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Edited by Peter Cosgrove and Andy Amphlett 2002 3 The Biodiversity and Management of Aspen woodlands: Proceedings of a one-day conference held in Kingussie, Scotland, on 25th May 2001 CONTENTS: Foreword and overview Peter Cosgrove and Andy Amphlett . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 The ecology and history of Aspen woodlands Peter Quelch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Fungi and Aspens: Promoting biodiversity, Aspen friends and foes Ernest and Valerie Emmett . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 The importance of Aspens for lichen Les and Sheila Street . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Bryophytes on Aspens Gordon Rothero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Aspen, a vital resource for saproxylic flies Graham Rotheray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 The Large Poplar Longhorn Beetle, Saperda carcharius in the Scottish Highlands Tracey Begg and Iain MacGowan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Byctiscus populi, a leaf rolling weevil dependent on Aspen Jon Mellings and Steve Compton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 The importance of Aspen for Lepidoptera Mark Young . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Beavers: Aspen heaven or hell? Dave Batty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Colour photographs insert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i - viii Variation in Aspen in Scotland: genetics and silviculture Bill Mason, Eric Easton and Richard Ennos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Improving the availability of native Aspen for use in northern Scotland Mark Banham and Paul Young . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Woodland management measures for Aspen woodlands Denis Torley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 Agri-environment management measures for Aspen woodlands Alison McKnight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 Delivering action: how Aspen fits into the UK Biodiversity Action Planning process Peter Cosgrove . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 The Trees for Life Aspen Project Alan Watson Featherstone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 The management of Invertromie wood, Scotland’s fourth largest stand of Aspen Tom Prescott . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74 Habitat fragmentation Iain McGowan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Aspen in myth and culture Anne Elliott . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Delegate discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 Delegates list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 4 Foreword Peter Cosgrove Cairngorms Biodiversity Officer, Cairngorms Partnership, 14 The Square, Grantown-on-Spey, Morayshire, PH26 3HG. E-mail: petercosgrove@cairngorms.prestel.co.uk Andy Amphlett The Royal Society for the Protection of Birds (RSPB), Abernethy Forest Nature Reserve, Forest Lodge, Nethybridge, Inverness-shire, PH25 3EF. E-mail: Andy.Amphlett@rspb.org.uk These proceedings are the result of hard work and enthusiasm of many individuals and organisations involved in action and research into the biodiversity and management of Aspen woodlands in the UK. This interest and effort culminated in a one-day conference held at The Duke of Gordon Hotel, Kingussie in the heart of Aspen country on Friday the 25th May 2001. Over 120 people interested in the biodiversity and management of Aspen woodlands attended the conference. The quality of both the presentations and the poster sessions convinced the organisers of the need to publish this material as a fitting permanent record of the conference. Most of the papers in these proceedings were presented in one form or another at the conference, with a small number of additional important papers invited from other contributors. It is hoped that these proceedings have captured the expertise and interest of the various specialists and enthusiasts that was so evident on the 25th May 2001. In particular, it is hoped that these papers will stimulate further positive action and research into the biodiversity and management of Aspen woodlands in the UK. As a focus for future action, Trees for Life have offered to establish and host a web-site and central information resource on Aspen that is easily accessible to land managers, researchers and the general public. If you would like to become more involved in Aspen action please visit Trees for Life’s website: http://www.treesforlife.org.uk Finally, we would like to thank the sponsors and partners; Aberdeenshire Council, Butterfly Conservation, Cairngorms Local Biodiversity Action Plan, Cairngorms Partnership, Forest of Spey Project, Forestry Commission, Highland Council and the Highland Local Biodiversity Action Plan Partnership, RSPB, Scottish Natural Heritage (SNH), and Woodland Trust Scotland, who came together to make this conference happen. We are very grateful to the proceedings authors and photographers who contributed their time and efforts so freely. In particular, special thanks are due to Tom Prescott of the RSPB, and to Anne Elliott and Peter Beattie of SNH for organising such a successful and enjoyable event. 5 Overview As a woodland type, or as a significant component of other woodlands, Aspen is restricted, in the Scottish Highlands, to a very limited number of sites mainly in the North-east. Here its local abundance, in parts of Badenoch and Strathspey especially, making a striking contribution to the landscape, seems at odds with its lack of formal recognition in current national vegetation classifications. With one exception, the papers in these proceedings concentrate on Aspen in the North east Highlands, where the conference and fieldtrip were held. Links could and should be made with Scandinavian ecologists, who view Aspen, especially old individual trees, as keystone components in preserving biodiversity in boreal forests. There, Aspen is a focus of current research, e.g. as part of the University of Helsinki’s Biodiversity in Boreal Forests project (http://www.helsinki.fi/science/biobof/). In the Scottish Highlands, Aspen is particularly associated with well drained, often moist, mineral soils. Here it was a very early post-glacial colonist (before Scots pine) and has persisted in mixed woods with Birch, Hazel, Willow and Rowan, which are probably of great antiquity. It also occurs more rarely, as stands within the native pinewoods. As a tree species, Aspen is widespread across the British Isles appearing to be especially frequent in South-east England (Perring and Walters 1962). Examination of a selection of recent county Floras from England which map Aspen at the tetrad scale reveals Aspen to be very frequent in some areas, ranging from just 8% of tetrads in Devon (Ivimey-Cook 1984) to 35% in Kent (Philp 1982) and a remarkable 41% in Sussex (Hall 1980). Do large Aspen stands occur outside the Highlands? The scant descriptions in these Floras make it hard to place Aspen into an ecological context, but the resource seems to be very large elsewhere, warranting more attention. Rare species confined to, or with nationally important populations on Aspen include flies, moths, beetles, fungi, lichens and mosses, as described in subsequent papers. In terms of practical nature conservation, a number of these species are in need of emergency “first aid”. The invertebrates, as is so often the case, are in the greatest need of targeted (and monitored) management. They include a number of species with critically low populations which utilise relatively ephemeral components of the total Aspen resource, e.g. the decaying cambial layers under the bark of large diameter logs on the ground, or the foliage of Aspen suckers less than 1m high. A number of lichens and one moss are similarly restricted to just a few individual Aspen trees, though in the medium term they may be able to persist on these trees. In a turn around from usual situations, these proceedings lack information (with one notable exception - European beaver) on the vertebrate fauna associated with Aspen. For example, we appear to know next to nothing about the bird species and communities associated with Aspen in this country. Elsewhere in Europe, Aspen woodland and its dead wood resources attract several species of hole nesting birds, including various species of woodpeckers, some of which are absent from the UK. Aspens are also used by other, perhaps unexpected, species such as Capercaillie (Tetrao urogallus). The ‘Bird species of UK Aspen woodlands’ paper has yet to be written, but breeding records of Buzzard (Buteo buteo), Great spotted woodpecker (Dendrocopus major) Redstart (Phoenicurus phoenicurus) and Redwing (Turdus iliacus) from the afternoon fieldtrip suggests it is an area worthy of further investigation. For all of these ‘Aspen dependent’ species, chance events or uninformed management could be devastating for local populations. All require regular population and distribution monitoring and habitat management trials aimed at securing populations. It is beholden on specialists, advisors and site managers to consider the implications of any proposed actions (or inaction) on other taxonomic groups or habitats. Mellings and Compton report the apparent loss of the BAP wee- vil, Byctiscus populi, at one site due to the removal (for unspecified conservation reasons) of 6 Aspen scrub. Though statistically unlikely, creation of dead wood to increase potential breeding sites for threatened Diptera could lead to a loss of a similarly threatened lichen or moss. Practically, we either accept that risk (not recommended!) or we ensure that adequate baseline surveys are carried out prior to management, and that site managers know the exact location of important trees. Unfortunately, the current lack of skilled field lichenologists and bryologists is a critical problem for facilitating informed management decisions. Peter Quelch’s goal of protecting, regenerating and expanding all existing Aspen woods, stands and trees, as well as planting into new areas deserves support. However, it has to be remembered that it will be decades before some components of the overall Aspen habitat will have increased, e.g. large diameter trees and snags. Clonal variation is almost certainly a significant determining factor for the epiphyte communities of Aspen and quite plausibly for other groups e.g. Diptera. New plantings of Aspens should follow the protocol adopted by Trees for Life (Watson) and include material from as wide a range of locally occurring clones as possible. Much attention has centred on the importance of the largest Aspen stands, as being the only instances whereby natural processes can maintain a continuity of supply of key micro-habitats. Rothero highlights the possible significance of smaller stands and wayside Aspens for bryophytes, and Coppins et al. (2001) have demonstrated the outstanding importance of some small Aspen stands for lichens. Such examples should be targeted for survey and conservation. Given that Aspen will sucker so freely, it is obvious that exclusion or other control of grazing animals will be an important tool to expand existing stands. Complete exclusion of browsers may not be desirable, as the maintenance of successional habitats with associated pollen and nectar sources may be of value to foraging adult invertebrates. Aspen stands occur in a wide variety of contexts and important habitats may occur within the bounds of a projected Aspen expansion zone. Complete exclusion of grazing from such areas may be damaging to other interests. Again, adequate survey prior to formulating management plans is required. Several contributors discussed and highlighted the grants and financial assistance available to land managers to progress practical action for Aspen and its dependent species. Specific examples of the practical work carried out to date are presented, including the challenges of reconnecting isolated Aspen stands to facilitate important ecological processes, such as species dispersal or gene flow. As a number of authors point out, we are only just beginning to identify and understand the complex biodiversity associated with Aspen in the UK, and clearly much is still waiting to be discovered. Finally, Anne Elliott’s paper illustrates that interest in Aspen is not just the domain of ecologists and specialist researchers. Aspen has strong cultural links for the people of the Scottish Highlands and their support will be crucial if any action for Aspen is to be successful. We should not lose sight of the fact that Aspen woodlands are a beautiful and striking feature of the Highland landscape, and worthy of conserving for that reason. Indeed it can be argued that Aspen helps improve the quality of life for local residents and helps make the Highland area special for visitors and tourists. Aspen seems to have survived as an ancient remnant up to now largely by default, rather than by design. These proceedings provide compelling evidence of why this situation should change and how Aspen conservation and management should move up the UK conservation agenda in the future. 7 References Coppins, B., Street, S. and Street, L. 2001. Lichens of Aspen woods in Strathspey. Report to British Lichen Society and SNH. Hall, P.C. 1980. Sussex Plant Atlas. An Atlas of the distribution of wild plants in Sussex. Booth Museum of Natural History. Perring, F.H. and Walters, S.M. 1962. Atlas of the British Flora. 2nd. Edition (1976). EP Publishing. Philp, E.G. 1982. Atlas of the Kent Flora. Kent Field Club. Ivimey-Cook, R.B. 198). Atlas of the Devon Flora. The Devonshire Association. 