Buxbaumia viridis leaflet - Plantlife

LOWER PLANTS AND FUNGI PROJECT - TRAINING DAYECOLOGY AND MANAGEMENT OF DEADWOODFOR BUXBAUMIA VIRIDIS AND OTHERBRYOPHYTESCOURSE NOTESwritten for Plantlife Scotland by Gordon Rothero,Course Leader and Consultant BryologistApril 2008Date of course:Venue:Course Leader:17 th April 2008, 9.30am – 5.00pmRSPB Abernethy National Nature Reserve, StrathspeyGordon RotheroBuxbaumia viridis © Gordon Rothero

Buxbaumia viridis - Status and world distributionIn the United Kingdom, Buxbaumia viridis is rated as Endangered in thebryophyte Red Data Book (Church et al., 2001), has a Biodiversity Action Planand is listed on Schedule 8 of the Wildlife and Countryside Act. TheEndangered threat category means that the plant is deemed to be at a very highrisk of extinction in the wild because of its small range and patchy distribution andthe small number of plants in total.Buxbaumia viridis has a scattered distribution in montane and boreal habitatsacross the northern hemisphere from south-west Asia and China to westernNorth America. It is a species of conservation concern in North America but itsstatus in Asia is not known. It is sparsely distributed across Europe and appearson the Red List of most countries where it occurs. The European Committee forthe Conservation of Bryophytes rates Buxbaumia viridis as Vulnerable in Europeand it is listed in Annex II of the EC Habitats and Species Directive and onAppendix 1 of the Council of Europe Bern Convention.Its status on European Annex II theoretically means that Buxbaumia viridis is a“plant species of Community interest whose conservation requires thedesignation of Special Areas of Conservation”. Its listing on Schedule 8 meansthat “it is an offence (subject to exceptions) to pick, uproot, trade in, or possess(for the purposes of trade) Buxbaumia viridis without a licence.” So, please donot collect Buxbaumia viridis. If you want verification a digital photo is usuallyideal.History of recording and current UK distributionAll the UK records for Buxbaumia viridis are in the north and east of Scotland,extending from East Ross in the north and, historically, to Arbroath in Angus inthe south. There are two concentrations of recent records, one in the glens westof Inverness and the other on Speyside. It seems likely that some other sitesfurther west will be found but Buxbaumia viridis is a boreal-montane species,presumably not suited to the wetter, milder west. It has never been seen insouthern Britain and all of the more southerly sites in Europe are associated withthe mountains.Buxbaumia viridis was first recognised in the UK (as B. indusiata) fromBalnagowan near Tain in East Rossshire in March 1867 from a collection by MrsClarke. However, the announcement of this discovery prompted Prof. G Dickie tore-examine plants in his herbarium, sent to him by Mr A Cruickshank (asBuxbaumia aphylla), collected from “a dense fir wood at Pannanich, nearBallater” in July 1847 (Dickie, 1867a). These also proved to be Buxbaumiaviridis. Presumably inspired by this, Dickie revisited Deeside accompanied byJohn Roy and found Buxbaumia viridis on Craigendinnie Hill above Aboyne inJune 1867 (Dickie, 1867b) and collected it here again in both 1869 and 1870.There are also two enigmatic literature records from this period, one from a “Ben

