NDVI-based vegetation dynamics and its resistance and resilience to different intensities of climatic events

The growing season normalized difference vegetation index (NDVIGS) of vegetation and their responses to climate extremes are critical in assessing the resistance and resilience of the terrestrial ecosystem. Using satellite-derived NDVIGS and widely used Standardized Precipitation and Evapotranspiration Index (SPEI) datasets of 18 sites in cold steppe, humid temperate and temperate dry steppe ecoregions for the period of 1982-2012, the NDVIGS response, resistance, and resilience to climate extreme intensity were assessed. The results showed that the mean NDVIGS varied significantly across ecoregions, where higher mean NDVIGS was observed in humid temperate and lower was in temperate dry steppe. The NDVIGS at most sites in three ecoregions showed significantly positive correlations with increasing SPEI. The responses of NDVIGS to climate extreme intensity revealed that moderate and extreme dry events decreased NDVIGS, while moderate and extreme wet events increased NDVIGS in all ecoregions. The results showed that vegetation resistance and resilience were highly dependent on climate extreme intensity. Resistance and resilience to moderate wet, extreme wet, moderate dry and extreme dry events in all ecoregions varied significantly, where vegetation in cold steppe and humid temperate ecoregions showed lower resistance but higher resilience to moderate and extreme dry events, and higher resistance but lower resilience to moderate and extreme wet events. Vegetation in temperate dry steppe showed higher resistance to moderate dry and higher resilience to moderate wet events. The study results suggest that more productive ecosystems (i.e. higher NDVIGS in cold steppe and humid temperate ecoregions) generally provide a lower (higher) resistance but higher (lower) resilience to dry (wet) events. Knowledge from this study also implies that less productive ecosystem (i.e. lower NDVIGS in temperate dry steppe) provides higher resistance to moderate dry and higher resilience after moderate wet events. This study highlights the impacts of climate extremes on NDVIGS, and improves our understanding of the resistance and resilience of vegetation to climate extreme intensity, which is of importance in the face of climate change.