Archives for January 2021

After centuries of exploitation for their fur, flesh and secretions, Eurasian beavers (Castor fiber) were extinct over much of their range, with only a few relic populations totaling about 1200 individuals by the start of the 20^th Century. In Britain, they were extinct by the 16^th Century. On mainland Europe, recognition of the ecosystem services beavers provide led to many countries adopting reintroduction programmes: for example, from 1922 in Sweden; 1966 in Bavaria; 1988 in Romania. Thompson et al. (2021) have evaluated the costs (to landowners) and very substantial ecosystem services provided by beaver presence, mainly in habitat and biodiversity enhancement, and in greenhouse gas sequestration. Through protection measures and reintroduction efforts, beavers have now recovered across most of their former range, with recent population estimates of 1.5 million individuals (Halley et al., 2021). Initially, Britain was resistant to beaver reintroduction, mainly because of the concerns of major landowners and forestry interests; however, more recently several high-profile projects have come into being.

In Scotland, serious discussion of the issue began in the 1990s, and the national conservation agency Scottish Natural Heritage (SNH, now NatureScot) suggested a trial reintroduction in 2000. The Government rejected this proposal, but a change of Government and more discussion led to a new proposal, which got the go ahead in 2008. The plan was for a trial reintroduction at a well-contained site in Knapdale Forest, Argyll, to be managed by the Scottish Wildlife Trust in collaboration with the Royal Scottish Zoological Society, and to be monitored independently by researchers commissioned by SNH. The Scottish Beaver Trial began in 2009, when 17 wild beavers from Telemark, Norway, were quarantined for six months in Devon, then released in May 2009 at three freshwater lochs in Knapdale. The trial continued until 2014 (Jones and Campbell-Palmer, 2014). SNH chose the monitoring topics: these included beaver ecology, otters, fish, woodland habitat and dragonflies, but NOT amphibians or reptiles (nor did they agree to permit independent study of the effects on herpetofauna). However, another population existed, formed from accidental escapes or releases in Tayside and these animals were unprotected from landowners who objected to their presence. The Tayside population generated more conflict with some landowners, especially in prime agricultural land where the damming of drainage ditches can lead to impacts on arable farming. After consideration of the data generated through the Scottish Beaver Trial, general public support and consultation with various interest groups and land management sectors, the Scottish Government agreed in November 2016 that the beavers could remain in Scotland. Going on further in May 2019 the Government granted legal protection for all beavers living in the wild (although landowners may still apply for a licence to have animals removed if they can show they are causing damage that cannot be mitigated via alternative means).

In England, the Devon Wildlife Trust received a Government licence in 2014 for a five-year study of the beaver population (origins unclear) already living in the catchment of the River Otter. The study report (Brazier et al., 2020) resulted in DEFRA’s agreeing that the population, now 15 family groups, can stay. As with the Scottish trial, herpetofauna were not a focus of the study. Nevertheless, the study concluded that the ‘effect of beaver engineering and feeding has delivered significant ecological benefits with new areas of wetland habitat created and managed, with documented benefits for amphibians, wildfowl and water-voles’. Although no regular monitoring of amphibians was carried out, in an area where beavers had constructed 13 dams along a 180 metre stretch of stream, counts of common frogspawn had increased from 10 in 2011 to 681 in 2017.

Although we lack studies on the impacts of beaver activities on amphibians in Britain, Dalbeck et al. (2020) have recently reviewed ten papers based on work in six central and eastern European countries (Switzerland, Germany, Lithuania, Denmark, Russia and Poland); they could find no reports so far from southern, western or northern Europe. They focussed on beaver impacts on streams and rivers, rather than on lakes. As is well known, beavers create dams using the logs and branches they cut down, producing ponds with low flow rates. Their tree-felling activities have several effects on local habitats: opening gaps in the forest canopy allows more light to reach the forest floor and water surface, raising temperatures and promoting primary productivity; a great quantity of rotting wood is produced and this promotes invertebrate diversity and habitat complexity. All these effects are potentially beneficial to amphibians. However, river ponds are good habitats for many species of fish, generally not considered helpful to amphibians because they consume eggs and prey on larvae. Indeed, in the UK, we do not regard streams as good amphibian habitat in general, unlike the situation in North America, where many species, especially urodeles, are primarily stream dwellers.

