Temporal and spatial dynamics of alpine grassland biomass in the Three-River Headwater Region

The Three-River Headwaters Region, located in the hinterland of the Qinghai-Tibet Plateau, contains the headstreams of the Yangtze River, Yellow River, and Lancang River. It is an important area for water conservation and protection of ecological functions in China. To analyze the dynamics of the Three-River Headwaters Region, a back propagation artificial neural network (BP-ANN) was used to simulate the grassland aboveground biomass (AGB). The grassland AGB was estimated from 2001 to 2016, and the characteristics of the temporal and spatial changes of the grassland AGB from different grassland types and river basins were analyzed. The results showed that: 1) The CXYN model based on BP-ANN is suitable for grassland biomass inversion (R2=0.769 9,RMSE=429.1 kg·ha-1); 2) In the past 16 years, the grassland AGB, overall, tended to be stable and restored; 3) The spatial distribution of AGB included significant regional differences, with a decreasing trend from the southeast to the northwest. The AGB was up to 3 000 kg·ha-1 in some parts of the southeast, but was very low (less than 500 kg·ha-1) in some parts of the northwest.