8 The ecology and history of Aspen woodlands Peter Quelch Native Woodland Adviser, Forestry Commission, Whitegates, Lochgilphead, Argyll, PA31 8RS. Email: peter.quelch@forestry.gov.uk Introduction This paper gives a quick overview of Aspen, both as a tree species and as a rare woodland type in Scotland. The ecology of Aspen is well covered by Rick Worrell, along with other selected papers and booklets. Much has been written about the folklore of Aspen (Elliott, this volume) and why it is such an enigmatic and well loved tree. This paper will examine where Aspen occurs naturally in today’s landscape, and then to ask if we are satisfied with the status quo. If we are not, what greater part could Aspen play in Scotland’s woods and forests, and what actions should be considered on its behalf? At present, Aspen is a well liked but ‘Cinderella’ species, somewhat neglected, and yet with an unrealised potential. Recognition of its values for biodiversity have emphasised Aspen’s importance, and this gives the context for this paper. Aspen in the Biodiversity Action Plan (BAP) process Simple woodland classifications tend to label woodland types by their dominant tree species, i.e. Oakwoods, Birchwoods, Pinewoods and so on. We can therefore recognise ‘Aspen woods’ where locally Aspen predominates in certain stands of semi-natural broadleaves in Badenoch and Strathspey, alongside Birch, Rowan, Hazel, Sallow and Alder. The UK BAP process uses such a classification in selecting the main native woodland types and allocating targets for action (for an overview of woodland classifications see Hall and Kirby, 1998). But what is the status of those native woodland types which are not given BAP plans? - Birchwoods – after many years of discussion it has now been agreed that upland Birchwoods should have their own Habitat Action Plan (HAP). - Hazel is not covered separately in the BAP process, despite some lobbying on behalf of the western coastal hazelwoods, which are exceptionally rich habitats for oceanic bryophytes and lichens. Certain rare lichens characteristic of this habitat, (e.g. Arthothelium macounii, or Pseudocyphellaria norvegica) then become surrogates in the BAP process for the habitat they depend on, since they have been given Species Action Plans (SAP). - Juniper – this native shrub species is covered by having its own SAP, but no HAP. - Aspen is mentioned in the SAPs for three invertebrate species which depend on it as a habitat, (Hammerschmidtia ferruginea, Byctiscus populi and Epione parallelaria), and two bryophytes (Orthotrichium sp.), but Aspen has neither its own HAP or SAP. Aspen woodlands are however recognised as important habitats in some Local Biodiversity Action Plans (LBAP), e.g. the Cairngorms LBAP. Aspen in woodland classifications In the National Vegetation Classification (NVC) (Rodwell 1991), Aspen is described as a component of upland Ashwood (W9b), but even then only occurring rarely. Aspen is also mentioned as an infrequent component in several lowland woodland types: W5, W6, W8, W10, and W16. Aspen woodlands are not recognised as a distinct woodland type in either NVC, or in the Peterken Stand Type classification (Peterken 1993), where Aspen is associated with the Rowan/Birch stands of Type 12A. Rackham (1986) recognises Aspen woodlands as a subset of Peterken’s Birch/Hazel woods, at least for East England. In their classic survey of native 9 pinewoods, Steven and Carlisle (1959) record Aspen as rare or occasional in most of the pinewoods they surveyed, but never abundant. Interestingly they record more than usual Aspen in Glen Strathfarrar pinewoods, which appear to be one of the most natural woodland remnants in the country today. Aspects of Aspen ecology Like Birch and other successful colonisers, Aspen can tolerate a wide range of soil types, from lime-rich sites to acidic heaths (for example, Aspen suckers are spreading onto acidic heath at Crannach pinewood, Bridge of Orchy). Like Oak and Ash, Aspen actually prefers good well drained mineral soils, a site type that it finds in greater areas in Badenoch, Strathspey and Deeside. While sites that it occupies are often moist, it is not a wet woodland species in the same way as Alder or the Willows, or even Bird cherry. Aspen grows at a wide range of altitudes, from sea level (coastal Aspen at Assynt and on Rum) to high altitude gullies almost to the tree-line. Aspen history Aspen has an ancient history in Scottish woodlands, being a very early coloniser, arriving with Birch, Sallow and Rowan during the pre-Boreal period 10,000 years ago, earlier than Hazel, and before Scots pine began to dominate. All this happened well before Oak, Alder, Ash, Elm and Holly joined the flora. I see Aspen not so much as a rare and neglected woodland type, but more as a tree species which is now under-represented as a component of natural woodland types in Scotland, despite its ancient lineage. I also find it significant that Aspen is host to so many specialist species, despite the fact that the tree itself is not now very common or in extensive stands. To me this dependency indicates a very long ecological association, and this is backed up by the history of Aspen in Scotland. Aspen and ancient woodlands Aspen seems to be strongly linked to ancient woodland sites, both in Scotland and in England where it is also a somewhat rare component of usually ancient woodlands (Rackham 1986, 1990). Indeed, I would go further and suggest that Aspen in Scotland is actually an ancient woodland indicator species. Most examples that I find are linked to ancient woodlands, large or small. For example, I recently came across Aspen in the Ryvoan Pass (Glenmore Forest) in a very mixed old-growth stand at high elevation, alongside veteran Scots pine, Juniper and Rowan, as well as very old grey Sallow and Alder. Aspen has strong connections, not only with ancient woodland patches, but sometimes to the tiny woodland refugia of the most natural origins. Aspen in Europe In Europe and Scandinavia, where Aspen is more abundant, it is usually as a component species of the northern sub-boreal temperate forest zone (Worrell 1996), rather than as a woodland dominant on certain soil types (compared to say, Oak or Beech). Its natural place seems to be in the small group of broadleaved associates in northern coniferous forests, along with Birch, Rowan, Sallow, and Alder, where together they typically occupy about 15-20% of the forest, alongside the Pine and Spruce (Peterken 1996). Reasons for current distribution of Aspen Why has Aspen survived where it is to be found today even sometimes after all other tree species have gone? The reasons for Aspen’s ability to survive, albeit in low numbers, include: - Aspen is actually a poor coloniser (in modern times at least), for while it can produce viable seed this is a rare occurrence. - Aspen trees are dioecious, so individual trees and even whole clones are either male or female. As individuals become separated from the opposite sex, it is not surprising that Aspen does not reproduce well in its currently fragmented condition. 10 - Nevertheless, Aspen is very good at self-perpetuation on a local scale by producing masses of suckers in response to felling, windthrow, fire or other disturbance. It seems that vegetative reproduction keeps Aspen going in the same locality almost indefinitely. - While grazing animals do eat the suckers (it is more palatable than Alder, but less so than Ash and Elm), sufficient survive to grow into new trees, unless grazing pressure is kept at very high levels. - Aspen is not an inherently rare species like the various Whitebeams for example, partly because it has wide soil and altitude tolerance. - Aspen has not traditionally been a valuable species for its timber, bark, or coppice shoots (unlike Oak and Hazel) and so has not been deliberately protected or cultivated. - Aspen has probably been reduced in status partly through poor seeding ability (compared to Birch and Sallow), combined with susceptibility to grazing, but also an inability to form veteran trees (unlike Oak, Holly, Ash, Pine and Alder, which can all survive as stems of many centuries age). Long-lived trees have more time in which to set viable seed and produce new generations during lulls in grazing pressure. The reason why Aspen cannot live a long time and form a huge hollow and ancient stem must surely be that the soft white wood is not durable against rot fungi (unlike Oak and Pine for example). - If it were not for its suckering ability, Aspen may well have been lost entirely from Scotland. Are we happy with Aspen’s current distribution? So, apart from the relatively small number of Aspen dominated woods in Badenoch, Strathspey and Deeside, Aspen is a survivor in small patches over most of Scotland. It is found on the sea cliffs of the west coast, in ancient grazed pinewoods in the central Highlands, in remote refugia like the lochside screes of Loch Muick, in the Border cleugh woodland remnants, and in the forgotten corners of many an ancient woodland. Should Aspen be left alone to inhabit these sparse niches - the remote and craggy woodland refugia? Should Aspen continue to be treated as a somewhat enigmatic tree rarity, a minor species, mainly of interest to woodland historians and romantics as a ghost of the once great natural woodlands? Or does Aspen have a wider role in Scottish woods and forests? A possible new scenario for Aspen? Lets look again at the role Aspen plays in, for example, central Swedish forests, where Aspen forms a constituent of the broadleaved component of the mixed pine/spruce forests, along with Birch, Sallow and Alder. Why could we not encourage both Birch and Aspen as a normal component of Scottish upland forests, up to a proportion of say 25%, rather than the current five or 10% normal maximum? The biodiversity and landscape benefits would be high, and Aspen timber grown in forest conditions is (like other Poplars) straight and utilisable, though not of high value (less than Birch, similar to Alder?). Birch and Sallow regenerate profusely, Alder readily coppices even in the face of moderate deer numbers, while Aspen suckers after felling. So the species in this group can perpetuate themselves at low cost, and all are relatively fast growing. Conclusion I think that Aspen would be sold short if we continued to confine it to woodland refugia and regard it as a rarity. There is evidence that it was once a great component of Scottish natural woodlands, and there seems to be no good reason why, with help, it could not be so again. It is time for a ‘Comeback Code’ for Aspen! 11 Actions needed to bring Aspen back into its rightful place could include the following: - Protecting, regenerating, and expanding where possible, all existing Aspen woods, stands and trees. - Careful planting of Aspen (of both sexes) into some degraded semi-natural woodlands where it is missing - Planting Aspen into forestry restock areas in sufficient numbers, that Aspen becomes a self-perpetuating component of a group of mixed broadleaves which between them would cover 15-25% of the gross area of many upland and lowland conifer forests. References Ennos R, Worrell R, Arkle P, Malcolm D, 2000. Genetic variation and conservation of British native trees and shrubs, Technical Paper 31, Forestry Commission, Edinburgh. Hall JE, Kirby KJ, 1998. The relationship between Biodiversity Action Plan Priority and Broad Woodland Habitat Types, and other woodland classifications, JNCC Report 288, Joint Nature Conservation Committee, Peterborough. Peterken G, 1993. Woodland conservation and management, Chapman and Hall, London. Peterken G, 1996. Natural woodland, Cambridge University Press, Cambridge. Rackham O, 1986. The history of the countryside, Dent, London. Rackham O, 1990. Trees and woodland in the British landscape, Dent, London. Ratcliffe P, 1999. Aspen woodlands: a case for conservation, paper to the Native Woodlands Advisory Panel for Scotland, Forestry Commission, Edinburgh. Rodwell J, 1991. British Plant Communities, Vol I, Woodlands and Scrub, Cambridge University Press, Cambridge. Steven and Carlisle, 1959. The native pinewoods of Scotland, University of Aberdeen. Trees for Life, 2001, Aspen information and papers, on www.treesforlife.org.uk Worrell R, 1995. European Aspen (Populus tremula L.): a review with particular reference to Scotland, I Distribution, ecology and genetic variation, Forestry 68(2), pp 93-105; II Values, silviculture and utilisation, Forestry 68(3): 231-243 Worrell R, 1996. The Boreal Forests of Scotland, Technical Paper 14, Forestry Commission, Edinburgh. Worrell R, Gordon AG, Lee RS, McInroy A, 1999. Flowering and seed production of Aspen in Scotland during a heavy seed year, Forestry 72(1): 27-34 12 Fungi and Aspens: Promoting Biodiversity Aspen friends and foes Ernest and Valerie Emmett Drumlins, Newtonmore Road, Kingussie, Inverness-shire, PH21 1HD. E-mail: E-cubed@netcomuk.co.uk It has been estimated that about 80% of all the organic energy on the Earth is locked up in wood of various kinds. This enormous store of energy is under constant attack, both when the trees are alive and more so when they are dead: from fungi, bacteria, insects and smaller animals. (Ryvarden 2001). Foremost in the relationships with trees are the fungi and these play several different roles, not all of them detrimental to the health of the tree and some also provide food – for insects and other invertebrates, as well as mammals. The fungi can be classified under three main headings: Categories of Forest Fungi Mycorrhizal Endo- Important for most (all?) plants Ecto- Important for most trees, e.g. Aspen Saprophytes or Detrivores Litter decomposers Pathogenic/parasitic Principal causes of tree death The Mycorrhizal species are essential for the healthy growth of the tree. These fungi are of two sorts: endo-mycorrhizal and ecto-mycorrhizal. The hyphae of the latter sheath the tree’s roots and, by breaking down material in the forest soil, they provide the tree with nitrogenous and other nutrients, including mineral trace elements. In exchange, the fungus receives carbohydrates manufactured by the tree during photosynthesis. Endomycorrhizal species are the most widespread, but their presence is not revealed by the formation of fruitbodies on the soil surface. These fungi enter the plant root cells forming specialised inclusion bodies, where exchange of nutrients occurs. With Aspens, the ectomycorrhizal fungi are more important, and fairly specific associates in this category include familiar toadstool shaped fungi such as Leccinum aurantiacum, Leccinum duriusculum and Lactarius controversus. These are the friends of the Aspen, helping it to grow. The second group of fungi are the Saprophytes and these include both host specific and cosmopolitan species. They are the litter decomposers, reducing fallen leaves, twigs and other already dead woody material to humus, a principal part of forest soils. These fungi include some that look like familiar toadstools with lamellae (“gills”). Others are poroid fungi (the Polypores), releasing their spores from pores instead of lamellae. Some others that help to decay the woody material look rather like paint splashes and sheets of fungal tissue adhering to the surface but loose at the edges; and yet others form hard warty growths on twigs and branches. These are the Corticioid fungi. They do not have lamellae or pores; instead, they form amorphous sheets of spore bearing tissue covering the surface of logs and twigs. 