Orthotrichum Pallens Bruch Ex Brid

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Orthotrichum pallens Bruch ex Brid. Pale Bristle-moss ORTHOTRICHACEAE SYNONYMY: Orthotrichum arnellii Groenv. Orthotrichum aurantiacum Groenv. Orthotrichum boreale Groenv. Orthotrichum immersum Brid. Orthotrichum obscurum Groenv. Orthotrichum pallidum Groenv. Orthotrichum paradoxum Groenv. Orthotrichum polare Lindb.

Status: Current GB status (www.jncc.gov.uk) - Natural England Species Recovery Programme Endangered (2008) Status in Europe: Not threatened UK BAP Priority Species (2007) Lead Partner: Plantlife International

UK Biodiversity Action Plan: These are the current BAP targets following the 2001 Targets Review: T1 - Maintain populations of this species at all extant sites. T2 - Establish by 2005 ex situ stocks of this species to safeguard extant populations. Progress on targets as reported in the UKBAP 2002 and 2005 reporting rounds can be viewed on the BARS (Biodiversity Action Reporting System) website: http://www.ukbap- reporting.org.uk/status/species_habitat_nat_status.asp?C=1&X=%7B38BDA9AD-4F27-4FA9-A7A0- 2FD9B1728CB5%7D&P=&F=&S=Orthotrichum+pallens&submitted=1&txtLogout= The full Action Plan for Orthotrichum pallens (UK Biodiversity Group 1999) can be viewed on the following web page: http://www.ukbap.org.uk/UKPlans.aspx?ID=488 UKBAP species actions are currently under review following the recent revision of UKBAP species (2007). The current UK list of Priority Species can be viewed on the following web page: http://www.ukbap.org.uk/PrioritySpecies.aspx?group=6 Contents

1 Morphology, Identification, Taxonomy & Genetics 1.1 Morphology & identification 1.2 Taxonomic & genetic considerations 2 Distribution & Current Status 2.1 World 2.2 Europe 2.3 United Kingdom 2.3.1 England 2.3.2 Northern Ireland 2.3.3 Scotland 2.3.4 Wales 3 Ecology & Habitat Requirements 3.1 Atmospheric pollution 3.2 Communities & vegetation 3.3 Dispersal & strategy 3.4 Habitat requirements in the UK - conclusion 4 Threats 5 Management Implications 6 Ex situ Conservation 7 Recommendations for Future Work 8 References 9 Acknowledgements 10 Contacts 11 Links 1 Morphology, Identification, Taxonomy & Genetics

1.1 MORPHOLOGY & IDENTIFICATION

Description According to Hill et al. (1994), "Orthotrichum pallens is a somewhat characterless species, which may therefore be under-recorded." While it is rather small and inconspicuous, there are a number of useful characters that can help in determining material. When sporophytes are approaching maturity, in early summer, the calyptra stands out very clearly because of its pale, shining appearance, making the sporophyte look large in comparison with the gametophyte (Stephen Wharton, pers. comm.). Furthermore, the calyptra is glabrous, plicate and has an orange tip (not dark, as in O. stramineum). The capsules are emergent, not exserted (as in O. pulchellum). The leaves are rather dark green and obtuse (paler and more pointed in most other species), more or less straight and imbricate when dry (more neat-looking than O. affine), and rather opaque, because of the relatively strong papillae (more shining and translucent in O. affine). Microscopically, the stomata on the capsule are rather few, well-distributed and clearly immersed, but the guard cells hardly obscure them at all. O. affine has superficial stomata, and O. tenellum, O. stramineum and O. pumilum have the stomata much more obscured by the guard cells. In addition, the stomata of O. tenellum tend to be more restricted to the lower half of the capsule, and O. stramineum has numerous hairs on the vaginula.

According to Crum & Anderson (1981), distinctive features of O. pallens include "the autoicous sexual condition (with perigonia terminating short branches), strongly ribbed, strangulate capsules, slightly to distinctly immersed stomata, peristome teeth united in 8 pairs, 16 slender endostome segments, and a naked calyptra."

Figure 1 - Orthotrichum pallens at Green Bank, Weardale (Photograph by Stephen Wharton)

Figure 2 - Orthotrichum pallens at Green Bank, Weardale (Photograph by Nick Hodgetts)

1.2 TAXONOMIC & GENETIC CONSIDERATIONS

The specific status of Orthotrichum pallens appears to be taxonomically uncontroversial, at least at present.

2 Distribution & Current Status

2.1 WORLD

Orthotrichum pallens is circumboreal and scattered in Europe, N. Asia and N. America.

