Predicting autumn phenology: How deciduous tree species respond to weather stressors

Shifts in the timing of autumnal leaf coloration and leaf drop in temperate forests with climate change can have substantial impacts on community and ecosystem processes (e.g. altered carbon/nitrogen cycling and biotic interactions). However, the environmental control of autumn phenology remains significantly understudied in striking contrast to spring phenology. In this study, we used linear mixed effects model with ground-based phenology observations in northeastern USA and found that both weather stressors (e.g. heat- and drought-stress and heavy rainfall) during the growing season and spring phenology significantly affected inter-annual variation in autumn phenology of twelve dominant deciduous tree species. While warm temperatures and drought lead to later fall phenology for most species, heavy rainfall and heat stress lead to earlier leaf coloration and leaf drop. We also found that the phenological sensitivities to weather stressors are diversely species-specific. Under future climate change projections, we predicted that greater summer heat-stress in the future will cause abbreviated leaf coloration seasons for most species. Our mixed-effects modeling framework suggested that accounting for phenological variations among individual trees, species and sites largely improved model predictions, which should not be overlooked in phenological model development. Our study improves our understanding of how species-specific autumnal phenology responds to weather stresses, and describes a new modeling framework to investigate both inter-annual phonological changes and local variations among trees, species, and sites. Our predictions on autumn phonological shifts will help in assessing the effects of climate change on forest community and ecosystem processes in the future.