Abstract: MODIS NDVI data from 2000 to 2014 were adopted to extract the time series of the vegetation coverage in Gannan Plateau, and its spatial and temporal variation were analyzed. The response of vegetation coverage to climatic variations at annual and monthly time scales was analyzed by using phenological phase, temperature and precipitation time series at Gannan meteorological stations from 2000 to 2014. The results showed that the annual mean temperature increased with an annual rate of 0.04 ℃ and the annual mean precipitation increased with an annual rate of 4.7 mm in the Gannan Plateau from 2000 to 2014. Spatially, precipitation decreased from the southwest to the northeast and the annual mean temperature decreased from the southeast to the northwest. During the past 15 years, the vegetation coverage increased from the southeast to northwest in Gannan Plateau. The mean vegetation coverage was 77.5%, and exhibited apparent spatial heterogeneity, being the highest (77.8%) in forest and the lowest (60.3%) in alpine and subalpine grassland. There was a slight increase of vegetation coverage over the study period with an annual rate of 0.32%. The increase in sloping grassland area was as high as 1.04% per year and the plain grassland area increase was 0.47% per year, while the increases in coverage of alpine and subalpine meadow and forest were lower (0.19% and 0.10% per year, respectively). On the contrary, the marsh wetlands, alpine and subalpine grassland had a slight decrease of vegetation coverage over the study period (-0.03% and -0.06% per year, respectively). At the annual time-scale, there were no significant positive correlations between vegetation coverage and annual temperature or precipitation. However, the vegetation coverage was mainly affected by temperature in alpine and sub-alpine grassland, alpine and sub-alpine meadow, sloping grassland, plain grassland and marsh wetlands, while the vegetation coverage in forest was mainly affected by precipitation. At the monthly timescale, the time-lag response of vegetation coverage to precipitation occurred mainly in early and late growing season, while the time-lag response to temperature occurred mainly in key growth stage, and such response to precipitation was better than that to temperature.

Key words: land use type, spatial heterogeneity, paddy field and irrigable land, Kriging interpolation., soil organiccarbon density