering the history of Betula nana in Britain, the plant associations in which it occurs throughout its present-day range are worth noting. t is characteristically a species of open situations and has thus been regarded as sensitive to shading and afforestation. However, in southern Sweden, Malmer (1965) mentions it as a characteristic species of upland wooded bog or poor fen vegetation. The trees in these situations are rather widely spaced individuals of Pinus sylvestris or Betula pubescens and produce opencanopy woodland. Over the rest of its range, B. nana is concentrated into two main DwaK Birch 190 onwards o Before HJO f Fig.. The distribution oi Betula nana (L.) in Britain, with the 1965 Teesdale record added. (By permission of the Botanical Society of the British sles and Thomas Nelson & Sons Ltd., taken from their Atlas of the British Elora, 196.) vegetation types: (i) the sub-alpine dwarf shrub type, with such species as ^^> vulgaris, Vaccinium myrtillus, V. vitis-idaea, Empetrum nigrum, E. hermaphroditum, Salix lapponum and S. hei'baeea; and () in the tundra type of vegetation, especially in the north of its range, with such arctic-alpine species as Dryas octopetala, Kobresia simpliciiiscula, Armeria maritima, Bartsia alpina and Saxifraga hirculus.

3 Sub-alpine dwarf shrub type Betula nana in Teesdale 5 The species associated with Betula nana in Teesdale today correspond closely with those associated with it in Scotland, i.e. in the Calluneto-Eriophoretum complex (Pennine Blanket Fog) of McVean and Ratclifl^e (196). A floristic comparison of various Table i. Species associated with Betula nana in Scotland and Teesdale {Frequency; Domin scate: 4 M quadrats) Species Betula nana Callima vulgaris Empetrum hermaphroditum E. nigrum Erica tetralix O.xycoccus microcarpus Vaccinium myrtillus ', vitis-idaea Rubus chatnaemorits Eriophorum angustifolimn E. vaginatum \olinia caeridea Jiincus squarrosus Dicranum scoparium Hylocomium splendens Hypnum cupressiforme Plagiothedum undidatum Pleurozium schreberi Rhytidiadelphus loreus Sphagnum nemoreum S. papillosum S. rubellum S. russozl-ii Odontoschisma sphagni Ptilidium ciliare Cladonia cf deformis C. impexa C. rangiferina C. sylvatica C uncialis Total No. species _ S 6 18 Site Site, An Bhuidheanach, Monadhliath, nverness, 00 ft. Site, Loch Nagar, Aberdeenshire, 00 ft. Site, Camghouran, Loch Rannoch, Perthshire, 1650 ft. Site 4, Widdybank Fell, Upper Teesdale, 1700 ft. (Scottish sites from McVean and RatclifTe (196).) sites is given in Table i. These associations also correspond closely with its occurence in Scandinavia and north-west Germany (Clark, personal communication; Ruse, 1965; Overbeck and Schneider, 198). Tundra type Pohle (190) described a typical Russian tundra vegetation as consisting of a turf of Sphagnum, Potytrichum and Dicranum, together with dwarf bushes of Betula nana, Satix glauca, S. lanata, S. herbacea, Arctostaphylos alpinum, Vaccinium uliginosum, V. vitis-idaea, Rubus chamaemorus, Bartsia atpina, Pedicularis tapponica and Polvgonum viviparum. This Russian tundra vegetation is very similar to the celandic 'fla' vegetation which has been described and which included Betula nana, Empetrum hermaphroditum, Salix gtauca, S. herbacea, S. lanata, Dryas octopetala, Silene acatilis, Tofieldia pusilla. S

