Beavers as ecosystem engineers - A review of their positive and negative effects

Abstract

The paper reviews the environmental activity of beavers (Castor fiber L. and Castor canadensis L.) and their impact on different aspects of the environment. Beavers inhabit almost all climatic zones but are most abundant in Russia, USA, and Canada. Beavers' ecosystem engineering activities include building dams and creating ponds. The dams provoke hydrological alteration, soil overwetting, changes in local micro- and nanorelief. The water stagnation in beaver ponds below dams results in lack of oxygen, a high carbon concentration, and the death of many aquatic organisms. The flooding water above the dam causes vegetation death due to overwetting and at the same time a rise in the biodiversity of water organisms. This paper includes original data gathered by Tomsk State University on lack of oxygen and subsequent fish death in dammed ponds. All environmental changes are cumulative and have strong contextual dependence. The beavers' environmental activity has positive and negative consequences.