Plant-pest interactions in time and space: A Douglas-fir bark beetle outbreak as a case study

A conceptual model of Douglas-fir bark beetle (Dendroctonus pseudotsugae) d ynamics and associated host tree mortality across multiple spatial and temp oral scales was developed, then used to guide a study of the association be tween the occurrence of beetle-killed trees and factors that might render t rees more susceptible to attack. Longterm records of beetle kill showed tha t beetle epidemics were associated with windstorms and drought at statewide and local spatial scales. At the landscape scale, beetle kill was associat ed with (i) portions of the landscape that were potentially drier (southern aspects, lower elevations) and (ii) portions of the landscape that had mor e mature and old-growth conifer vegetation. The patches of beetle-killed tr ees were aggregated with respect to other patches at scales of approximatel y 1 and 4 km. At the scale of the individual tree, there was not a strong r elationship between beetle kill and resistance to attack measured by tree g rowth rate prior to attack. Our results show that landscape-scale phenomena and temporal patterns were more strongly correlated with beetle-kill event s than was recent growth history at the scale of individual trees. We sugge st that the multi-scale approach we employed is useful for elucidating the relative roles of fine- versus coarse-scale constraints on ecological proce sses.