|Forest Investment Account|
|Abstract of FIA Project 6080009|
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Study to assess the efficacy of ground beetles (Coleoptera: Carabidae) as ecological indicators in two variable-retention experimental sites: year 2 final report
|Author(s): Pearsall, Isobel A.||Imprint: Nanaimo, B.C. : Pearsall Ecological Consulting, 2003||Subject: Forest Investment Account (FIA), Coleoptera, Effects of logging on, Variable retention harvesting, Adaptive management||Series: Forest Investment Account (FIA) - Land Base Investment Program|
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 30% site, and the forest specialist, Scaphinotus angusticollis, was more abundant in the control than the other sites, but was second most abundant in the 30% site. In general, the 5% and 10% dispersed retention treatments did not appear to differ from the clearcut in terms of beetle assemblage, diversity and evenness. The 30% site clustered slightly apart from the clearcut, 5% and 10% sites, and did appear to provide a more appropriate habitat for forest species such as Scaphinotus angusticollis and staphylinids than did the other retention treatments. Clearcut blocks generally had greater numbers of carabid species than the other blocks, and higher diversity, but reduced overall carabid abundance (at least at Tsitika). Species richness at Tsitika declined as the % retention increased, with lowest numbers overall in the control treatment. However, abundance of carabids was highest in the control site, due to large catches of S. angusticollis. At Stillwater, species richness was similar among the clearcut, 5% and 10% treatments. Here, highest diversity was found in the 30% site, followed by the clearcut. Page 6 of 6 In general, the clearcut blocks at both sites, but particularly at Stillwater, were typified by containing invasive and winged species such as Notiophilus sylvaticus, Amara spp., Bembidion spp., Harpalus spp., Loricera decempunctata and Synuchus impunctatus and very few of the forest species. Most of these species were not found in the control sites. By-catch may be very useful, particularly catches of arachnids, crickets, millipedes and staphylinids, as clear patterns were evident among the different sites. Crickets and spiders were most abundant in cut blocks, whereas staphylinids and millipedes were most common in the control blocks. Most other by-catch was too rarely caught to be very informative. In summary, group retention harvesting appeared to be an effective method for preservation of forest specialist species in a site, at least in the short-term. One-year postharvest, forest specialists were similarly abundant in all group retention patches as in the original old-growth control at Tsitika. Forest specialists also were found in higher abundance in the cut matrix surrounding patches than in the traditional clearcut. Thus patches appear to serve as source areas for these species, which immigrate into the cutover areas. Dispersed retention harvesting was not as effective at preservation of forest specialists as group retention, and the 5% and 10% dispersed retention sites were functionally similar to a clearcut in terms of carabid captures. At a 30% level of tree retention, there was some impact on carabid assemblages, and this treatment was more similar to the control than were the other treatments. Future monitoring will be vital, to examine how the carabid assemblages change over time in patches, surrounding matrices, and in the dispersed blocks. At this time, the direction of carabid species succession is uncertain, since we do not know the possible extent of competitive interactions and whether the size of patches is adequate for long-term survival of beetles. Pitfall trapping was cost-effective and highly efficient at catching small and large beetles. The most abundant species were very easy to identify and sample sizes were adequate for statistical analysis. The carabid beetles as a group were highly sensitive to harvesting methods, and the results of this study indicated clearly that carabid beetles would be an ideal focal species to be used in forest biodiversity and adaptive management studies of this nature.
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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Updated August 02, 2006
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