Beavers are back in Britain, ‘wood’ you like to know why?

This is article no. 3 in a series on animal conservation. Next article: Pangolins: from poached to protected (coming soon). Previous article: Conserving the California condor

Eurasian beavers (Castor fiber) transform freshwater habitats so dramatically that they are nicknamed ‘ecosystem engineers’. Their dam-building and tree-felling activities could reduce flood risk and increase biodiversity. After being hunted to extinction centuries ago, beavers have been reintroduced to Britain in both organised and illicit ways. This article will describe where they have been reintroduced in Britain, and the impact they could have.

Ecological importance of beavers

By building dams, Eurasian beavers alter their habitat - often for the better. Beaver dams are made from wood, stones, and mud. They control the flow of river water, reducing the risk of floods and droughts. The resulting slower water is a good place for amphibians to lay eggs and undergo the aquatic part of their life cycle. As water builds up behind the dam, it converts the area into a wetland - a source of drinking water for animals like bats and an excellent carbon sink. Meanwhile, invertebrates can lay eggs or hide from predators in the spaces within beaver dams (Figure 1). Further up the food chain, beaver dams have complex effects on fish. Although the still water provides habitat for overwintering and rearing young, dams restrict the movement of fish species like salmon. However, most studies have concluded that beaver dams benefit freshwater biodiversity.

Dams are not the only way Eurasian beavers improve their landscape. To access food and construction materials easily, beavers dig canals – which make the habitat better drained and more complex. Moreover, beavers gnaw at tree trunks and branches, sometimes knocking over entire trees. This creates deadwood where terrestrial invertebrates can live. Felling trees also allow sunlight to reach the river surface, promoting aquatic plant growth. When beavers gnaw at willow trees, they create propagules, which disperse along the beaver-made canal network and grow downstream. These new willow trees stabilise the river bank and further reduce the flood risk. Humans often trim back trees to stimulate their growth – called coppicing – but beavers do this free of charge. Coppicing, dam building, and canal digging are just a few ways beavers save the human costs of restoring and protecting natural habitats.

Extinction and reintroduction

However, Eurasian beavers used to be more exploited than appreciated. They were hunted for their fur, meat, and a secretion called castoreum, which is used in perfume and pharmaceuticals. Exactly when and how the beaver population went extinct from Britain is unclear, but the last written record of a beaver is from 1526 in Scotland and 1780 in England. Since then, the British turned wetlands into farmland and forgot about beavers … until recently.

After centuries, beavers returned to Scotland in the late 2000s. A handful of beavers were spotted in River Tay about 15 years ago, after either an enclosure escape or an illegal release. There are 114 families in this illegal population, which has genetic origins in Germany. The first official beaver reintroduction occurred in Knapdale Forest, Scotland, in 2009 – but this population did not grow as quickly as the River Tay one. With scepticism, the reintroduction of Eurasian beavers to Scotland was deemed a success, and they became a ‘European Protected Species’ in Scotland in 2019.

Seeing Eurasian beavers thriving in Scotland encouraged reintroduction plans in England. In the English county of Devon, River Otter showed signs of beaver presence since 2008 and breeding since 2013. Authorities were worried these illegally released beavers would spread foreign diseases to local wildlife, but the public campaigned to let the beavers be. Public affection for beavers led to the River Otter Beaver Trial in 2015, where two breeding pairs were released into the river after thorough health checks. By 2019, the number of breeding pairs grew to seven (Figure 2). Therefore, beavers have successfully returned to England.

Conclusion

Beavers alter their landscape through dams, canals, and felling trees. However, in Britain, they were hunted to extinction a long time ago. Although beavers first returned to England and Scotland illegally, they now live in healthy, growing populations. Hopefully they will remain protected and loved by the public, helping us to restore wetlands and improve British freshwater biodiversity.

Written by Simran Patel

Related article: Vicuna conservation

REFERENCES

Andersen, L.H. et al. (2023) ‘Can reintroduction of beavers improve insect biodiversity?’, Journal of Environmental Management, 337, p. 117719. Available at: https://doi.org/10.1016/j.jenvman.2023.117719.

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Brazier, R.E. et al. (2021) ‘Beaver: Nature’s ecosystem engineers’, WIREs Water, 8(1), p. e1494. Available at: https://doi.org/10.1002/wat2.1494.

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Hooker, J. et al. (2024) ‘Re-establishing historic ecosystem links through targeted species reintroduction: Beaver-mediated wetlands support increased bat activity’, Science of The Total Environment, 951, p. 175661. Available at: https://doi.org/10.1016/j.scitotenv.2024.175661.

Wilson, J.B., Bradley, J. and Bremner-Harrison, S. (2024) ‘The short-term impact of Eurasian beavers (Castor fiber) post-reintroduction on amphibian abundance and diversity in a lentic environment’, The Glasgow Naturalist, 28(2). Available at: https://doi.org/10.37208/tgn28224.