4 54 T- ^- HUTCHNSON Bartsia alpina, Carex capillaris, C. bigelowii and Equisetum variegatum. Bocher (1959) and Nordhagen (194) have described similar tundra associations, which containecl Betula nana from north-west Greenland and Norway respectively. t is notable that, south of the Scottish Highlands, Upper Teesdale is one of the very few places where many of the above arctic-alpine species occur. The importance of this element of the Teesdale fiora has already been stressed by Blackburn (195) and Pigott 95) Although both the tundra and the sub-alpine drawf shrub type of vegetation occur in Teesdale today, B. nana is there confined to the sub-alpine dwarf shrub type, as it is in Scotland. t seems likely, however, from the evidence of Neasham Late-glacial deposits (see later) that it formerly occurred in the Teesdale area in a tundra vegetation. HSTORY OF Betula nana N BRTAN The species is well known from nter-glacial and Late-glacial deposits, especially the latter. t was apparently of widespread occurrence during the Late-glacial period, occurring down to sea-level over much of lowland Britain, in the sub-arctic heaths and open tundra vegetation of the day. Remains are characteristically found with such species as Astragalus alpinus (now confined to the Scottish Highlands), Dryas octopetala, Draha incana, Lxcopodium selago, Plantago maritima. Primula farinosa, Salix herbacea, Saxifraga aizoides, Silene acaulis, Pohgoniim viviparum, Arctostaphylos uva-ursi, Empetrum nigrum and Carex bigeloivii (Godwin, 1956). As already mentioned it is with such species that it occurs today in the north of its range. Late-glacial finds are not confined to England and Scotland, remains having been found at a number of sites in reland, e.g. Jessen (1949) and Mitchell (195), where the species is no longer native. During the later part of pollen zone H and the early part of zone V, Betula nana declined rapidly, probably due both to the spread of woodland and to the climatic amelioration. Reports of B. nana from zone V include those of Walker (1955) from Kentmere, Westmorland; Seagrief and Godwin (Seagrief, 1959; Seagrief and Godwin, i960), who found remains at Wareham in Dorset, Nursling in Hampshire, and Elstead in Surrey; Pigott and Pigott (196) who found B. nana type pollen at Malham, Yorkshire; Birks (1965) who found pollen at Bagmere, Cheshire; and Bartley (1966) who found pollen at sites neat Bamburgh on the Northumberland coast. The species associated with it in these Post-glacial deposits included Artemisia, Helianthemum, Menyanthes, Salix, Thalictrum and Valeriana. The only record of Betula nana later than zone V in Britain, apart from modern Scottish peats near present-day colonies, appear to be that of Tallis (1964) who reported B. nana type pollen from zone V of the blanket bog peats on Kinder, Derbyshire, at 1900 ft (610 m). Pollen of the 'Late-glacial' species, Armeria maritima, Thalictrum and Juniperits also occurred. Tallis's work is of particular interest in that it suggests that assemblages of 'Late-glacial' species may have persisted at least into Boreal times on high ground in a number of localities from which they have now disappeared. An excellent example of Betula nana persisting from Late-glacial times to the present day is that given by Overbeck and Schmitz (191) and Overbeck and Schneider (198), who examined peats on which B. nana grows in north-west Germany. Of particular interest is the continuous record of the species through successive layers of ombrogenous peat to the scattered, living plants on the peat surface.

5 THE NEW PHYTOLOGST, 6s, P.AT': 0 A section of Phragmites peat fr^im pper ^iv-csdale, show in^ a pcrtcctu' leaf. A Phragmites rhizome can be seen at tlie base DF the piltinx-. x 4. Hcltiht uiu T. C. HUTCHNSON BETULA XAXA /.V TEESDALE ng: /)ci;'r 54)

6 M'W 'lv'olocilst, 65, PLATE 1 # # # Sub-fossil and liviny lea\cs of Bitiihi iiaiui from a nup.ibl-r of sources.. i. Sub-fossil (fun peat) Teesdale; and, Tecsdale, County Duibam; 4. Btn \\'y\is, Ross and Cromarty; 5, Glen Clova, Angus; 6, Loch Ericbt, ln\cincss; 7, t nknown site, Ross; 8, Ben na Board, Aberdeen; 9, Moutier, Jura Mountains, France. T. C. LTCXSOX HETULA XAXA N TEESDALE

