Effects of grazing on niche of major plant populations in alpine steppe in Qinghai Lake Region

Alpine steppe is the major vegetation community around Qinghai Lake Region. It is regarded as an important ecological barrier of the Qinghai-Tibetan Plateau and a rich site forage base for yak and sheep production. However, the alpine steppe vegetation degraded by overstocking. Therefore, it’s important to study the effects of grazing on community of alpine steppe around Qinghai Lake Region. In this study, the vegetation under different grazing intensity were investigated, based on grazing trial for 3 years in alpine steppe around Qinghai Lake Region. Levins niche breadth and Pianka niche overlap index were used to calculate niche characteristics of major plant populations under different grazing gradients to explain the mechanism of grazing succession of community. Our results showed that dominant species of community had changed after grazing 3 years. The dominance of plants with good palatability (Stipa purpurea, Poa sp., Medicago ruthenica, etc.) decreased and the dominance of plants with grazing resistance or bad palatability (Kobresia humilis, Thermopsis lanceolata, etc.) increased with the increase of grazing intensity. S.purpurea had the widest niche breadth, and after then was Thermopsis lanceolata, with the values being 0.994 and 0.959, respectively. Potentilla multifida and Astragalus polycladus had wider niche breadth because of its stronger environmental adaptation ability. The niche breadths of Elymus nutans and K.cristata under different grazing gradients were narrow, indicating that grazing restricted the growth of high grasses. Species with wider niche breadth had higher niche overlap with other species. The narrower niche overlap could be seen as the result of interspecific differentiation on resource utilization. The major plant populations had niche differentiation result from grazing. With increasing grazing intensity, community with S.purpurea and Poa sp. being the dominant populations may be in degradation direction on community with K.humilis, K.pygmaea and T.lanceolata being the dominant populations, indicating that habitat of community had obviously degraded. Therefore, it’s important to control grazing intensity of rangeland.