The responses of spring phenology to temperature and photoperiod

Abstract:

Vegetation phenology, such as leaf-out and flowering, is sensitive to the cumulative effects of weather and climate variability, serving as an indicator of the integrative biological impact of climate change. However, a comprehensive understanding of the causal relationships between temperature, photoperiod and phenology and the underlying mechanisms is still lacking, leading to considerable uncertainties in the projection of land-atmosphere interactions and feedbacks in Earth system models. We focus on three primary questions: (1) how does spring phenology respond to urban warming? (2) How does spring phenology respond to asymmetric diurnal warming? (3) How does photoperiod affect spring phenology? We first investigated the changes in spring phenology and its covariation with temperature in 85 large U.S. cities. Results show that spring phenology came significantly earlier but the magnitude of the covariation between phenology and temperature decreased in cities. Second, we used satellite images to characterize the response of spring phenology to daily minimum and maximum temperatures across the Appalachian Trail regions in the Eastern United States. Results showed that warming in daytime and nighttime played distinct or even contrasting roles in phenological changes, and such effects showed large regional variations. Third, we investigated the photoperiod effect on spring leaf-out for six deciduous tree species using the Pan European Phenological database (PEP725). We found photoperiod moderated excessively early and late spring leaf-out that caused by temperature variation. Photoperiod considerably decelerates the advancement of spring leaf-out (19 days by 2100) and mitigate spring frost risks under the projected climate warming. These results quantify the phenological responses to changing environments and improve the prediction of phenological response under a warming climate.