Beaver (Castor canadensis Kuhl) colonization, wetland community change and resilience: Bruce Peninsula National Park

Beaver (Castor canadensis Kuhl, 1820) are an agent of disturbance that create and sustain a diversity of wetlands and wetland processes within Bruce Peninsula National Park (BPNP) and environs. The foci of this study were to: i) estimate changes in the densities of beaver colonies during a prolonged period of landscape colonization (ie., 1938--2009); ii) characterize landscape community changes resulting from patterns of colonization, and, iii) discuss the implications for the resilience and sustainability of wetlands as a result of these landscape changes. Historically beaver were abundant in the region but were likely extirpated during the fur trade as early as the 18th Century. In the 1950's beaver began to recolonize the study area and dramatically change the quantity, kinds, and spatial diversity of wetlands across the landscape. Between 1970 and 2009 the density of beaver colonies, measured as the number of active beaver colonies per kilometre of stream length, increased threefold from 0.22 to 0.68. The number of wetlands created or influenced by beaver activities increased from 45 in 1967 to 603 in 2006. Wetland surface area increased from 1082 hectares to 1767 hectares, or 63%. Wetland diversity (patch richness and evenness) was measured using Shannon's and Simpson's diversity indices, and increased from 0.41 to 0.60 and 0.14 to 0.23 respectively. Beaver activities may enhance wetland resilience to large scale disturbance, such as climate change, by sustaining processes that increase wetland community response diversity. However, increased wetland resilience caused by beaver activities may decrease the ecological integrity of other desirable ecosystem states such as cold water streams. Further, conflicts between beaver and human infrastructure within and adjacent to the park will continue as long as beaver are present.