Hearag” in Strath Glass (a hill which does not seem to be mapped), published byBuchanan White (White, 1870) and Buxbaumia viridis appears in a list ofcryptogams from Loch Lomond published by Stirton (Stirton, 1876). Some 20years after the first records, Buxbaumia viridis was found much further south, inEthie Woods near Arbroath by W Smith in 1887and this is still the most southerlyrecord.After this the plant was seemingly lost until 1951 when it was found by FrancisRose on Alvie Estate near Aviemore on Speyside. The link with current sites forthe species starts in 1961 when Noel Pritchard found Buxbaumia viridis in ReeligGlen close to Moniack by Beauly and he continued to visit this site and see theplant in most years until 1970. It was not seen again here until 1993 when theauthor was contracted by SNH to look for the plant in Reelig Glen (Rothero,1993). In 1999 SNH employed the author to look at the phenology of Buxbaumiaviridis at Reelig (Rothero, 1999) and experience gained during this work leddirectly to the discovery of a number of other sites in the next two years, notablyon Rothiemurchus and Abernethy Estates on Speyside. As most of these findswere made in company with other people, knowledge of and enthusiasm for theplant spread (a little) and, inevitably, other discoveries have followed.09Key to symbols1950 onwardPre 1950'8760 1 2 3 4 5By far the greatest concentration of stands is now on the RSPB’s AbernethyEstate where, following the initial finds by the author and Andy Amphlett (RSPB),Stewart Taylor (RSPB) has enthusiastically pursued the plant and has nowaccumulated records from some 30 stands. Buxbaumia viridis has been found inseveral places close together near Bridge of Brown and once further downSpeyside, near Dufftown, while further west, Stewart Taylor found a population inGlen Tromie. Sandy Payne (SNH ret.) has found several stands near SouthClunes above Moniack and there is a record from Ruttle Wood near the RiverBeauly; further north, Dave Genney (SNH) found a good stand on a log nearRogie Falls, the first record for Ross-shire since 1867. The plant was againfound on Deeside after an absence of over 130 years by the Tullich Burn near

Ballater, again by Sandy Payne on his own ground, but targeted searching in2007 failed to find any other Deeside sites. In the last few weeks Sandy Paynehas found a further Deeside site at Quithel Wood SSSI. The stand belowKindrogan Crag near Pitlochry never reappeared after the first year and it mustbe considered extinct here. A number of these sites are on Forest Enterpriseground.What is it and what does it look like?Buxbaumia viridis is a moss but it is very different to virtually all other mosses inthat the only part that is visible in the field is the relatively large fruiting body (thesporophyte). With most other mosses, what you see is the green leafy stage (thegametophyte) with more or less frequent, relatively small sporophytes. TheBuxbaumia viridis sporophyte has a stalk of about 10-15m in length and a largecapsule so that the whole structure can be over 20mm tall which is quite large onthe scale of mosses. During the winter months the capsule is a bright greencolour, gradually turning brown in spring as the spores develop and, when thecapsule is ripe, the cuticle on the capsule splits and peels back (Fig 1). TheAmerican common name of “bug-on-a-stick” is quite an apt description.The only other moss that can possibly be confused with it is the closely relatedBuxbaumia aphylla. This has a similar life cycle and superficially similarappearance but the capsule has a distinct angle (bottom right picture in Fig 1) sothat the upper surface is rather flat, hence the common name ‘shield moss’, andconfusion is unlikely although old capsules of both species can be difficult (Fig 1).Buxbaumia aphylla is also rather rare, though it currently has no conservationstatus, and all records are welcome. It can grow on dead wood but will also growon humus-rich soil on banks and root-plates and there are a number of recordsfrom old pit-bings in central Scotland.What to do if you find Buxbaumia viridisIf you think that you have found the moss and/or want any advice about what dodo next, the first point of contact should be Matilda Scharsach, PlantlifeScotland's Lower Plants and Fungi Officer, (Tel 01786 469778,matilda.scharsach@plantlife.org.uk) or David Genney(David.Genney@snh.gov.uk Tel. 01463 725253) who is the Scottish NaturalHeritage Lower Plants and Fungi Officer.

Fig 1. Top left - Buxbaumia viridis young capsule; top right - mature capsule;bottom left - old capsule; bottom right - Buxbaumia aphylla.

