"Beavers are vegetarians and feed on aquatic plants and woody shrubs. They are exceptional ecosystem engineers"
The Eurasian beaver (Castor fiber) is one of the largest living species of rodent. Long prized and hunted for its fur and “castoreum” or scent gland product, which was said to have medicinal properties, its numbers dwindled to near extinction with just 1,200 individuals by 1900. Beavers disappeared from the British landscape in the 16th century, the last reference dating to 1526. Now protected, it recovered in Europe to a population of about 639,000 by 2003 (Nolet & Rosell 1998) but has been absent from Britain until recent years.
Beavers are vegetarians and feed on aquatic plants and woody shrubs. They are exceptional ecosystem engineers; using iron-coated incisors that never stop growing, beavers coppice, strip and even fell trees to provide wood with which to build lodges, dams and canals that create interconnected networks of water pools. The pools created by the dams serve several functions: for example, to provide protection from their natural predators (in their historical landscape these would include bears, wolves, and wolverines), to create favourable conditions for growth of food plants, to enable an underwater entrance to their den within their lodge, and even to provide safe space in which to teachtheir young (known as kits) to swim.
Because of this capacity to change the landscape, beavers can increase wetland habitat by 50% (Hood & Larson 2014). This has amazing knock-on effects for invertebrates and amphibians, which in turn benefits the predators that feed on these species (e.g. fish, waterbirds) in a process known as a trophic cascade. Beavers’ natural coppicing activity stimulates tree regrowth and prevents domination by any one tree species. In Devon, areas cleared by beavers have begun to re-establish a rare environment called “culm grassland” which provides habitat for rare and specialized species such as the Marsh Fritillary. All of this makes the beaver a keystone species.
Beavers are classic providers of “ecosystem services”. For example, beavers provide a natural form of flood defence. Catchments containing beaver-created pond networks retain vast amounts of water in tributaries and side-streams compared to areas without beavers – water that might otherwise cause downstream flooding. Instead, this water is released more slowly into the main river. This “natural flood defence” is completely free and self-perpetuating, and could potentially achieve similar effects as our current flood defences, which are enormously costly.
Additionally, slower throughflow of water means insoluble pollutants such as fertilizers are deposited in the beaver pools – a natural filter that means less nitrogen and phosphorus leaves the site, so less is transmitted downstream.
Monitoring of beaver activity in Devon has even detected sphagnum moss beginning to become established, which could eventually create a peat bog environment, an area of massive biodiversity and a major carbon sink.
Beavers have many other effects upon their ecosystems that benefit humans – for example:
- Felling trees opens up patches of forest, encouraging more diverse flora, and increases dead-wood nesting sites for birds and bats
- Regulation of stream flow
- Raised water table, creating new wetland habitat
- Increased sediment removal from water
- Reduction in erosion and water turbidity
- Increased nutrient cycling
- Increased connectivity between parts of the ecosystem (e.g. surface and groundwater, channel and floodplain)
- Improved capacity to neutralize acidity
- Retention of carbon and pollutants and purification of water
According to The Millennium Ecosystem Assessment, ecotourism is another example of an ecosystem service. In the beavers’ case, it has been estimated that releasing beavers into the wild may inject millions into local economies via attracting tourists.
For more information about beavers in England go to: http://beaversinengland.com