Attack by bark beetles (Coleoptera : Scolytidae) following spacing of mature lodgepole pine (Pinaceae) stands

Variation in bark beetle attack following spacing of mature lodgepole pine stands in the East Kootenays of British Columbia was analyzed in relation to stand location (site), spacing treatment, and harvesting injury. Observations were made on three sites, each having three treatments: 4 × 4 m spacing, 5 × 5 m spacing, and untreated control. There was no statistically significant difference in the numbers of attacked trees among sites or treatments. However, in the spaced plots 94.3% of the attacked trees sustained harvesting injury or were located adjacent to skid trails. Dendroctonus valens LeConte was the dominant species attacking trees on the two drier sites, and Dendroctonus murrayanae Hopkins was the dominant species on the third site. There was no statistically significant variation in the percentage of attacked stumps among sites or spacing treatments. On average, 80.7% of the stumps were attacked; attacked stumps had larger diameters than unattacked stumps. Thirteen species of bark beetles were found attacking stumps. Hylurgops porosus LeConte was the most numerous species at all three sites. Based on the fit of the Michaelis–Menten equations to species accumulation curves, an estimated 76–90% of the number of species attacking stumps at the three sites were observed in bark samples. Margalef’s index of diversity for the two drier sites (Cranbrook = 1.15, Parson = 1.13) was nearly identical and higher than at the moist site (Elkford = 0.89). Pairs of sites had five to six species in common, and the Sorensen coefficient of similarity ranged from 0.52 to 0.71, indicating moderate similarity in species composition. The abundance versus species rank relationship was fitted by three models: the MacArthur broken stick model, the geometric series, and the Zeta distribution. The latter gave good fit to data from two sites, but none of the fitted models gave satisfactory fit to data from the third site, mainly because of the high abundance of the second ranked species ( Orthotomicus caelatus Eichhoff). Our results indicated that stand characteristics affected species assemblages and abundances of bark beetle species that attacked stumps. Management practices that minimize injury to trees during the spacing operations are emphasized to reduce attack by bark beetles.