2.2 EUROPE

According to Hill et al. (1994) its main European distribution is in northern and central Europe, whereas it is rare in southern Europe and absent from most of the Mediterranean islands. Nyholm (1974) describes it as 'scattered' in Scandinavia, but present in most provinces in Sweden and Norway. It has been recorded in Ireland, where it is also very rare (Hill et al. 1994). It is classified by Hill & Preston (1998) and Hill et al. (2007) as European Boreo-temperate.

2.3 UNITED KINGDOM

Overview In Britain Orthotrichum pallens has a predominantly northern distribution. Recorded from 20 sites to date in the United Kingdom (18 in northern England, and 3 from Scotland), recent records for O. pallens are restricted to Weardale in Co. Durham, Wharfedale in Yorkshire and an outlying southern occurrence in Hertfordshire. Hodgetts (2003) reviewed the status of O. pallens in Britain, and visited all known extant populations in Weardale. Subsequently, O. pallens was rediscovered in Wharfedale (Hodgetts 2006) and a new colony was found in Watford (Rothero 2008). O. pallens is listed as Endangered in the British Red Data Book for mosses and liverworts (Church et al. 2001). This information in this dossier updates and corrects the first edition (Hodgetts 2007).

Figure 4 - British distribution of Orthotrichum pallens

Open circles: pre-1980. Closed circles: 1980-2008.

The total number of reliable records of O. pallens went down considerably when Tom Blockeel revised the specimens for the Census Catalogue (Blockeel & Long 1998). Those that are confirmed are listed in Table 1.

