Beavers and Ecosystem Services

European beavers build dam systems in sub-optimal habitat to create an environment which suits their living purposes. In the upper reaches of wooded river systems beaver dam systems are significant hydrological features which can modify the water table on both a local and catchment level. They are commonly built in water courses of less than 3 m in breath which are too shallow to afford suitable living habitat (Coles.2006). The typical living environment of a beaver family in a headwater stream system will comprise a significant complex of impoundments of varying heights with water flowing from one to another either over the land surface or through natural channel systems.

Beaver dams play a role in slowing water run-off during periods of flooding and can help sustain flows during periods of low water. This effect is more pronounced on small upland streams than flood plain wetlands (Johnston & Naiman, 1987) and has been mimicked by human engineers to successfully offset flooding in the Northumberland village of Belford. Beaver dam complexes increase water retention times and greatly enhance the absorption capacity of wider landscapes. Although the amount of water held above a dam will vary according to local conditions studies in Brittany show that on low gradient streams this can be more than 6 times the volume of an un-dammed stream. On steeper gradients it can be up to 35 times the volume (Coles.2006).  Beaver dams are flexible structures which contain sloping ramps of organic material on their water side. These features which arise as a result of both silt deposition and beaver activity ensure that maintained dams generally remain in place in flood conditions with water flowing over the top. Where dams are abandoned their degradation is slow and unlikely to cause particular problems.

Beaver generated landscapes have been linked to the significant amelioration of diffuse pollution from human activities. Accumulation of organic matter as a result of beaver activity can be very important to phosphorus and nitrogen dynamics within water bodies (Devito & Dillon, 1993). The sediments which leach from surrounding landscapes are contained within beaver ponds and accumulate over time. In intensively farmed landscapes these silt particles can attach to phosphate based fertiliser molecules by electrolysis. Where the silts are contained the phosphates are subsequently locked into the surrounding environment. The open nature of beaver generated environments commonly results in a vigorous associated community of vascular plants. Where agricultural nitrates leech into these environments they are rapidly absorbed.  It has been estimated from studies in Bavaria that up to 28kg of soluble nitrates can be captured through the annual habitat creation activity of a single beaver ( ). In both North America and Europe beavers have been specifically introduced into some river systems to combat environmental degradation and pollution. This potential aspect of beaver related ecosystem service provision is of national financial significance.

Ref.  Coles, B., 2006. Beavers in Britain’s Past. Oxbow Books, Oxford, UK.