Overgrazing often lowers species richness and productivity of grassland communities. For Mongolian grassland ecosystems, a lack of detailed information about food-web structures makes it difficult to predict the effects of overgrazing on species diversity and community composition. We analysed the delta13C and delta15N signatures of herbaceous plants, arthropods (grouped by feeding habit), wild and domestic mammals, and humans in central Mongolia to understand the predominant food-web pathways in this grassland ecosystem. The delta13C and delta15N values of mammals showed little variation within species, but varied considerably with slope position for arthropods. The apparent isotopic discrimination between body tissue and hair of mammals was estimated as 2.0 per thousand for delta13C and 2.1 per thousand for delta15N, which was large enough to cause overestimation of the trophic level of mammals if not taken into account when using hair samples to measure isotopic enrichment.

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Backgrounds: In arid grasslands, wells are subject to heavy trampling and grazing pressure, which can increase vulnerability to local land degradation. To investigate trampling and grazing, we surveyed plant communities at three well sites in the desert steppe of Mongolia, using 1600-m line transects from the wells. The sites (Bshrub, Sshrub, and shrubL) differed by concomitant shrub type (big shrub, small shrub, and shrub-limited) and livestock pressure (light, medium, and heavy). A plant classification scheme based on edibility and morphology (rosette or creeping type) was used to separate grazing and trampling effects on plant communities. Results: Edible plants were dominant at all sites but a fraction of grazing-and trampling-tolerant plants increased in the order Bshrub, Sshrub, and shrubL, following livestock pressure. Clear transition zones from inedible to edible plant groups were recognized but at different locations and ranges among the sites. Trampling-tolerant plants explained 90% of inedible plants at Sshrub with camels and horses, but grazing-tolerant plants prevailed (60%) at shrubL with the largest livestock number. Plant coverage increased significantly along the transects at Bshrub and Sshrub but showed no meaningful change at shrubL. Herbaceous plant biomass showed significant positive and negative trends at Bshrub and shrubL, respectively. Conclusions: Both grazing and trampling can produce larger fractions of inedible plants; in this, camel and horses can have considerable effects on desert-steppe plant communities through trampling.

To examine different effects of herbivorous large mammals’ grazing pressure on plant diversity along a slope in a Mongolian nomadic pasture, we compared species richness, Simpson’s index of diversity, and the total plant coverage of plants between protected pasture from livestock grazing and grazed pasture on the near ridge, upper slope, lower slope, foot slope and valley bottom. The species richness and Simpson’s index of diversity decreased and the total coverage increased downwardly with increase in pasture soil moisture along the slope. The species richness of the protected pasture decreased, changed little, and increased on the near ridge and the upper slope, the lower slope and the foot slope, and the valley bottom, respectively. Simpson’s index of diversity of the protected pasture decreased compared with the grazed pasture only on the valley bottom. The total coverage became lower in the grazed pasture. As the reason for our results, we discuss positive and negative effects of livestock grazing on the species diversity of plants. The positive effect is shown on the valley bottom, where soil moisture and plant growth becomes high with the total coverage over 100%, due to relaxing indirectly the competitive exclusion among plants due to the grazing of dominant plants. The negative effect is obtained on the near ridge and the upper slope, where the soil moisture and the plant growth are low, because of elimination of some plants from the pasture by direct grazing damage.

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