|Forest Investment Account (FIA) - Land Base Investment Program|
|FIA Project 6355001|
|Study to access ground beetles (Coleoptera: Carabidae) as ecological indicators in Weyerhaeuser's West Vancouver Island operational sites: year 4 final report|
|Project lead: Weyerhaeuser Company Ltd.|
|Author: Pearsall, Isobel A.|
|Imprint: Nanaimo, BC : The Author, 2005|
|Subject: Forest Investment Account (FIA), Coleoptera, British Columbia, Effects of logging on, Variable retention harvesting, Adaptive management|
|Series: Forest Investment Account (FIA) - Land Base Investment Program|
|During 2004, we examined the oldest operational VR that was available in West Vancouver Island. Prior work during 2002 had been carried out in two experimental VRAM (Variable Retention Adaptive Management) sites in Tsitika and Stillwater, and we had noted that group VR was apparently better able than dispersed VR to retain forest specialists, at least over the short term (one-year post-harvest). This year’s examination of older VR site allowed us to determine whether the same patterns held true 4-6 years post-harvest.|
A total of three group retention sites (G1, G2, G3) and three dispersed retention sites (D1, D2, D3) were chosen. The levels of retention in the six sites were G1- 10%, G2-16%, G3-34%, D1-12%, D2-18%, D3-38%. The sites were harvested 1998-2000. All sites were in the CWHxm except for the 34% group site G3 which was in the CWHvm1. We also set traps in second growth (O1) adjacent to site G3 as our control site. The original forests for all sites were similar in age (~61yrs) except for D1 and D2, which were a little older (88 years). All six sites were dominated by Douglas-fir (Pseudotsuga menziesii) and Western hemlock (Tsuga heterophylla). Ground vegetation was similar among sites.
Abundance of carabids caught in the operational VR sites during 2004 was much lower than in the three previous years of this study. There may be several reasons for this: either the catches were low because 2004 was a particularly dry year, or there was something inherent in the VR sites that resulted in low abundance. However, both the species assemblage and the abundances we saw in the 2nd growth control sampled during 2004 were similar to those found in other climax communities sampled over 2001-2003 and was dominated by three forest species S. angusticollis, P. crenicollis and Zacotus matthewsii. It would thus appear, that the low abundances seen during 2004 in the operational VR sites were related to how well these sites have retained carabid species, rather than to any specific difference about communities of West Vancouver Island, or to the particularly dry weather conditions of 2004. • Dispersed Retention sites in West Island four to six years post-harvest, showed very impoverished communities of carabid beetles in comparison to communities from the uncut forest. Not a single Zacotus matthewsi, a forest specialist, was present in any of the three dispersed retention sites sampled during 2004, and very low numbers of two other forest specialists, Scaphinotus angusticollis and Pterostichus crenicollis were caught.
Only the patches in the 34% Group Retention sites in West Island showed possible retention of the original communities associated with the uncut forest, and clustered more closely than the other treatments with the 2nd growth control in a cluster analysis. Although the other patches were able to retain some Scaphinotus angusticollis, Zacotus matthewsii and Pterostichus crenicollis, the mean catches of these species were generally much lower than in the control site. 5
Our results differed from previous years’ results, as we found greatest species richness in the 2nd growth control, followed by the group retention site, with lowest species richness in the dispersed retention sites. This pattern also held true for diversity and evenness measures. Prior work has consistently shown that highest diversity, evenness and species richness was generally associated with clearcuts, and the opposite pattern prevailed in forested sites. This was not the case during 2004, although we did find lower catches in the dispersed sites overall.
Overall, 4-6 years post-harvest, it appeared that these operational VR sites were not able to retain the original forest communities adequately. We did not sample in a traditional clearcut in West Island during 2004 however, so we are not able to compare whether there are differences among the matrices of the group retention sites, dispersed sites, and traditional 5 year-old clearcuts. It is possible that clearcut sites may have been ever more bereft in terms of carabid species richness and abundance, but we would need to do further work to determine this.
In general, our catches of species were too low and too variable to be able to find pronounced edge effects. In many cases, patches were very small, less than 50 m diameter, and in general, they were all dry and very poor in terms of vegetation. Using patches that are too small could account for the impoverished communities in the group sites. In the dispersed sites, even with a 38% level of retention, we still found a greatly impoverished community, made up of generalist species only, and almost completely lacking any forest specialists.
The year was particularly hot and dry. It is feasible that this affected the survivorship of carabids in the sites. The patches in the group retention sites were generally much smaller than those sampled during 2002 in the experimental VRAM (Variable Retention Adaptive Management) site at Tsitika. It will be important to focus on the effect of patch size in future studies, given that this may have impacted how well the patches in West Island retained forest specialists. Thus for future work we propose 1) to assess whether similar results are apparent at other locations such as North Island and South Vancouver Island, and 2) to assess more fully the effect of patch size and type on long-term retention of forest species.
|Final Report (1.8Mb)|
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Updated August 16, 2010
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