Wetland vegetation dynamics in response to beaver (castor canadensis) activity at multiple scales

Beaver activity is often considered a hydrologic disturbance that resets succession. We determined how beaver impoundment and wetland size and water chemistry affected the vegetation and succession of 25 beaver meadows and ponds using the space-for-time substitution. We used aerial photography to investigate whether a large 1947 fire in one region of Mount Desert Island, Maine, led to differences in regional temporal fluctuations in beaver pond occupancy over 60 y and determined whether these fluctuations led to different regional distributions of beaver wetland plant community types. Cluster analysis segregated 4 wetland groups: sedge meadows, sedge fens, shrub fens, and forested fens, which segregated along gradients of time since dam collapse, water chemistry, and wetland size. Beaver did not affect water chemistry or wetland size. Pond vegetation was a function of community type prior to flooding, water chemistry, and geomorphic setting. The successional model consisted of 2 separate cycles, corresponding to differences in pH and peat accumulations. Beaver pond creation rates differed in burned and unburned regions over time. Due to increased activity in the burned region, there was a different distribution of plant communities between the regions. Wetlands abandoned at the peak of beaver pond creation in 1979 were flooded for shorter durations, resulting in forested fen vegetation.. Beaver activity created different successional cycles within different water chemistry and geomorphic contexts. Water chemistry, wetland size, and initial wetland state, which primarily determined non-forested wetland type, were not influenced by beaver.