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Habitat dynamics of beaver (Castor canadensis) at two spatial scales
Terho Hyvönen & Petri Nummi
Habitat dynamics of the Canadian beaver (Castor canadensis) were studied in a boreal forest landscape at two scales: the beaver pond level and the landscape level in southern Finland. To explore the changes in tree species composition due to beaver browsing and flooding, six abandoned beaver ponds were sampled (altogether 537 sample plots). For habitat dynamics at the landscape scale, the variation in the flooded area and the number of active beaver colonies were recorded over 18 years (1980-1998). At the pond level, flooding appeared to effect more rapid and more pronounced changes in woody growth production than browsing. Coniferous trees were particularly susceptible to flooding, and deciduous trees were more susceptible to browsing. Deciduous trees dominated during succession following a flood. At the landscape level, mean occupation time of colony site was found to be short (2.6 years) and the mean area of beaver impoundments was small (0.14 % of the total area). Re-colonization of habitats occurred on average nine years after previous abandonment. A reason for the short occupation time may have been the scarcity of food. The results suggest that both browsing and flooding should be considered when studying the dynamics of woody growth used by beavers.
Key words: beaver, boreal forest, Castor canadensis, disturbance dynamics, landscape ecology