Mapping asynchrony between gypsy moth egg-hatch and forest leaf-out: Putting the phenological window hypothesis in a spatial context

Spring phenology in temperate forest ecosystems is responding in diverse ways to global climate change, with unknown consequences for insect disturbances that affect forest productivity. Adaptive forest management that anticipates changes in insect disturbance regimes requires an understanding of the mechanistic links between climate and disturbance behavior. Phenological mismatches between insects and their hosts have the potential to modify patterns of defoliation that are a significant disturbance in temperate forests. Yet the frequency and extent of phenological mismatches have not been quantified over forest landscapes. Forest dwelling, spring-feeding defoliators must synchronize larval emergence annually with leaf-out phenology of host trees. Lack of synchrony can limit population expansion, unless dispersing larvae successfully locate phenologically compatible hosts. We quantified the potential for successful dispersal of an introduced defoliator in a forest landscape by mapping phenological asynchrony from 2000 to 2010. Maps compared MODIS derived leaf-out with gypsy moth egg-hatch from the BioSIM insect phenology model. Mean temporal differences between gypsy moth egg-hatch and leaf-out were sufficient (+10 days) to severely limit 1st instar survival in 5 of 11 years. Biologically meaningful phenological asynchrony extended over distances of 3.1–4.9 km, well beyond typical gypsy moth dispersal thresholds (