Climate-driven shifts in tree phenology: global patterns, trends, and ecological implications

Abstract

Shifts in the seasonal timing of tree phenological events, including budburst, leaf emergence, flowering, and fruiting, are among the most sensitive biological indicators of climate change. We conducted a systematic review of 145 empirical studies published between 2004 and 2024, encompassing 116 tree species across tropical, subtropical, temperate, and boreal biomes, to synthesize global trends, dominant climatic drivers, and ecological consequences of phenological changes. Temperature emerged as the primary driver in temperate and boreal systems, where spring leaf-out and flowering advanced by 2.5–5.1 days/°C of warming. In contrast, phenology in tropical and subtropical ecosystems was more strongly regulated by precipitation and drought variability, with increased rainfall advancing flowering and fruiting by 3–5 days and drought stress delaying events by 7–10 days. Additional influences included photoperiod, solar radiation, relative humidity, elevated CO₂, soil moisture, and urban heat island effects, while extreme events such as heatwaves and late frosts frequently disrupted expected phenological patterns. These shifts have far-reaching implications for growing-season length, carbon uptake, evapotranspiration, nutrient cycling, and trophic synchrony, with cascading effects on biodiversity and ecosystem resilience. Despite this importance, evidence remains geographically biased toward Europe and North America, and mechanistic understanding is constrained by reliance on observational approaches and limited representation of species-specific responses in dynamic global vegetation models. Integrating long-term monitoring, remote sensing, trait-based data, and machine learning into modelling frameworks is essential to improve the projections of vegetation–climate feedbacks under future climate scenarios.