Central Europe supports 19 species of amphibian (six urodeles and 13 anurans). Dalbeck et al. (2020) categorised these into four groups, according to their habitat preferences: forest (6 spp.), open country (5), ubiquitous (4) and pioneers (3). All 19 species were reported from beaver ponds at least occasionally, but only forest and ubiquitous species were found frequently in such ponds. Two pioneer species (green and natterjack toads) and great crested newts were rarely found in beaver ponds. From the UK viewpoint, it is interesting that our two species of greatest conservation concern, great crested newts and natterjack toads, may not benefit significantly from beaver reintroductions. None of the reviewed studies included before and after data, but one of the German reports did compare the amphibian fauna of beaver ponds (mean 4.1 species +/-1.4 SD) with that of nearby beaver-free floodplain ponds (1.2+/-1.3) indicating a significant enhancement in the beaver ponds. Some of the studies compared the fauna of beaver ponds in headwater, small sized streams with those in wider rivers. Species richness was highest in small stream ponds, with a maximum of eight species found in a single German pond.

Sadly, the UK has a much less rich amphibian fauna than central Europe. Nevertheless, the reviewed results indicate that the habitat engineering work performed by beavers should have a positive impact on some of our species. It is, therefore, time that some relevant studies be carried out in Scotland and Devon. With beavers now having been active in Britain for some years, it should be possible to design studies that compare beaver-affected areas to similar areas that are beaver- free.

What about reptiles? The habitat changes wrought by beavers ought to be beneficial for them too, especially the creation of sunlit gaps in the forest, where animals can bask, and the habitat complexity generated producing refuges and hibernacula, and promoting invertebrate diversity. Dalbeck et al. (2020) do not report on impacts on reptiles, nor are they considered in the two British project reports. In the USA, there have been a few reports (e.g. Metts et al., 2001; Russell et al., 1999) on the impacts of beavers on reptiles (and amphibians), but they are not directly applicable to Europe since they concern a different species of beaver (C. canadensis) and a very different reptile fauna. Nevertheless, Metts et al. concluded that ‘disturbances resulting from beaver-created wetlands increase regional abundance and diversity of herpetofauna’. Another topic for research as beavers come back to Britain?

References

Brazier, R.E. et al. (2020). River Otter Beavers Trial: science and evidence report. University of Exeter, Devon Wildlife Trust and others. Available online.

Dalbeck, L., Hachtel, M. and Campbell-Palmer, R. (2020). A review of the influence of beaver Castor fiber on amphibian assemblages in the floodplains of European temperate streams and rivers. Herpetological Journal 30, 135-146.

Halley, D. J., Saveljev, A. P. and Rosell, F. (2021). Population and distribution of beavers Castor fiber and Castor canadensis in Eurasia. Mammal Review 51, ISSN 0305-1838

Jones, S. and Campbell-Palmer, R. (2014). The Scottish Beaver Trial: the story of Britain’s first licensed release into the wild. Final Report. Scottish Wildlife trust and the Royal Zoological Society of Scotland. Available online.

Metts, B.S. (2001). Evaluation of herpetofaunal communities on upland streams and beaver-impounded streams in the upper piedmont of South Ca

Russell, K.R. et al. (1999). Amphibian and reptile communities associated with beavers (Castor canadensis) ponds and unimpounded streams in the piedmont of South Carolina. Journal of Freshwater Ecology 14, 149-158.

Thompson, S. et al. (2021). Ecosystem services provided by beavers Castor spp. Mammal Review 51 (published on-line).

 Roger Downie, University of Glasgow and Froglife Trustee

Roisin Campbell-Palmer, Independent Beaver Ecologist, Associate of University of Exeter