Table 1 - Records of Orthotrichum pallens – historical and extant

Locality County Vice- Grid ref. Alt. Date Recorder Notes county Watford, Hertfordsh 20 TQ089974 60 2007 C.T.W. On willow branch Cassiobury Park ire Tipper in wet willow/alder scrub by river. Specimen in BBSUK Near Calder Lancashire 60 - - 1900 A. Wilson & Blackstock & Bridge, Garstang A. Wheldon Rothero (1999). Specimen in NMW York, Clifton Ings Yorkshire 62 SE55 - 1842 R. Spruce Baker (1906) York, Clifton Ings Yorkshire 62 SE55 - pre-1888 H. Ibbotson Lees (1888). 'West side of R. Ouse, above Clifton Ings' Addingham Yorkshire 64 SE05 - 1855 B. Braithwaite Carrington (1905) Addingham Yorkshire 64 SE05 - 1858 Unknown Specimen in BM Addingham Yorkshire 64 SE08215054 100 4.5.2005 N.G. On ash tree on Hodgetts bank of R. Wharfe. Specimen in BBSUK Addingham Yorkshire 64 SE08215054 100 17.10.200 N.G. At least 15 5 Hodgetts cushions on ash tree on bank of R. Wharfe Bolton Abbey Yorkshire 64 SE05 - 25.3.1856 B. Specimen in BM Woods Carrington Bolton Abbey Yorkshire 64 SE05 - 1934 H.N. Dixon Cheetham (1945) Woods Mickley, nr., S. Yorkshire 64 SE27 - pre-1888 J.G. Baker Lees (1888) side of R. Ure Crook Beck Durham 66 NZ167353 145 20.6.1999 T.S. & J. Bole of ash in Wharton dense scrub above Crook Beck Crook Beck Durham 66 NZ167353 145 21.6.1999 T.S. & J. Branch of elder Wharton in dense scrub above Crook Beck Crook Beck Durham 66 NZ16733533 145 21.1.2003 N.G. One tiny tuft ca. Hodgetts & 1 x 1 cm on ash T.S. bole Wharton Frosterley Dam, Durham 66 NZ034 43674 160 22.4.2004 N.G. On three ash Weardale Hodgetts et trees by river al. Frosterley Dam, Durham 66 NZ03513690 160 22.4.2004 N.G. On alder Weardale Hodgetts et between lay-by al. and river Green Bank, lay- Durham 66 NZ050369 167 4.6.1999 T.S. & J. On branch of by, Weardale Wharton, wych elm in conf. T.L. hedge by old Blockeel road Green Bank, Durham 66 NZ047369 - 1999-2000 T.S. & J. On roadside ash roadside, Wharton Weardale Green Bank, Durham 66 NZ04693694 150 20.1.2003 N.G. Single small tuft roadside, Hodgetts & of about four Weardale T.S. shoots seen on Wharton the SE side of one tree Green Bank, Durham 66 NZ05003697 150 20.1.2003 N.G. Small scattered roadside, Hodgetts & tufts in thrashed Weardale T.S. hedge at the side Wharton of lay-by over a length of ca. 200 m Green Bank, Durham 66 NZ04593694 150 20.1.2003 N.G. Single colony of roadside, Hodgetts ca. 7 x 2 cm Weardale found on an ash tree on the south side of the main A689 road Green Bank, Durham 66 NZ050369 150 22.4.2004 N.G. Several tufts roadside, Hodgetts et Weardale al. Green Bank, Durham 66 NZ047369 150 22.4.2004 N.G. Large amount of roadside, Hodgetts et fruiting material Weardale al. in stand of field maple in strip between lay-by and main road Green Bank, Durham 66 NZ046369 15 0 22.4.2 004 N.G. Very unhealthy roadside, Hodgetts et Weardale al. Green Bank, Durham 66 NZ048369 160 4.6.1999 T.S. & J. Wych elm woodland, Wharton branch, bole of Weardale ash & branch of dead tree in woodland by R. Wear Green Bank, Durham 66 NZ04933688 160 20.1.2003 N.G. Tiny tuft of two woodland, Hodgetts & fertile shoots Weardale T.S. seen on ash tree Wharton Harehope Gill, Durham 66 NZ033360 190 14.5.2000 T.S. & J. Bole of ash in Weardale Wharton open woodland near ruined building Harehope Gill, Durham 66 NZ033359 205 29.5.2000 T.S. & J. Bole of mature Weardale Wharton ash on bankside above wood Harperley Hall, Durham 66 NZ117346 - 15.5.2000 T.S. & J. Trunks of ash at Weardale Wharton edge of riverside wood Harperley Hall, Durham 66 NZ11693466 120 22.1.2003 N.G. Single 5 x 5 mm Weardale Hodgetts sterile tuft of ca. 5 shoots on riverside ash Harperley Hall, Durham 66 NZ11723460 120 22.1.2003 N.G. Small scattered Weardale Hodgetts colonies with O. pumilum on ash at woodland edge Harperley Hall, Durham 66 NZ11723460 120 22.4.2004 N.G. Small scattered Weardale Hodgetts et colonies with O. al. pumilum on ash at woodland edge Holebeck House, Durham 66 NZ054368 150 2.1.2000 T.S. & J. Branch of alder & road to, Wharton bole of sycamore Weardale by roadside above River Wear, upriver of bridge Holebeck House, Durham 66 NZ05463672 150 20.1.2003 N.G. Abundant on road to, Hodgetts & partly-fallen Weardale T.S. alder Wharton Holebeck House, Durham 66 NZ05463672 150 22.4.2004 N.G. Abundant on road to, Hodgetts et partly-fallen Weardale al alder, but less so than in 2003 Witton Park Durham 66 NZ168308 80 5.8.1999 T.S. & J. Bole of crack- Wharton willow by River Wear, north bank upstream of viaduct Witton Park Durham 66 NZ16903086 80 21.1.2003 N.G. Several tufts on Hodgetts elders by river Witton Park Durham 66 NZ16903086 80 22.4.2004 N.G. Several tufts on Hodgetts et elders by river al. Wolsingham, Durham 66 NZ069370 140 24.5.1999 T.S. & J. Bole of crack- River Wear Wharton willow by River Wear Wolsingham, Durham 66 NZ073368 140 27.5.1999 T.S. & J. Branch of willow River Wear Wharton by backwater of River Wear. Also on bole of white willow Wolsingham, Durham 66 NZ072369 140 27.5.1999 T.S. & J. Bole of crack- River Wear Wharton willow in riverside wood by River Wear Wolsingham, Durham 66 NZ072369 140 5.5.2000 T.S. & J. Bole of crack- River Wear Wharton willow in riparian woodland Wolsingham, Durham 66 NZ06363716 140 20.1.2003 N.G. Scattered shoots River Wear Hodgetts on roadside elder Wolsingham, Durham 66 NZ06893697 140 20- N.G. Single tuft on River Wear 23.1.2003 Hodgetts branch of crack willow Wolsingham, Durham 66 NZ07043697 140 20- N.G. Single tuft on River Wear 23.1.2003 Hodgetts branch of crack willow Wolsingham, Durham 66 NZ07063697 140 20- N.G. Four tufts on River Wear 23.1.2003 Hodgetts half-fallen dead tree Wolsingham, Durham 66 NZ07113696 140 20- N.G. On elder by river River Wear 23.1.2003 Hodgetts Wolsingham, Durham 66 NZ07163695 140 20- N.G. Single tuft on River Wear 23.1.2003 Hodgetts branch of crack willow Wolsingham, Durham 66 NZ07193695 140 20- N.G. At least 3 tufts River Wear 23.1.2003 Hodgetts on fallen crack willow Wolsingham, Durham 66 NZ071369 140 22.4.2004 N.G. Refound on River Wear Hodgetts et several trees al. Wolsingham Durham 66 NZ074368 150 27.5.2000 T.S. & J. Wooden fence by Bridge Wharton road above railway line Wolsingham, Durham 66 NZ064372 - 1999-2000 T.S. & J. On elder south of West Wharton Field House Tomintoul, Water Highland 94 NJ11 - 4.8.1983 M.F.V. On wych elm of Ailnack Corley Glen Nevis Highland 97 NN17 - July 1961 C.C. On ash. Paton & Townsend Warburg (1962). 'Lower Glen Nevis' Rosemarkie Highland 106 NH75 - July 1894 R.D. Wilkie - Source: Threatened Bryophyt e Datab ase

Several old records are e ither e rroneous or unreliab le. Tom Blo ckeel found that several specimens were misidentified and other records were not supported by a specimen at all, so had to be rejected. These are s ummarised below (Table 2.).

