Vegetation Phenology Shifts Under Climate Change: Cross-Season Mechanisms and Consequences for Ecosystem Productivity.

Vegetation phenology-the timing of recurring life-cycle events-has shifted markedly under climate change, with far-reaching consequences for terrestrial ecosystems and the climate system. Yet phenological research has largely focused on discrete events, often overlooking the continuous and seasonally connected nature of vegetation development. Here, we synthesize recent evidence into a cross-season framework in which spring (start of the growing season), peak (timing of maximum greenness/photosynthetic capacity), and autumn (end of the growing season) phenology are treated as dynamically linked phases. Within this framework, spring phenology is governed by chilling-forcing dynamics, which are modulated by contemporary environmental cues, previous-year autumn phenology, and resource status. Peak phenology is primarily driven by early-season development and carbon uptake, both of which are influenced by spring phenology and temperature. Autumn phenology integrates late-season environmental conditions with legacies of earlier development, mediated by carbon source-sink balance and water and nutrient availability. Across these phases, the evidence points to reciprocal coupling between phenology, carbon uptake, and developmental processes: phenological shifts reshape the seasonal trajectory of productivity and growth, and the resulting carbon dynamics feedback to regulate subsequent developmental transitions. This seasonally integrated perspective provides a mechanistic basis for predicting how non-linear, season-specific climate change will reorganize the terrestrial carbon cycle, and calls for phenology models that explicitly represent cross-season linkages.