Nettlebed Common Bryophyte Report J A Webb February Nettlebed Common. Bryophyte Survey Report

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1 Nettlebed Common Bryophyte Survey Report Dr Judith A Webb Ecological Consultant 2 Dorchester Court Blenheim Road Kidlington Oxon OX5 2JT Website: February 2015 The Bank Hair-cap moss Polytrichastrum formosum, frequent at Nettlebed Common, photo J.Webb Introduction I was requested to survey bryophytes in parts of Nettlebed Common adjacent to a series of shallow pools (some ex-clay pits) mainly to the south and east of Mill House. The aim of this survey was to identify any areas or particular trees that had interesting, scarce or rare bryophytes so that they could be preserved in any remedial scrub/ tree or pond work. This work is an initiative of the Nettlebed and District Commons Conservators, with funding for the preliminary site surveys from the Chilterns Commons Project overseen by Rachel Sanderson. Winter is the best time for such a survey as most bryophytes are growing strongly in cool and wet conditions and many will be fruiting, aiding identification. I was informed of the known records for bryophytes accumulated for the site so far. The lists supplied show that it is particularly important site for species of acid wetlands, with three species of Sphagnum Bogmoss previously recorded. 1

2 Methods The site was visited on and for 2 hours each time. The designated area was thoroughly searched and small samples of some bryophytes removed for verification. These samples were all checked microscopically using reference identification texts at home. Whilst on site, trees with identified important epiphytic bryophytes were marked with small strips of numbered orange hi-vis tape pinned to bark with a drawing pin. GPS grid references were taken for each where possible. This is to aid the identification and preservation of these trees in the tree/shrub work to be carried out shortly. Whilst on site I ranged more widely than the designated area and recorded some additional bryophyte species on trees and around other pools. These records will be compiled and submitted at a later date. Results A total of 39 species of bryophytes were found in the designated survey area and the list of species recorded is to be found in the Appendix. The area is very bryophyte-rich generally, due to the moist conditions. On trees and on the ground there were extensive sheets of common bryophytes like Kindbergia praelonga, Pseudoscleropodium purum, Rhytidiadelphus squarrosus, Polytrichastrum formosum, Hypnum cupressiforme, Mnium hornum, Atrichum undulatum, Brachythecium rutabulum, Calliergonella cuspidata (in wet hollows), Drepanocladus aduncus (fairly common in strandline zone on previously inundated logs around the pools). The leafy liverwort Lophocolea bidentata was very common on tree bark, rotting logs and in the temporary inundation zone on logs around pools. More basic conditions must occur where there are sheets of Thuidium tamariscinum. Bare clay banks had the most acid bryoflora with Pellia epiphylla, Dicranella heteromalla, Calypogeia fissa, C. arguta and little else. On tree bark the first bryophyte colonist appears to be extensive light-green sheets of the small branched thalloid liverwort Metzgeria fruticulosa. This has abundant gemma production at this time of year and colonisation of new tree bark sites is mostly by dispersal of these very numerous vegetative gemmae. Whilst nearly all the bryophytes thrive under acid, low nutrient conditions, Kneiff s Hook-moss Drepanocladus aduncus usually prefers more base-rich wetlands and its presence around some pools may be indicative of slight nutrient enrichment. Notes on bryophyte species of interest 1. Lesser Cow-horn Bog moss (on old records as superseded name of S. auriculatum var inundatum) The lawns of Sphagnum species seen around the margins of the more open unshaded pools are confirmed to be entirely composed of this species, which is very scarce in Oxon and has its main population on the Chiltern Commons (Killick et. al., 1998). 2

