The role of developmental and climate factors in driving autumn phenology across the Northern Hemisphere

Abstract

Autumn phenology regulates the length of the growing season and carbon uptake in terrestrial ecosystems. Under climate change, delayed autumn phenology has been widely reported, but the driving factors are still unclear, especially the impact of developmental factors. In this study, based on satellite-derived end of the growing season (EOS) and photosynthesis data over the Northern Hemisphere (>30° N) from 1982 to 2016, we comprehensively explored the potential factors influencing EOS, including developmental and preseason climate factors, and compared their effect sizes across different climate zones and vegetation types. We found the magnitude of the EOS shift was heterogeneous. The EOS delay was greater in humid regions than in arid regions, with the strongest delay in evergreen needle-leaved forest and the smallest delay in deciduous needle-leaved forest. Partial correlation analysis showed that EOS was significantly correlated with the start of the growing season (SOS) and growing season photosynthesis in only a very small proportion of pixels. A slightly prevalent positive correlation was detected between EOS and developmental factors in deciduous forests and non-warm-dry climate regions, suggesting opposing effects of earlier SOS and increased photosynthesis on autumn phenology. For climate factors, preseason warming may postpone EOS except in warm-dry areas, while increased preseason precipitation may prompt EOS to occur earlier in humid-region forests. For warm-dry regions and grasslands, water supply was also a key factor in delaying leaf senescence. Further analysis indicated that preseason temperature was the primary driver responsible for the EOS changes across all climate zones and vegetation types, while the effects of SOS and growing season photosynthesis were relatively minor. Our findings highlight the complexity of factors influencing EOS, and call for the investigation of the driving mechanisms of autumn phenology at different scales and under different climate backgrounds.