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Carabid beetles as indicators of biodiversity for varialbe retention harvesting
Pearsall, Isobel A.
This proposed project contributes to knowledge gaps associated with Sustainability Program Theme 3, topic 3.1, Indicators and monitoring systems. Under the Coast Forest Strategy, Weyerhaeuser?s adaptive management program is examining the effectiveness of retention systems and stewardship zoning in maintaining the forest attributes necessary to sustain biodiversity and essential ecosystem functions. Biological processes are difficult to measure directly, but the adaptive management program has identified a range of indicator organisms and structures that might prove useful in assessing ecosystem health. Ideally, indicator organisms are individual species, groups of species or structures that perform critical ecosystem functions or are particularly sensitive to disturbances. Work done 2001-2004 has clearly identified that carabid beetles are highly sensitive indicator species, with significantly different communities in clearcut, immature and mature forests. We have identified disturbance specialists, generalists, forest and old-growth specialists. Our work has shown that the responses by carabids are sensitive at small enough spatial and temporal scales such that they may be used to indicate edge conditions, and to assess how quickly sites recover and re-establish typical old-growth communities. Past studies have included examination of carabid communities in operational forest blocks of different ages from a number of site series throughout Vancouver Island, a comparison of carabid communities in two of Weyerhaeuser?s experimental variable retention (VR) sites (group versus dispersed retention), and an examination of carabid communities in some of the oldest operational VR sites on West Vancouver Island. Our studies have established the change in carabid communities with forest age, and we have begun to develop a VR type and level response curve, but we have not yet established a response curve for carabid beetles to the size of retained patches. Results of work done in experimental group VR blocks on North Vancouver Island during 2002 indicated that patches are able to retain the original old-growth forest communities of beetles, at least in the short term. Increasing the level of tree retention resulted in improved retention of forest beetle species. However, patches in 30% retention treatments were generally larger than patches in 20% or 10% retention, and thus % tree retention, size of patches and proximity of patches were confounded. Recent work in West Vancouver Island during 2004 showed that operationally harvested VR patches were unable to retain the original forest species. We suggest that this is related to the size of the patches, as the operational patches were generally much smaller than those set up in the experimental sites. It is generally understood that there may be threshold patch sizes, below which immigration and reproduction would be too low to maintain the patches as adequate source areas for forest carabid species. No work has yet been carried out to address this in the Pacific Northwest. In 2005-2006, we propose to make a detailed examination of the effect of patch size on carabid communities. We wish to work in two group size experimental VR sites: these study sites are part of a series of Variable Retention Adaptive Management (VRAM) experiments that are the foundation of Weyerhaeuser?s AM program. Each VRAM site was installed with random allocation of treatments. The sites were chosen to be as uniform as possible in timber type, site series and topographic features. The Port McNeill (to be studied in 2005) and the West Island (2006) group size experiments are made up of 5 treatments: clearcut, uncut, and three variable retention treatments (dispersed, small groups and large groups) each with a minimum size of 20ha. In addition, we wish to work in 3 operational VR large patch sites and 3 similar sites with small patches in West Vancouver Island and North Island during 2005 and 2006, respec ...
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Executive Summary
Final Report

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