ABSTRACT
Atmospheric variability can impact biological populations by triggering facultative migrations, but the stability of these atmosphere-biosphere connections may be vulnerable to climate change. As an example, we consider the leading mode of continental-scale facultative migration of Pine Siskins, where the associated ecological mechanism is changes in resource availability, with a mechanistic pathway of climate conditions affecting mast seeding patterns in trees which in turn drive bird migration. The three summers prior to pine siskin irruption feature an alternating west-east mast-seeding dipole in conifer trees with opposite anomalies over western and eastern North America. The climate driver of this west-east mast-seeding dipole, referred to as the North American Dipole, occurs during summer in the historical record, but shifts to spring in response to future climate warming during this century in a majority of global climate models. Identification of future changes in the timing of the climate driver of boreal forest mast seeding have broadly important implications for the dynamics of forest ecosystems.
