Changes of spatial-temporal characteristics based on MODIS NDVI data in Inner Mongolia grassland from 2000 to 2008

Time-series MODIS NDVI datasets for 2000-2008 were used in the study to investigate the changes of spatial-temporal characteristics in annual NDVImax for seven typical grassland types, i.e., temperate steppe, temperate desert, low-land meadow, temperate desert steppe, temperate meadow steppe, temperate steppe desert, up-land meadow in Inner Mongolia grassland. The analysis focused on the spatial change trends, the standard deviations and the occurrence time point of annual NDVImax for the period of 2000-2008. The results indicated that grassland vegetation in Inner Mongolia presented an obvious recovering trend over the past several years. The mean of annual NDVImax in seven grassland types showed an obvious increasing trend. For the changes in grassland areas over different grades, the areas with NDVImax values in (0, 0.4 were decreased largely, and the areas with NDVImax values in (0.4, 1 showed a increasing trend for the study period. Overall, the restoring grassland took up about 67.15% of the total area; the deteriorating grassland took the rest. The grassland vegetation in Inner Mongolia in 2008 was the best in the past nine years. The study also showed that there was about total area except temperate desert grassland where the NDVImax occured from the end of June to the end of September in each year. Especially August was the most important growing season for temperate steppe and meadow steppe in Inner Mongolia grassland.