Asymmetric Spring and Autumn Phenology Control Growing Season Length in Temperate Deciduous Forests

Forest phenological responses to climatic variation among species and populations across broad spatial scales remain poorly understood. Here, we quantify four decades of phenological dynamics for 10 major deciduous tree species by compiling a unique dataset that integrates high spatial resolution remote sensing with extensive field inventory data across the Northeastern and Midwestern United States. We found that spring and autumn phenology impose asymmetric controls on growing season length, with spring regulating interannual variation and autumn driving long-term trends. Spring phenology across all species was primarily controlled by temperature, while autumn phenology was influenced by spring phenology and an interacting suite of species-specific environmental factors. Our study demonstrates the promise of combining high resolution remote sensing with forest inventory data to investigate phenological dynamics over large regions. More importantly, our results provide new insights into how species-specific sensitivities to environmental drivers regulate growing season length in temperate forests.