7 Betula nana in Teesdale 55 Peat deposits at Neasham, County Durham (Lower Teesdale), were investigated by Blackburn (195), who found Late-glacial beds containing B. nana and its hybrid with B. pubescens, together with Cardaminopsis petraea, Armeria maritima, Dryas octopetala, Thalictrum alpinum, Juniperus, Aretostaphylos uva-ursi, Salix herbaeea and Selaginella selaginoides. All except Cardaminopsis petraea are present in Upper Teesdale today, which is situated about miles (56 km) from the Neasham site. Blackburn suggested that this assemblage of plants may have been able to persist in Upper Teesdale to the present day, despite the climatic changes and spread of woodland over the area. REMANS OF Betula nana N THE PEAT OF UPPER TEESDALE n November 1965, an eroding surface of peat close to the Betula najia colony was cut well back and samples were taken for a preliminary examination. The profile consisted of 0 cm of Eriophoriim-Calluna peat overlying 45 cm of darker, well humified Sphagnmn- Calluna peat. This gave way to a fen peat which continued for a further 10 cm to bedrock. The final 0 cm of this peat consisted of wet, silty Phragmites peat. Numerous Phragmites rhizomes and Menyanthes seeds were found throughout the fen peat layers. Carex seeds and roots were numerous in the upper 0 cm of the fen peat, as were Sphagnum leaves. At a depth of cm from the bog surface, within the Phragmites layer, numerous leaf remains of Betula nana were found, many in an excellent state of preser\"ation (Plate 0). The morphology of these leaves was similar to that of the leaves of the living plants on the surface (Plate 1). Along with these leaf remains, numerous small twigs of birch occurred, possibly of B. nana. Clark and Blackburn (personal communication) found a similar localized area of Phragmites peat on Cronkley Fell, Teesdale, at much the same altitude. This contained numerous stumps of pine and birch, pollen of Helianthemum and the moss Paludella squarrosa. The age of the peat remains A number of workers have examined peats in the Upper Teesdale area, e.g. Erdtman (198), Raistrick and Blackburn (19), Godwin and Clapham (1951) and Johnson and Dunham (196), and all concluded that there was no evidence for the commencement of peat formation in the area earlier than the Boreal period, zone V, and that much of it commenced in zone VL n view of these findings and the general absence of Betula nana remains in Britain later than zone V, the dating of the present B. nana leaf remains in Upper Teesdale is of particular interest. Preliminary examination of the peat associated with the leaf remains has been made by Miss A. P. Conolly and Miss C. Brown at Leicester, and by the author. This peat was from a depth of 90 cm. Whilst a precise dating is not yet possible the samples are clearly from after the commencement of zone Vila, i.e. after the commencement of the Alnus rise, since Alnus comprised some 0% of the tree pollen and Quercus and Pinus about 1% each. Ulmus pollen represented about 10% of the tree pollen. The general picture corresponded to that given by Pigott and Pigott (196) and Johnson and Dunham (196) for late zone Vila in the North Pennines, although such close dating is not yet possible. n view of the need for a more accurate dating of the leaf remains, and the possibility that a full investigation of the profile may reveal a continuous record for Betula nana, and in view of the close proximity of the site to sugar-limestone and fiushed areas which contain numerous Late-glacial relict species, a full investigation of the profile is to be

8 T. C. HUTCHNSON undertaken. However, the preliminary dating of the B. nana remains as post early zone Vila, strongly suggests that the living plants on the bog surface are the last remnants of a colony having continuity with plants probably from the Atlantic period. ndeed, the finding at Neasham in Lower Teesdale of a Late-glacial flora containing B. nana, suggests that the plant may even have been continuously present in Upper Teesdale since Late-glacial times. The present find and that of Tallis (1964) further suggests that B. nana may have persisted at a number of sites in England to a much later date than generally supposed. POSSBLE AREAS OF SURVVAL N TEESDALE t is apparent from the literature, e.g. Raistrick and Blackburn (19), that trees covered the hills in the Teesdale area during early Atlantic times at least to 000 ft (645 m). For example, stumps have been found up to 50 ft (750 m) and are prevalent on hoth Cronkley and Widdybank Fells. The question is then how could Betula nana, a species of open situations, have survived this afi^orestation? t is of interest that Raistrick and Blackburn (19) pointed out that over most of the hill slopes and on to the fell tops, the forest, even at its maximum, consisted merely of birch-hazel scrub, large trees being rare. Since B. nana occurs in comparatively sparsely wooded poor fen communities in Sweden today (Malmer, 1965), it seems likely that it would be capable of continued persistence in such open-canopy woodland even at the forest maximum. Pigott (1956) discussed the possibility that the Teesdale fiora is a relic from the Lateglacial period and speculated about the habitats in which survival during the ensuing Post-glacial period could have occurred. He emphasized five habitats which probably remained sufficiently open. These were: (a) in areas which have always been above the treeline throughout the Post-glacial period; (b) on cliffs; (c) on high limestone areas which carry a shallow, base-rich unstable soil; (d) in calcareous marshes; and (e) on erosion banks of the river and tributaries. With regard to the survival of B. nana, only situation (a) appears directly applicable. The higher hills in the Teesdale area have certainly been above the treeline throughout the Post-glacial period (Pigott, 1956), and arctic-alpines such as Carex bigelowii, Salix herbacea and Polytrichum alpinum still survive on them. t is, therefore, quite possible that Betula nana survived the forest maximum at higher altitudes and re-invaded the present site at a later date. However, the finding of deep Phragmites peat near the sugar-limestone, both on Cronkley and Widdybank Fells, suggests that a base-rich Hush or fen community formerly existed, fed by the alkaline waters of the nearby spring lime. Such a fen area at 1700 ft (548 m) is unlikely to have been covered by large trees and it is in this fen peat that the leaf remains oi Betula nana have been found. This would seem to represent a further area of survival for Late-glacial relics. f B. nana survived the forest and climatic optimum in this fen or fen-margin situation, as is suggested, then the present-day occurrence of B. nana in Scotland, Germany and Scandinavia suggests that it could certainly survive in the succeeding blanket bog vegetation to the present day. ACKNOWLEDGMENTS should like to thank Miss A. P. Conolly for her confirmation of the leaf remains and Miss C. Brown for her preliminary pollen dating of the associated peat. Professor J. H. Burnett, Dr. W. A, Clark and O. L. Gilbert for their helpful criticism of the script and