Table 2 - Unconfirmed or erroneous records of Orthotrichum pallens

Locality County Vice- Grid ref. Alt Date Recorder Notes county . Clough Wood, Derbyshire 57 SK26 130 1989 T.L. Blockeel Blockeel & Long Winster (1990). Specimen is O. pulchellum (Blockeel & Long 1999) South Lancashire Lancashi re 59 - - - Anon. Corley & Hill (1981). Not included in Census Catalogue (Blockeel & Long 1998) & remains unconfirmed Rokeby North- 65 NZ01 - 1906 R. Barnes Published in the west Naturalist, 1897, Yorkshire p. 184 (Tom Blockeel, pers. comm.) but no specimen traced Tanfield North- 65 SE27 - 1954 J. Appleyard "Doubtful record west in the Yorkshire Yorkshire Naturalists Union ledgers. This does not appear in the published report for that locality in the Naturalist, whereas Bryum pallens does. I suspect a transcription error." (Tom Blockeel, pers. comm.) Darlington, nr.* Durham 66 NZ21 - pre-1905 Anon. In a hedgerow (Ingham 1905). No specimen traced (Graham 1988). Not included in Census Catalogue (Blockeel & Long 1998) & remains unconfirmed Dailly Ayrshire 75 - - 14.5.186 J. Shaw Corley & Hill 1 (1981). Specimen is O. stramineum (Blockeel & Long 1999) South South 92 NJ11 - - Anon. Corley & Hill Aberdeenshire Aberdeens (1981). Not hire included in Census Catalogue (Blockeel & Long 1998) & remains unconfirmed

*The account in Graham (1988) says, "In a hedgerow near Darlington, new to South Durham (R. Barnes) 1890. This is a very rare species and no specimen has been traced, so the record mu st rema in doubtful". In view of its pres ent known distribution, it is not unlikely that the record is genuine. The records from VC59, VC65 and VC92 may be genuine too, but must remain doubtful in the absence of specimens.

2.3.1 ENGLAND

The distribution of Orthotrichum pallens in England is centred on Weardale in Co. Durham, with smaller populations in Yorkshire and Hertfordshire. There are further scattered old records from Yorkshire and Lancashire. O. pallens may survive elsewhere, or, like other epiphytes, be recolonising from the continent, but it is an inconspicuo us and easily over looked sp ecies.

Hertfordshire In 2007, Orthotrichum pallens turned up unexpectedly in Cassiobury Park, Watford, growing by the R. Gade and the Grand Union Canal, on a willow branch in wet willow/alder scrub (Rothero 2008).

Yorkshire and Lancashire The old records of Orthotrichum pallens from Yorkshire and Lancashire contain few details. In Lancashire, the only site was 'near Calder Bridge, Garstang'. In Yorkshire it was recorded from Clifton Ings (near York), Addingham, Bolton Abbey Woods and near Mickley. There are no habitat details, but O. pallens might have occurred as an epiphyte almost anywhere in these areas. In 2005, targeted survey work suc ceede d in refinding O. p allens at Addingham, where at least 15 cushions grew on a s ingle youn g ash tre e on the w est ban k of the R. Wharfe (Hodgetts 2006). There may be more in the area. Note that the arbitrary grid reference (SE04) previously assigned to the old Addingham records has been changed to SE05 in view of this discovery.

Co. Durham Orthotrichum pallens was first reliably recorded in Co. Durham by Stephen Wharton in 1999, and further fieldwork showed that it was present at a number of sites in Weardale (Hod getts 2003). The best site for the species, both in terms of population size and the quality and extent of the ha bitat, is the riparian swamp woodland on the north bank of the River Wear at Wolsingham. O. pallens was found here in 2003 on six trees, with an additional colony on a roadside elder just to t he west . No doubt it grows on o ther trees too - in 1999- 2000 it was found on 'doze ns' (Stephen Wharton, pers. comm.). Green Bank is also a very important site for O. pallens, although it has clearly deteriorated since it was found here in 1999-2000, because of unsuitable management. In 2003, the hedge had been cut back with no regard for the epiphytic flora, and there had been substantial felling in the woodland, destroying most of the O. pallens colonies there. However, there were still a number of small O. pallens colonies present. In 2004 the population in the stand of field maple in the strip between the lay-by and the main road had apparently increased.

