Spatial–Temporal Dynamics of Grassland Net Primary Productivity in China and Its Response to Climate Factors

Abstract

Grasslands in China are mainly located in ecologically fragile regions, which are sensitive to climate change. During recent decades, grasslands have experienced prominent warming and drying. Therefore, investigating the response of grasslands to climatic variations is necessary for a better understanding of the cumulative consequences of climate change. Grassland net primary productivity (NPP) is an important indicator for evaluating grassland ecosystem conditions. We used multisource remote sensing data and meteorological data to estimate the grassland NPP from 1982 to 2010, based on the Carnegie–Ames–Stanford approach (CASA) model. The spatial pattern and change trends of grassland NPP were evaluated. The response of grassland NPP changes to climatic variations was also analyzed. The results revealed that the spatial distribution of grassland NPP showed an increasing trend from the northwest to southeast across China. During the period from 1982 to 2010, the grassland mean NPP was 282 gC/m2/year, and NPP exhibited apparent spatial heterogeneity, being highest (710 gC/m2/year) in the dry heat savanna shrub and grass and lowest (58 gC/m2/year) in the alpine desert. The total annual NPP was 988.3 Tg C. Grassland NPP has increased slightly in the past 30 years, at a rate of 0.6 gC/m2/year. Regions showing increasing NPP accounted for 67.2% of the total grassland areas, within which areas with extremely significant (P < 0.01) and significant (P < 0.05) increases accounted for 35.8% and 8.0% of the total grassland area, respectively. Regions showing extremely significant and significant decreases encompassed only 5.8% and 4.8% of total grassland area, respectively. Clear increases in grassland NPP were observed in the west of the Qinghai–Tibet Plateau, the Alxa Plateau, and western area of Xinjiang. Areas with a decrease in grassland NPP were mainly distributed in the western regions of Inner Mongolia. Furthermore, the increasing rate of NPP showed temporal variation and differed among different grassland types. The correlation coefficient between NPP and precipitation was larger than that between NPP and temperature. Moreover, the response of grassland NPP to temperature and precipitation differed for different grassland types. There were significant positive correlations between annual precipitation and NPP in temperate desert steppe, temperate steppe, and temperate meadow steppe.