Effects Of Different Livestock Grazing On Plant Community Structure In The Typical Steppe Of Inner Mongolia

Grazing is the most important land use in the natural steppe region of Inner Mongolia.Grazing livestock is an important component of the grazing grassland ecosystems.Different livestock species and their combinations have different effects on grassland plant communities.However,most of the grazing studies on the Inner Mongolian grasslands are on the effects of grazing intensity and time,rarely on the effects of different grazing livestock species.In present study,we took a typical steppe community dominated by Leymus chinensis and Stipa grandis in Xilinguole,Inner Mongolia as an example,to examine the effects of grazing at moderate intensity by three livestock species(sheep,cattle and goat)on the structure and functioning of grassland plant communities.Fourteen experimental grassland plots were used,representing four treatments(sheep,cattle or goat grazing,plus no-grazing control)replicated by four times.The results show:1)Livestock species had an effect on the species diversity and composition of plant communities: Compared with non-grazing grassland,sheep grazing significantly reduced the important value of Cleistogenes squarrosa(P<0.05);cattle grazing significantly reduced the important values of L.chinensis and S.grandis(P<0.05);and goat grazing significantly reduced the important value of S.grandis(P<0.05).Compared with sheep-grazing grassland,goat-grazing and cattle-grazing grassland had significantly lower important value for L.chinensis(P<0.05),but higher important value for C.squarrosa(P<0.05).There was no significant difference in the important value of S.grandis among the grasslands grazed by three livestock species.Compared with non-grazing grassland,cattle grazing significantly improved species richness,community Shannon-Wiener index(H)and Simpson dominance index(R)(P<0.05);whereas no significant difference was detected in plant diversity indices between the sheep-or goat-grazing grassland and non-grazing grassland.The three diversity indices of cattle-grazing grassland were significantly higher than sheep-grazing grassland(P<0.05).2)Livestock species had an effect on plant above-ground biomass(AGB): Compared with the non-grazing grassland,sheep grazing significantly reduced the AGB of S.grandis,C.squarrosa and other miscellaneous grasses(P<0.05),while cattle and goat grazing significantly reduced the AGB of L.chinensis,S.grandis and C.squarrosa(P<0.05).The AGB of C.squarrosa was lower under sheep grazing than under cattle or goat grazing(P<0.05);the AGB of L.chinensis was lower under cattle grazing than under sheep grazing(P<0.05).The intake of L.chinensis by grazing goats was significantly higher than that by grazing cattle(P<0.05),but showed no difference from that by grazing sheep.3)Grazing of different livestock species altered the biomass composition of plant functional groups in grassland community: Compared with non-grazing grassland,sheep or goat grazing significantly increased the relative biomass of rhizomatous grasses,but decreased that of short bunch grasses(P<0.05).Cattle grazing significantly increased the relative biomass of annual and biennial plants(P<0.05).However,no significant difference was detected in the above net primary productivity(ANPP)among the grasslands grazed by different livestock species.4)Livestock grazing affected the spatial pattern of plant communities: Compared with non-grazing grassland,livestock grazing reduced the spatial heterogeneity of plant population in the community;the community patches dominated by S.grandis and L.chinensis existed in the non-grazing grassland,but not in the grazing grasslands.This indicated that the spatial heterogeneity in plant populations was predominantly determined by structural factors such as the micro-habitat and soil,though it was affected by grazing animals.5)Under moderate grazing conditions,grazing for three consecutive years has no significant effect on the water content and bulk density of the 0-20 cm soil layer.Soil total nitrogen and total carbon content in 0-10 cm soil layer was lower in the cattle-grazing than no-grazing grassland(P<0.05),while soil total phosphorus content was higher in the sheep-grazing than no-grazing grassland(P<0.05).The reasons need to be further studied.Our study is the first one that compares the effects of three major livestock species on grassland communities using a designed experiment.Our results has deepened our understanding of the grassland dynamics under different livestock grazing,and provided useful information for developing sustainable grazing management regimes,especially through optimizing livestock structure.