Selective grazing of livestock creates lightly- and heavily-grazed vegetation patches, which together contribute to the whole community in grazed grasslands. While Intermediate Disturbance Hypothesis has predicted moderate grazing intensity can increase species diversity, grazing patchiness complicates predicted responses to grazing intensity from ecological theory and may influence how various management regimes affect biodiversity at the whole community scale. We examined effects of management regime and grazing intensity on plant species diversity, community composition, aboveground net primary production (ANPP), and soil compaction, based on a grazing manipulation experiment in a typical steppe of Inner Mongolia. Two management regimes (traditional continuous grazing and grazing and mowing alternated annually) and seven levels of grazing intensity were applied in a randomized block design over the past 10 years. We assessed how α- and β-diversity contributed to γ-diversity, and how these relationships responded to both grazing intensity and management regime. We divided β-diversity into its nestedness and replacement components across lightly- and heavily-grazed patches within plots. Nestedness is effect on β-diversity caused by differences in the number of species between patches. Replacement reflects the substitution of species in some patches by different species in other patches.
Results/Conclusions
The mixed grazing-mowing regime had a higher number of palatable species, higher species evenness, and higher Shannon-Wiener diversity than the continuous grazing regime, both in lightly-, heavily-grazed patches and the whole plots, and especially at moderate and high grazing intensities. The two regimes did not differ in total β-diversity. However, the nestedness component of total β-diversity was dominant in the continuous grazing regime. Although species richness and ANPP did not differ significantly between the two management regimes, soil hardness in heavily-grazed patches was significantly higher under the continuous grazing regime than the mixed grazing-mowing regime. Loss of rare species under both management regimes, even at low to moderate grazing intensities, suggested that selective grazing and patch formation may not conform with the Intermediate Disturbance Hypothesis. Furthermore, our study indicates that the mixed grazing-mowing regime is more sustainable for long-term grassland management than the continuous grazing regime by controlling the creation of heavily-grazed patches.