Beaver as Engineers: Influences on Biotic and Abiotic Characteristics of Drainage Basins

Summary

We review how beaver (Castor canadensis) affect ecosystem states and processes (e.g., biogeochemical cycles, nutrient retention, geomorphology, biodiversity, community dynamics, and structural complexity) by altering the physical properties of stream channels and riparian forests. Beaver influence the distribution, standing stocks, and availability of chemical elements by changing the hydrology; alter stream geomorphology as dams trap sediments; and change microclimates as water surface area increases and with the opening of previously closed forest canopies. Beaver also increase plant, vertebrate, and invertebrate diversity and biomass, and also alter the successional dynamics of riparian communities. Both abiotic and biotic influences are spatially extensive and long-lasting, affecting system level patterns and processes for decades to centuries. We conclude that ecosystem-level states and processes can be altered radically by the population dynamics of certain species such as beaver and that the magnitude and diversity of animal influence on ecosystems has been underestimated.