Monitoring of beaver trial shows changes to woodland structure

Beaver teeth marks on birch tree

Nearly a year and a half after their release, about 10% of trees in the survey area show signs of beaver activity

Two new reports on the Scottish Beaver Trial in Argyll show that beavers are changing some of the woodland structure but so far having little effect on fish in streams.

Beavers were reintroduced to Knapdale forest near Lochgilphead in May 2009 as part of a five year scientific trial run by the Scottish Wildlife Trust and the Royal Zoological Society of Scotland, hosted by Forestry Commission Scotland. After an absence of more than 400 years, the effects of beavers on the environment are being closely monitored by Scottish Natural Heritage (SNH) in partnership with a number of other independent organisations. The reports will help inform future decisions on whether the European beaver should be permanently reintroduced to Scotland.

The woodland monitoring has been carried out by researchers from The James Hutton Institute, who surveyed land around the edges of the lochs where the beavers live. Nearly a year and a half after their release, about 10% of trees in the survey area were showing signs of beaver activity. Most of these had been felled, with many trees also showing signs of gnawing. As well as feeding on bark, twigs, shoots and leaves, beavers use felled trees and branches for building their lodges and dams and store them underwater for food in the winter. Beaver activity is concentrated in particular areas the majority of trees affected (72%) were within 10 metres of lochs and streams, with the most intensive felling within 350 metres of beaver lodges.

The average size of trees gnawed or felled was 5cm across, but beavers often felled much bigger trees. Most were less than 20cm in diameter but a few were up to 30cm.

Results to date show that beavers are showing a strong preference for willow and rowan, and that they avoid alder. One striking observation was that beavers will travel a distance from the water's edge to find willow. Other trees at Knapdale are used in proportion to their availability. Birch is one most often used by beavers but this is because it is the most commonly found tree in the survey area.

However, most trees will not die when they're felled by the beavers. Of the trees affected, new growth had already been found on 44% of stumps and partially-felled trees. Trees which have been felled later on in the summer may not start to regrow until the following spring.

As well as their effect on trees around the lochs, an area of woodland has been flooded by a beaver dam at Dubh Loch. While the willow and alder may survive, other species may die but remain standing as dead wood for some time. Ultimately this particular area may change to very wet willow woodland or even wetland.

The second report, produced by the Argyll Fisheries Trust, showed that so far beavers are having little observable effect on freshwater fish in streams in the trial area. This is because beavers aren't using streams as much as might have been expected - most beaver activity is taking place on the lochs. However this may change as the beaver numbers increase. The streams will continue to be monitored and the fish and fish habitat in some of the lochs will also be studied.

The fish species found in the survey include brown trout, European eel, stickleback and flounder. Minnow were also found. They are probably not native to this region of Scotland but are likely to have been brought in by anglers, using them as bait.

Martin Gaywood, who leads the independent scientific monitoring of the trial for SNH said: "These annual reports are vital to the beaver trial, because they'll show us how beavers influence the environment in and around these lochs. Beavers have complex effects on other wildlife, and measuring these changes is essential. This trial will give the Scottish Government the information it needs to decide whether beavers should be reintroduced on a wide-scale in Scotland."

Notes to Editors: Online copies of the report are available at the following links:

Woodland monitoring 2010

Survey of fish populations 2009

The Scottish Beaver Trial is a partnership project between the Royal Zoological Society of Scotland (RZSS), the Scottish Wildlife Trust (SWT) and host Forestry Commission Scotland, to undertake a time-limited trial reintroduction of the European beaver to Knapdale in mid-Argyll. Further information on the Scottish Beaver Trial.

The trial is part of Scotland's Species Action Framework, which sets out a strategic approach to species management in Scotland. In addition, 32 species were identified as the focus of new management action for five years from 2007, including European beaver. SNH works with a range of partners in developing this work.

Monitoring of the trial

The Scottish Government has asked Scottish Natural Heritage to coordinate the independent scientific monitoring of the trial, reporting on whether the conditions of the licence are being fully addressed on the ground. SNH will report the outcome of the trial to Scottish Ministers.

SNH is working with a number of independent organisations to carry out the monitoring work. They are Argyll and Bute Council, Argyll Fisheries Trust, Historic Scotland, British Dragonfly Society, The James Hutton Institute, Scottish Environment Protection Agency, Royal (Dick) School of Veterinary Studies, University of Oxford Wildlife Conservation Research Unit and University of Stirling. Each organisation is contributing resources towards the monitoring of the trial, along with SNH which is contributing £275,000. Further information on SNH monitoring of the trial.

The Argyll Fisheries Trust is a charitable company limited by guarantee. Our role is to identify fish and their use of habitats in the trial area and monitor any changes that may take place as a result of beaver and their use of habitat. This role within the project is undertaken in fulfilment of part of our mission to understand the biology and ecology of all freshwater fish species, their environment and factors that affect them. 

Scottish Natural Heritage is the Government's adviser on all aspects of nature and landscape across Scotland. Our role is to help everyone understand, value and enjoy Scotland's nature now and in the future.