Effects of timber harvesting and forest fire on the ecological diversity of carabid beetles (Coleoptera: Carabidae) in aspen dominated mixedwood forests (Populus tremuloides Michx) in western Manitoba
Shaddock, Jeffrey Kenneth
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Carabid beetles (Coleoptera: Carabidae) were sampled in burned and timber harvested mixedwood forests to determine the effects of disturbance type on carabid beetle communities. Three forest age classes within each disturbance type were compared: sites burned in 1980, 1961 and 1932; and sites harvested in 1995, 1980 and 1967. A total of 13873 carabid beetles, representing 51 species, were caught using pitfall traps during varying summer sampling periods in 2000, 2001 and 2002. The catch frequency of carabid beetles was generally higher in burned forests compared to harvested forests, although there was a high degree of variation within burned forests. The differences in catch frequency between disturbance types were due primarily to high catch frequencies of forest generalist carabid beetle species, such as Platynus decentis (Say), Pterostichus adstrictus Eschscholtz, and Synuchus impunctatus (Say) in burned forests. There were no significant differences detected between burned and timber harvested sites in the number of species of carabid beetles, log a diversity, evenness, or the Berger-Parker (dominance) index. The Jaccard index of B diversity indicated that the differences between the carabid beetle communities of burned and harvested sites were greatest in the most recently disturbed sites, and least in older sites. Each disturbance resulted in an initial increase in the number of species of carabid beetles that are known to inhabit open areas, such as Agonum cupreum Dejean, Agonum cupripenne Say, and Cymindis cribricollis Dejean; and an initial decline in the catch frequency of forest generalist species. It is unclear whether these effects are caused by timber harvesting or are normal for any large-scale disturbance. Forest generalist carabid beetle species were slower to return to harvested sites than to burned sites. The catch frequency of carabid beetles was highest in May/June, steadily declined over the collection period, and was lowest in August. Older forests had significantly higher catch frequencies of carabid beetles and lower levels of diversity than more recently disturbed forests, possibly due to differences in the quantity of leaf litter and coarse woody debris.