13 Examples of detrivores specific to Aspen are the Polypores: Ceriporiopsis anaerina, Antrodia malicola and mellita, and the Corticioid: Peniophora polygonia. The two Antrodias mentioned have not yet been found in Britain, but it is hoped that they will be found in Scotland. The cosmopolitan species are legion; for example, many Mycena species. One that was found in an Aspen grove on The Royal Society for the Protection of Birds’ (RSPB) Insh Marshes Reserve last November may be a new species for science requiring description. The Poroid and Corticioid fungi are among the dominating species in the decay of Aspens. In two Norwegian studies of the species occurring on cut and fallen logs, it was found that most of them were Polypores and Corticioids (Table 1). Table 1. Taxonomic diversity of wood decaying fungi on Aspen Locality and Number of species South Norway (Andersen - 1995) 123 Logs Polypores 21 (14.2%) Corticioids 64 (42.6%) Agarics 43 (29%) Heterobasidio-mycetes 16 (10.3%) Other 6 (3.9%) Total 155 South Norway (Hermansen 1974 - 76) Polypores 31 (27.7%) Corticioids 81 (72.3%) Agarics Heterobasidio-mycetes Other Total 112 Note that in one of these studies, the Aspen logs yielded 155 species of fungi, an indication of the value of lying timber for biodiversity. The diversity of the fungal species increases as the wood decay proceeds: in the early stages of decay relatively few fungi colonise the wood, but as defensive substances are removed by early colonisers, a succession of species become involved. By the last stage, when the trunk is losing its shape completely, a great number of species have inhabited the former tree, during its decay cycle. Some of the rarer fungi fruit only sporadically, with long gaps of many years between appearances of the sporocarps, although they are presumably present throughout in the vegetative state. In several long-term studies, while some species fruited regularly, others were only recorded once. It has also been found that some fungi can only invade decaying wood after a pioneer species has overcome the wood’s armoury of defensive chemicals and started the partial decay. (Niemelä et al. 1995). So far, nearly 100 species of fungi have been recorded on or with Aspen in Britain (Table 2), by members of the British Mycological Society – mostly in England, reflecting where most mycologists live or collect and where Aspen is not considered a common tree. The authors anticipate increasing the number of species recorded from Aspen in the coming years. The third group, the Pathogenic fungi, are especially interesting, and include several species that are specific to Aspen. They are not friends of the Aspen but do great things for biodiversity. They include the group known as Rusts, as well as larger poroid fungi, the Polypores, often referred to as Bracket fungi. Aspen is the host for several species of Rust (Melampsora spp.), which cause decay spots on the leaves and some will blacken and kill the growing tips of new shoots. Heavy infestation can result in defoliation of the Aspen. These fungi thus reduce the growth rate of the tree and obviously are detrimental to the life cycle of insects that feed on the young leaves and growing shoot 14 tips, such as the Dark-bordered beauty moth (Epione vespertaria). A spectacular flower parasite is Taphrina johansonii, and this obviously interferes with seed production where it occurs. It is probably of limited significance in Badenoch and Strathspey, where flowering is rare – although in 2001 the trees were flowering and the Taphrina was found locally in Strathspey. Another small parasite is the Ascomycete, Encoelia fascicularis, which can be found erupting like small brownish black cups from the bark of living trees and on fallen branches on the ground. This fungus causes carbonising rots. The wood decaying parasites include a significant Polypore, Phellinus tremulae, which is responsible for the death of most Aspens. It is a “white rot” type fungus, decomposing both the lignin and the cellulose. The wood from decayed trees has little economic value. Sporocarps can be found erupting as wedge shaped brackets from the trunks of Aspens, or else as a coating on the underside of branches at the point where they emerge from the main trunk – the “branch creepers”. This fungus, which is the most serious pathogen of Aspen, was previously not recorded from Britain until last year, when it was found for the first time on the RSPB Insh Marshes Reserve (Emmett and Emmett 2001) – and so it is not even on the Red Data List for fungi. It was thought that Britain did not have any Aspen trees large enough to support it. In Fennoscandia, where Aspen is much more common, it usually occurs on large and old trees. In Badenoch, however, it has been found on comparatively young trees – the diameter at breast height of the smallest of the infected trees measured so far, is under 20cm and the largest is about 50cm. Since the first recording of Phellinus on the Insh reserve, it has been found at many sites in the Badenoch and Strathspey area: at three places in Kingussie, at Kincraig, at Loch an Eilein on the Rothiemurchus estate, Granish near Aviemore, at two sites near Grantown on Spey and westwards towards Laggan, and it has also been found on the RSPB Abernethy Forest reserve and across the Cairngorm massif near to Balmoral. It is likely to be found at other Aspen sites and this has been confirmed from other areas; for example, recent records from Glen Affric (Watson- Featherstone this volume). The Aspens that grow on the poorer soils, for example on stony moraines, seem to produce sporocarps more readily than those that grow on the richer, damper sites closer to water bodies. These findings confirm similar ones made by mycologists in Finland and Norway. The problem in recording fungi is that most of them are ephemeral and there may not be a friendly mycologist on hand when a fungus fruits! Fortunately, Phellinus tremulae is perennial, the fruit bodies are persistent and one can see the annual growth phases on the fruit bodies. They are not easy to spot in the early stages of their growth though, often looking like a thumbnail on the trunk. The fungus is typically a parasite of living trees, but fruit bodies remain alive for a few years after the death of the host tree. It is said not to form new fruit bodies on dead trunks (Balaban and Kotlaba 1970). The current authors, however, have observed fruit bodies that have apparently formed after trees have fallen. Entomologists hunting rare saproxylic insects in decaying Aspens, record a sweet smell in the soft decay material that the larvae feed on. Cultures of the Phellinus are unusually interesting in that they emit a sweet smell like Oil of Wintergreen, due to the presence of methyl benzoate, methyl salicylate, benzyl alcohol, linalool and ethyl benzoate (Collins and Halim 1972). It is likely that mycelium of the Phellinus is present in the decomposing sapwood which is home to the larvae of these invertebrates, and contributes these compounds to the mixture of smells. 15 References: Ballaban, K. and Kotlaba, F. 1970. Atlas drevokaznych hub. – 136 pp Praha. Collins, R. and Hallim, A. 1972. An Analysis of the odorous constituents produced by various species of Phellinus. Canadian. J. Microbiology. 18: 65-66. Emmett, E.E. and Emmett, V.E. 2001. Phellinus tremulae, a new British Record on Aspens in Scotland, Mycologist 15:3 105-106. Niemelä, T. 1974. On Fennoscandian Polypores. III. Phellinus tremulae (Bond.) Bond. and Borisov, Ann. Bot. Fennici 11: 202-215. 1974 Niemelä, T., Renvall, P. and Penttilä, P. 1955. Interactions of fungi at late stage of wood decomposition. Ann. Bot. Fenn. 32: 141-152. Ryvarden, L. 2001. An Introduction to Wood-rotting Fungi, Biological Institute, University of Oslo, Norway. (For work by Andersen and Hermansen, see Ryvarden 2001) Table 2. Species of fungi recorded in association with Aspen Source: British Mycological Society Fungus Recording Database Arcyria cinerea Armillaria bulbosa Auricularia mesenterica Badhamia panicea Bjerkandera adusta Bolbitius vitellinus Boletus erythropus Brevicellicium olivascens Byssomerulius corium Ceriporiopsis aneirina Chalara cylindrosperma Clitopilus prunulus Comatricha nigra Coprinus disseminatus Cortinarius Cortinarius crocolitus Cortinarius decipiens Creopus gelatinosus Crepidotus cinnabarinus Crepidotus mollis Cristinia rhenana Cryptodiaporthe populea Cryptosphaeria populina Cylindrobasidium laeve Cyrtidula hippocastani Daedaleopsis confragosa Dothiora sphaerioides Drepanopeziza Encoelia fascicularis Enteridium lycoperdon Epicoccum nigrum Exidia nucleata Flammulaster carpophiloides Ganoderma applanatum Gymnopilus junonius Hebeloma Hebeloma sacchariolens Hymenoscyphus caudatus Hymenoscyphus immutabilis Hyphodontia gossypina Inonotus radiatus Kirschsteiniothelia aethiops Laccaria laccata Lasiosphaeria ovina Leccinum aurantiacum Lactarius controversus Leccinum duriusculum Leccinum fuscoalbum Leccinum populinum Lenzites betulina Leucostoma niveum Leucostoma persoonii Linospora ceuthocarpa Macrotyphula juncea Massarina emergens Melampsora allii-populina Melampsora epitea var. epitea Melampsora larici-populina Melampsora populnea Mitrophora semilibera Mollisina acerina Mycena acicula Mycena galericulata Mycena pura Nemania serpens Oxyporus populinus Panus conchatus Patellariopsis clavispora Peniophora lycii Peniophora polygonia Peziza udicola Phaeocalicium praecedens Phanerochaete velutina Phellinus ferruginosus Phellinus tremulae Pholiota squarrosa Phomopsis putator Physarum robustum Platystomum compressum Pleurotus ostreatus Polydesmia pruinosa Rosellinia aquila Scopuloides hydnoides Stictis radiata Taphrina johansonii Taphrina populina Tomentella crinalis Trametes pubescens Trichoderma viride Tricholoma fulvum Tricholoma populinum Troposporella fumosa Tympanis spermatiospora Typhula setipes Uncinula adunca var. adunca Valsa sordida Venturia macularis Xerocomus subtomentosus 16 The importance of Aspens for lichen Les and Sheila Street c/o Flaxfield, High Road, Havenstreet, Ryde, Isle of Wight, PO33 4DL E-mail: Les.Street@espb.org.uk Aspens differ greatly, both structurally and chemically, from the majority of Highland woodland trees and in particular from Birch and Scots pine. In Strathspey, especially, they provide a very important niche substrate for epiphytes that is otherwise virtually absent. One hundred and thirty species of lichen and 12 lichenicolous fungi have been recorded on Aspen in Strathspey (Table 1). The bark of Aspens can be both fissured and smooth. The characteristic ‘diamond-shaped’ rough parts provide a coarse substrate favouring some species such as the ‘strap-like’ green Ramalina spp. some of them up to 25cm long. The smooth areas host a different suite of lichens such as Lecidella elaeochroma and Pertusaria or Arthonia spp. which are crustose. Older trees tend to be more rough and fissured, and bark on the oldest can even superficially resemble that of Oak. Scots pine, for example, cannot host these species and birches and pines typically hold the genera Bryoria, Usnea and Hypogymnia, which, themselves, are less common upon Aspens. Different parts of each Aspen can also provide a variety of microhabitats. On the lower parts of the trunk, usually overgrowing bryophytes, are lichens such as Peltigera membranacea, a ‘doglichen’, so-called because the Velcro-like rhizinae attaching it to its substrate are said to resemble dogs’ teeth. At the other end of the tree, small lichens such as Rinodina sophodes subsist on small twigs. The most significant feature of Aspen bark is its low acidity. Whereas Scots pine and Birch are typically around pH 3.2-3.5 (ranges respectively 3.4-3.8 and 3.2-5.0), Aspen bark is pH 5-6 (Mikko Kuusinen, Annales Botanici Fennici, 1994). Interestingly, some Strathspey Aspen clones host lichen epiphytes more typical of acidic substrates, while others hold those favouring more neutral or alkaline conditions. Further research may reveal the reason for this being natural variation in bark pH. There is also evidence that Aspens probably provide a naturally enriched substrate. Therefore, species that prefer nutrient-rich, basic habitats grow on them such as Xanthoria parietina (probably the best-known British lichen occurring as orange splodges on most old asbestos roofs) and Physconia distorta, a whitish-grey placodioid species with pruina that resemble caster sugar. Both of these have prominent jam-tart shaped apothecia (fruiting bodies). It can be noted that the Xanthoria plants show a preference for the western facing sides of Aspens and one method of quickly spotting Aspen stands from afar is to look for any tree sporting orange lichens. The longest established stands, as with most woodlands, are those which have the richest lichen assemblages. At Invertromie (Strathspey), the Aspen seminar study area, there appear to have been a succession of pulses of vigorous Aspen regeneration. One is presently underway following some fencing to exclude deer and rabbits. Another occurred in the late 1980s when sheep grazing ceased and at least two others; one around 30-50 years ago and another, earlier one, are evident resulting in the varied age structure seen today. The most species rich Aspen stands hold some very scarce and endangered lichens. The Aspen seminar field trip study area at Invertromie, for example, revealed one new UK lichen species Arthonia patellulata, another not seen for over 150 years with the apposite specific name Lecanora populicola and two more lichens, each confined to less than 20 UK sites. One is Sclerophora pallida, a vulnerable Red Data Book (RDB) lichen resembling minute ginger coloured pinheads which is found on the dry under-hangs of boughs and trunks. The other a RDB (vulnerable) and ‘Schedule 8’ (legally protected) rarity called Pannaria ignobilis. This has an oddly disjunct distribution from Norway to the Mediterranean and is found locally in central Scotland. 17 Another interesting feature is the presence of several lichens normally considered more ‘oceanic’ or ‘western’ in their distribution. Examples include Pannaria conoplea, Degelia plumbea and the large, leafy lungworts Lobaria pulmonaria and L. scrobiculata which are relatively common along the western seaboard of Scotland from Argyll to Assynt, but scarcer well inland amid the central Highlands of Scotland (F Dobson, Lichens [distribution maps], 2000). These species and others demonstrate yet another important feature in that they are all closely associated with, and some confined to, ancient woodlands. Ecological indices have been developed defining lichen species linked to native pinewoods and western Scottish broadleaved woods and it may be possible, in future, for a similar version to be developed providing better evaluation of the ecological continuity of Aspen woods. It is clear already from the range of bryological, lichenological and entomological taxa present, that many Aspen woods show strong evidence of very long ecological continuity. Each taxonomic group speaker used the Aspen seminar as a forum to make a plea for feedback from delegates and lichens are no exception: an extremely rare species resembling a small dark pinhead about a millimetre long called Phaeocalicium praecedens apparently exists only on Aspen twigs. If something resembling this is found, please collect and send a small sample specimen provided there is plenty locally present to Sheila Street. The study of lichens associated with Aspens in Britain is in its infancy. Only recently, Brian and Sandy Coppins discovered the first UK occurrence of a species called Bacidia igniarii on Aspen. Further research in Strathspey since the Aspen seminar has revealed a yet more diverse lichen flora living upon Aspens including two more new species to the UK: Caloplaca ahtii and (once it is confirmed) Rinodina laevigata plus the best UK population of the attractive, and now rare, RDB critically endangered Schedule 8 lichen Caloplaca flavorubescens. This research is also beginning to provide insight into the processes involved with this special and complex symbiotic association. Judging by the diverse range of specialist epiphytes or invertebrates that these Aspen stands sustain, they are evidently ancient ecosystems requiring further study. Further reading and key references Coppins, B. and Coppins, A. M. 2000. Thoughts on aspen and its present and future role as a habitat for other organisms (unpublished). Coppins, B. and Coppins, A. M. 1990. Forest of Glentanar – Lichens (unpublished). Coppins, B., Street, S. and Street, L. 2001. Lichens of Aspen woods in Strathspey. Unpublished report to the British Lichen Society and Scottish Natural Heritage. Dobson F. S. 2000. Lichens. Richmond Publishing. Hedenås H. and Ericson L. 2000. Epiphytic macrolichens as conservation indicators: successional sequence in Populus tremula stands. Biological Conservation 93: 43-53. Hereford and Worcester County Council incentive tree planting scheme leaflet (1987) The Black Poplar. Humphries C. J., Press J. R., and Sutton, D. A. 1981. Trees of Britain and Europe Country Life Books. Kuusinen M (1994) Epiphytic lichen flora and diversity on Populus tremula in old growth and managed forests of southern and middle boreal Finland, Annales Botanici Fennici 31:245-260. Moberg R and Holmåsen I (1990) Lavar, Interpublishing AB, Sweden. Nature Conservancy Council. 