Pitfall trapping was used to examine the epigaeic (ground-dwelling) carabid fauna in two experimental coastal western hemlock stands, one on the mainland of BC, at Powell River, and one at Tsitika, Northern Vancouver Island, between May and October 2002. At the Stillwater site the treatments are clearcut, 2nd-growth, 5%, 10% and 30% dispersed retention. At the Tsitika site, they are clearcut, old-growth, 10%, 20% and 30% group retention. Both sites were harvested during 2001, Stillwater during the fall 2001 whereas the Tsitika site was harvested in the late summer. The main objective was to determine which VR method (group or dispersed) was most effective in terms of preservation of forest specialist carabids. For Tsitika, I wanted to examine whether patches contained similar beetle assemblages as found in original old growth, and to assess how the level of retention affected species composition, diversity and abundance of carabids within the cut matrices. I also wished to determine whether carabid beetles showed a marked response to patch edges. For Stillwater, I proposed to assess whether the levels of tree retention were high enough to provide suitable habitat for the original species assemblages. Carabid beetles were trapped using 15 pairs of pitfall traps in each of the five Stillwater treatments, and in the old-growth control and clearcut treatments at Tsitika. Sampling design varied in the remaining three group retention treatments at Tsitika, with traps placed within patches (groups of leave trees), at the edge of patches, and in the cut matrix surrounding patches Carabid beetles were identified to family or genus, and the by-catch was identified only to order. A total of 14 and 18 carabid species and 4727 and 5053 individuals were collected from the Tsitika and Stillwater experimental sites, respectively. At the Tsitika site, the most abundant species captured was Scaphinotus angusticollis (Fischer von Waldheim), whereas at the Stillwater site, the most abundant species caught was Synuchus impunctatus Say, followed closely by Scaphinotus angusticollis. There were more invasive species recorded at the Stillwater site, which could be a function of the different levels of disturbance at these two experimental sites. At both sites, different species showed different activity periods. Many of these species could be separated based on habitat preference into the following categories: forest specialists Page 5 of 5 (e.g. S. angusticollis, Z. matthewsii, P. crenicollis), generalists (e.g. P. neobrunneus, P. lama, P. herculaneus) and disturbance specialists (e.g. Synuchus impunctatus, Notiophilus sylvaticus). Carabid assemblages were significantly different among the different treatments at Tsitika. One year after forest harvesting, patches within all group retention treatments were able to retain forest specialist beetles equally well as the old-growth control. The cut matrices around patches did harbour a slightly different beetle assemblage than the clearcut, and contained greater numbers of some of the forest specialists, namely, Scaphinotus angusticollis, and Pterostichus crenicollis. Cluster analysis of the total catch in the different treatments at Tsitika showed that, overall, patch retention sites were more similar to the control site than the clearcut. When we examined the clusters at a finer resolution, at the specific location of the traps, we found that the traps placed in cut matrices around patches all clustered with the clearcut, whereas the patch traps clustered with the control. Edge traps and traps placed close to the edge in the 30% treatment clustered somewhere in between. The clusters formed indicated that the matrices around patches were affected by the level of retention. Specifically, the greater the level of retention, the higher the level of dissimilarity of a patch from the clearcut. At Stillwater, the disturbance specialist, Synuchus impunctatus, was more abundant in cut sites than the control and
Pearsall, Isobel A.. 2003. Study to assess the efficacy of ground beetles (Coleoptera: Carabidae) as ecological indicators in two variable-retention experimental sites: year 2 final report. Forest Investment Account. Forest Investment Account Report
Topic: FLNRORD Research Program
Keywords: carabid beetles, pitfall trapping, coastal western hemlock, adaptive management, variable-retention harvesting, dispersed retention, group retention, old-growth, clearcut, indicator species
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