Spatio-temporal changes in grassland degree in the Qinghai-Tibet Plateau from 2000 to 2015

The study of spatiotemporal variation of grasslands shed light on understanding the causes and effects of transition of grassland quality．This article aims to provide basic data on the cause and effects as well as the mechanisms of grassland degradation．The grassland degree index (GDI) calculated from weighted index of NPP and NDVI was applied to represent the quality and coverage of grassland．Transition matrix and the slope index of GDI demonstrated the spatiotemporal pattern．From 2000 to 2015, total area of Class Ⅰ (high-quality grass) and Class Ⅳ (poor quality grass) remained unchanged．Some 28.11% of class Ⅰ grassland changed into class Ⅱ．The proportion of class Ⅱ that transformed into class Ⅰ and class Ⅲ were 18.19% and 21.53%, respectively．About one third (28.54%) of class Ⅲ transformed into class Ⅳ．From 2000 to 2015, grassland has undergone a trend of degradation-restoration-degradation pattern．The map of slope demonstrated that grassland conditions in the north has improved, while in the south has deteriorated, several local areas had undergone severe degradation in particular．