1988. Keys to woodland NVC vegetation communities Ripple W and Larsen E. 2000. Historic aspen recruitment, elk and wolves in northern Yellowstone national Park USA Biological Conservation 95: 361-370 Steven H M and Carlisle A (1959) Native Pinewoods of Scotland. Hartnolls. Trees for Life 2000. Caledonia Forest Species Profile – Aspen. 18 Table 1. Strathspey Aspen Lichen species list Annotations: Column 2: Status RDB (CE) = Red Data Book species (Critically Endangered) RDB (V) = Red Data Book species (Vulnerable) Sch. 8 = Listed on Schedule 8 of the Wildlife and Countryside Act Nr = Nationally rare species (recorded in only 15 or fewer 10km squares) Ns = Nationally scarce species (recorded in only 16-100 10km squares). Other status details are written in full or annotated with superscript references. Column 3: Substrata Pp = Populus tremula Al = Alnus glutinosa B = Betula spp. C = Corylus avellana J = Juniperus communis L or ~L = lignum S = Salix spp. Sb = Sorbus aucuparia T = terricolous Sx = saxicolous -by = on bryophytes -st = on stumps -tw = on twigs or thin branches Column 4: Relative abundance (RA) D = Dominant, A = Abundant, F = Frequent, O = Occasional, R = Rare Species Status Substrata RA Arthonia mediella Ns Pp R A. muscigena Ns Pp-by R A. patellulata Nr – new to UK Pp R A. punctiformis Pp,C O A. radiata Pp,C O A. subfuscula Nr Pp R A. vinosa Pp R Bacidia absistens Ns Pp R B. arceutina Pp O B. igniarii Nr Pp O B. naegelii Pp O B. rubella Pp O B. vermifera RDB(CE) Nr Pp R Biatoridium delitescens RDB(V) Nr Pp R Bryoria fuscescens Pp,B,Sb,L F Buellia disciformis Pp,B,C,Sb F B. griseovirens Pp,C O B. punctata Pp R Calicium glaucellum Pp,L R C. viride Pp O 19 Species Status Substrata RA Caloplaca ahtii Nr - new to UK Pp R C. cerina Pp F C. cerinella Ns Pp F C. cerinelloides Ns Pp O C. ferruginea Ns Pp F C. flavorubescens RDB(CE) Sch.8, Ns Pp R C. obscurella Pp O Caloplaca phlogina Pp R Candelariella xanthostigma Pp R Catillaria nigroclavata Ns Pp O Catinaria neuschildii RDB(V) Nr Pp R C. aff. atropurpurea Ns Pp R Chaenotheca chrysocephala Pp R C. furfuracea Pp R Chrysothrix candelaris Pp,B,Al F Cladonia chlorophaea Pp O C. coniocraea Pp- and B-by F C. fimbriata Pp-by R C. glauca Pp,B R C. pyxidata Pp base F Cliostomum griffithii Pp R Collema occultatum Ns Pp R Degelia plumbea Pp O Evernia prunastri Pp,B,C, Sb F Fuscidea arboricola Ns Pp R Hypocenomyce scalaris Pp R Hypogymnia physodes Pp,B,C,S,Sb A H. tubulosa Pp, B F Lauderlindsaya acroglypta Ns Pp O Lecania cyrtellina Ns Pp R L. sambucina Nr Pp R Lecanora carpinea Pp,C F L. chlarotera Pp A L. confusa Pp R L. conizaeoides PpL R L. expallens Pp, B, C A L. persimilis Ns Pp O L. populicola [RDB(EX)]Nr Pp O L. pulicaris PpL,B F L. rugosella Ns Pp F L. sambuci Ns Pp O L. symmicta Pp R 20 Species Status Substrata RA L . turgidula PpL R Lecidella elaeochroma Pp,C A f. soralifera Pp-tw R L. lobificans Pp O L. umbricola Ns Pp R Lobaria amplissima (as Dendriscocaulon umhausense – the cyanobacterial morph) Pp R L. pulmonaria Pp,C R L. scrobiculata Pp,Sb R Lopadium disciforme Ns Pp R Megalaria grossa Pp A Micarea nitschkeana PpL R Mycoblastus fucatus PpL,C O Nephroma laevigatum C,Pp O Ochrolechia androgyna Pp,Sb A O. microstictoides Pp,JSb O O. szatalaensis Ns Pp O O. turneri Pp R Opegrapha herbarum Pp R O niveoatra Pp O O. ochrocheila Pp R O. rufescens Pp R Pannaria conoplea Pp R P. mediterranea Pp-fallen R P. ignobilis RDB(V), Sch.8, Ns Pp R P. rubiginosa Pp R Parmelia exasperata Pp,B-tw F P. glabratula subsp. glabratula Pp,Al A P. saxatilis Pp,B,C,Sb A P. subaurifera Pp, B, F P. sulcata Pp, B, Al,C A Parmeliella triptophylla Pp O Peltigera collina Pp,C R P. membranacea T,Pp-by O P. praetextata PpL,T-by F Pertusaria amara Pp,Al,C,Sb A P. coccodes Pp R P. coronata Ns Pp O P. flavida Pp,Sb R P. hemisphaerica Pp,Sb R P. leioplaca Pp, C F 21 Species Status Substrata RA P. pertusa Pp,A,B F P. pupillaris PpL,J,Sb R Phaeophyscia orbicularis Pp F Phlyctis argena Pp,C,Sb A Physcia adscendens Pp O P. aipolea Pp A P. leptalea Pp O P. stellaris Pp O P. tenella Pp A Physconia distorta Pp, C A Platismatia glauca Pp,B,C,J,Sb, L A Pseudevernia furfuracea Pp,B,J,Sb,L F Pyrrhospora quernea Pp R Ramalina farinacea Pp,Al,C A R. fastigiata Pp R R. fraxinea Pp F Rinodina efflorescens Ns Pp,Sb O R. ? levitate Pp-tw R R. sophodes Pp-tw O Schismatomma graphidiodes RDB(V) Sch.8, Nr Pp R Sclerophora pallida RDB(V) Ns Pp,Sb R Scoliciosporum chlorococcum Pp O Sphaerophorus globosus Pp,Al,B,Sb R Sticta limbata Pp R Tephromela atra Pp F U. hirta Pp,B O U. subfloridana Pp,B,C,J,Sb F Xanthoria parietina Pp A X. polycarpa Pp O Lichenicolous fungi (all on lichens growing on Aspen in Strathspey) Arthonia subfuscicola in apothecia of Lecanora carpinea, not previously recorded in UK since 19th century Arthonia sp. in apothecia of Lecanora populicola. Similar to A. intexta in having 1–2-septate ascospores Dactylospora parasitaster associated with Biatoridium delitescens Laeviomyces pertusariicola on Pertusaria leioplaca Lethariicola sp. on Pertusaria coronata. Possibly the same undescribed species as previously found in Scotland on Pertusaria hymenea Lichenodiplis lecanorae on Caloplaca cerinella and Lecanora persimilis Muellerella lichenicola on Tephromela atra Phaeosphaerobolous alpinus on Lecanora carpinea Phoma physciicola on Physcia stellaris Stigmidium congestum in apothecia of Lecanora chlarotera Stigmidium pumilum on Physcia aipolia Vouauxiella lichenicola on Lecanora chlarotera The Biodiversity and Management of Aspen Woodlands 22 Other microfungi on Aspen Amphisphaerella dispersella on Aspen bark Dasyscyphius corticalis on Aspen bark Hysterographium elongatum on Aspen lignum Lahmia kunzei on Aspen bark ?Melaspilea cf. proximella on Aspen bark Teichospora sp. on Aspen bark Notes on Priority lichens and species new to the British Isles Arthonia patellulata Apparently the first correctly reported finds of this ‘Aspen specialist’ in the British Isles. Previous records have proven to be other species, although there is a 1968 record from Braemar that may be correct. Bacidia vermifera Status: RDB(CE). Previously recorded only from two 10km squares in Britain, both in Strathspey, one of which was Abernethy in 1980s. The finds during this survey increases the number of squares to four, and the first UK reports from Aspen. Biatoridium delitescens RDB(V) species, previously recorded from six 10km squares (four of which are Scottish). Not previously reported on Aspen from the UK. Caloplaca ahtii A recently described lichen from Fennoscandia and Alaska, where it is mainly found on Aspens. All the Scottish material is without apothecia. Caloplaca flavovirescens RDB(CE) and Schedule 8 lichen sparsely known from only a handful of isolated wayside trees, mostly Ash. Widely recorded in the 19th century, but now declined almost to extinction. Clais Eich and another site near Rothiemurchus are believed to be easily their best UK locations. Catinaria neuschildii RDB(V). The find at Kinchurdy is the fifth 10km square record in the UK, and the first from Aspen. Previous records are from Juniper and Oak. Lecanora populicola Until this survey RDB(EX). Not recorded in UK for over 150 years when it was last seen at Coltishall, East Norfolk. Seen at four sites. Pannaria ignobilis RDB(V) and Schedule 8. The discovery on a single old Aspen at Invertromie is the first and only record from Strathspey, and the first in the UK from Aspen. Its main populations are in the Great Glen and Strath Glass. Rinodina laevigata * If the identity is confirmed, this will be its first Scottish record and the first in Europe outwith Fennoscandia. Schismatomma graphidiodes This internationally rare RDB(V) and Schedule 8 species has its known world headquarters on the Oaks at Cawdor Wood near Nairn. Otherwise, it is known from only a handful of scattered, mostly Scottish localities. * currently awaiting formal confirmation 23 Bryophytes on Aspens Gordon Rothero Strolonag, Glenmassen, Dunoon, Argyll, PA23 8RA. E-mail: GPRothero@aol.com Introduction Away from the oceanic woodlands of the west, where there is a rich and interesting bryoflora on all broadleaf species, interest in epiphytic bryophytes has tended to centre on those tree species known to have ‘base-rich’ bark, particularly Fraxinus excelsior, Acer pseudoplatanus, Ulmus spp, Salix spp and Sambucus nigra. These tree species often have a good assemblage of bryophytes, particularly when growing in relatively open sites, hence the value of wayside and parkland trees. To my knowledge, Aspen has mainly been celebrated as the host species for the single British record for Orthotrichum gymnostomum and it has certainly been undervalued. Orthotrichum gymnostomum Orthotrichum gymnostomum is a small, yellow-green, blunt-leaved moss which has a scattered distribution over much of northern and central Europe and also records from south-west Asia, Afghanistan and Newfoundland (Hill et al. 1994). Though it has been found on the bark of a number of different tree species throughout its range, most records come from species of Populus and through northern Europe most records are from old Populus tremula (Nyholm, 1979). In this sense, in Europe at least, it is probably more host-specific than other epiphytic bryophytes. Though sporophytes are apparently rare throughout its range, the plant does produce large numbers of gemmae, specialised means of vegetative reproduction, on its leaves, a feature it shares with the closely related Orthotrichum obtusifolium. The solitary British record dates from 21st June 1966 when it was collected by J Dransfield in company with H.J.B. Birks and H.H. Lees near Loch an Eilein in the Rothiemurchus forest (Perry & Dransfield 1967). A small tuft consisting of about 15 stems was not recognised in the field and was collected. At first it was thought that the plant was Orthotrichum obtusifolium, but closer examination showed it to be Orthotrichum gymnostomum. After the discovery, other Aspens were searched but no further cushions were found. It would seem that the only cushion in that area had been collected, a sobering observation. The site of the host Aspen for the 1966 record is not obvious from the description. The habitat description talks of “open pine-birch woodland with occasional Aspens on a north-facing slope at about 800ft in altitude” (Perry & Dransfield 1967), but unfortunately the six-figure map reference delineates a hectare on a south-facing slope near the loch margin. Perry and Dransfield opine that, given the frequency of Aspen in the Aviemore area, Orthotrichum gymnostomum should turn up elsewhere in the vicinity. Thirty five years on, that hope has yet to be realised and the plant is now classified as extinct in the Bryophyte Red Data Book (Church et al. 2001). A number of competent bryologists have visited the Loch an Eilein area over the years and searched Aspens without success, but few have ventured further afield. Before giving up hope completely, it seemed a sensible idea to spend a small amount of time visiting some areas of Aspen in Strathspey and this suggestion was incorporated into a wider survey of ‘Priority bryophytes’ in Scotland, commissioned and funded by Scottish Natural Heritage. Other than the original locality, the sites to be visited were selected from a database of significant stands of Aspen compiled by the Malloch Society. It seemed sensible to look at as many Aspens as possible so only large stands were selected; at Invertromie, Insh, Torcroy, Creagan Breugach near Inverton, Speybank by Kincraig, Tomnagowan and Boat of Garten. I had no more success at Loch an Eilean than other bryologists; the most likely site seemed to 24 be Creag an Fhithich, the closest north-facing slope to the map reference with a few scattered Aspens, but a wider search was also made. Moving on to the other Aspen woodlands, two things were immediately apparent; Aspens had a much more diverse epiphytic bryophyte flora than I had realised, and searching all Aspens in a large woodland was not possible in the time available. Certainly more than 50% and probably more than 75% of the Aspens in the woods were checked, and it was the more bryophyte-rich trees that were targeted. On this basis I am reasonably convinced that Orthotrichum gymnostomum does not occur in the woodlands I visited. The general diversity of the flora is discussed below. Orthotrichum obtusifolium At Invertromie, one Aspen produced a small, blunt-leaved Orthotrichum species but this proved to be the closely related Orthotrichum obtusifolium. This species is very close to Orthotrichum gymnostomum and requires some familiarity with the group to distinguish it in the field. It has the same neat cushions with blunt leaves and differs mainly in the character of the leaf margins, plain or erect in Orthotrichum obtusifolium and curled in over the leaf surface in Orthotrichum gymnostomum. There are also critical differences in cell ornamentation that require a microscope but are diagnostic (Smith 1978). The initial disappointment was hardly justified as Orthotrichum obtusifolium is listed on Schedule 8 of the Wildlife and Countryside Act and, prior to this survey of Aspens in Strathspey, had just one extant site in Britain, at Leith Hall near Huntly. The woodland at Insh produced a further tiny stand of Orthotrichum obtusifolium but disappointingly, no more populations were found at the other sites visited. A third locality was found on a group of Aspens at Inveruglas by David Chamberlain, walking back to Insh village from a visit to the site at Invertromie. During the ‘Aspen day’ afternoon fieldtrip, I found a further small stand close to the original tree at Invertromie and a subsequent search by David Long has revealed further stands, including one large one, on three more trees. Orthotrichum obtusifolium, as the distribution map shows, has a much longer history in Britain than Orthotrichum gymnostomum. 