Grazing intensity by sheep affects spatial diversity in botanical composition of Inner Mongolian grassland

Abstract

Overgrazing by sheep causes degradation of grasslands in the Inner Mongolian steppe, yet our understanding of its impact on grassland plant communities is limited by lack of observations at high spatial resolution. Employing a nested experimental design in a long-term grazing experiment provides insights into effects of increasing sheep grazing intensity on community composition, diversity, and spatial patterns in the grassland vegetation. Effects of observed changes in the plant community are discussed based on monthly weight gain of sheep during grazing. The design of the long-term experiment included four triplicated grazing intensities applied during an 8-year period. At the end of that period, we evaluated vegetation coverage, categorized plant species by functional groups, and analyzed the data using a mixed linear model. Moreover, spatial autocorrelation methods were employed to investigate spatial patterns, visualized via a kriging model. We found that the plant community composition differed among grazing treatments, with high grazing intensity showing higher plant species richness and stronger clustering of plants at our fine scale of observation. These fine-grained spatial scale observations are usually not recorded in larger spatial scale analyses of grassland responses to overgrazing. While the grazing intensities used in our study did not influence individual sheep weight gain, total sheep weight gain per hectare increased with an increase in grazing intensity. Our study shows that in a sheep grazing intensity experiment in Inner Mongolia grasslands total sheep weight gain may increase at the expense of fine-scale species composition and spatial dynamics of the grassland vegetation. These insights may be used for determining trade-offs of sheep meat production with original composition and structure of grassland plant communities. Effects on other ecosystem properties and functions, such as on belowground biodiversity, remain to be assessed.