Insect Defoliators as Periodic Disturbances in Northern Forest Ecosystems

Comparative ecology of conifer-feeding spruce budworms (Lepidoptera: Tortricidae)

“…Two paradigms emerged; one in which spruce budworm populations rapidly switch between multiple equilibria as a function of resource availability (Ludwig et al 1978) and an alternative view in which populations oscillate gradually with a unique conditional equilibrium that varies according to the current state of different forcing agents such as natural enemies (Royama 1992). The ensuing debate has drawn useful attention to how the relative strength and direction of trophic interactions influence dynamics (Cooke et al 2007;Sturtevant et al 2015). I return to this in detail after first considering the pervasive effect of weather and the obfuscating effect of moth dispersal.…”

“…What is clear, however, is that the capacity and inclination for moths to migrate long distances is a phylogenetic trait common to all Choristoneura which adds significant potential for stochastic influence on local rates of change and results in a meta-population structure of sustained and synchronised outbreaks over a regional scale for all species ( Fig. 3; Cooke et al 2007). …”

“…Despite high variability in the range of outbreak periodicity and duration at the local level, budworm outbreaks appear synchronised over large areas via several potential mechanisms including correlated, large-scale weather-related perturbations and dispersal of moths (Cooke et al 2007). Once again, deviations from this generalisation are informative.…”

“…A qualitative working hypothesis using comparative analysis and the context of trophic interactions (Cooke et al 2007) offers a robust alternative that makes use of the weight of evidence provided by uncommonly rich historical knowledge available for budworms. I return to this point in the final section.…”

Remote sensing of forest pest damage: a review and lessons learned from a Canadian perspective

“…Remote sensing is likely to play an increasingly important role in change detection, especially at high altitudes and latitudes, where population monitoring costs are higher and where disturbance frequencies are most likely to rise under climate change (Gray 2013). As the outbreak progresses and peaks, there are serious limits to the accuracy of predictions derived from population models (Cooke et al 2007), and remote sensing is likely to play an increasingly important role for continually revising forecasts, particularly those done at very large scales. As continued annual defoliation results in cumulative mortality, the forest pest manager's context changes from pest population management to salvage logging, and the goals shift from detecting defoliation to quantifying mortality.…”