1. Fang J, Piao S, Tang Z (2001) Inter-annual variability in net primary production and precipitation. Science 293:1723a
2. Gansu Grassland Ecoloical Research Institute and Animal Husbandry Bureau of Nagqu Prefecture of Tibet (1991) Grassland resources and animal production in the Nagqu region of Tibet. Gansu Science and Technology Press, Lanzhou China
3. Gao Q, Wan Y, Li Y, Lin E, Sheng W, Jiangcun WZ, Wang B, Li W (2007) Trends of grassland NPP and its response to human activity in Northern Tibet. Acta Ecol Sin 27(11):4612–4619 (in Chinese)
4. Knapp AK, Smith MD (2001) Variation among biomes in temporal dynamics of aboveground primary production. Science 291:481–484
5. Li S, Niu Z, Li B (2005) Study on remote sensing driving factors of NPP process model. Res Soil Water Conserv 12(3):120–123