Abstract

In northeastern China, the degradation of semi-arid grasslands caused by overgrazing is a serious concern. We surveyed three grasslands with different degrees of grazing intensity (heavily, intermediately and lightly grazed grasslands) in the Heilongjiang Province. In each grassland, plant species diversity and its spatial heterogeneity were estimated by the frequency of occurrence of each plant species. Cleistogenes squarrosa, Chenopodium cenlrorubrum and a Carex species were commonly found in all three grasslands. Euphorbia humifusa var. pilosa and two Artemisia spp-occurred frequently in degraded grasslands, and are considered to be indicators of low-quality grasslands. The plant community in the lightly grazed grassland was composed of a few dominant species, several species that occurred occasionally and many rare species. On the other hand, that in the heavily grazed grassland was composed of a few highly dominant species and many rare species. We found 39, 53 and, 52 plant species within each plot (0.5×50m) in heavily, intermediately and lightly grazed grasslands, respectively. With increasing grazing pressure on the grasslands, species diversity decreased and the spatial heterogeneity of species diversity increased.