Where does it grow?Buxbaumia viridis grows on damp, dead wood. Most stands are on medium tolarge logs (or logs that have been large at some point), composed of well rottedwood that is easily penetrated with a knife blade. It will persist on the fragmentsthat fall away from the log and may even continue to produce sporophytes whenthe log is no longer apparent, the moss appearing to grow on the humus of thewoodland floor. A few sites are on dead wood that is still attached to a live treeand a number of recent sites on alder still have the bark in tact with the woodunderneath dead but still hard.Many of the sites have a strong association with watercourses, usually beingclose to a river and often where this is incised, presumably giving buffering fromchanges in humidity. However some other sites are well away from watercoursesalthough all are in sites that are quite humid, either because of aspect,canopy cover or proximity to damp ground.It is absent from those dry, dead trees typical of open pine woodland in the eastof Scotland; these logs, which often look grey from a distance, have few if anybryophytes on them though they may be very important for lichens. Until a fewyears ago Buxbaumia viridis was thought to be restricted in Scotland to large,rotten logs of Scots pine. The situation is rather more complicated now as themoss has also been recorded from birch, rowan, willow and alder as well asconifer logs which are not pine.In terms of frequency, current sites suggest that it is more common on deadwood from broadleaf trees than on pine and even where it occurs on pine it isoften in quite diverse woodland. Though most sites are on fallen logs, it doesoccur on rotten cut stumps and on cut logs and one site is on old timber from abridge washed away in a spate. Buxbaumia viridis sporophytes often occur onrather open patches of rotten wood (see Fig 3) but can also occur, protrudingthrough other bryophytes making them much harder to spot. Some analysis ofthe woodland history of the sites where Buxbaumia viridis grows might proveinteresting.The largest population at Abernethy is associated with ‘ancient woodland’ andthis is also true of Rothiemurchus. A long history of cover is also probable inReelig Glen and at other sites in incised river valleys but a more thoroughinvestigation is needed for this connection to be convincing; it may just be thatolder woods tend to have more suitable habitat.Sex and dispersalTo understand some of the conservation problems posed by this moss it isnecessary to delve a little deeper into its sex life. The capsule ripens duringspring and the spores in the capsule are dispersed in early summer, the actualdate depending on the microclimate at the site. The capsule has a prodigiousnumber of spores, some six million on average, so they are very small. Even so,most will land close to the capsule with only a small percentage being blown

further away. If the spores land on a suitable substrate they will germinate andproduce microscopic filaments, called protonema, which form an open mat andeventually these filaments will bud and produce the tiny leaves which encloseeither male or female sex organs which contain the sperm and eggs.These plants with the sex organs are minute compared with most other mosses,particularly the male plant in which the antheridium (male sex organ) is claspedwithin a single modified leaf. Searching for them in the field is not really anoption. Buxbaumia viridis does not make it easy for itself as it is dioecious, withmale and female plants being produced from different spores. This means thatfor fertilisation to be possible, both male and female spores need to germinateand produce patches of protonema and eventually shoots with sex organs closeenough to each other for the sperm to swim to the egg for fertilisation to takeplace. A connecting film of water is essential for this stage. Fertilisation probablyoccurs in the late spring or early summer in the year following spore germination,as the new sporophyte is tall enough to be visible by September. So, the wholecycle from spore production to ripe sporophyte takes a minimum of two years.Fig 2. Varied habitats for Buxbaumia viridis; clockwise from top left: alder inriparian woodland; cut log in plantation woodland; birch leaning on old wall; largeold conifer.

