Spatio-temporal variation in grassland degradation and its main drivers, based on biomass: Case study in the Altay Prefecture, China

Analyzing the spatio-temporal characteristics and identifying of main factors that drive grassland degradation are essential for formulating ecological restoration measures for grassland. In this study, we addressed two main scientific questions: (1) how to accurately characterize the spatial and temporal variability in grassland degradation; and (2) how to identify the dominant factors that affect grassland degradation. Based on the data obtained from 270 field sampling points (912 quadrats) and MODIS, we selected the temperature vegetation dryness index (TVDI), vegetation coverage (VC), biomass and ecosystem service values (ESVs) to study the degradation of grassland in Altay Prefecture, China. From 2000 to 2016, the area with decrease in TVDI accounted for 93.4% of the total grassland. The VC values in the warm steppe and mountain meadow areas decreased by 5.3% and 1.6%, respectively, and the biomass decreased by 80% and 76.4% in these areas. Compared with 2000–2005, the mean total ESVs decreased by 5.1% in 2011–2016, where the reductions in the ESVs for warm steppe and mountain meadow accounted for 54.3% and 38% of the total reduction, respectively. The results showed that the degradation trends were more significant in the warm steppe and mountain meadow than the other land types. These findings improve our understanding of the spatial heterogeneity of grassland degradation. Human disturbance was the main factor responsible for grassland degradation in Altay Prefecture, according to the framework developed in this study based on biomass and TVDI metrics. Our results provide a reference for characterizing the spatio-temporal variability of grassland degradation by combining statistical and spatial analyses, as well as a simple framework for application in similar regions to analyze the effects of climate change and human disturbance on grassland degradation.