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QuestionsFire and grazing can affect plant communities through different pathways in grasslands. However, little is known about how these disturbances affect plant communities in recovered semi-arid grasslands. Here we investigated effects of prescribed fire, sheep grazing and their interactions on above-ground biomass and species diversity in degraded semi-arid grasslands recovered from cropping agriculture.

LocationKeerqin grasslands, northeast China.

MethodsA short-term grazing and burning experiment with split-plot design was conducted, with burning applied at the main plot level and grazing applied at the subplot level. After 1year of spring burning and 2years of grazing by sheep, the above-ground biomass, species diversity, biomass proportion of plant functional groups and soil resource availability of the grasslands were measured and compared between treatments using a split-plot ANOVA model.

ResultsOne-year of spring fire significantly increased above-ground biomass, while 2years of grazing by sheep significantly decreased it. Species diversity was reduced by grazing in the burned plots but enhanced by grazing in the unburned plots. Fire significantly increased the biomass percentage of grasses and reduced that of forbs. Fire also changed soil water content and inorganic N concentration, and grazing enhanced light intensity to the soil surface. Moreover, above-ground biomass was positively related to soil water content and inorganic N concentration under both disturbances. Species diversity had a positive linear relationship with biomass percentage of grasses and a negative relationship with biomass percentage of forbs under sheep grazing.

ConclusionsBoth short-term fire and grazing are important in determining the above-ground biomass in degraded semi-arid grasslands, and their effects are opposite. Grazing coupled with fire has negative effects on species diversity. Thus, we advise that fire and grazing should be carefully applied when used in the same management regime to maintain above-ground biomass and species diversity in managing this grassland ecosystem.