Grazing Exclusion Effects on the Relationship between Species Richness and Vegetation Cover in Mongolian Grasslands

Understanding the role of plant diversity in maintaining vegetation cover is a central focus of assessing the vegetation dynamics of grasslands. The present study assessed the relationship between species richness and vegetation cover, as well as underlying biological mechanisms in three Mongolian grasslands, namely meadow, dry steppe and mountain steppe. Each of three grasslands was set by two treatments: grazing exclusion by fence and freely grazing. I measured plant species richness, vegetation cover, height and phenology. I examined three biological mechanisms, namely plant interactions, the role of dominant species and vegetation growth periods. The results showed that higher species richness generally increased vegetation cover independent of fencing treatment and grassland type. Plant interactions were the strongest in fenced plots of the mountain steppe. Dominant plant species invested more in vegetation cover rather than the height in grazed plots than fenced ones in Mongolian grasslands. Taking vegetation growth periods into account did not alter the strength and the direction of the relationship between species richness and vegetation cover. I thus infer that examining changes in species diversity will allow for a better understanding of vegetation cover dynamics in grasslands. This will help to assess how ecosystem functioning might be impacted by grazing disturbances in Mongolia.