3 Sphagnum lawn area in centre on edge of shallow pool, photo J. Webb Lesser Cow-horn Bog-moss in lawn around clay-pit pool. Photo J. Webb Two other Bog-moss Sphagnum species were previously recorded from this area, namely S. palustre and S. fimbriatum, but these were not re-found despite diligent searching and checking in the appropriate area. Possible reasons for the loss of these species include the pool areas becoming too deeply-shaded, or an episode of drying-out of the pools in the past, or increased water level or a combination of these factors. S. fimbriatum is quite a shade-tolerant species, so possibly drying or flooding might be a factor here if it has indeed been lost. Scheduled tree works around these shaded pools should improve the conditions for these species and if they do persist in an unrecognised form, enable their recovery. Slight raising of water levels might make the sphagnum species present better able to survive a hot dry summer and thus increase resilience to climate change. 3

4 2. Heart-leaved Spear-moss Calliergon cordifolium. This semi-aquatic moss was occasionally found in extensive sheets in shallow water in the margins of some pools. Previous recorded in 1998 from this site. Very local in Oxon, only 5 hectads (Killick et.al., 1998) but the Chilterns acid ponds seem to be a centre for it. I have seen it previously only on Otmoor and North Leigh Common. 3. Tree Fringe-wort Ptilidium pulcherrimum. This small leafy liverwort with attractively frilly leaves with long thin teeth was found in patches of not more than 50cm each on the basal sections of the trunk on only two mature birch trees adjacent to shallow pools. It is delicate and likely to need very humid conditions. Tree Fringe-wort Ptilidium pulcherrimum on base of birch, photo J. Webb It is not previously recorded for this site. Rare in Oxfordshire, Killick et al quote presence in 5 hectads but say it was increasing in the Midlands and Southern England. Current distribution from the NBN 4. Forcipated Pincer-wort Cephalozia cf. connivens. Tentative identification. Only a couple of strands of this tiny leafy liver wort with pincer-shaped leaves were found crawling through specimens of a moss when it was examined under the microscope at home. The moss had been collected from a tree bole by a pool, but the location not recorded as the liverwort had not been detected in the field and its importance not realised. Not previously recorded for this site. Delicate and likely to need humid conditions it is reported as rare in the Midlands and more common in the wetter and cooler west and north. Presumed lost from Oxon by Killick et. al. (1998). 5. Creeping Finger-wort Lepidozia reptans. This is another very small leafy liverwort on birch tree bases with leaves each divided to four finger -like lobes. Delicate and likely to need humid conditions it is not previously recorded for this site and scarce in Oxon, only 4 hectads mentioned in Killick et. al. (1998) here quoted as almost confined to the Chilterns. Relatively common in the wetter and cooler north and west of the UK. 4

5 6. Notched Pouch-wort Calypogeia arguta. Quite frequently found on some bare clay banks. Not recorded on this site before. Rare in Oxon according to Killick et. al. (1998) with 6 hectads, but Chilterns is one of its centres, with nearby Peppard Common being quoted. Marked upright or fallen trees with scarce important bryophytes: Example of a tree base important to scarce bryophytes Flag 1. A fallen rotting log by shallow pool has a very tiny patch of the liverwort Creeping Finger-wort Lepidozia reptans. There are more important populations, so detailed grid ref not recorded. Flag 2. On shady side of fallen tree trunk near pool, interest nice large patch of moss Plagiothecium nemorale, SU Flag 3. Living upright mature birch tree near pools, base extensively bryophyte covered. Interest - liverworts: Tree Fringe-wort Ptilidium pulcherrimum and Creeping Finger-wort Lepidozia reptans, SU Flag 4 Living upright mature birch tree, interest - liverwort Creeping Finger-wort Lepidozia reptan, SU Flag 5 Living upright mature birch tree, interest - liverwort Creeping Finger-wort Lepidozia reptans, SU Flag 6 Living upright mature birch tree, interest - liverwort Creeping Finger-wort Lepidozia reptans, SU Flag 7 Living upright mature birch tree, interest - liverwort Creeping Finger-wort Lepidozia reptans, SU

