Abstract
An understanding of the factors controlling plant community composition will allow improved prediction of the responses of plant communities to natural and anthropogenic environmental change. Using monitoring data from 1980 to 2009, we quantified the changes in community composition in Leymus chinensis and Stipa grandis dominated grasslands in Inner Mongolia under long-term grazing-exclusion and free-grazing conditions, respectively. We demonstrated that the practice of long-term grazing exclusion has significant effects on the heterogeneity, the dominant species, and the community composition in the two grasslands. The community composition of L. chinensis and S. grandis grasslands exhibited directional changes with time under long-term grazing exclusion. Under free grazing, the L. chinensis community changed directionally with time, but the pattern of change was stochastic in the S. grandis community. We attributed the divergent responses to long-term grazing exclusion in the S. grandis and L. chinensis grasslands to litter accumulation and changes in the microenvironment after grazing exclusion, which collectively altered the growth and regeneration of the dominant species. The changes in the grazed grasslands were primarily determined by the selective feeding of sheep during long-term heavy grazing. Overall, the responses of the community composition of the Inner Mongolian grasslands to long-term grazing exclusion and heavy grazing were divergent, and depended primarily on the grassland type. Our findings provide new insights into the role of grazing in the maintenance of community structure and function and therefore have important implications for grassland management.
Highlights
The composition of plant communities is controlled by many environmental factors and disturbances [1,2,3,4]
This information can enhance our ability to predict the response of plant communities to natural and anthropogenic environmental change and provide a scientific foundation for future grassland management
The long-term grazing exclusion enhanced the soil organic C and N concentration in S. grandis and L. chinensis grasslands, but the soil pH decreased to some extent (Table 2)
Summary
The composition of plant communities is controlled by many environmental factors and disturbances [1,2,3,4]. Understanding the changes in community composition under long-term grazing exclusion and continued grazing is very important for ecologists. This information can enhance our ability to predict the response of plant communities to natural and anthropogenic environmental change and provide a scientific foundation for future grassland management. Inner Mongolian grasslands are primarily affected by complex grazing regimes [11,15], and fire plays a relatively weak role [16,17]. A marked increase in grazing intensity or a decades-long period of grazing exclusion should be somewhat equivalent to a disturbance and may influence the community structure of grasslands in the region
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