Beaver impacts
Understanding The
Ecosystem Engineer
How beaver activities benefit biodiversity but can bring challenges.
Beaver Foraging
They have a preference for tree species with soft wood such as willow, birch, alder, aspen, ash, poplar and hazel but what they will eat is relative to what is available.
Foraging by beavers brings a range of biodiversity benefits. Selective feeding and tree felling opens up woodland canopy, allowing more light to reach the ground, enabling the regeneration of understorey vegetation, increasing the diversity of plant, lichen and bryophyte species, and improves feeding opportunities for insectivorous birds and bats.
Opening up of the canopy also results in increased light hitting water-bodies which has been shown to increase breeding in amphibians and can raise the water temperature leading to an increase in the number of aquatic invertebrates but increased temperatures may favour non-salmonid species which have a greater tolerance for lower oxygen levels in the water.
The increase in standing and felled deadwood on land and in water from beaver foraging has also been shown to provide valuable habitat for fungi, invertebrates and beetles which act as a food source for many species of amphibians, birds and fish. Deadwood both on land and in water provides shelter for many species from their predators, along with breeding sites. Finally deadwood in water increases scour resulting in more dynamic and naturalisation of river systems.
Tree felling can be undesirable and hazardous in some locations. Sensitive trees in the immediate riparian zone may require mitigation to prevent them from being felled. Find out how you can protect trees from beaver browsing here or how making space for beavers can also provide a solution.”
Beaver damming
Beavers build dams to increase and maintain the water depth in their territory which protects them from predation, opens up new areas for browsing and keeps the entrances to their multiple burrows and lodges submerged.
In freshwater habitats, with wide water courses and/or where water depth is naturally sufficient such as the main channel of a river or a loch, beavers are unlikely to builds dams.
Water levels at a site is the main decisive factor in triggering dam building activity, not the sound of running water as is often reported.
Dam building tends to occur in late summer and autumn, but beavers repair and build dams throughout the year whenever necessary.
Beavers will utilise natural and artificial features in their territory when dam-building such as narrowing of a channel, large rocks, culverts, or fallen trees already in place. Dam placement and building technique will vary according to the hydrology of the site.
Dam construction will typically begin with a beaver depositing a base layer of mud, stones and vegetation. Larger sticks are then placed on the structure pointing upstream and weighed down with more mud and stones. Finally vegetation and mud will be used to plug any remaining gaps. Beavers have been found to skillfully integrate all sorts of available materials into their leaky structures without tree felling.
Beaver dams provide a host of benefits for beavers and people. The creation of new complex wetland behind a dam provides new habitat for a diverse range of plant and invertebrate species. This in turn provides breeding, foraging and shelter opportunities for a range of birds, bats, mammals and amphibians.
By impounding water and slowly releasing it through leaky structures beaver damming activity makes river systems more resilient to drought by increasing base flows in dry periods and decreasing the risk of flooding downstream during high flows.
Research has even shown that by impounding water beaver created wetlands keep plants green and soil wet during droughts and even wildfires providing a refuge for wildlife which may even help limit fire spread.
Beaver damming can cause localised flooding problems for people, but any land-manager tackling a beaver damming conflict should seek professional advice. Find out the options available to mitigate beaver damming issues and who to contact to get support here.
Burrowing and Lodge Building
Lodges and burrows act as the focal point of a beaver’s territory. They both provide a safe space where beavers can rest and breed protected from water and predators. Lodges and burrows are a protected feature under current legislation and cannot be disturbed or damaged without the appropriate licence.
Both lodges and burrows normally contain an entrance tunnel starting underwater, a feeding chamber at water level and a sleeping chamber above water level.
Whether a beaver digs a burrow or builds a lodge is based on water depth and bank characteristics of their territory. In wetlands or water bodies with very low profile banks, beavers tend to build upwards, creating very visible lodges. In water bodies with deep water and steeper banks, beavers may live entirely in a range of burrows.
Most beavers have a mixture of burrows and bank lodges in their territory, with a bank lodge built around a chamber of burrows with a visible cap on top.
Burrowing by beavers can create weakness in flood banks, increasing erosion and resulting in more dynamic river systems but it can be a health & safety risk as burrows can collapse damaging or flooding nearby property or machinery.
Any land-manager tackling a beaver burrowing conflict should seek professional advice. Find out the options available to mitigate burrowing conflicts and who to contact to get support here.
This material was originally prepared for NatureScot as an objective review of the evidence around the effects of beavers.
