Support for the reintroduction of long extinct species to Britain has been gaining momentum in recent years. The rewilding movement, spearheaded in this country by the recently formed NGO Rewilding Britain, seeks to restore ecosystems and reverse the loss of biodiversity through the reintroduction of apex predators, such as the lynx and wolf, and other keystone species, such as the beaver. The Eurasian beaver (Castor fiber) was once widespread across Britain. Extensive hunting, mainly for their pelts but also for castoreum (an oily secretion from the tail) and meat, resulted in their extirpation from Britain in the early 16th century (1).
Beavers are ecosystem engineers; they have the capacity to alter their surrounding environment through the construction of dams and channels, creating ponds and wetland habitat in river systems. These ponds provide deep water for protection from predation. Beavers are herbivores; they feed on a variety of plant matter consisting mainly of woody vegetation, which involves the felling of many broad-leaved trees (1).
In 2009, following a lengthy process, a license was granted for a trial release of five beaver families in the Knapdale Forest in Scotland. The Scottish Beaver Trial (SBT) has sought to assess the impacts of beaver reintroduction, resulting in an independent report of the findings by Scottish Natural Heritage (SNH) this year. A small-scale fenced beaver trial was also initiated in Devon in 2007 with a pair of beavers.
There have also been unofficial releases of beavers into the wild, either through escape from captive populations or illegal reintroductions by eco-vigilantes known as ‘beaver bombers‘. In the Tayside catchment of Scotland there are between 150-200 beavers in 32-33 family groups. In 2012 the Scottish Minister for Environment and Climate Change recommended the toleration of unlicensed beavers in Tayside for the duration of the SBT to enable research to compliment the findings from the licensed trial. The River Otter in Devon is also home to two breeding pairs and at least five younger beavers; they were allowed to remain in January 2015 for a five year study period through a Natural England license after being found clear of tapeworm infection.
Impacts on Biodiversity
Beavers are known to have a positive effect on a wide range of species. A study in the Eifel region of Germany assessed the impacts of beaver reintroduction on amphibians, including four species that are also native to Britain (2). They found that beaver ponds generated preferred breeding habitat for all native amphibians species. In particular the common frog (Rana temporaria) and the palmate newt (Lissotriton helveticus) seemed to benefit significantly from this restored habitat. In forested valleys in northern Poland nightly bat activity was higher in sections of the river valleys where beavers had transformed the habitat, creating damp clearings that are ideal foraging areas for many bat species (3).
However as with the reintroduction of any species there are drawbacks to consider. Potential beaver territory in Scotland overlaps heavily with native aspen and Atlantic hazel woodland. Beavers are likely to exploit these woodlands for food and dam construction. The impact on not only native woodland but also the species it supports requires further study. For example Atlantic hazel woodland supports two globally restricted communities of lichen, and 16 native moth species are totally dependent on aspen leaves as a food source (1).
Human: Beaver Conflict
Conflict between landowners and beavers is inevitable, highlighted by the shooting of more than 20 beavers in Tayside in November this year, as beavers currently have no legal protection in Britain. Beavers in the Tayside catchment have previously damaged flood defences through burrowing and caused river bank erosion due to divergence of the river around beaver dams.
The SNH report has assessed the potential impacts on forestry, agriculture and fisheries. There is particular concern over whether beaver dams impede the movement of migratory fish; this is likely to occur in narrow streams but not in main river sections where beavers are unlikely to create dams (4). This concern is warranted as recreational angling is worth £113m to the Scottish economy, £73m for Atlantic salmon alone. The report concludes that impacts can largely be mitigated by the implementation of an appropriate management strategy including funding for surveillance, monitoring and further research (1).
Beavers provide a range of provisioning and regulation ecosystem services including increased groundwater storage, flow stabilisation and flood prevention. A study focusing on the hydrological effects of recently reintroduced beavers in Belgium found that beaver dams significantly lowered downstream peak flows and increased intervals between major floods (5). Beavers also offer cultural ecosystem services such as educational, recreational and spiritual benefits to humans (1).
The Future for British Beavers
The SNH report is now in the hands of the Scottish Government and a decision on the long-term future of beavers in Scotland is likely in early 2016. Any decision on wide scale reintroduction of beavers to England will be at a much later date following the conclusion of the Devon trials.
Despite potential negative impacts the Scottish Beaver Trial has found an overall positive influence on biodiversity. The range of ecosystem services beavers provide also outweighs inevitable conflicts with landowners. The beaver looks to be an ideal candidate species to begin the process of rewilding the British landscape.
- A. Stringer et al., Beavers in Scotland : A report to the Scottish Government. Scottish Natural Heritage (2015).
- L. Dalbeck, B. Lüscher, D. Ohlhoff. Beaver ponds as habitat of amphibian communities in a central European highland. Amphibia-Reptilia. 28, 493–501 (2007).
- M. Ciechanowski, W. Kubic, A. Rynkiewicz, A. Zwolicki. Reintroduction of beavers (Castor fiber) may improve habitat quality for vespertilionid bats foraging in small river valleys. Eur. J. Wildl. Res. 57, 737–747 (2011).
- P. S. Kemp, T. a. Worthington, T. E. L. Langford, A. R. J. Tree, M. J. Gaywood. Qualitative and quantitative effects of reintroduced beavers on stream fish. Fish and Fisheries. 13, 158–181 (2012).
- J. Nyssen, J. Pontzeele, P. Billi. Effect of beaver dams on the hydrology of small mountain streams: Example from the Chevral in the Ourthe Orientale basin, Ardennes, Belgium. J. Hydrol. 402, 92–102 (2011).