25 Map 1. Showing the Distribution of Orthotrichum obtusifolium in the British Isles (not available in text format) Orthotrichum obtusifolium was widespread in Britain in the 19th century, though it has always been rare. The reasonable presumption has been made that most of the English localities were casualties of increasing air pollution, though with a rare species, chance events will always play their part. Of the four relatively recent (post-1960) sites, three are in Scotland (Cortachy in Angus, Fochabers and Leith Hall). At Cortachy the plant grew on ‘parkland’ Elms which all seem to have succumbed to Dutch Elm disease, and this may also have been the fate of the Elm on which it was recorded at Fochabers. At Leith Hall there is a healthy population on some eight trees, both Elm and Sycamore, and this remains the best British population. At the English site in Norfolk, a single tuft was found on an elder twig in 1989, and shades of Orthotrichum gymnostomum was collected and has not been seen again. The new populations near Insh have increased both the geographical spread of recorded localities and the number of host species. Historically, Ash has been the most favoured substrate in Britain followed by Elm and Sycamore, but in northern Europe and North America, Orthotrichum obtusifolium shows a marked preference for Aspen, so its occurrence on this tree in Scotland should be no real surprise. The sites at Invertromie and at Inveruglas are in relatively open wood- 26 land where light levels in summer remain quite high and all historic records come from similarly open sites. It may well be that further survey work on Orthotrichum obtusifolium, and possibly Orthotrichum gymnostomum as well, should target smaller stands of Aspen on more open sites rather than areas of woodland with a complete canopy. Other bryophytes on Aspen The survey of large numbers of Aspen revealed that a good proportion of mature trees have an excellent epiphytic flora. Table 1 gives a list of bryophytes recorded from Aspen in Strathspey in 2000 and no doubt more could be added. Table 1. Bryophytes recorded on Aspen in selected woodlands on Speyside in 2000 Liverworts Frullania dilatata Frullania fragilifolia Frullania tamarisci Metzgeria furcata Radula complanata Mosses Dicranum scoparium Dicranum fuscescens Homalothecium sericeum Hypnum andoi Hypnum cupressiforme Leucodon sciuroides Orthotrichum affine Orthotrichum lyellii Orthotrichum obtusifolium Nationally rare, Schedule 8 Orthotrichum speciosum Nationally rare Orthotrichum stramineum Orthotrichum striatum Orthotrichum tenellum Syntrichia laevipila Ulota bruchii Ulota crispa Ulota drummondii Ulota phyllantha Zygodon conoideus Zygodon rupestris Zygodon viridissimus var viridissimus Apart from the excellent diversity of species, there are three important conclusions to be drawn from the list. The first is a simple observation, that Aspens in Strathspey are the centre of distribution for the nationally rare moss Orthotrichum speciosum. Given the restricted distribution of recent records of this species (see Map 2), its abundance on many Aspens in the woods visited is quite remarkable. The robust cushions with clearly visible capsules are a feature of most of the better trees, sometimes forming large stands. The second is that three of the mosses which occur regularly on Aspen in the area, Ulota drummondii, Ulota phyllantha and Zygodon conoideus, are ‘Atlantic bryophytes’ (see Hodgetts 1997), an affinity which is also reflected in the lichen flora. 27 Map 2. Showing the distribution of Orthotrichum speciosum in the British Isles (not available in text format) The third observation is more subtle, but could be of considerable importance. The loss of Elms to disease, and the general loss of wayside and parkland trees over the past 100 years, has deprived epiphytic bryophytes of favoured sites, so much so that some species, like Orthotrichum obtusifolium but also Orthotrichum pallens and Orthotrichum pumilum are now endangered in Britain (Church et al. 2001). It may be that Aspens on open sites in the east of Scotland could have populations of these species that have been overlooked. Even if this does not prove to be the case, the substrate that Aspens provide for a good assemblage of regionally important species, which might otherwise be in decline, is a worthwhile discovery. One further observation of epiphytic populations on Aspens is puzzling. Though some Aspens are clothed in a variety of epiphytic mosses, species which are known to need bark of a reasonably high nutrient status, others are almost devoid of bryophytes, except those which can 28 cope with nutrient-poor conditions. So we have Aspens, close together and experiencing similar light and nutrient regimes, some having a flora similar to Ash or Elm and others to Birch or Alder. A similar situation seems to exist with the epiphytic lichen flora. One obvious explanation, given the structure of Aspen woodland, is that this may be a clonal difference, some trees being genetically different to others. Another possible explanation may relate to the sort of fungal infestation that the Aspen is subject to. Aspens seem particularly prone to damage and most large trees show signs of fungal invasion; does this affect the nutrient status of the bark or the run-off? Conclusion It is clear from the survey of a limited number of Aspens in 2000 that the importance of the species for epiphytic bryophytes has been distinctly under-estimated. Though Orthotrichum gymnostomum was not refound, the discovery of three new populations of Orthotrichum obtusifolium, the abundance of Orthotrichum speciosum and the diversity of epiphtyic mosses on Aspen fully justify the survey. Any increase in Aspen woodland will benefit bryophytes, and this is as true of smaller groups of trees as of larger woodlands, so there is a different emphasis here compared with the entomological interest. The epiphytic interest of the larger Aspens should be borne in mind when considering the management of the woodland for insects which require dead wood but sensible precautions should prevent any possible conflict. References Church, J.M., Hodgetts, N.G., Preston, C.D. & Stewart N.F. 2001. British Red Data Books. Mosses and liverworts. Peterborough, JNCC. Hill, M.O., Preston, C.D. & Smith A.J.E. 1991. Atlas of the Bryophytes of Britain and Ireland, Vol 3 Mosses (Diplolepidae). Harley Books. Nyholm, E. 1979. Moss Flora of Fennoscandia II Musci; fascicle 4. Swedish Natural Science Research Council. Hodgetts, N.G. 1997. Atlantic bryophytes in Scotland. Botanical Journal of Scotland. 49: 375-386. Perry, A.R. & Dransfield, J. 1967. Orthotrichum gymnostomum in Scotland. J. Bryol. 5: 218-221. Smith, A.J.E. 1978. The Moss Flora of Britain and Ireland. Cambridge University Press. 29 Aspen, a vital resource for saproxylic flies Graham Rotheray National Museums of Scotland, Chambers Street, Edinburgh EH1 1JF. E-mail: ger@nms.ac.uk Saproxylic organisms are those that depend on dead wood at some stage in their life cycle. They vary from woodpeckers to fungi, but the most biodiverse groups are Coleoptera (beetles) and flies (Diptera). Over most of Europe saproxylic organisms are under threat, due to the removal of woodland cover and impoverishment of what remains (Speight 1989). Over the past 12 years, members of the Malloch Society have been involved in a study of saproxylic Diptera in Scottish woodlands. In comparison with Coleoptera, Diptera are poorly known (Rotheray et al. 2001), and part of our aim was to redress this imbalance. Our emphasis was on finding breeding sites and rearing larvae. During the study we visited over 300 woodlands throughout Scotland. We obtained 2061 records of 258 species in 32 families. Two hundred and six species were reared, many for the first time. We reared 53 red-listed species. In addition, we recorded nine species new to Britain and 10 new to science, which further demonstrates how poorly known this fauna is (Rotheray et al. 2001). Most records came from common and relatively widespread boreal trees such as Silver birch, Betula pubescens E., Scots pine, Pinus sylvestris L. and also from Ash, Fraxinus excelsior L. However, another tree species was also important, Aspen, Populus tremula L. For example, we found that for red-listed and other significant species (defined here as ‘new to Britain’, ‘new to science’), Aspen was the third most important tree species after Birch and Pine of 22 tree species examined. It had three Red Data Book (RDB) category 1 “endangered” species reared from it, including the UK BAP Priority species, Aspen hoverfly Hammerschmidtia ferruginea (Fallen) (Diptera, Syrphidae) (Table 1). No other tree species had as many RDB 1 species associated with it (Rotheray et al. 2001). Altogether a group of 39 species were reared from Aspen, of which 14 were red-listed or otherwise significant. Many of the red-listed and significant Diptera associated with Aspen appear to be confined to it. We did not rear them from any other tree species. Possibly these species will use other Willows and Poplars (Salicaceae) in different geographical regions, but this does not appear to be the case in Scotland. Thus, Aspen has a rich, specialised and unique fauna of saproxylic Diptera associated with it. Table 1. Rare and notable insects bred from Highland Aspen Species and Status** Ecataetia christiei (Dipt.Scatopsidae) New species Mycetobia obscura (Dipt. Anisopodidae) New to Britain Lonchaea hackmani (Dipt. Lonchaeidae) New to Britain Medetera freyi (Dipt. Dolichopodidae) New to Britain Hammerschmidtia ferruginea (Dipt.Syrphidae) RDB 1 (UK BAP) Homalocephala biumbratum (Dipt.Ottitidae) RDB 1 Strongylophthalmyia ustulata (Dipt.Tanypezidae) RDB 1 Tachypeza heeri (Dipt.Hybotidae) RDB 2 Tachypeza truncorum (Dipt.Hybotidae) RDB 3 Medetera inspissata (Dipt.Dolichopodidae) RDB 3 Brachyopa pilosa (Dipt.Syrphidae) RDB 3 Gnophomyia viridipennis (Dipt. Tipulidae) Notable Clusoides apicalis (Dipt.Clusidae) Notable Stegena coleoptrata (Dipt.Drosophilidae) Notable Lonchaea peregrina (Dipt.Lonchaeidae) Notable 30 Systenus pallipes (Dipt.Dolichopodidae) Notable Xylota tarda (Dipt.Syrphidae) Notable Criorhina ranunculi (Diptera Syrphidae) Notable Saperda carcharius (Col. Cerambycidae) Notable ** The status rating of the Dipteran species is based upon Falk (1991) and that of Saperda carcharius on Hyman and Parsons (1992). The most important microhabitats used for breeding by saproxylic Diptera include tree-holes, exudations of tree sap, decaying sap under bark and decaying sapwood and heartwood. With the exception of exuding tree sap which is associated with live trees, all these microhabitats are found in stumps and live and dead trees and branches. Although some tree species exhibit a tendency to have more of one type of microhabitat than others, (e.g. tree-holes in Beech, decaying sapwood in Birch), all were features of most of the 22 tree species examined, including Aspen. For saproxylic Diptera associated with Aspen, the most important microhabitat was decaying sap under bark. When a tree or branch dies one of the first stages in the decay process is bacterial decomposition of the cambial layers between the bark and the sapwood. In Aspen this process results in the gradual build-up of a dark, oily, pungent-smelling layer under the bark, and it often includes the inner layers of the bark. This decay process is common to all trees, but in no other species did we find a layer as thick and wet as in Aspen. This layer develops patchily at first but will eventually, under suitable conditions of shade and light and perhaps other as yet unknown features such as the state of fungal decay within the wood, encompass the entire underside of the bark. Eventually the bark separates from the sapwood, cracks and this lets in air. Bacterial decomposition of the sap ends at this point and the oily layer dries out and becomes unsuitable. The dynamics of this decay process are unclear, but the initial build-up takes about two years and lasts for another three years or so. The thickness of the oily layer depends on the thickness of the branch or tree. In branches below about 10cm, the oily layer of decay is too thin to provide a breeding site for most of the important Diptera. It is within this oily layer of trees and branches above 10cm diameter that most of the important saproxylic Diptera dependent on Aspen breed. Their larvae either feed directly on the bacteria or acting as predators feeding on other insect larvae. A key characteristic of this particular microhabitat is that it is dynamic and does not last long. Thus, for populations of saproxylic Diptera, a continuous input of fresh fallen or dead wood is required. A particular feature of the important saproxylic Diptera associated with Aspen is their geographical distribution. Most of them are confined to just 14 sites in north-eastern Scotland. These sites contain large stands of Aspen, above 4.5 hectares. Although Aspen is widespread in Scotland it is only in the north-east that such large stands exist. The survival of these Diptera may thus be explained. It is only in these large stands that there is enough Aspen to provide a sufficient input of new fallen or deadwood for breeding. Few of these vital stands are protected and some have sustained damage in the past few years. One particular problem is grazing by rabbits and deer which often remove the bark of fallen wood thus ruining the breeding site. Another problem is competition from faster growing conifers and removal of fallen wood by people. An additional potential threat is the plan to release beaver into Scotland with their preference for eating Aspen (Batty – this volume). Measures are required to protect these core Aspen stands if this rich community of saproxylic Diptera is to be conserved. In the short-term, continual inputs of wood can be created by felling one or two trees per year. Aspen stands are often characterised by wind-blown trees lying on their sides, but still alive attached by their root plate. Trees such as these are perhaps good candidates for felling to provide an increase in breeding potential. Over the long-term, Aspen stands 31 can be protected from grazing with fencing as has been started at the Royal Society for the Protection of Birds (RSPB) Reserve at Invertromie (Prescott, this volume). Such protection should enable the fast-growing Aspen to recover and offers the potential to extend Aspen stands and link them up to create a fully functioning ecological unit, C McGowan, this volume). This is all the more urgent, given recent assessments of the abundance of Aspen dependent saproxylic Diptera. These reveal them to be at a low point in numbers due to the lack of suitable fallen wood in many stands. Some may argue, why bother to conserve insects such as these flies in the first place? It should be understood that just because these organisms are flies does not mean they lack significance. Scottish Aspen is unique for the richness of its associated saproxylic flies. Many are rare in not only a British but also a European context. Some are accorded the highest level of threat within the RDB and one is a UK Biodiveristy Action Plan Priority species. If such a wealth of uniqueness and rarity is not worth saving, what is? However, there is another aspect to the saproxylic Diptera associated with Aspen that is important. When Aspen spread north following the retreat of the ice about 10-11,000 years ago, many insects that depended on it also moved north. Some of these have separated from populations of the same species further south to varying degrees. Some vary just in ecology, like the hoverfly Brachyopa pilosa. In southern Britain, this species breeds in association with Oak, Beech and Poplar, but in Scotland it appears to be restricted to Aspen. It seems that this species has undergone a change in Scotland and is therefore special and adds to the biodiversity of the British Isles. Other insects appear to have gone one further step and speciated with the new species becoming dependent on Aspen. For example, we discovered a new species of scatopsid (small black flies) confined to Aspen, Ectaetia christii. This new species is very similar to a widespread southern species, Ectaetia clavipes to which it is most closely related (Rotheray and Horsfield 1997). All of these features make Scottish Aspen and its saproxylic Diptera special and important to European natural history. This deserves to be recognised as such and treated accordingly. Acknowledgements I am very grateful to fellow members of the Malloch Society who helped discover the significance of Scottish Aspen for saproxylic Diptera. These include Geoff Hancock, Steve Hewitt, David Horsfield, Iain MacGowan, David Robertson and Kenn Watt. I am also grateful to Scottish Natural Heritage, World Wide Fund for Nature and to the RSPB for financial support. All of us are very grateful to Tom Prescott of the RSPB who has already done much to ensure the survival of Aspen and its dependent flora and fauna in Scotland. References Graham Rotheray, Geoff Hancock, Steve Hewitt, David Horsfield, Iain MacGowan, David Robertson and Kenn Watt. 2001. The biodiversity and conservation of saproxylic Diptera in Scotland. Journal of Insect Conservation In Press. Rotheray, GE Horsfield D. 1997. Ectaetia christii sp. n., a Scottish species similar to Ectaetia flavipes (Diptera, Scatopsidae). Dipterists Digest 4: 41-4. Speight, MCD. 1989. Saproxylic Invertebrates and their Conservation. Nature and Environment Series, No. 42. Strasbourg: Council of Europe. Falk S., 1991. A Review of the scarce and threatened flies of Great Britain (Part 1) Research and Survey in Nature Conservation No.39, Nature Conservancy Council, Peterborough. Hyman P.S and Parsons M.S., 1992. A review of the scarce and threatened Coleoptera of Great Britain (Part 1), UK Nature Conservation No. 3, Joint Nature Conservation Committee, Peterborough. 