There are a lot of ‘unknowns’ in this life cycle. We have a very incompleteknowledge of what conditions, of substrate or climate, promote spore germinationand even less knowledge of what conditions promote the growth of fertile maleand female plants from the protonema. One suggestion that is often made is thatBuxbaumia viridis might be saprophytic ie, deriving nutrients from the decayingwood through a relationship with the fungi that are certainly present. Interestingand tempting though this theory is, particularly given the shape of the sporophyte,it is not true.One possible explanation of the rarity of Buxbaumia viridis is that there is ashortage of male plants in the vicinity of the females, a known problem in othermosses like some common species of Dicranum in sub-optimal habitat. It ispossible that mats of female protonema produce sex organs for years but nomale spore germinates close by. Sporophyte production does seem to varyconsiderably from year to year and the most thorough study, in Sweden,suggests that this is related to substrate moisture content; if the previous summerwas dry there are fewer sporophytes in the next year. However, what isconsidered a ‘dry’ or ‘wet’ summer may not be the same in northern Sweden asin eastern Scotland and moisture may not be a limiting factor here. The wettestsummer (May-August) in the Swedish study had c. 285mm of rain, a figure closeto the mean rainfall for that period in Aviemore.In addition, it is probable that the protonema is persistent and may well be able toproduce fertile plants over a number of years, as long as the substrate remainssuitable. This means that it is difficult to know whether the persistence of theplant on any one log is due to the persistent protonema or to recurrent sporegermination. Just to add one more variable, protonema observed in thelaboratory can produce brood cells which are presumed to be stress-tolerant andthus provide a means of vegetative survival during adverse conditions andpossibly a means of dispersal. Such cells have never been seen in the field inBuxbaumia viridis but have been observed in a range of other moss species.ThreatsDespite the encouraging news of recent finds, Buxbaumia viridis remains a rareplant, currently known from just 11 sites and the small size of this metapopulationis a potent threat. The total number of sporophytes produced bythese sites varies markedly from year to year but is probably less than 200 evenin a good year. This is a very small total to sustain a plant which, in the mediumto long term, is totally dependent on spores both to sustain its populations oncurrent sites and for dispersal to new sites.A direct threat to the total spore production is the grazing of the green capsule byherbivores; of the capsules observed in Reelig Glen, Moniack in 1998 only 38%reached dehiscence (spore release). ‘Grazing’ is particularly prevalent on thosefew sites where numerous capsules occur together; one stand in Rothiemurchushad 33 sporophytes with 29 capsules nipped off and on a recent stand inAbernethy only 7 capsules remained out of 66 sporophytes (Fig 3). Initially it wasthought that slugs and snails were the culprits as both are known to graze moss

Deadwood managementFallen trees should be left to rot unless health and safety dictates otherwise andthis is probably the policy on many amenity woodlands already. This is a longterm policy in that large logs, particularly of conifers, can take a long time for thebark to slough off and for the wood to rot enough to be sufficiently soft forBuxbaumia viridis. Large conifer logs may not reach a suitable condition for 30years or more depending on size and microclimate but smaller broadleaf specieslike birch may come into condition much more quickly. Studies, both here and inSweden, suggest that large logs can remain in suitable condition for 10 to 20years but again this will depend considerably on the site and broadleaf treesseem to rot away more quickly, though this may be just a factor of size. The bestpredictor of the occurrence of Buxbaumia viridis on any one log on a site is theexistence of other stands on the site. The second best predictor is the amount ofsuitable habitat, basically, the number of large, well-rotten logs and stumps inrelatively humid areas that there are on the site. On a site that already hasBuxbaumia viridis, conservation management should seek to provide a continuityof dead wood; this means that managers need to think now about the amount ofdead wood that will be in suitable condition in perhaps 20 to 30 years time.Is it possible to do more? Logs preferred by Buxbaumia viridis tend to be in morehumid sites, often close to watercourses and it might be sensible, on specificsites, if logs could be moved from drier sites to more humid areas. It might alsobe possible to speed up the decay process by removing the bark but the loosebark on rotting logs is important for other groups of organisms. Many logs are‘unavailable’ to Buxbaumia viridis because they are rapidly covered by robustwoodland-floor bryophytes. This is particularly true in woodland like Glen Affricwhere ‘leggy’ heather, with a prodigious bryophyte biomass below, covers muchof the woodland floor. Removing these mosses on a proportion of logs mightopen up more habitat for Buxbaumia viridis but again at the cost of removinghabitat suitable for other plants and animals.Large areas of woodland within the target area (see distribution map above) tendto be managed on a rotation of clear fell and restock and in such woodlands mostwoody debris is too small for Buxbaumia viridis and there are no known sites forthe moss within such woodland. In plantations with larger watercourses orravines running through them, there may be areas with more light and a morediverse flora. Perhaps felling a few large trees to waste into these more humidsites might be a way to provide suitable habitat in the future if felling regulationsallow this.MonitoringBuxbaumia viridis is a colonising species exploiting an ephemeral habitat whichis patchy and unpredictable. Even if the protonema is long-persistent, the log willeventually decay away and conditions thus become unsuitable for Buxbaumiaviridis so the plant is dependent on dispersal by spores for its long-term survivalon any one site. This means that the plant is very difficult to monitor even on

