Characterizing Ecosystem Variability Of Northern China Steppes Using Onset Of Green-Up Derived From Time-Series AVHRR NDVI Data

摘要

The objective of this study was to explore satellite-based vegetation phenology to characterize ecosystem variability in the northern China steppes. Advanced Very High Resolution Radiometer (AVHRR) maximum Normalized Difference Vegetation Index (NDVI) composite data set from 1982 to 1990 was used to detect the onset of vegetation green-up for the steppe ecosystems. Our findings show a strong linkage between onset of green-up and climatic factors in the region. An Ecosystem Variability Index (EVI) was derived using the coefficient of variation for date of onset of green-up. The EVI showed the meadow steppe/forest ecosystems to be least ecologically variable and the desert steppe to be most variable. Large areas of typical steppe, near the desert steppe ecotone, exhibited similar EVI values to those of the desert steppe, suggesting greater ecosystem variability in this typical steppe area. This suggests that large expanses of typical steppe in this region are undergoing ecosystem changes that could result in lower grassland productivity and eventual changes in land use practices.