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Responses of ground beetle (Coleoptera: carabidae_ species and assemblages to forest practices in the interior Douglas-fir forests of British Columbia Jarrett, Jeffrey R.

Abstract

The Opax Mountain Silvicultural Systems Project was initiated in 1993 to address concerns over the widespread use of uniform stand-level partial cutting in the dry Douglas-fir forests of BC's Southern Interior. Various alternative harvesting methods were tested, and responses of several wildlife indicator groups were measured. The following study examined responses of ground beetle (Coleoptera: Carabidae) species and assemblages using a variety of diversity indices. The alternative harvesting practices were: 1) 20% and 2) 50% removal using individual-tree selection (I.T.S.); 3) 20% and 4) 50% removal using patch-cuts of 0.1, 0.4, and 1.6 ha; 5) 35% removal using 50% I.T.S. on 70% of the treatment area, leaving 30% in reserves; and 6) uncut controls. Results showed that species richness, evenness, and heterogeneity were greater in logged treatments. However, only in the heterogeneity values of Mud Lake assemblages (1996/1997) was there a general increase in diversity that accompanied either an increase in percent forest removal, or a change from control to I.T.S. to patch-cut methods of harvest. Other than taxonomic distinctness, no other distinctness index decreased in logged treatments, and none of the distinctness indices displayed any trend in decreasing with an increasing percentage of forest removal, or to a change from control to I.T.S. to patch-cut methods of harvest. In multivariate analysis, carabid assemblages within each site (Mud Lake and Opax Mountain.) showed patch-cut treatments to cluster/map together and I.T.S. treatments to cluster/map together. Dominance structure tables generally showed that carabid assemblages from lower percent removal treatments, as well as from I.T.S. methods, to most resemble dominance structure found in control blocks. Species analysis showed that carabid species respond to logging in a variety of ways. Because every method of harvest evidently benefited some species at the expense of others, no one treatment appears sufficient for the whole carabid community. Instead, a mix of harvesting methods that maintained the greatest number of all native forest species, including sensitive species, and over an indefinite period of time, would be the best strategy for the preservation of carabid biodiversity.

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