current sites as the process will involve checking not only the known sites oneach occasion but also all other suitable logs on the site on every monitoringvisit. On the site with the longest history of monitoring, at Reelig Glen, none ofthe logs visited as part of the study in 1999 had sporophytes in 2008, but theplant still occurs on other logs on the site. One log here had sporophytes in 1993and then produced no more until 2002.The protonema of Buxbaumia viridis is quite distinct from that of the otherspecies that tend to grow with it and there is some suggestion that a sampling ofsuitable-looking logs might reveal a more widespread distribution of plants thatdo not produce sporophytes. Confirmation of the identity of the protonema wouldalmost certainly involve use of a microscope and so samples would need to beremoved from each log deemed suitable and, though the samples need only besmall, this exercise could be quite destructive. It would be interesting to carry itout on a limited scale on logs on a known site.ResearchResearch should seek to provide more information on the ecology of the plant,particularly about the various ‘unknowns’ detailed above. It would be valuable toknow answers to the following questions:• At what stage does a log become suitable for the germination and growthof protonema?• Is this stage also suitable for the production of sporophytes or does the loghave to decay further?• What factors influence the production of fertile plants on the protonema?• In nature, is there an imbalance of males and females?• Once a protonemal mat has produced sex organs and sporophytes does itdie back or does it persist to produce another cohort of sporophytes?• If the protonema is persistent, how long does it persist?• If the protonema is short-lived, this suggests that continuity on any one logdepends on spore germination from a previous generation. Is this true?• Are there any common factors linking the sites other than the presence ofsuitable logs?Observation suggests that the same log often produces sporophytes severalyears in succession but also that sporophytes can be sporadic on any one log,sometimes with a gap of several years without sporophytes. This either means apersistent protonema which fails to produce sporophytes for some years andthen is successful or a further colonisation by spores. In practical terms,research into the possibility of artificially ‘seeding’ dead wood with spores toproduce sporophytes would be interesting; Karin Wiklund at Uppsala University inSweden grew spores and produced fertile plants (but not sporophytes) in petridishes (Wiklund, 2002). Prof. Jeff Duckett at Queen Mary College, London hassucceeded in growing on new protonema from existing filaments at the base ofold sporophytes and has kept these in cultivation for two years or more (Pers.com.).

Indicator species and other bryophytes on dead woodBuxbaumia viridis tends to occur with very ordinary species and usually amongstcommon mosses and liverworts that, though they grow well on logs, are notparticularly associated with dead wood. Table 1 shows a list of associatescompiled in 2001 and it is probable that, even with the substantial increase in theknown stands, that this list would not change greatly if current sites weresampled. Of these species, it is the more moisture-demanding liverworts that arethe best indicators and, although Buxbaumia viridis rarely if ever grows in thedense mats of Nowellia curvifolia and Riccardia palmata, these two species aregood indicators of the ‘right’ conditions.Table 1. Associates of Buxbaumia viridis on five stands on three sites.Species 1 2 3 4 5 FDicranum scoparium A F F O 4Lophocolea bidentata F F F 3Mnium hornum F O F O 3Dicranum fuscescens O O 2Hylocomium splendens O A 2Lepidozia reptans F F 2Lophozia ventricosa O F 2Oxalis acetosella F F 2Pohlia nutans O O 2Riccardia palmata O F 2Cladonia sp O O 1Deschampsia flexuosa R 1EurhynchiumF 1praelongumNowellia curvifolia F 1Pinus seedling R 1Rhytidiadelphus loreus O 1Tetraphis pellucida O 1Tritomaria exsectiformis R 1Sites: 1 = Lochan an Eilein I, 2 = Loch an Eilein ii, 3 = Kindrogan,4 = Moniack I, and 5 = Moniack iiFinal column F = frequencyA = abundant; F = frequent; O = occasional; R = rareDead wood is a good substrate for bryophytes and a large number of species canbe associated with it over the period of decay. For the initial period after the treefalls, the bryophytes that were growing on it while it was upright persist but thetrue epiphytic mosses like species of Ulota or Orthotrichum will soon disappear.Other common species on trees like Dicranum scoparium and Isotheciummyosuroides var.myosuroides may well spread along the log until the bark startsto fall away. On the decorticated sections more specialist liverwort species like

