New reports on the effect of Scotland’s beavers on woodland and fish

Beaver science - Not rocket scienceOctober 2011. Two reports on the Scottish Beaver Trial in Argyll, published by Scottish Natural Heritage (SNH), 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 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.

Most trees affected were on the banks near the beaver lodges!
The woodland monitoring has been carried out by 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.

Prefer willow - avoid alder
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.

Most trees survive
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.

Little effect on fisheries
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."

http://www.wildlifeextra.com/go/news/beaver-trial011.html