The alder by the road to Holebeck House is also an important site, as it supports the largest single colony of O. pallens found during the 2003 survey (Hodgetts 2003). The colony near Harperley Hall is important because O. pallens grows with O. pumilum, an even rarer species. There are also plenty of young ash trees here potentially suitable for colonisation. The colony at Witton Park is moderately important as the easternmost colony, and the one furthest downstream in Weardale. The much smaller colonies at Crook Beck and Harehope Gill (where it may have disappeared altogether) are of less importance.

2.3.2 NORTHERN IRELAND

Not recorded.

2.3.3 SCOTLAND

Orthotrichum pallens has not been refound recently at its Scottish sites. Glen Nevis and Tomintoul, its most recent sites, have been searched thoroughly, and both have seemingly suitable habitat (Gordon Rothero, pers. comm.). The grid reference for the Tomintoul site "seemed a bit unlikely", according to G. Rothero, and the original recorder was unable to remember which part of Glen Nevis he visited when O. pallens was found there. The grid references for both may be fabrications added 'after the event' in order to produce dots for the distribution maps, as with so many old records. Numerous other wayside trees all over the east of Scotland have also been investigated without O. pallens being recorded (G. Rothero, pers. comm.).

2.3.4 WALES

Not recorded.

3 Ecology & Habitat Requirements

The following account of the ecology of Orthotrichum pallens is given by Hill et al. (1994): "It grows on the bark of ash, hazel, sycamore, willow and wych elm, often in rather open sites such as riversides. In Ireland it has been found on the trunk of a roadside sycamore at the edge of a village in unremarkable flat country with little shelter. In a Scottish locality it was also found on the trunk of a solitary tree, a wych elm by a river, but here with more shelter. Lowland. Autoecious; sporophytes common." Additional host trees in Weardale are alder, elder, field maple and holly. O. pallens does not appear to be very specific regarding which species of woody plant it grows on.

Although, like other species of the genus, it favours trees and shrubs with highly textured base-rich bark, such as elder, willow, ash, elm and sycamore, it is also found on alder (generally a poor substrate for epiphytes) and holly, as well as dead wood of various trees. At Green Bank, O. pallens seems to prefer older, moribund branches at the top of the hedge, particularly the thick, gnarled sections at branch junctions, where it is well-illuminated and/or receives extra nutrients from bird excrement. It may be significant that all the modern sites are close to rivers, and O. pallens may be favoured by shelter (but well-lit shelter) and a relatively high humidity.

Crum & Anderson (1981) say that O. pallens can sometimes grow on "dry calcareous and granitic rocks" in North America, and Nyholm (1974) says "sometimes on rocks" in Fennoscandia. It is only known as an epiphyte in Britain.

3.1 ATMOSPHERIC POLLUTION

Like most species of Orthotrichum, O. pallens is sensitive to atmospheric pollution, particularly sulphur dioxide SO2. However, unlike several species, its distribution has not contracted dramatically from a formerly much wider range - it has always been a rare and scattered plant. It may have disappeared from some of its English sites because of pollution, but its apparent disappearance from Scotland is less easy to explain.

In Weardale, Wharfedale and Watford, the sheltered nature of the riversides may protect O. pallens from atmospheric pollution to a certain extent. It does seem to be very restricted in its occurrence in Weardale, not occurring on apparently suitable trees downstream from Witton Park, or on more exposed ground away from the sheltered riverside. One theory (Stephen Wharton, pers. comm.) is that dust from the cement works at Eastgate could be raising the pH of tree bark in the valley downwind to the east, increasing the buffering affect and reducing acidification. This theory is supported by the fact that normally saxicolous or terricolous species such as Bryum argenteum, Grimmia pulvinata, Tortula muralis, Schistidium crassipilum and even Rhytidiadelphus squarrosus were all found growing as epiphytes during the survey. Tilcon and Tarmac also quarry in Weardale. The Eastgate cement works is now (2003) closing, so it will be interesting to monitor the epiphytes downwind. It may be that dust from the cement works enabled O. pallens to survive in times of high acid atmospheric pollution. Now this has lessened, it is to be hoped that O. pallens may be able to survive without the help of cement dust.

O. pallens may now be beginning to recolonise as the air quality has improved. In recent years there have been several unexpected records of pollution- sensitive species from eastern England, where they are presumably colonising from the Continent. For example, Antitrichia curtipendula and Orthotrichum obtusifolium have been recorded on apple trees in Cambridgeshire orchards (Hodgetts et al. 2006, Rothero 2008), and O. consimile has been recorded from elders in Derbyshire and south-east Yorkshire (Blockeel & Wall 2008).