the copper-coloured Nowellia curvifolia (Fig 4) and Riccardia palmata will movein, provided that the site is humid enough, but other common bryophytes likeLophocolea bidentata, Scapania umbrosa and Cephalozia species may also beabundant.If the log falls onto ground where there is a robust ground flora, large woodlandfloormosses like Hylocomium splendens, Rhytidiadelphus loreus andRhytidiadelphus triquetrus may well overwhelm the log and out-compete thesesmaller species. In such a case the log may be subsumed into the woodlandfloor without ever becoming ‘interesting’.Fig 4. Diversity on logs; left Nowellia curvifolia; right Anastrophyllum hellerianum.Where the log remains relatively free of these large mosses and the normalprocess of decay continues so that the surface is soft and retains moisture anumber of other interesting species may occur. Quite common in the east isAulacomnium androgynum, recognised by its ball of gemmae (small greenpropagules) on a modified stem. In the west, the more common species isTetraphis pellucida, with the gemmae here held in a cup of modified leaves.Less common are the closely related liverworts Tritomaria exsectiformis andTritomaria exsecta, both with red gemmae on the upper leaves; these twospecies can only be separated under the microscope, with the latter speciesmuch the rarer of the two and having a very western distribution.Smaller in scale again is the nationally scarce liverwort Anastrophyllumhellerianum (Fig. 4) which can be locally frequent on logs in Scots pinewoodland. The small size of the plant – only a few millimetres tall and the darkred gemmae on narrow erect shoots mean that the plant is easily recognised buthard to find. Finally, there is the enigmatic liverwort Lophozia longiflora, recordedon just two occasions in the UK, both times from logs near Loch Morlich. It ispossible that the British concept of Lophozia longiflora is too restricted (the plantis very similar to the common Lophozia ventricosa) and that some plants thatwould be accepted as Lophozia longiflora in Scandinavia, are rejected here.

ReferencesDickie, G (1867a). Note on the occurrence of Buxbaumia indusiata inAberdeenshire. Trans Bot Soc Edin 9, 142-3.Dickie, G (1867b). On the discovery of Buxbaumia indusiata near Aboyne.Trans Bot Soc Edin 9, p192.Rothero, GP (1993). Current Status of Buxbaumia viridis in Moniack Glen. SNHResearch and Advisory Services Directorate Report, unpublished.Rothero, GP (1999). The phenology of Buxbaumia viridis in Moniack Glen.SNH Research and Advisory Services Directorate Report, unpublished.Stirton, J (1876). Notes on the Flora and Fauna of the west of Scotland VCryptogamic Flora. Blackie & Son, Glasgow.White, F.B. (1870). On the occurrence of Luzula arcuata and Buxbaumiaindusiata in Inverness-shire. Trans Bot Soc Edin 10, p382.Wiklund K, 2002. Substratum preference, spore output and temporal variation insporophyte production of the epixylic moss Buxbaumia viridis. Journal ofBryology, 24: 187-195.Gordon RotheroApril 2008