9 Betula nana in Teesdale 57 Dr. A. W. Davison for his help with the first plate. The work was carried out during the tenure of a Sir James Knott Fellowship of the University of Newcastle upon Tyne. REFERENCES BAKER, J. G. & TATE, G. R. (1868). A new flora of Northumberland and Durham. Trans, nat. Hist. Northumb. Durham,. BARTLEY, D. D. (1966). Pollen analysis of some lake deposits near Bamburgh in Northumberland. A'^^t,' PhytoL, 6s, 141. BiRKS, H. J. B. (1965). Late-glacial deposits at Bagmere, Cheshire, and Chat Moss, Lancashire. Nezi: PhvtoL, 64, 70. BL.\CKBURN, K. B. (195). The dating of a deposit containing an elk skeleton found at Neasham, near Darlington, County Durham. New PhytoL, 51, 64. BocHER, T. W. (1959). Floristic and ecological studies in M.W. Greenland. Meddr Grenland., 156, 4. DRUCE, G. C. (19). The Conutal Flora of the British sles. Arbroath. ERDTMAN, G. (198). Studies in the post arctic history of the forests of N.W. Europe.. nvestigations in the British sles. Geol. For. Stockh. Forh., 50, 1. GODWN, H. (1956). The History of the British Flora. Cambridge L'niversitj Press. GODWN, H. & CLAPHAM, A. R. (1951). Peat deposits in Cross Fell, Cumberland. Nezv PhvtoL, 50, 167. JESSEN, K. (1949). Studies in Late Quaternary deposits and floral-history of reland. Proc. R. r. Acad., 5B, (6), 85. JOHNSON, G. A. L. & DUNHAM, K. C. (196). The Geology of Moor House. Nature Conservancy Monograph. Her Majesty's Stationary Office, London. MCVEAN, D. N. & RATCLEFE, D. A. (196). Plant Communities of the Scottish Highlands. Nature Conservancy Monograph i. Her Majesty's Stationery Office, London. MALMER, N. (1965). The plant co\'er of Sweden. Acta phvtogeogr. suec, 50, 149. MTCHELL, G. F. (195). Further identifications of macroscopic plant fossils from rish Quaternary deposits, especially from a Late-glacial deposit at Mapastown, Co. Louth. Proc. R. r. Acad., 55B, (1), 5. NORDHAGEN, R. (194). Sikilsdalen og Norges Fjellbeiter. Bergens Mus. Skr.,. O\-ERBECK, F. & ScHMiTZ. H. (191). Zur geschichte der Moore, Marshen und Walder N.W. Deutschlands.. Das Gebeit von der Niederweser bis zurunteren Ems. Mitt. Prov. Zielst. Natur.,, i. OvERBECK, F. & SCHNEDER, S. (198). Moorunterschugen bei Luneberg und dei Bremen und die Reliknatur von Betula nana L. in N.W. Deutschland. Z. Bot.,, i. PGOTT, C. D. (1956). The vegetation of Upper Teesdale in the North Pennines. JJ*. FcoL, 44, 545. PGOTT, C. D. & PGOTT, M. E. (196). Late-glacial and Post-glacial deposits at Malham, Yorkshire. NetoPhytoL, 6, 17. PoHLE, R. (190). Pflanzengeographische Studien fiber die Halbinsel Kanin und das angrezende Waldgebeit. Theil. St. Petersburg. RASTRCK, A. & BLACKBURN, K. B. (19). The Late-glacial and Post-glacial period in the North Pennines.. The Post-glacial peats. Trans, nth. Nat. Un., i, 79. RUSE, O. (1965). n 'The plant cover of Sweden'. Acta phytogeogr. suec, 50. SE.'\GREF, S. C. (1959). Pollen diagram from Southern England: Wareham, Dorset; and Nursling, Hampshire. New PhytoL, 58, 16. SEAGREE, S. C. & GODWN, H. (i960). Pollen diagrams for Southern England: Elstead, Surrey. Neii- PhvtoL, 59, 84. T.U.LS, J. H. (1964). The pre-peat vegetation of the Southern Pennines. New PhytoL, 6, 6. W R, D. (1955). Studies in the Post-glacial history of the British vegetation. XV. Skelsmergh Tarn and Kentmere, Westmorland. New PhytoL, 54,.

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