32 The Large Poplar Longhorn Beetle Saperda carcharius in the Scottish Highlands Tracey Begg Department of Zoology, University of Glasgow. E-mail: tracey.begg@rspb.org.uk Iain MacGowan Scottish Natural Heritage, Battleby, Redgorton, Perth. E-mail: Iain.MacGowan@snh.gov.uk The Large Poplar longhorn beetle Saperda carcharius (Linnaeus) (Cerambycidae), is classified as a notable A species considered to occur in 30 or fewer 10km Grid Squares of the National Grid (Hyman and Parsons, 1992). In the Scottish Highlands, the known distribution of this species has recently been extended from four to 13 10km squares (MacGowan and Begg In Prep.). Larvae of Saperda carcharius are found in trunks of Aspen (Populus tremula) the preferred larval tree, but other Poplar species, Salix and occasionally Quercus may be utilised (Uhthoff- Kaufmann, 1991). Saperda probably spends 2-4 years as a larva within an aspen tree (Hyman and Parson, 1992), after which the adults emerge during July and August. Adults may be found until October. During the emergence period, frass and wood fibres are ejected through a circular hole in the bark formed by an enlargement of the oviposition site. This makes it possible to determine where larvae are present and adults have emerged. Studies conducted at two sites, Invertromie in Strathspey and a site in Deeside during the emergence period in 2000, revealed that where trees had emergence holes, or showed signs of larval activity, the tree circumference (measured at chest height) was within the range 13-187cm. The mean circumference was 47.4cm. The circumference of over 200 Aspen trees across the Scottish Highlands was measured and showed that the mean circumference for aspen overall lies in the 81-90cm circumference size range. This demonstrates that Saperda carcharius is selecting for smaller trees. Within each aspen stand, most activity was found to be on trees at the edge of the stand, next to open ground with only a few sites being found within dense cover. Trees found bordering walls, fences or along road verges commonly had an abundance of emergence holes, possibly due to the open aspect consistent with these sites. Where conditions are favourable and grazing pressure is low, Aspen regenerates by producing suckers from the parent tree, giving rise to dense stands of young trees. These trees are used by Saperda larvae. Although larval activity does not directly kill the host tree, it no doubt weakens it by allowing the entry of damaging tree diseases, fungal attack and by weakening the stem, making it more susceptible to wind blow and other damage. The thinning of Aspen stands to produce relatively open stands of larger trees is, in general, a benefit to the other insects and lichens associated with Aspen. By being an agent in the thinning process, Saperda carcharius acts in an ecologically beneficial manner and plays an important role in the ecology of Aspen stands. References Hyman and Parsons. 1992. A review of the scarce and threatened Coleoptera of Great Britain, Part 1, UK Nature Conservation Series Number 3, Joint Nature Conservancy Council, Peterborough. MacGowan, I. and Begg, T. 2001. Notes on the distribution, status and ecology of the large poplar longhorn beetle, Saperda carcharius (Linnaeus) (Cerambycidae) in the Scottish Highlands. In Prep. Uhthoff-Kaufmann, R. R. 1991. The distribution and occurrence of the genus Saperda F. (Col. Lamiidae) in Great Britain. Entomologists Record 103: 129-134. 33 Byctiscus populi, a leaf rolling weevil dependent on Aspen Jon Mellings Centre for Biodiversity and Conservation, University of Leeds, Leeds LS2 9JT. E-mail: bgyjhm@leeds.ac.uk Steve Compton Centre for Biodiversity and Conservation, University of Leeds, Leeds LS2 9JT. E-mail: pab6sgc@leeds.ac.uk Introduction Byctiscus populi (Coleoptera: Attelabidae) is an attractive, metallic green or coppery coloured leaf-rolling weevil associated with Aspen Populus tremula and occasionally Poplars. Fowler (1891) stated that B. populi was found ‘on young Aspens’, and Morris (1999) refers to ‘anecdotal evidence that these weevils prefer young growth of suckering and regenerating trees to large, mature individuals’. The UK range of B. populi appears to have declined in the past few decades. It is classified as Red Data Book 3 ‘rare’ and UK Biodiversity Action Plan (BAP) - Priority listed species (Morris, 1999). In accordance with recommendations in the UK Species Action Plan, research was initiated in 2001 at the University of Leeds, the designated Lead Partner for this species. Former and extant sites are being resurveyed to update records, and thereby establish a picture of the species’ current status. Since ecological knowledge of B. populi is largely anecdotal, priority is being given to field and laboratory-based research to examine aspects of its biology and habitat requirements. These findings will be used to advise on practical management actions to aid recovery of B. populi. Here we discuss the current UK distribution of B. populi, describe some initial findings regarding its biology and habitat requirements and suggest possible causes for its decline. Ecology Field studies were carried out during summer 2001 at Monkwood (just north of Worcester, Worcestershire), which supports a strong population of B. populi. Comparative studies were also carried out by Lianne Evans (University of Leeds) and Dmitry Telnovs in Latvia, where B. populi is still common. Besides Aspen, B. populi is said to be associated with White poplar (Populus alba) and Black poplar (Populus nigra) (Hyman and Parsons, 1992). However, in the UK and Latvia it appears to occur almost exclusively on Aspen. Field observations and captive rearing of Latvian and UK specimens have provided a reasonably complete picture of its lifecycle. Emergence of adults, mating and oviposition The adult insects appear from May onwards, when they can be seen feeding on the leaves of Aspen. Mated females lay batches of between one to four eggs in cigar-like rolls formed from one, or occasionally two, Aspen leaves, with more eggs deposited in longer leaves (Evans, 2001). The larger, longer leaves found at the growing tips of Aspen suckers are the favoured oviposition sites, with plants as short as 30cm utilized. Trees above two or three metres are used more rarely than smaller individuals. As many as four individuals, both females and more rarely males, may cooperate in the rolling of a single leaf roll. This suggests that some rolls may contain the eggs of more than one female. The rolls are sometimes detached almost immediately, or may remain on the trees for several weeks. 34 From egg to larvae Eggs of captive-reared Latvian beetles took an average of just under four days to hatch. The first instar larvae then proceeded to feed on the wilted leaf roll from within. Usually at this point the leaf was still attached to the food-plant. The number of larval instars remains undetermined, but mature larva of 4-6mm in length, vacated the roll after an average of around 16 days. It is possible that larvae occasionally complete their development while the roll is still attached to the tree. Prepupa, pupation and emergence In common with B. populi’s slightly larger sister species B. betulae, larvae were found to pupate in pupal chambers in the soil at a depth of between 5–60mm. A prepupal stage lasts up to four weeks, followed by a comparatively short pupation, lasting less than a week in some cases. Whereas B. betulae overwinter as adults in the pupal chamber (Bily, 1990), captive-reared B. populi specimens emerged above the soil surface and began feeding shortly after. Number of broods and hibernation of the adults In Monkwood, B. populi adults were observed rolling leaves throughout the summer between May and the beginning of August, when suckers were still seen to be producing fresh leaves. The peak activity was around the end of June, when both beetles and leaf rolls were very numerous. It is likely that the beetle is bivoltine or even continuously brooded through the summer. Captive-reared beetles provided with a choice of rough pieces of bark and soil in outdoor conditions in late October 2001, settled beneath the soil and within cracks in the bark and appeared to enter diapause. Whether any final generation adults overwinter as adults in their pupal cells, as described for B. betulae, is unknown. Distribution Internationally, B. populi occurs over the whole of the Palaearctic region, being fairly common in central Europe (Harde, 1998). In the UK, Morris (1999) stated ‘There are post-1970 records from east Sussex and east Kent, but historically it was more widely distributed, being recorded from much of southern England northwards to east Norfolk, east Gloucestershire and Worcestershire’. Now considered to be ‘rare’ and declining, it is clear from Fowler’s (1891) summary: ‘very local, but not uncommon where it occurs’, that B. populi was patchily distributed even at the end of the 19th century. A meeting on the conservation of UK BAP phytophagous beetles, funded by English Nature, was held in London in February 2001. It became evident that B. populi has continued to decline, having probably become extinct at two of the seven sites for which post 1980 records were available. Ian Menzies, who had regularly recorded the species at Bookham Common Special Site of Scientific Interest (SSSI), Surrey, noted that he had recorded no further specimens since 1991. Similarly, four miles away at Wisely Common, Peter Hodge reported the beetle’s recent demise as a result of extensive clearance of pioneer Aspen scrub, removed for conservation purposes! Four possible post-1990 B. populi site records are available, two of which are based on our surveys this year. The first is Oversley Wood, a Forestry Commission site in Warwickshire. Here the most recent of several records since 1987 was made by Lane & Forsythe in May 1999 (Lane & Forsythe, 1999). They beat a single specimen from Aspen and described the Oversley population as ‘small and vulnerable’. Aspen is one of the dominant species in sections of this site and our 2001 site visits found several leaf rolls on ride-edge aspen suckers, though no adults were seen. This suggests the population is still extant at Oversley, but remains very small. The second recent B. populi site record was added by Darren Mann (pers. comm.), who found the beetle at Wappenbury Wood (a Warwickshire Wildlife Trust Reserve approximately 30km from Oversley Wood) during the 1990s. Aspen suckers proliferate along rides at Wappenbury, though conservation efforts have apparently reduced their abundance in recent years. Leaf scars 35 consistent with B. populi were found during our 2001 site visit, but we failed to confirm the continued presence of the beetle. Orlestone Forest, a Kent Wildlife Trust-managed ancient woodland, near Ham Street was visited in mid-August 2001. B. populi had last been recorded at the site in 1972, with records dating back to the mid-1960s. No adult beetles were found, but two leaf rolls, almost certainly created by B. populi, were discovered in a sunny, ride edge location. Interestingly, the habitat at this site was very similar, in terms of vegetative composition, structure and management, to Monkwood, another site where the beetle survives. Morris (1990) has described Worcestershire as a ‘blank spot’ because of the apparent underrecording of Coleoptera there. We investigated two woods in the county where there were old (1950s) records for B. populi, one of which was Monkwood, where we found what may be currently the strongest UK population of this species. This wood is a Worcester Wildlife Trust Reserve and SSSI. An ancient coppice woodland, and once a ‘Harris brush wood’, it is now managed jointly by the Worcester Wildlife Trust and Butterfly Conservation. Leaf rolls were noticed even before the site was entered, on low aspen suckers at the woodland boundary adjacent to the road. Subsequent searches within the wood revealed a number of discrete patches of Aspen sucker growth along ride edges and in areas of recently-coppiced Hazel (Corylus avellana). B. populi adults and leaf rolls were found in reasonable numbers on virtually all the patches of pioneer, ride-edge Aspen throughout the site. In contrast, the beetle and its rolls seemed largely absent from mature trees (although rolls sometimes occurred on the lower branches of standards in sunny conditions). More tellingly, where aspen suckers occurred as an understorey in areas heavily shaded by mature trees, B. populi was almost always absent. The second site in Worcestershire, which has recently been acquired by Worcester Wildlife Trust, was Randen Wood, between Bromsgrove and Kidderminster, where the beetle appears to have been lost. Aspen was present in this wood in small isolated patches, but the woodland canopy was closed, allowing little light to penetrate. There was no sign of recent management and no evidence that B. populi was present. The contrasting fortune of the beetle at the two Worcester sites and its distribution within Monkwood and elsewhere provides strong indications of the habitat needs of B. populi and the management required for it to persist. Small Aspens, growing in sunny, sheltered conditions are what this species requires. The Dark-bordered beauty (Epione vespertaria) appears to have very similar habitat requirements to B. populi. This moth is known mainly from Aspen sites in Scotland, and it would be well worth looking for B. populi at these sites, even though it has not been recorded previously north of the border. Suitable small Aspens are typically found along woodland rides at the English sites, but in Latvia they are also a common feature of roadside verges, derelict land, footpaths and other habitats, hence the beetles much greater abundance there. Perversely, maintenance of open rides is important for the persistence of this species, but thorough ride clearance that results in the elimination of Aspen suckers and bushes deprives it of suitable host plants. Acknowledgements Our work on Byctiscus populi has been funded by the English Nature. References Bily, S.,1990. A colour guide to beetles, ed. London: Hamlyn. Evans, L. 2001. A study on Byctiscus populi (L.1758) (Attelabidae) in Latvia and implications for conservation management in the UK. Unpublished MSc. project, University of Leeds. Fowler, W.W., 1891. The Coleoptera of the British Isles, vol 5. London: Reeve and Co. Harde, K.W. and Severa, F., 1998. A Field Guide in Colour to Beetles. Leicester: Blitz Editions. 