The effects of climate change and grazing activities on grassland yield in the Tibetan Plateau, China

Accurate and periodic assessment of grassland yield (GY) and grazing pressure is of great importance for the management and utilization of alpine grasslands. Based on remote sensing data, meteorological datasets and observational plant biomass data, we used the Global Production Efficiency Model and Soil and Atmosphere Model (GLOPEM-CEVSA) to estimate GY and the grazing pressure index (IP) over the Tibetan Plateau during 1988-2013. Under the effect of climate change and human activities, we endeavor to their dynamics and identification of key drivers. During this period, average annual total GY was 515.8 kg/ha/yr and gradually decreased from the southeast to the northwest of the TP. Annual GY fluctuated from year to year but had an overall positive trend (4.2 kg/ha/yr). For the total area, the proportion showing a significant increase in GY was 45.2%, while only 12.6% showed a significant decrease. The average IP on the TP was 1.6, indicating that the grassland remained still overloaded, but IP decreased gradually with a slope -0.9%/yr. Warming temperature and the effectiveness of ecological restoration programs jointly promoted the increased grassland yields and reduced grazing pressure. Rising temperature promoted positive increase of GY for almost all the region. Annual precipitation was related to a less significant decreasing trend of GY over all the TP apart from an increase of GY in the middle area of the north. The grazing pressure index decreased over the years by control of livestock numbers, the reduction of grazing pressure assisting restoration of alpine grasslands. Grassland protection and restoration projects have mitigated grassland degradation in some areas, promoted grassland restoration, and increased incomes of herdsmen. The study indicates that continuation of these projects is critical for the restoration and sustainable use of the TP grasslands.