Climate-Driven Shifts in Tree Phenology: Global Patterns, Trends, and Ecological Implications

Abstract

Shifts in the seasonal timing of tree phenological events such as budburst, leaf emergence, flowering, and fruiting are among the most visible 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 assess global trends, climatic drivers, and ecological implications of phenological change. Temperature emerged as the dominant driver in temperate and boreal systems, where spring leaf-out and flowering advanced by 2.5-5.1 days per °C of warming. In contrast, precipitation and drought variability exerted stronger control in tropical and subtropical ecosystems, with increased rainfall advancing flowering and fruiting by 3-5 days, while drought stress delayed events by 7-10 days. Beyond these, photoperiod, solar radiation, relative humidity, elevated CO 2 , soil moisture, and urban heat islands also influenced phenological timing, and extreme events such as late frosts and heatwaves frequently disrupted expected patterns. Collectively, these climatic pressures not only alter growing-season length, carbon uptake, evapotranspiration, and nutrient cycling but also disrupt synchrony with pollinators, dispersers, and herbivores, thereby threatening biodiversity and ecosystem resilience. Geographically, evidence is strongly skewed toward Europe and North America, leaving tropical and Southern Hemisphere forests underrepresented despite their high biodiversity and climate sensitivity. Methodologically, reliance on observational datasets and statistical correlations limits mechanistic understanding, while species-specific responses remain poorly represented in Dynamic Global Vegetation Models (DGVMs). Integrating long-term monitoring, remote sensing, trait-based approaches, and machine learning into DGVM frameworks is critical for capturing the complex interplay of climatic drivers and improving forecasts of vegetation-climate feedbacks. Overall, tree phenology is both a sensitive indicator and an active regulator of ecosystem responses to climate change, and resolving geographical, taxonomic, and methodological gaps is essential for enhancing predictive capacity under future climate scenarios.