Response of vegetation to increased grazing intensity in temperate desert steppe

The objective of this study was to examine the spatial variations of aboveground plant biomass, species composition, leaf area index (LAI) and normalized difference vegetation index (NDVI) along two gradients of grazing intensity in temperate grassland in the Ordos Plateau, China. Two spatial transects, one located in desert steppe and other in sandy rangeland, along grazing intensity gradients were selected based on the distance from water source and accessibility by livestock. Oven-dried aboveground plant biomass, coverage, density, height, and frequency were measured at three randomly selected 1-m² sample plots around each of the five points along each transect, along with leaf area index measured for each plot. Normalized difference vegetation index values were derived from Landsat image acquired in mid-summer. Along the desert steppe gradient, aboveground biomass changed from 111.9 g/m2 in closed plots to 86.8 g/m2 in moderately grazed plots and further declined to 12.3 g/m2 in heavily grazed plots. Dominant species changed from Stipa breviflora and Cleistogenes songorica in closed plots to Artemisia songorica and Stipa breviflora in moderately grazed plots and then to Eragrostis poaeoides in heavily grazed plots. Both LAI and NDVI were significantly different among closed, moderately grazed and heavily grazed areas. Similar patterns with different magnitudes were observed along the sandy transect. In summary, long-term grazing had significant impact on various plant community features, including aboveground biomass, coverage, dominant species, LAI, and NDVI in the study areas.