6 General recommendations Trees marked with flags as having interesting scarce bryophytes should not be felled. In addition care should be taken not to fell too many trees around them so that the important bryophytes which like humid conditions are then exposed to too much unaccustomed sun and thus heat and drying-out. The leafy liverworts will be particularly sensitive to lack of humidity. As not all important bryophytes may have been located in this brief survey, and bryophyte mats are important for many invertebrates, all bryophyte-covered, lying, deadwood should be retained on site and if in an originally shaded position, should be re-located to a new shaded position if tree felling would expose the log to heat and drying. Any tree scheduled for felling that has an extensively mossy bole with several bryophyte species (even if common) could be pollarded above the bryophyte zone rather than clear felled. Slight raising of the water level in some pools will not disadvantage the semi-aquatic bryophyte species and may be beneficial in helping them survive a period of hot dry weather. Reference Killick, J., Perry, R. and Woodell, S., (1998) The Flora of Oxfordshire, Pisces Publications Acknowledgements I thank R. d Ayala for showing me the area to be surveyed and assisting with the GPS grid references. 6

7 Appendix: List of Bryophyte Species on Nettlebed Common in area of scheduled works (interesting species highlighted) Nettlebed Common ponds area J A Webb, , Map Ref. Abundance Comment Atrichum undulatum Common Smooth-cap frequent soil Brachythecium rutabulum Rough-stalked Feather-moss locally frequent patches on soil or tree bases Calliergon cordifolium Heart-leaved Spear-moss SU locally frequent wet hollows Calliergonella cuspidata Common spear-moss occasional wet hollows Calypogeia arguta Notched Pouchwort rare rotting logs and bare clay banks Calypogeia fissa Common Pouchwort frequent on bare clay banks Cephalozia cf. connivens Forcipated pincerwort v rare tree base near pond Dicranella heteromalla Silky Forklet-moss frequent bare clayey soil, shaded Dicranoweissia cirrata Common pin-cushion occasional on tree bark Dicranum scoparium Broom Fork-moss occasional tree bark Drepanocladus aduncus Kneiff's Hook-moss SU occasional pond margins in flood zone Eurychium striatum Common Striated Feathermoss occasional soil Fissidens bryoides Lesser Pocket-moss occasional shaded bare clayey banks Frullania dilatata Dilated Scalewort rare pne patch on fallen willow trunk Hypnum andoi Mamillate Plait-moss frequent tree bark Hypnum cupressiforme Cypress-leaved Plait-moss abundant tree bark Hypnum jutlandicum Heath Plait-moss occasional clayey soil Hypnum resupinatum a plait-moss common tree bark Isothecium myosuroides Mouse-tail moss occasional tree bark, mostly around boles Kindbergia praelonga Common Feather-moss abundant soil, tree bark, near ponds Lepidozia reptans Creeping Fingerwort occasional with mosses on tree bases Lophocolea bidentata var bidentata Bifid Crestwort frequent tree bark, clay soil, rotting wood, Metzgeria fruticulosa forked veilwort locally frequent tree bark, with abundant gemmae Metzgeria furcata a veilwort occasional tree bark Mnium hornum Swan's-neck Thyme-moss frequent soil, tree boles Orthotrichum affine Wood Bristle moss occasional drier tree bark and twigs Pellia epiphylla Overleaf Pellia occasional bare soil, clayey banks in shade Plagiomnium undulatum Hart's-tongue Thyme-moss rare soil Plagiothecium nemorale Woodsy silk-moss SU rare fallen trunks and tree bases Polytrichastrum formosum Bank Hair-cap locally frequent soil Pseudoscleropodium purum Neat Feather-moss locally frequent on soil Pseudotaxiphyllum elegans Elegant Silk-moss rare bare clayey soil, shaded Ptilidium pulcherrimum Tree fringe-wort SU rare on two birch trees Radula complanata Even Scalewort occasional tree bark Rhytidiadelphus squarrosus Springy turf-moss locally frequent soil SU locally frequent wet hollow SU m dia patch wet hollow SU m dia patch wet hollow SU wet hollow Thuidium tamariscinum Common tamarisk-moss locally frequent moist soil, rarely tree boles Ulota phyllantha Frizzled Pincushion rare tree bark Zygodon conoideus lesser yoke-mosss rare birch tree bark 7