Beavers have become synonymous with the recovery movement in the UK. Their widely publicized return is likely to have a profound impact on the landscape, say the authors of one study.
The Eurasian beaver, once a common sight throughout Europe, had almost completely disappeared by the end of the 16th century thanks to hunting and river modification for agriculture and engineering.
But beavers are making a comeback in the UK and several other countries. They have already been released into the wild in Scotland and into sections of closed rivers in England. Now expanding the the wild release of beavers in England is at stake.
Ecosystem recovery, increased biodiversity, protection against floods and improved water quality are some of the advantages of having beavers around. But reintroducing wild animals to the landscape will always involve trial and error, and understanding the potential consequences, both good and bad, is vital.
The beaver is a talented environmental engineer, capable of creating his own ecological niche, adapting perfectly to his environment, by building dams. These dams are made of materials that the beaver can carry or float, usually wood, stones, and mud, but also fence posts, crops from nearby fields, satellite dishes, and older children’s toys.
The prey creates a peaceful, aquatic home for beaver families to sleep, eat, and avoid predators. And the effects of dam construction extend outward, with the potential to transform entire ecosystems.
Our review Beaver Strike Considers evidence from across Europe and North America, where wild beaver populations have expanded since around the 1950s.
There is clear evidence that beaver dams increase water storage in river landscapes by creating more ponds and wetlands, as well as raising groundwater levels. This could help rivers, and their inhabitants, cope with increasingly common extreme weather conditions, such as floods and droughts.
Beavers are gifted environmental engineers who use trees to build dams. Image: Fietzfotos
If you observe beaver dams in the wild, the water often gets very close to the top of the dams, suggesting that they might not be of much help in a flood. Nevertheless, some studies they are finding that beaver dams can reduce flood peaks, likely by diverting water into floodplains and slowing downstream flow. However, we do not know if beaver dams reliably reduce floods of different sizes, and it would be unwise to assume that they are always capable of protecting downstream structures.
The good news is that it appears that all the additional water supply could help supplement rivers during dry spells and act as critical refuges for fish, amphibians, insects and birds during droughts.
Beavers have an important role to play in regeneration efforts
Beaver dams increase the time it takes for things carried by rivers to move downstream. In some cases, this can help slow the spread of pollutants like nitrates and phosphates, commonly used in fertilizers, which can harm fish and damage water quality.
The impact of beavers on phosphates is unclear, with so many studies find phosphorus concentrations increasing downstream of beaver dams such as those encountering a decrease or no change. But beavers seem especially adept at removing nitrates – a welcome skill, as high nitrate concentrations in drinking water could endanger child’s Health.
All that water storage means beavers create a wonderful mosaic of calm, slow, fast-moving aquatic habitats. In particular, they increase the biodiversity of river valleys, for example, helping macroinvertebrates like worms and snails, key to healthy food chains, to thrive.
By damming rivers, beavers create habitats for other species. Image: Duernsteiner
The beaver party can leave anything from swamps or bogs to wet floodplain forests and drier grassland meadows that develop in its wake. This gives beavers an important role in regeneration efforts.
But nuance is key here. The evidence for the impacts of beaver dams on river valley fish populations and vegetation, for example, is highly mixed. Because they are such great agents of disturbance, beavers promote plants that germinate quickly, such as woody shrubs and grasses.
While this can reduce forest cover and help some invasive plants, over time it can also help create valleys with a much richer mosaic of plant life. So while the presence of beavers is likely to bring benefits, more research is needed to clarify precisely how beavers change ecosystems.
Net zero carbon
Beavers are excellent at trapping carbon by storing organic matter as plant debris in slow-flowing ponds. However, this also means that beaver ponds can be sources of greenhouse gases, such as CO2 and methane, that contribute to the greenhouse effect. This led an author wondering “if the beaver is aware that the greenhouse effect will reduce the demand for fur coats”.
Can beavers still be useful in achieving net zero carbon? The short-term answer is probably yes, as beaver activities appear to trap more carbon than release it.
However, the long-term results are less clear, as the amount of carbon beavers keep in the ground depends on how willing they are to stay in a river valley and how willing we are to leave them. A clearer understanding of where beavers fit within the carbon cycle of river systems is needed if we are to make better use of their carbon sequestration abilities.
Research suggests that beavers could help landscapes adapt to more extreme weather conditions. Image: K Mitch Hodge
Beavers are returning to landscapes under human rule, the very thing that originally drove them from vast swaths of European river systems.
In the UK, this means that they will lack natural predators and may compete with cows and sheep for food, possibly resulting in unstable wild population trajectories.
Although good data About long-term beaver activity is available in Sweden, Norway and Switzerland, our different climate and landscapes mean that it is difficult to make a simple comparison.
Using beavers in rebuilding can be incredibly profitable
Using beavers in rebuilding can be incredibly profitable, as dam construction and the biodiversity benefits that flow from it are largely done for free. But we must be tolerant of uncertainty about where and when they choose to do their work.
Working with wild animals, who probably don’t share our priorities, is always an unpredictable process. The expansion of beavers in the wild has a bright future as long as we can manage the expectations of the people who own and use land inhabited by beavers.
Joshua Larsen is Senior Lecturer in Water Sciences at the University of Birmingham. Annegret Larsen is an assistant professor of geography at Wageningen University, the Netherlands.
Lead image: David Parkyn / Cornwall Wildlife Trust