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The biodiversity of flying Coloptera associated with integrated past management of the Douglas-fir beetle (Dendroctonus pseudotsugae Hopkins) in interior Douglas-fir (Pseudotsuga menziesii Franco) Carson, Susanna Lynn

Abstract

Increasing forest management resulting from bark beetle attack in British Columbia's forests has created a need to assess the impact of single species management on local insect biodiversity. In the Fort St James Forest District, in central British Columbia, Douglas-fir (Pseudotsuga menziesii Franco) (Fd) grows at the northern limit of its North American range. At the district level the species is rare (representing 1% of timber stands), and in the early 1990's growing populations of the Douglas-fir beetle (Dendroctonus pseudotsuage Hopkins) threatened the loss of all mature Douglas-fir habitat in the district. In response to beetle populations and increasing management needs, forest managers initiated a 5-year operational research study on the impact of pheromone trapping and harvesting on flying beetle diversity. Beetle diversity was measured from pheromone baited and unbaited Lindgren funnel traps located in mature/old growth, beetle attacked, leading Fd habitat from preharvest, through 4/5th season postharvest conditions. Pheromone traps were baited with known Douglas-fir aggregation pheromones; frontalin, MCOL, and seudenol, and all traps were collected weekly or bimonthly through the duration of the seasonal Douglas-fir beetle flight (April/May through August/September) from 1994-1997. A total of 484,000 individuals, representing 625 identified species and recognisable taxonomic units (morphospecies), from 67 families were trapped in preharvest and postharvest baited and control sites. Whittaker plots indicate logarithmic species distributions for both pheromone-baited and control trap catches, although the rank position of species varied between treatment conditions and trapping year. Between pheromone-baited and control traps, under preharvest conditions, trap catch analysis resulted in significant differences (α = 0.05) for eight out of nine diversity indices including; Margalef's (d), Shannon-Weiner (H'₁₀), Brillouin, Fisher's (α), Pielou's (J), 1-Simpson's (1-D), Taxonomic diversity (δ), and Taxonomic distinctness (δ*) . Significant differences between baited and control data across all treatment years (preharvest, post 1, post 2, post 3, post 4/5) were observed for 6 out of 9 indices. Similarities observed in species richness (S) and Margalef's (d) measures are thought to be an artefact of low sampling effort. Changes observed in diversity and species abundance are thought to have resulted from the disproportionate trapping of an unknown number of non-target species by pheromone-baited traps relative to unbaited traps. Differences in diversity observed across harvest years occurred within the context of, and in addition to, a dynamic and changing species assemblage responding to harvesting and the resulting habitat change. The results suggest that the effect of single species management, in this circumstance, is not limited to the target organism and pheromone trapping along with harvesting as part of an IPM program can influence species composition at the community level.

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