Spatiotemporal associations between forests impacted by mountain pine beetle and adjacent replantings impacted by Warren root collar weevil.

摘要

A concern to reforestation efforts following the recent outbreak of mountain pine beetle, Dendroctonus ponderosae Hopkins, is the migration of the below-ground herbivore Warren root collar weevil, Hylobius warreni Wood, from stands with a high percentage (>80%) of mature, dead lodgepole pine, Pinus contorta var latifolia Dougl. ex. Loud., into adjacent young, replanted stands, resulting in significant levels of mortality to juvenile trees. The effects of the spatial patterns of salvage harvesting following outbreaks of mountain pine beetle on the development of Warren root collar weevil pressure in neighbouring, regenerating stands was examined in young lodgepole pine stands in the central interior of British Columbia, Canada. Gradients of tree mortality caused by feeding of Warren root collar weevils were observed and found to be dependent on characteristics of the adjacent, unsalvaged stands. Mortality was exacerbated by high components of dead pine in these stands, and became worse over time. To investigate whether reduced host availability is a potential causal factor explaining such patterns, I constructed three research plots consisting of combinations of live tree, dead tree and mixed (i.e., live and dead) tree habitats and observed dispersal patterns of labelled insects. Weevils were more likely to be captured close to the release location in the mixed and live habitats vs. the dead habitat. Movement rate was high in the dead habitat compared with the live and mixed habitats. In the plot with the dead habitat adjacent to the location of release, the probability of capture was lower, but movement rate and dispersal distance were greater, indicating that Warren root collar weevils will disperse out of a habitat with dead trees into a habitat with live trees. Implications to reforestation strategies following savage harvesting are discussed.