Differentiating anthropogenic modification and precipitation-driven change on vegetation productivity on the Mongolian Plateau

Context The Mongolian Plateau, comprising Inner Mongolia, China (IM) and Mongolia (MG) is undergoing consistent warming and accelerated land cover/-land use change. Extensive modifications of water-limited regions can alter ecosystem function and processes; hence, it is important to differentiate the impacts of human activities and precipitation dynamics on vegetation productivity. Objectives This study distinguished between human-induced and precipitation-driven changes in vegetation cover on the plateau across biome, vegetation type and administrative divisions. Methods Non-parametric trend tests were applied to the time series of vegetation indices (VI) derived from MODIS and AVHRR and precipitation from TRMM and MERRA reanalysis data. VI residuals adjusted for rainfall were obtained from the regression between growing season maximum VI and monthly accumulated rainfall (June-August) and were used to detect human-induced trends in vegetation productivity during 1981-2010. The total livestock and population density trends were identified and then used to explain the VI residual trends. Results The slope of precipitation-adjusted EVI and EVI2 residuals were negatively correlated to total livestock density (R-2 = 0.59 and 0.16, p < 0.05) in MG and positively correlated with total population density (R-2 = 0.31, p < 0.05) in IM. The slope of precipitation-adjusted EVI and EVI2 residuals were also negatively correlated with goat density (R-2 = 0.59 and 0.19, p < 0.05) and sheep density in MG (R-2 = 0.59 and 0.13, p < 0.05) but not in IM. Conclusions Some administrative subdivisions in IM and MG showed decreasing trends in VI residuals. These trends could be attributed to increasing livestock or population density and changes in livestock herd composition. Other subdivisions showed increasing trends residuals, suggesting that the vegetation cover increase could be attributed to conservation efforts.