Spatio-temporal changes in the speed of canopy development and senescence in temperate China.

Abstract

China has been suggested to be the country with the largest vegetation greenness over the last four decades. In this study, we investigated the change in the speed of canopy development and senescence as well as its linkage with climate at monthly scale across temperate China, using satellite-derived Normalized Difference Vegetation Index (NDVI) data from 1982 to 2015. A significant increase in mean monthly NDVI occurred across all growing-season months except June and November, but this greening trend was mainly contributed by the faster speed of canopy development in April and the slower speed of canopy senescence in October. The average of VNDVI (the difference in NDVI between 2 consecutive months) over temperate China is significantly increased only in April (7.75 × 10-4 year-1 , p < .05) and October (4.98 × 10-4 year-1 , p < .05). In contrast, VNDVI in November is significantly decreased, indicating an increasing trend in the magnitude of leaf fall in the last month of the growing season due to both increase in season maximum greenness and slower canopy senescence in October. We also found clear seasonal differences in the correlations between VNDVI and climatic factors, especially temperature. In April and October, the correlations between VNDVI and temperature were generally positive, while they were negative in June. VNDVI in spring (early growing season) and summer (middle growing season) was also positively correlated with precipitation in semiarid regions. Such seasonally distinct climatic controls on VNDVI should be considered in modelling vegetation responses to climate change. Overall, our findings can help quantify the contribution of different climatic drivers on the shifts in canopy development and senescence and better elucidate the change in vegetation greenness under future climate change.