Trends in fall phenology across the deciduous forests of the Eastern USA

Decadal trends in delay of the end of the season (EOS) have been recently observed across a large fraction of the forested areas in the Northern hemisphere. However, the spatial patterns of EOS variability and its environmental forcings at local scale are largely unknown within deciduous forests. In this study, we investigated short- and long-term changes in EOS and its relationship with variability of air temperature and precipitation across the deciduous forests of the Eastern USA from 1989 to 2008. We used high-resolution (1 km2) satellite data in conjunction with meteorological measurements. Our results show strong evidence of widespread delay in EOS throughout larger areas than what was previously reported. Equally important, the results show that EOS variability and EOS response to summer air temperature varied significantly across the Eastern USA. EOS response to climate variability was in general correlated with the latitude of the forest, but different patterns for different areas were observed as well. No clear relationship was observed between EOS and precipitation, probably because of the complexity of the link between water relations and senescence mechanisms and controls in deciduous trees. Overall, our results show the importance of local scale heterogeneity (likely driven by both biotic and abiotic factors) in determining significantly different patterns in the relationship between EOS and climate variability across Eastern USA.