Temporal and Spatial Changes of Vegetation Phenology and Its Correlation With Net Primary Productivity in Northeast China From 2001 to 2022

The study of vegetation phenology and net primary productivity (NPP) plays a crucial role in understanding how ecosystems react to climate change. This study monitored vegetation phenology and NPP in Northeast China (NEC) from 2001 to 2022. The results showed that: 1) variations in latitude and longitude had a highly significant effect (p < 0.01) on all vegetation phenology parameters. Besides, the start of the growing season (SOS), the end of the growing season (EOS), and the length of the growing season (LOS) in NEC exhibited advancing (-0.26 days/a), delaying (0.14 days/a), and prolonging (0.40 days/a) tendencies, respectively. Forest EOS had advanced (-0.13 days/a) instead; 2) SOS, EOS, and NPP showed a negative correlation, while LOS, small integral value (SIV) and NPP were positively correlated. Among them, the strongest correlation ( $r$ = 0.74) was found between SIV and NPP scatter points. The correlation between NPP and vegetation phenology under different precipitation and temperature circumstances is complicated. This study can serve as a resource for comprehending the responses of vegetation phenology in the NEC to climate change.