1. Beavers create habitat diversity across catchment landscapes by impounding small streams. This increased habitat diversity leads to increased species richness of plants and animals in small streams. As managers work to balance conflicting management goals (e.g. protection of timber and human structures versus maintenance of biological diversity) the influence of beaver population management practices on habitat availability needs to be assessed. Two questions of initial concern are: (i) how do different levels of management influence the availability of beaver created habitats and (ii) do relationships developed in one region apply to other regions? 2. To address these questions, historical aerial photography was used to determine the extent and rate of impoundment of streams by beavers Castor canadensis over a 77 000 ha south-eastern North American landscape during a 40-year period of beaver population recovery. Between 1950 and 1983, beaver populations were protected from trapping and hunting. From 1983 to the present, beaver numbers were reduced by fatal trapping, to protect roads, railroads and timber. Trapped beavers were assigned to specific colonies associated with beaver-created patches in the landscape, and growth rates and size after management of individual patches receiving different levels of management were compared. Results from this study were also compared with previous studies conducted in Minnesota, USA. 3. Growth rate, patch size following management and the composition of habitat types within patches were not related to management activity, suggesting that the levels of management used in this study did not influence the temporal dynamics of beaver-created patches. The extent and rate of beaver impoundment on the southeastern Upper Coastal Plain of North America was less than that reported from central North American landscapes over comparable periods. 4. These results have the following implications for management: (i) management activities should be monitored on a regional basis; (ii) conflicting beaver population management goals should be addressed, evaluated and balanced; and (iii) beavers do not present a threat to flowing-water species in south-eastern North America and need not be controlled for this reason.
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文章 : 英语