3.2 COMMUNITIES AND VEGETATION

Very little work has been done on communities of epiphytic bryophytes and lichens, but it seems that, in Weardale, Orthotrichum pallens is part of the community defined by lichenologists (James et al. 1977) as the Xanthorion parietinae. This community has increased recently in an apparent response to falling levels of SO2 and increasing nitrogen pollution, and often includes usually saxicolous bryophytes such as Grimmia pulvinata and Tortula muralis.

Table 3 - Associates of Orthotrichum pallens in Weardale

Species Frequency Mosses Amblystegium serpens rare Brachythecium rutabulum rare Hypnum cupressiforme frequent Leskea polycarpa rare Orthotrichum affine abundant Orthotrichum diaphanum abundant Orthotrichum pumilum rare Orthotrichum stramineum rare Orthotrichum tenellum occasional Pylaisia polyantha rare Syntrichia virescens rare Ulota bruchii occasional Zygodon viridissimus rare

Liverwort Radula complanata rare

Lichens Parmelia subrudecta occasional Parmelia sulcata occasional Phaeophyscia nigricans occasional Phaeophyscia orbicularis occasional Physcia adscendens frequent Physcia tenella frequent Xanthoria parietina frequent Xanthoria polycarpa occasional

Alga Desmococcus sp. frequent

Associates at Addingham, Wharfedale, were Orthotrichum affine, O. cupulatum, O. diaphanum, Hypnum cupressiforme, Eurhynchium crassiphyllum and Scleropodium cespitans.

3.3 DISPERSAL AND STRATEGY

It appears that O. pallens is a colonist species, in the sense of During (1992). That is, the lifespan of an individual colony is probably rather short (a few years at most), and it has a high reproductive effort, producing many capsules with small (<20 µm) spores to facilitate dispersal and colonisation. From field observations it appears that Orthotrichum pallens may be a poor competitor, and that it is a small plant which favours growing on rather thin, often dead or moribund, twigs and branches where the competition is relatively low. It was also found growing on larger boughs and trunks, but O. affine and O. diaphanum appear to be more vigorous plants in that habitat. In these circumstances, O. pallens probably completes its life cycle quickly, producing spores and 'moving on' before being out-competed by O. affine and other epiphytes.

3.4 HABITAT REQUIREMENTS IN THE UK - CONCLUSION

The most simple requirement of Orthotrichum pallens is a steady and continuous supply of suitable tre es which it can use as a substrate for colonisation. However, precisely wh at this might mean is another matter, given that so little is known of its ecology in detail. It probably needs relatively base- rich bark, such as can be found on certain trees naturally (ash, field maple, etc.); or may, perhaps, by provided artificially by lime-rich deposition from nearby quarries. Hopefully the latter is no longer necessary in Weardale, now that the level of SO2 pollution is insignificant, but the situation requires monitoring. Ideally, the sort o f habitat provided by the riparian woodland at Wolsingham should be maintained. This is a small but continuous area within which colonies of O. pallens can grow, mature, die and move on, behaving as a metapopulation. Similarly, the hedge and woodland at Green Bank and to a lesser extent the other sites can also harbour sustainable populations, if the management is amenable. In time O. pallens may disperse itself more widely in this part of northern England if favourable atmospheric conditions continue to prevail.

The habitat requirements at its othe r two recent sites are probably similar. At Addingham, Wharfedale, riversi de ash trees and associated riverbank vegetation should be retained and disturbed as little as possible. Adjacent pastures should not be subjected to more intensive farming management. At Cassiobury Park, Watford, the stand of riparian willow/alder scrub should be retained and not subjected to disturbance or ‘tidying-up’.

4 Threats

Table 3 - Summary of the threats to the survival and spread of Orthotrichum pallens in Britain. Threat

Pollution Habitat destruction Ivy Closure of nearby quarries

Pollution This is a potential threat if there is any large scale change or a local pollution episode resulting in the release of a significant amount of SO2 or other toxic chemicals. In the worst case, the entire Weardale population of O. pallens could potentially be wiped out in a single pollution event. On a smaller scale, it is likely that the colonies closest to the main road are being impacted negatively by pollution from vehic le emissions and/or salt-spreading during the winter - one of the Green Bank colonies, very close to the road, looked very unhealthy in 2004. Less severe pollution events could possibly have an effect on the fertility of O. pallens, perhaps leading to fewer spores being produced. It is not known how tolerant O. pallens is of bark eutrophication, but it is possible that excessive eutrophication (for example from muck-spreading) could have an effect on exposed trees. The latter operation could also affect the Addingham population.

