Forest landscapes determine their pests: jack pine budworm spatial dynamics under host scarcity

Abstract Context Jack pine budworm (JPBW), Choristoneura pinus pinus, is a major defoliator in Canada, yet remains absent from theoretical discourse on outbreak synchrony, despite sharing key life history traits with the archetypal “cross-scale” pest, spruce budworm (C. fumiferana). JPBW has primarily been studied in host-rich landscapes, raising questions about its behavior in host-sparse regions. Objectives We asked whether scale-crossing JPBW outbreaks are contingent on host density, and whether reduced outbreak incidence in host-sparse landscapes reflects synchronized or desynchronized population limitation. Methods We applied a systematic framework for analyzing spatiotemporal tree-ring data, adapted from recent reconstructions of spruce budworm and forest tent caterpillar. This framework integrates temporal and spatial methods to evaluate periodicity, coherence, and landscape-scale synchrony. Results In the pine-sparse Border Lakes region (~30,000 km 2 ), we identified 14 growth disturbances between 1910 and 2006, typically recurring every seven years and affecting 30% of trees annually at peak. Reanalysis of data from a host-rich site in Manitoba confirmed strong correspondence between JPBW defoliation and growth reductions. Nine episodes in the host-rich site coincided with published outbreaks, whereas signals in the host-sparse Border Lakes remained spatially variable and weakly correlated across sample areas. Conclusions Despite high fecundity and dispersal potential, JPBW in host-sparse landscapes behaves endemically. Pest status, we argue, is not a fixed insect trait but an emergent property of host availability and spatial scale. The JPBW system constitutes a third example from the Border Lakes region where the “catastrophe” theory of outbreak origin is more consistent with data than a “clockwork” theory of spatially synchronized cycling.