36 Hymen, P.S. and Parsons, M.S., 1992. A review of the scarce and threatened Coleoptera of Great Britain, Part 1. Peterborough: JNCC. Lane, S.A. and Forsythe, T.G., 1999. Noteworthy beetles found in Warwickshire (VC 38) in 1999. The Coleopterist, 9: 102 – 104. Morris, M.G., 1999. Byctiscus populi (a leaf-rolling weevil) Action plan. In UK Biodiversity Group Tranche 2 Action Plans, Vol 5: Invertebrates (March 1999). Peterborough: JNCC. 2001, Minutes of meeting on phytophagous beetle conservation, Royal Entomological Society, London. (unpublished). 37 The importance of Aspen for Lepidoptera Mark Young Centre for Ecology, University of Aberdeen, Culterty, Newburgh, Ellon, Aberdeenshire, AB41 6AA. E-mail: m.young@abdn.ac.uk Introduction The species of Lepidoptera that use Aspen as a larval foodplant are summarised by Emmet (1991), who lists all British Lepidoptera and their life histories. Depending on interpretation of the use made of Aspen by generalist feeders, there are around 40 moth species regularly found on the tree in UK overall, about 25 in Scotland and, of these, 26 are specialised Aspen feeders in UK, whereas only about 14 are mainly confined to Aspen in Scotland (Table 1). Southwood (1961) originally counted the number of herbivorous insects on British tree species, (although this analysis has been upgraded recently for Lepidoptera by Young (1997)). By this reckoning, Aspen harbours a rather modest total, compared with Oak, Birch and Sallow, for example. However, the number found on different trees is positively correlated with the abundance and distribution of each tree and, although Aspen is widespread, it does not compare with other forest trees in its abundance, nor in the tendency to form extensive woodland. Its ‘apparency’ to moths is relatively low. In Scotland, every large stand of Aspen tends to have a regular attendance of 10-12 moth species, which form a distinct assemblage. Table 1. Species of Lepidoptera associated with Aspen in Scotland, including only species feeding mainly or exclusively on Aspen. (Data from Emmet, 1991). A. Number of species regularly feeding on Aspen in UK 40 species in Scotland 25 species Number of species specialising on Aspen in UK 26 species in Scotland 14 species B. Species feeding mainly or exclusively on Aspen in Scotland Ectoedemia argyropeza (Zell.) larvae mine in petiole & leaf Stigmella assimilella (Zell.) larvae mine in leaf [Paraleucoptera sinuella (Reutti) larvae mine in leaf (? extinct)] Anacampsis populella (Cl.) larvae in folded/rolled leaves Ancylis laetana (Fabr.) larvae in folded leaf Epinotia cinereana Haw larvae in folded/spun leaves E. maculana (Fabr.) larvae in spun leaves [Gypsonoma nitidulana (L. & Z.) larvae in spun leaves (extinct?)] G. sociana (Haw.) larvae in spun leaves Tethea or (D. & S.) (Poplar Lutestring) larvae in flat-spun leaves Lobophora halterata (Hufn.) (Seraphim) larvae free on leaves Epione vespertaria (Linn.) (Dark-bordered Beauty) larvae free on young regrowth Pheosia tremula (Cl.) (Sallow Prominent) larvae free on leaves Clostera curtula (Linn.) (Chocolate Tip) larvae in spun leaves Orthosia populeti (Fabr.) (Lead-coloured Drab) larvae on catkins then leaves Acronicta megacephala (D. & S.) (Poplar Grey) larvae in spun leaves Characteristic species on Aspen Since Aspen is closely related to other Poplars, and reasonably closely related to Salix spp., it is not unexpected to find that it shares a number of species with them. The Pale prominent (Pterostoma palpina) and the Poplar hawk (Laothoe populi) are examples of species which will readily use most Sallow and Poplars species, whereas the Swallow prominent (Pheosia tremula) 38 and the Poplar grey (Acronicta megacephala) are restricted to Poplars. However, the latter illustrates an interesting feature in that it is apparently restricted to Aspen and does not use other Poplars in the north of its UK range. This extra specialisation applies to several species. Finally there are some species, such as the Seraphim (Lobophora halterata) and the Lead-coloured drab (Orthosia populeti), that are always restricted to Aspen. Most tree species have some moth larvae that feed on the bark, flowers or that bore into the twigs. However, all Aspen’s specialised feeders use only the leaves, except that the Leadcoloured drab also feeds on the flowers at first. It is traditionally believed that the flat petiole, leading to the trembling of the leaves, makes it difficult for insect herbivores to remain attached to Aspen leaves, and it may not be coincidence that most species live between spun or folded leaves. For example, the Poplar lutestring (Tethea or) uses a series of strong silk pads to attach one leaf on top of another and Ancylis laetana makes a neat chamber of a folded leaf. Even small stands of Aspen will harbour the commoner species of moth, especially those that will also use Sallow or other Poplars. However, it is only Aspen woodlands of a significant size that include the rarer, specialist species. The Chocolate-tip (Clostera curtula) is found locally only in the larger Aspen woods. No-one knows how large such a woodland needs to be for this species to survive, but it is clear that it is associated with mature trees, as is the Lead-coloured drab. As will become clear below, other species require regenerating growth and so there is a clear conservation need for large stands of Aspen that include both mature and regenerating stems. The majority of the species that live on Aspen can apparently survive in rather generalised woodlands, but the rare species described below clearly need very much more specialised conditions. The Dark-bordered beauty and its conservation The Dark-bordered beauty (Epione vespertaria) has always been a rare species but is now very localised indeed and, by nature of this localisation, must be considered threatened in UK. Its English and southern Scottish localities are already published in the literature and so can be safely repeated here, whereas its northern Scottish localities are referred to by a generalised name (Table 2). At Strenshall Common, Yorkshire and Newnham Bog, Northumberland Dark-bordered beauty larvae are known to feed exclusively on Creeping willow (Salix repens) and they have been confirmed recently from these sites, but not from the small handful of other historic English sites. At Adderstonlee Moss, Roxburgh it is also assumed that S. repens is the foodplant, in the absence of Aspen, but no larvae have been found to confirm this. Nor has the adult moth been seen there recently, but it must be admitted that the few recent searches have been in less than ideal conditions (K.P. Bland, D.A. Barbour, pers. comm.). Table 2. Sites for the Dark-bordered beauty (Epione vespertaria) in UK since 1990. (Editor’s note: excludes details of newly discovered Deeside site) 1. Strenshall Common, Yorkshire Larvae recently found on Salix repens. 2. Newham Bog, Northumberland Larvae recently found on Salix repens. 3. Adderstonlee Moss, Roxburgh No recent sightings, larvae presumed to feed on Salix repens. (No Aspen present). 4. Near Balmoral, Aberdeenshire Larvae recently found exclusively on low regrowth of Aspen. Adults also seen. 5. Near Grantown, Strathspey Adults recently found. Larvae presumed to feed on low regrowth of Aspen. (No Salix repens present). 39 In contrast, at the ‘Balmoral’ and ‘Grantown’ sites, the larvae feed exclusively on Aspen (Leverton et al., 1997) and are confined to regenerating shoots. There is no clear height above which such growth becomes unsuitable, but recently larvae were found on shoots of less than 50cm height and at the ‘Balmoral’ site the moths are seen only where there is abundant suckering of less than 1m height. At ‘Balmoral’, this regrowth has been favoured by irregular cutting of a roadside verge and by the recent clearance of mature woodland to create a pylon wayleave. At ‘Grantown’, intermittent grazing seems to have allowed regrowth, although the number of available shoots is very low there and only a small number of moths have been found. The colony seems to be in serious danger. Visits have been made to several possible sites, near those on Deeside and Speyside, but so far with only limited success. In summer 2001, a new site on Deeside was discovered, taking the total to three sites in the Cairngorms. Suitable regeneration of Aspen does occur in places near the known sites and there is no convincing reason why these should not be used. However, a successful site will have to have had a continuity of regrowth always available and the adult females are rather sluggish, so that colonisation may only be possible over short distances. The clear conservation priority is to secure management of the existing sites, so as to maintain and extend the availability of suitably low growing shoots; and then, secondly, to consider the suitability and security of other nearby sites, with a view to possible introductions. Species in need of relocation Finally, there are two species that used to be found on Aspen in Strathspey but are now apparently extinct. Urgent survey work is needed to relocate these, or to confirm their absence. Gypsonoma nitidulana was found until 1911 on old Aspens near Aviemore but has not been seen in Britain since then. Its relocation may seem to be a hopeless cause but there are ample examples of other species that have been rediscovered after such an interlude such as Ethmia pyrausta, recently re-recorded after over 100 years (Smith and Young, 1997). G. nitidulana is rather nondescript and its relocation will require collection of larvae by a specialist. Paraleucoptera sinuella, by contrast, should be reasonably easily recorded, for its larvae make rather characteristic leaf blotches. It was recorded by Bankes, a well-known and reliable lepidopterist, in an Aspen spinney near Aviemore Railway Station in 1910 and it survived there until the 1950s, since when it has inexplicably vanished. It was also found in 1945 near Grantown, indicating that it was not wholly restricted to one site. Abroad, it ranges from Europe to Japan and is often rather common on other Poplars and Salix spp., as well as Aspen. The adult is generally found in June and again in August, and the larvae in July and September but there may be only one generation per year in Scotland. Adults are tiny white moths, with minute gold streaks on the wings, but the larvae form oval blotch mines on the leaves. These are 1-1.5 cm long and 0.5-0.8 cm wide when fully formed and are at first brown but then later black. The larval droppings (the ‘frass’) are placed at the centre of the mine, often in a spiral array of fine grains, leaving clear margins to the mine. However, old mines go black and indistinct as the leaves decay. Furthermore, there are other insects that also mine Aspen leaves and so confuse matters. Once the larvae are fully fed, they emerge from the mine and spin a small and sparse rectangular white silk web on a leaf within which they form a dense yellowy-white cocoon, in which to pupate. No other insects form such a spinning and its presence is diagnostic for this species. There is a real hope that P. sinuella will be refound in Strathspey in future, by searching for its mines and cocoons. Conclusions Conservation of Aspen feeding Lepidoptera requires a general effort to provide a continuity of all ages of tree, in sufficiently large stands to provide for the larger, specialist species. The Dark-bordered beauty has more specialised and exacting requirements, however, and its three remaining sites in northern Scotland will need careful management, to sustain the continuity of regenerat- ing growth. It has survived by accident so far, but we must now act deliberately to secure its future. 40 References Emmet, A.M. 1991. Chart showing the Life History and Habits of British Lepidoptera. In: Emmet, A. M. and Heath, J. The Moths and Butterflies of Great Britain and Ireland. 7:2. Harley Books, Colchester. Leverton, R., Young, M.R. and Barbour, D. 1997. Epione paralellaria D. & S. (Lep.: Geometridae) and its association with Aspen (Populus tremula) in the Scottish Highlands. Entomologists’ Record & Journal of Variation. 109: 49-55. Smith, R. and Young, M.R. 1997. The rediscovery of Ethmia pyrausta (Pallas, 1771) (Lepidoptera: Ethmiidae) in Britain. Entomologists’ Gazette 48 (2): 85-87. Southwood, T.R.E. 1961. The number of species of insect associated with various trees. Journal of Animal Ecology 30: 1-8. Young, M.R. 1997. The Natural History of Moths. T. & A.D. Poyser, London. 41 Beavers: Aspen heaven or hell? Dave Batty SNH Casework Support Officer, Kilmory Industrial Estate, Kilmory, Lochgilphead, Argyll, PA318RR. E-mail: Dave.Batty@snh.gov.uk The paper will provide a background to the ecology of European beavers, discuss their potential impact on woodland in general and on Aspen in Scotland in particular. European beaver The European beaver, Castor fiber, is Europe’s largest rodent (average weight c 25kg), and is a separate species from the North American beaver Castor canadensis. It has a semi-aquatic lifestyle, and inhabits freshwater, either slow-running rivers or lochs. They generally use water as their main means of travel and are only occasionally found more than c60m from water. Beavers are social animals and live in family groups consisting of the two parent animals plus the young of the year and sometimes the young of the previous year. The number of animals in a group varies, but an average of 3.8 has been recorded. The group occupy a territory around their lodge, which they defend against other groups. They also use a larger home range, which they might share with other neighbouring groups. Beavers normally have their young in May-June, and most litters are either two or three young. The young stay with the parents until they are sexually mature and ready to disperse from the home territory, usually at around two years old just before the new young of the year are born. However, the dispersing young may return to the home territory if they fail to find a suitable area elsewhere. European beavers tend to live in natural holes in banks or excavate burrows with an underwater entrance. Where the banks are not high enough, the Beavers may construct bank lodges consisting of a burrow covered by piles of wood. The lodge contains a vestibule and, typically, one nesting chamber above water level. Beavers build dams from a variety of materials including wood, mud and sometimes stones. The main reason for dam building is to raise the water level and keep the entrance to their burrow or lodge below the water surface. This reduces the chances of predation and danger to the young. Beavers will also excavate canals to facilitate the transport of material. This can increase their potential feeding range. Beavers are herbivores, feeding entirely on plant material. They eat an extremely wide range of herbaceous and woody plants, with at least 149 and 80 species recorded respectively. During the late spring and summer they mainly eat herbaceous plants, especially aquatic ones, and take a wide range of grasses, forbs, ferns, shrubs and leaves. The bark and leaves of trees and shrubs forms only a small part of their diet. Where