Land surface phenology of China's temperate ecosystems over 1999-2013: Spatial-temporal patterns, interaction effects, covariation with climate and implications for productivity

Phenology is an important indicator of ecosystem functioning and has played a significant role in indicating plant productivity. Using 15-year SPOT-VGE data (1999-2013), we obtained the start (SOS), end (EOS) and length of growing season (LOS) with an improved modeling algorithm from time series of normalized difference vegetation index (NDVI) for temperate ecosystems of China (>30° N). Spatial and temporal patterns of SOS and EOS were analyzed. Furthermore, the interaction effects between phenological metrics were also considered. Using partial correlation, we quantitatively determined the contribution of climate (i.e., temperature and precipitation) on SOS and EOS in a spatially explicit way. More importantly, we also revealed the impacts of SOS and EOS on interannual variability of gross primary productivity (GPP). Our results showed that China's temperate ecosystems experienced intense phenological changes over 1999-2013 with high spatial heterogeneity. EOS was positively correlated with SOS, suggesting an earlier SOS may generally be accompanied with an earlier EOS. Spring temperature mainly controlled SOS but the role of spring precipitation on SOS cannot be overlooked. Warmer autumn delayed EOS consistently while autumn precipitation can either lead to earlier or later EOS. Unlike previous reported results, we found that both SOS and EOS had contrasting effects on annual GPP, i.e., annual GPP can either increase or decrease (depending on the location) with an earlier SOS or EOS, implying the complicated interactions between phenological changes and interannual variability of plant productivity.