Habitat destruction This is probably the most important threat to O. pallens at present. In Weardale, much of the Green Bank site has been damaged or destroyed by tree felling and hedge-thrashing. Any such destruction of substrate trees and shrubs obviously has a negative impact on O. pallens. The most important site, the woodland at Wolsingham, is adjacent to a park and housing estates. Any moves to replace the current secondary woodland with housing, more formal 'amenity land' or anything else designed to 'increase the amenity value' of the site are likely to threaten O. pallens. Threats of this kind are not unlikely, since the site might be considered unattractive by some, being rather scruffy secondary woodland on the riverbank. It is easy to imagine some well-meaning councillor coming up with the idea of making a 'riverside park' here, or some such 'improving' project. Similar concerns could be expressed about the Witton Park population. Tree felling is a clear threat at all the O. pallens sites. Key trees should therefore be well documented, and known to any local parties likely to engage in felling operations. The single ash at the woodland edge at Harperley Hall is particularly important, and its loss would be a great blow to both O. pallens and O. pumilum.

Habitat destruction could also occur through road maintenance or improvement schemes, as some of the sites are very close to the edge of the main A689 road. O. pallens is also vulnerable to other routine acts of maintenance etc. For example, the fence at Wolsingham Bridge where O. pallens was seen in 2000 has now been removed, and nearby scrub cleared, so there seems little chance of recolonisation taking place here. In the woodland at Green Bank, there is evidence that further activities may be planned for the site, possibly connected with the Kingfisher Leisure park on the other side of the river: for example, in 2003 there was a pile of cut-down telegraph poles, several of the remaining trees had been marked with paint spots, and there were many newly-placed stones on the opposite bank.

The small site at Crook Beck is very vulnerable to change. It is a local eyesore and a magnet for drug-users and hooligans, so it is very likely to be redeveloped at some point. At present, the site is used by local youth for play and drug-taking and the O. pallens can easily be scraped off the tree by climbing, or damaged by fire. The elders appear to be dying, the bark becoming more acidified and the branches becoming decorticated. Dicranoweisia cirrata and Hypnum cupressiforme are increasing at the expense of Orthotrichum spp., although O. diaphanum is still present.

The small population at Addingham, Wharfedale, would be destroyed if its ash tree was felled as part of riverbank management, or fell in extreme conditions of weather or water flow. The Watford population relies on a stand of riverine scrub in an urban park. This kind of habitat is generally very vulnerable to ‘tidying-up’ operations, and the local council should be alerted to the importance of the site.

Ivy Growth of ivy might be a threat at some sites. For example, the roadside ash trees at Green Bank are being colonised vigorously by ivy, and this is bound to shade out O. pallens eventually.

Closure of nearby quarries While this may not be a threat at all, it is possible that the relatively large and healthy population of O. pallens in Weardale is directly related to deposition from the limestone quarries. With their closure, the future of O. pallens in the area is uncertain, and the population should continue to be monitored regularly.

5 Management Implications

Little active management is required at the sites where Orthotrichum pallens is currently known. Management is mainly a matter of 'controlled neglect', in which felling, tidying-up and other disturbing operations should be kept to a minimum.

6 Ex situ Conservation

Several samples of Orthotrichum pallens were collected from Witton Park in 2004 for ex situ conservation. These were sent to the micropropagation unit at Kew Gardens, where a project on ex situ bryophyte conservation, funded by English Nature (now Natural England) was involved with growing and bulking up rare bryophytes. That project is not now operational, but material is retained in cold storage.

7 Recommendations for Future Work

It is suggested therefore that the following recommendations be observed:

 Take whatever action is considered appropriate locally to safeguard Weardale populations.  Maintain extent and structure of secondary riparian woodland at Wolsingham.  Retain riparian willow/alder scrub in Cassiobury Park, Watford  Retain low-intensity riverbank management at Addingham, Wharfedale  Monitor condition of known populations every 3 years.  Survey nearby sites where O. pallens could potentially occur every 5 years.  Revive ex situ project at Kew, to continue to bulk up ex-situ stocks of O. pallens in case re-introduction is needed at some point in the future.

8 References

Baker, J.G. 1906. Flora of North Yorkshire. London.

Blackstock, T.H. & Rothero, G.P. 1999. New vice-county records and amendments to the Census Catalogue. Bulletin of the British Bryological Society 73: 36-47.

Blockeel, T.L. 2008. Orthotrichum consimile in Derbyshire. Field Bryology 94: 23-26.

Blockeel, T.L. & Long, D.G. 1990. New vice-county records and amendments to the Census Catalogue. Bulletin of the British Bryological Society 56: 23-34.

Blockeel, T.L. & Long, D.G. 1998. A checklist and census catalogue of British and Irish bryophytes. Cardiff, British Bryological Society.

Blockeel, T.L. & Long, D.G. 1999. The new Census Catalogue: supplementary lists of deleted, recent and replacement records. Bulletin of the British Bryological Society 73 (supplement): 1-28.

Blockeel, T.L. & Wall, C. 2008. Orthotrichum consimile: another English record and a postscript. Field Bryology 96: 26-27.

Braithwaite, R. 1896-1905. British Moss Flora. Vol. III. London, L. Reeve & Co.