the preferred herbaceous plants are not available, Beavers will utilise more woody species. This change is most obviously seen in the autumn and winter when woody plants form the vast majority of the diet. Beavers will store branches underwater in the autumn for use in the winter when other food is not available. Trees and shrubs are used for their foliage and their bark, especially in the winter. There is a marked preference for hardwoods, especially Aspen, Birch, Willow, Rowan, Oak, Alder and Ash. Beavers tend to focus their activities around their burrow or lodge and this influences their foraging behaviour. They travel by water and generally feed up to 100m from the water’s edge but most is carried out within 20-60m. Most of their preferred trees and shrubs are harvested near the water’s edge. However, observations from Norway indicate that Beavers will travel up to 200m or more to use Aspen, and it is considered that any accessible Aspen within 500m may 42 be at risk of some exploitation. In addition, any Aspen within c 30m of the water would be vulnerable to heavy exploitation. It should be noted that Beavers can only use stands of Aspen that are accessible to them and that they are not as athletic as sheep or deer! Most trees and shrubs felled are less than 10cm in basal diameter, in Finland the mean being c3cm and in Norway the majority <5 cm. The result is that the vast majority of the hardwoods will then coppice naturally, providing other browsing species are not present, to provide another potential ‘crop’ for the Beavers to harvest in the future. Experience from re-introductions to Brittany and Poland is that the Beavers coppice the woodland rather than clear fell. Although the majority of trees used are small, Beavers are capable of felling trees of greater diameter, up to 1m. Where Beavers have been re-introduced, there has been a range of young regeneration and old mature trees, so the potential situation of just mature Aspen trees has not occurred. Therefore, given Beavers’ predilection for Aspen, it would be advisable to have a range of trees of different ages and sizes in an area. Re-introduction proposal The European beaver was once widespread across Europe, including Scotland and the rest of Britain, and northern Asia to Siberia. It probably occurred in Scotland until the early 16th century when it was hunted to extinction for its fur. It suffered a similar decline in Europe until by the 19th century there were only a few populations remaining in Norway, Germany and France. However, through legal protection, translocation and re-introduction it has now been successfully returned to much of its former range. Scottish Natural Heritage (SNH) is now considering the re-introduction of European beaver to Scotland because: - It is listed on the EC ‘Habitats Directive’; - It is recognised as being a ‘keystone species’ in the ecology of woodland and freshwater systems; - It would benefit biodiversity; and, - Since humans were responsible for its extinction in Scotland, it has been argued that there is a moral responsibility to redress the loss. Some years ago, SNH began to examine seriously the possibility of returning European beaver back to Scotland. SNH commissioned work on the suitability of habitats in Scotland to support Beaver and also on the effects of Beavers on hydrology, fish and woodland habitats in Europe. A national consultation was carried out in 1998 to ascertain the views of everyone who might have an interest in the subject. Based on that, SNH decided to go ahead, in principle, with a trial re-introduction which would be in a limited area for a specific period of time. Interest from the Forestry Commission led to an assessment of their holdings in Scotland and Knapdale Forest in Argyll was identified as the most suitable area for a trial. A fully planned trial is proposed with monitoring to determine, amongst other things: - How the Beavers behave in Scotland; - Impact on woodland habitat; - Impact on other wildlife interests; and, - Impact on water quality. The trial would last for five years, but if insurmountable problems were encountered during that period the trial would be curtailed prematurely. If the trial proceeds, it is intended that Beavers will be captured in autumn 2002, spend six months in quarantine and then be released in spring 2003. The trial would end in 2008. After the five years, there will be an assessment to help provide information for an informed decision on whether a wider-scale Beaver re-introduction should 43 take place. At this stage there will be wide consultation. The trial will be taken forward by SNH in partnership with Forest Enterprise, Scottish Wildlife Trust and Argyll and Bute Council. SNH will make a final decision over the trial in autumn 2002. However, approval will then be needed from the First Minister, as Beavers are not currently part of the native UK fauna and as such a licence is required under the Wildlife and Countryside Act 1981 to release them into the wild. Potential impact on Aspen It has already been noted above that Aspen is a favoured food for Beaver and that they will preferentially select it. This could put more pressure on an already restricted resource, both in terms of quantity and quality. However, at present Aspen is under pressure from grazing animals; both domestic (sheep and cattle), and wild (primarily deer, rabbits and hares). A key question is how to reduce or eliminate any extra threat from Beavers? Direct methods would include the identification of areas of Aspen at high risk from Beavers due to their proximity to water and their accessibility to Beavers. These areas could be easily fenced against Beavers, and, if of high value, might need to be fenced against other animals as well. Relatively low stock-proof fencing should be adequate, avoiding potential significant problems of fence collisions for ‘woodland grouse’. Given that Beavers burrow for other purposes, it would probably be sensible to have an apron of netting on the ground to deter burrowing, especially in soft ground. If there are concentrations of Aspen along particular river systems, an alternative method would be not to re-introduce Beavers to that catchment. Beavers usually travel via water and experience from the continent is that it can take some time for Beavers to move from one catchment to another one. However, perhaps the best method for dealing with a potential threat to Aspen from a Beaver reintroduction is to increase the quantity and quality of the Aspen resource, be it areas of Aspen woodland or Aspen stands in other woodland types. In this way the aim would be to manage existing Aspen and create new Aspen areas such that if/when Beavers arrived there would be sufficient habitat for both the Beaver and Aspen. The proposed trial re-introduction of European beaver to Scotland could be used as the publicity to raise the profile of Aspen with the public, land owners and managers, and also the bodies which could provide the funds for its management and expansion. European beaver could be used as an Aspen flagship species to heighten awareness. If the trial went ahead, it would be 2008/2009 before any decision could be made about any wider re-introduction of European beaver to other parts of Scotland. This provides considerable time to begin the active management and expansion of the Aspen resource in Scotland, and to look at ways of improved funding for this work through, for example, Woodland Grant Scheme and agri-environment schemes. If this work took place, and the decision was made not to proceed with a wider re-introduction, then the net result would still be both a raising of awareness of Aspen and a considerable expansion in the Aspen resource. The return of European beavers to Scotland might be hell for an individual Aspen, but potentially heaven for the Aspen resource as a whole. It is for people with an interest in Aspen to decide how they want to view Beavers, either as a problem or, more sensibly, as an Aspen opportunity. 44 Further reading: Collen P. 1997. Review of the potential impacts of re-introducing Eurasian beaver Castor fiber L. on the ecology and movement of native fishes, and the likely implications for current angling practices in Scotland. Scottish Natural Heritage Review 86. Conroy J. and Kitchener A. 1996. The Eurasian beaver (Castor fiber) in Scotland: a review of the literature and historical evidence. SNH Review 49. Gurnell A. 1997. Analysis of the effects of beaver dam-building activities on local hydrology. SNH Review 85. Kitchener A. and Lynch J.M. 2000. A morphometric comparison of the skulls of fossil British and extant European beavers, Castor fiber. SNH Review 127. Macdonald D., Maitland P., Rao S., Rushton S., Strachan R. and Tattersall, F. 1997. Development of a protocol for identifying beaver release sites. SNH Research, Survey and Monitoring Report 93. Reynolds P. 2000. European beaver and woodland habitats: a review. SNH Review 126. Scott Porter Research & Marketing Ltd. 1998. Re-introduction of European Beaver to Scotland: results of a public consultation. Scottish Natural Heritage Research, Survey and Monitoring Report 121. Webb A., French D.D. and Flitsch, A.C.C. 1997. Identification and assessment of possible beaver sites in Scotland. Scottish Natural Heritage Research, Survey and Monitoring Report 94. 45 Variation in Aspen in Scotland: genetics and silviculture Bill Mason Forest Research, Northern Research Station, Roslin, Midlothian, EH25 9SY. E-mail: bill.mason@forestry.gsi.gov.uk Eric Easton and Richard Ennos Institute of Ecology and Resource Management, University of Edinburgh, Darwin Building, The King’s Buildings, Mayfield Road, Edinburgh, EH9 3JU. E-mail: r.ennos@ed.ac.uk Introduction European Aspen (Populus tremula L.) is a widely distributed tree species in the northern temperate zone with a range stretching from Scandinavia to north Africa and from Britain to Japan. While the species is found throughout Britain, it is commonest in northern Scotland (Worrell, 1995a). However, a tendency to grow in small groves on the edges of woodland, a lack of regular seed production (Ennos et al., 2000), plus a palatability to grazing, have meant that the total area of Aspen woodland in Britain is estimated at around 500ha (J. Gilbert FC, pers. comm.) and woods of more than 1ha are rare. As a consequence, there have been very few studies of the silviculture and genetics of Aspen in Britain (Worrell 1995 a, b) and knowledge of appropriate management to favour this species is limited. The lack of knowledge is the more unfortunate because the importance of the species for both nature conservation and landscape interests is considerable (see other papers in these Proceedings). The purpose of this paper is to summarise some recent studies which provide useful guidance to those interested in increasing the area of Aspen woodland, either through natural colonisation or through planting. Propagation of Aspen The recent upsurge of interest in Aspen partially stemmed from recommendations that it be accepted for planting in the Native Pinewood schemes of the late 1980s (Hollingsworth and Mason, 1991). An average of 9ha of Aspen has been planted per year in Scotland since 1996 under the Woodland Grant Scheme (D. Wright, FC pers. comm.). Concern was expressed that the only Aspen material that could be purchased from nurseries in Britain at the time was of nonnative origin and probably not well adapted to Scottish conditions (Ennos et al., 2000). A small research project was carried out in the late 1980s to look at the possibilities of propagating Aspen by cuttings. This resulted in recommendations to excavate root sections in the field during the dormant season, place them in a heated greenhouse to promote suckering, and root the detached shoots as softwood cuttings in a mist house (Hollingsworth and Mason, 1991). Trials have generally shown high rooting percentages using this method (ie 90-100% rooting under mist) but there has been appreciable clonal variation in the number of shoots m-1 of root, and in growth after rooting (Hollingsworth and Mason, 1993). Although seed production by Aspen in Scotland is infrequent, there have been two recent reports of successful seed collections in Strathspey (Worrell, 1995b; Worrell et al., 1999). In addition, some of the native Aspen material offered by commercial nurseries in Scotland has been through at least one multiplication cycle in vitro before being grown on for forest planting (R.S.D. Ogilvy, Christie-Elite pers. comm.). Distribution in Scotland As a result of increasing confidence in the ability to propagate native Aspen, the next question was where could suitable locations of Aspen be found in Scotland. Discussions resulted in a small Forestry Commission/Scottish Natural Heritage project being established in 1992 with nine 46 objectives (see Table 1). Some of these objectives are discussed in more detail below. Worrell (1995a) recorded some 500 sites in Scotland where Aspen had been reported in the early 1990s. These locations1 are plotted in Figure 1 together with a further 100 sites recorded since the original survey; the 40 sites identified by Wilson et al. (2000) are included. The results indicate particular concentrations of Aspen in Perthshire, Deeside, Badenoch, Strathspey, Easter Ross and eastern Sutherland, with lesser frequency elsewhere. The recorded distribution was divided into eight zones as shown in Figure 1. This used the boundary between Regions of Provenance 10 and 20 (see Herbert et al., 1999) as the first divider, with subsequent divisions along major watersheds. Investigations of Scottish Aspen using genetic markers Once the range of the distribution of Aspen in Scotland had been ascertained, it became possible to undertake genetic analysis to find out more about the population biology and genetic variability of Aspen in Scotland. As indicated earlier in this volume, the reproductive biology of Aspen in Scotland is very different from that of most other native tree species. Flowering of the species is rare, and significant seed set is found at distant and irregular intervals (Worrell 1995a, Worrell et al., 1999). Seed is short lived, and the disturbed and open conditions required for seedling establishment are rarely found. Sexual propagation of the species is presently very problematic. On the other hand, the species has a remarkable ability to persist and spread via root suckers, so that individual genotypes have the potential to be extremely large and long lived. The management of native Aspen woods for conservation requires an understanding of how these special features have affected the level and distribution of genetic variation within Scottish Aspen populations. Two studies using genetic markers were therefore conducted to investigate these topics (Easton 1997). The objective of the first study was to look at the native Aspen resource in the whole of Scotland and assess its genetic variability relative to that of other tree species within their natural ranges. Three main questions were addressed: - Has the Scottish population retained genetic variability despite its reduced powers of sexual reproduction? - How is this genetic variability now distributed among the regions within Scotland? - Is there any evidence that restriction of sexual reproduction has led to inbreeding within the resource? The study was based on analysis of enzyme genetic markers. This represents genetic var