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Indicators of biodiversity within aspen stands of the Interior Douglas-fir zone
Oaten, Dustin K.
How does trembling aspen (Populus tremuloides) contribute to biodiversity within dry interior forest stands of British Columbia? Assessments of biodiversity, including species richness and community assemblages, should be a major consideration in determining the different levels of forest harvesting that occur across landscapes composed of different forest types. Tolko Industries Ltd. is one of the forest companies in British Columbia using measures of biodiversity and species richness in their land management process. Much of this work is focused within their Tree Farm License (TFL) 49 located near Kelowna, British Columbia, Canada. Preliminary work, within the TFL has suggested that the Interior Douglas-fir (IDF) biogeoclimatic zone should be given a relatively high conservation priority due to a high degree of species diversity as compared to other forest types (Hebert 2005). To this end, current forest retention practices by the company have focused on maintaining this forest type. However, the IDF zone is far from being a homogenous forest type: most patches are dominated by Douglas-fir (Pseudotsuga menziesii), but a smaller amount may be composed primarily of trembling aspen (Populus tremuloides), or a mixture of these and other tree species. Understanding the relative importance of these different habitats within the IDF is one of the next crucial steps in the overall forest management process. The trembling aspen component of IDF forests is of particular interest as this stand type has been shown elsewhere to have relatively high biotic diversity, compared to other forest types (Griffiths-Kyle and Beier 2002). However, it is unclear as to how trembling aspen contributes to overall biodiversity within BC?s IDF stands. There is also concern that the aspen component within North American forests is being significantly reduced by human activities, poor seedbed conditions and increased herbivory from ungulates and cattle (White et al. 1998). Indeed, within the Tolko TFL, less than 5% of the IDF is considered to be aspen-dominated. Because of the rarity of these stands, and because they appear threatened by anthropogenic influence, it is important that we further our understanding of their contribution to biodiversity across the landscape. A full assessment of the biodiversity of any habitat type is an extremely large if not impossible undertaking (Pearson 1994). Because of logistics, and the need to initiate a short-term project with achievable goals, we selected an initial suite of wildlife indicator species using information on relative home range size and dispersal ability, as well as the relative ease at which the animals may be monitored. For these reasons, we have selected carabid beetles, small mammals and cavity-nesting birds. In addition, these three groups of wildlife also have been touted as good choices of indicator species because their systematics are well known, they are relatively easy to sample, and their presence often indicates an overall degree of higher diversity (Pearce and Venier 2005, Rainio and Niemela 2003, and Mikusinski et al. 2001). During our first field season (2005), we conducted surveys of the carabid beetle, small mammal, and bird communities at 12 study sites (4 replicate stands of each of Douglas-fir leading, aspen leading, and mixed-wood) within IDFdk (Interior Douglas-fir, dry cool subzone) forests on Tolko?s tenured land base. Our general goals were and are two-fold: (1) to quantify the diversity patterns of the three indicator species across forest types and (2) to make recommendations towards the use of certain species as bioindicator species in a long-term biomonitoring project. Although we have not completed the analysis of all of the samples in the three taxa (particularly the beetles), preliminary results suggest consistently high species-richness value in the trembling aspen stands, compared to the Douglas-fir and mixed-wood stands. During the ensuing second year of this pro ...
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