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Missing Species of the Caledonian Forest Beavers and Aspen: looking to the future


This paper, which is from the proceedings of the 2nd Aspen Conference, was based on a presentation given by Dan Puplett at this conference in October 2008.

Beaver and aspen twigs

Beaver and aspen twigs, Aigas.
Photo by Laurie Campbell.

Introduction

In Spring 2008 the Scottish Government granted a licence for a trial reintroduction of European beavers (Castor fiber) in mid-Argyll. The key project partners are the Scottish Wildlife Trust (SWT) and the Royal Zoological Society of Scotland (RZSS). The trial site, Knapdale Forest, is managed by Forestry Commission Scotland (FCS). Scottish Natural Heritage (SNH) will carry out independent monitoring. Along with many others, Trees for Life (TFL) believes this project to be a very positive step in the enhancement of our natural heritage; the beaver is a keystone species in both wetland and woodland ecosystems, and has a beneficial influence on biodiversity (Gaywood et al 2008).

It is well known that aspen (Populus tremula) supports a wide variety of species, and that it is favoured by a number of herbivores, including red deer (Cervus elaphus) and roe deer (Capreolus capreolus) (Cosgrove et al 2005). It is also clear that beavers favour aspen where it is available. In the past, questions have been raised about the possible impacts beavers might have on aspen in Scotland.

In the 2001 Aspen Conference Dave Batty of SNH addressed this issue in his presentation Beavers: Aspen Heaven or Hell? (Batty 2002) and concluded that beavers could prove to be hugely beneficial for aspen, acting as a flagship species: raising awareness of the threat aspen faces from deer and livestock, and acting as a catalyst for aspen restoration. A summary of measures for reducing any potential aspen / beaver conflicts is listed below (Batty 2002):

  • Protect those trees that would be best left undisturbed - a variety of simple methods are available.
  • Avoid reintroducing beavers to an area if associated aspen biodiversity is deemed to be particularly vulnerable.
  • Ensure that there is a range of aspen trees of different sizes and ages in area.
  • Increase the quality and quantity of the aspen resource along with other riparian woodland, benefiting aspen and associated organisms, including beavers.

Batty suggested that the latter measure would be the preferred solution in most cases. TFL has been working on this principle from the early days of our project. We concur that aspen enthusiasts (who should perhaps be called 'tremulophiles?!') can rest assured that if we so choose, we could have aspen and beavers in an ecologically healthy landscape. The purpose of this paper is to give a brief update on some opportunities surrounding beavers and aspen, and also to present some of the work TFL has been undertaking towards enhancing aspen and riparian woodland, in line with the strategy outlined above.

Update and funding opportunities

An encouraging development has been the production of SNH's Species Action Framework (SNH, 2007). The Framework targets 32 key species for priority action between 2007-2012. One of the species is the European beaver, and the Framework states: "The beaver is a charismatic species which would serve to raise wider biodiversity issues such as riparian woodland management, aspen restoration, wetland biodiversity and dead wood habitat."

This is encouraging as it highlights how the possibility of beaver reintroduction is already raising the profile of aspen conservation at a policy level, and indicates the influence of ideas discussed at the previous conference. Furthermore, if the trial is successful there could perhaps be funding available in the future for aspen restoration, linking it to beaver reintroduction.

Aspen and beaver interactions

The beaver trial will include a robust monitoring programme which will answer many of our questions about the role of beavers in today's landscape (Scottish Beaver Trial 2008). While more detail on known beaver / aspen interactions is provided in Batty (2002), it is worth briefly noting here that while beavers can undoubtedly have a major impact on aspen, this tree can still thrive in the presence of this mammal. For example, at the Danish beaver release site at Klosterheden, there are large old aspen adjacent to the riverbanks that are intact, as well as coppiced shoots that have not been browsed (D. Batty, pers. comm.). On a visit to the beaver reintroduction site near Brasov, Romania, the project worker informed me that beavers had not had a dramatic impact on the riparian aspen in the locality (M. Scurto, pers. comm.). While these are only two of many cases in Europe, they illustrate the potential for the co-existence of beavers and an expanded aspen population in Scotland.

Trees for Life's riparian aspen work

TFL has been carrying out aspen restoration work in a number of areas since 1991. One of the locations we have been focussing on is Loch Beinn a Mheadhoin in Glen Affric NNR, which is managed by FCS. The loch already has many of the features of suitable beaver habitat. While there are no official plans for beaver releases in Glen Affric at any point, from TFL's perspective it is worth further enhancing the habitat in case such a decision is ever taken in the future.

There are currently 62 aspen stands in Glen Affric, and we have carried out further aspen enhancement work in a variety of locations within the glen. These have mainly involved planting in small stock-fenced exclosures, as well as protecting ramets of existing stands with small fences or tree guards. A total of 957 trees have been planted in the immediate vicinity of the loch, and some of these are already producing ramets.