Cheetham, C.A. 1945. Mosses, liverworts and lichens of Yorkshire. Transactions of the Yorkshire Naturalists' Union 36.

Church, J.M., Hodgetts, N.G., Preston, C.D. & Stewart, N.F. 2001. British Red Data Books. Moses and liverworts. Peterborough, Joint Nature Conservation Committee.

Corley, M.F.V. & Hill, M.O. 1981. Distribution of bryophytes in the British Isles. A Census Catalogue of their occurrence in vice-counties. Cardiff, British Bryological Society.

Crum, H.A. & Anderson, L.E. 1981. Mosses of Eastern North America. Volume 2. New York, Columbia University Press.

During, H.J. 1992. Ecological classifications of bryophytes and lichens. In: Bates, J.W. & Farmer, A.M. Bryophytes and lichens in a changing environment. Oxford, Oxford University Press.

Graham, G.G. 1988. The flora and vegetation of County Durham. Durham Flora Committee and Durham County Conservation Trust.

Hill, M.O. & Preston, C.D. 1998. The geographical relationships of British and Irish bryophytes. Journal of Bryology 20: 127-226.

Hill, M.O., Preston, C.D., Bosanquet, S.D.S. & Roy, D.B. 2007. BRYOATT. Attributes of British and Irish mosses, liverworts and hornworts. Huntingdon, NERC.

Hill, M.O., Preston, C.D. & Smith, A.J.E. (eds.) 1994. Atlas of the bryophytes of Britain and Ireland. Volume 3 Mosses (Diplolepideae). Colchester, Harley Books.

Hodgetts, N.G. 2003. The status of pale bristle-moss (Orthotrichum pallens) in Britain. Plantlife Report Number 221. Salisbury, Plantlife International.

Hodgetts, N.G. 2006. Survey of recent historical sites for pale bristle-moss (Orthotrichum pallens) in Britain outside Co. Durham. Salisbury, Plantlife International (unpublished).

Hodgetts, N.G. 2007. Orthotrichum pallens (pale bristle-moss) species dossier. Salisbury, Plantlife International.

Hodgetts, N.G., Preston, C.D. & Stevenson, C.R. 2006. Antitrichia curtipendula in a Cambridgeshire orchard. Field Bryology 89: 8-10.

Ingham, W. 1905. Mosses and liverworts. In: W. Page (ed.), The Victoria History of the Counties of England, Durham 1: 62-69.

James, P.W., Hawksworth, D.L. & Rose, F. 1977. Lichen communities in the British Isles: a preliminary conspectus. In: Lichen Ecology, ed. by M.R.D. Seaward (pp. 295-413). London: Academic Press.

Lees, F.A. 1888. The Flora of West Yorkshire. London, Lovell Reeve & Co.

Nyholm, E. 1974. Illustrated moss flora of Fennoscandia. II. Musci. Fascicle 4 (2nd edition). Stockholm, Swedish Natural Science Research Council.

Paton, J.A. & Warburg, E.F. 1962. New vice-county records. Transactions of the British Bryological Society 4: 356-377.

Rothero, G.P. 2008. New vice-county records. Musci. Field Bryology 95: 52-67.

UK Biodiversity Group 1999. Tranche 2 Action Plans. Volume III – plants and fungi. Peterborough, English Nature.

9 Acknowledgements

Tom Blockeel, Jenny Duckworth (ex-Plantlife), Brian Humphreys, Nicola Hutchinson (Plantlife), Amanda Miller (Plantlife), Ron Porley (EN), Gordon Rothero, Julie Stobbs (Durham County Council), Stephen Wharton, Sally Whyman (National Museum of Wales).

10 Contacts

Plantlife International, 14 Nicola Hutchinson – Rollestone Street, Salisbury, [email protected] Wiltshire, SP1 1DX. Tel: k 01722 342730 Nick Hodgetts [email protected]

11 Links

 British Bryological society http://www.britishbryologicalsociety.org.uk/.

Plantlife International’s Back from the Brink (species recovery) programme is supported by: Natural England, Scottish Natural Heritage & the Countryside Council for Wales. Work on Orthotrichum pallens is supported by;

Nick Hodgetts First draft dated 5th December 2008 Glossary autoicous: with male and female inflorescences on different branches of the same plant. calyptra: hood-like protective covering of the capsule. endostome: inner ring of tooth-like structures at the mouth of the moss capsule. gametophyte: the vegetative, haploid generation of the bryophyte life cycle. peristome: tooth-like fringe surrounding the mouth of the moss capsule. plicate: longitudinally folded, producing pleats or furrows (usually of leaves). sporophyte: the spore-producing, diploid generation of the bryophyte life-cycle. stoma, pl. stomata: a pore with two guard cells, sometimes present on sporophytes. vaginula: sheath at the base of the seta developed from part of the archegonium.