Selective grazing and seasonal precipitation play key roles in shaping plant community structure of semi-arid grasslands
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Many studies have examined how intensity of grazing and patterns of precipitation individually and interactively influence the spatial and temporal dynamics of grassland vegetation, such as dominance, succession, coexistence, and spatial heterogeneity. However existing models have rarely considered the diet preferences of grazers and how they interact with variation in precipitation amount and timing.
Objective and methods
We examined how plant community structure responds to the individual and combined effects of grazing intensity, selective grazing, and patterns of precipitation, based on a six-year grazing experiment with seven levels of field-manipulated grazing intensity in a typical steppe of Inner Mongolia.
The palatable species, mainly forbs, were most severely damaged at intermediate levels of grazing intensity; given that these species are the major contributors to plant community diversity, a U-shaped diversity-grazing intensity relationship resulted. In contrast, spatial heterogeneity of aboveground biomass and species composition peaked at intermediate levels of grazing intensity. Cold season precipitation positively correlated with the abundance of the dominant C3 grasses and correlated negatively with the subdominant forbs and C4 plants. Thus, when cold season precipitation increased, plant community species diversity decreased. Grazing intensity and precipitation did not interact in their effects on species richness.
These findings contrast with the predictions from current disturbance–diversity models and indicate that diet selection of grazing animals is an important factor shaping the diversity-grazing intensity relationship in semi-arid grasslands. Future grassland biodiversity conservation and management practices should take diet preference of grazing animals into account.
KeywordsSpecies richness Spatial heterogeneity Precipitation seasonality Diversity-grazing intensity relationship Intermediate disturbance hypothesis Dynamic equilibrium model C3/C4 abundance
We are very grateful for the very helpful comments from two anonymous reviewers. We thank Jun Hui Chen and Yang Wang for their helps with statistics. This work was supported by the Natural Science Foundation of China (30825008, 31300354) and the Deutsche Forschungsgemeinschaft (DFG) for the research group 536 MAGIM (Matter fluxes of grasslands in Inner Mongolia as influenced by stocking rate). We appreciate the Inner Mongolia Grassland Ecosystem Research Station (IMGERS) of the Chinese Academy of Sciences for providing lab and field facilities, accommodation and the precious long term climatic dataset. DUH received partial support from the Chinese Academy of Sciences through the fellowship program for Visiting Senior International Scientists.
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