FCS has been controlling deer numbers to the point where there is good regeneration of a number of tree species in parts of the glen, but young aspen can still be vulnerable, even in the presence of lower deer densities. The dimensions of the stock-fenced exclosures we erect are usually around 3m x 6m. Having stock-height fences dramatically reduces the threat to woodland grouse, and while deer are physically capable of jumping into these exclosures, they tend to be reluctant to enter such a confined space. It is rare for deer to get in and when it has happened it has probably been due to the netting being too low. Anecdotal reports suggest that there is a risk of deer becoming entangled in the netting if they do attempt to jump in, and although we have not encountered this problem, it should not be ignored; where practical, regular inspections of the fences should be made. We have erected 38 small fences around the loch over a seven-year period, and only one has shown signs of deer entry and damage to trees.

Growth rates are quite variable, with some of the trees that were planted in 2001 having reached only 50cm, while others are over 3 metres tall and are producing ramets. A variety of factors possibly come into play here, including the clone, individual site conditions and perhaps the presence of mycorrhizal fungi.

Glen Moriston and Dundreggan aspen

Glen Moriston holds more aspen than Glen Affric, with a substantial amount beside the River Moriston. TFL recently took ownership of the 4,000 hectare Dundreggan Estate in Glen Moriston. A small part of the estate is immediately adjacent to the River Moriston, and part of our management plan is to create a large riparian aspen zone, including 9,000 aspen trees mixed with willow (Salix spp) and other species, beside the river. We have an agreement in principle for this to be a joint project with FCS, who manage the adjacent land (more information).

Thoughts on strategy

The current trial beaver reintroduction will end in 2014 (provided there is no reason to use the exit strategy), and if a licence for a further reintroduction were granted, it would be a considerable time before there were substantial numbers of beavers in Scotland. Therefore we have a reasonable amount of time in which to significantly expand the aspen population (D. Batty, pers. comm.).

Even if beavers do not return, an increase in riparian woodland, with an aspen component, would be beneficial in its own right. While it is obviously important to take into consideration any valuable non-woodland riparian habitats, in the vast majority of cases there is nothing to lose and much to be gained by an increase in riparian aspen planting.

Clearly it is wise to take a strategic approach to make best use of resources. While we are working on riparian aspen planting it would be a good idea for the various organisations involved in aspen restoration to develop a coordinated strategy. This could involve identifying locations of aspen biodiversity hotspots and priority areas for planting at a landscape level. There will be an important role for the use of BEETLE (Biological and Environmental Evaluation Tools for Landscape Ecology) software in this process (Watts et al, 2007).

While work of this kind has already been carried out by individual organisations in specific geographical areas, there would be huge advantages in pooling information. Similarly, it is also strongly recommended that we develop a coordinated approach to aspen surveying. TFL has a substantial database of aspen stands in our 'Target Area', just north of the Great Glen, and others with an interest in aspen also have extensive records for specific areas. FCS already has a database containing some of Scotland's aspen stands, and it is possible that this could be used as a central database into which we could feed our existing data.

The collation of such information would not only be a valuable resource in future decisions about beavers, but will also be necessary for most aspects of managing aspen and its associated biodiversity in Scotland.

Dan Puplett

Acknowledgements

I am grateful to the following for their helpful responses to my inquiries in relation to aspen and beavers: Dave Batty (SNH), Martin Gaywood (SNH), Derek Gow, Jari Kouki, Roy Dennis, Simon Jones (SWT), Iain Valentine (RZSS), David Hetherington, Marius Scurto (Brasov Wildlife Unit). Thanks to Forestry Commission Scotland and various private landowners for continued cooperation and partnership. All opinions expressed are those of Trees for Life.

References

Batty, D. 2002. Beavers: Aspen heaven or hell? In: Cosgrove, P., and Amphlett, A. (eds) The Biodiversity and Management of Aspen Woodlands: Proceedings of a one-day conference held in Kingussie, Scotland, 25th May 2001, pp 41-44. The Cairngorms Biodiversity Action Plan, Grantown-on-Spey, UK.
Cosgrove, P., Amphlett, A., Elliott, A., Ellis, C., Emmett, E., Prescott, T. and Featherstone, A.W. 2005. Aspen - Britain's missing link with the boreal forest. British Wildlife 17 (2), 107-115.
Gaywood, M, Batty, D. and Galbraith, C. 2008. Reintroducing the European Beaver in Britain. British Wildlife 19 (6) 381-391.
Scottish Beaver Trial website: http://www.scottishbeavers.org.uk
Scottish Natural Heritage. 2007. A Five Year Species Action Framework: Making a difference for Scotland's Species. Scottish Natural Heritage Publications: Battleby.
Watts, K., Ray, D., Quine, C.P., Humphrey, J.W. and Griffiths, M., 2007. Evaluating Biodiversity in Fragmented Landscapes: Applications of Landscape Ecology Tools. Forestry Commission Information Note 85. Forestry Commission: Edinburgh.

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