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During 2002-2004, a broad-scale survey on the plant diversity of grassland communities along a natural elevation gradient in the permafrost regions of the Qinghai-Tibet plateau, China, was conducted to investigate the effect of highway construction nearly 30 years ago.

Richness index was not significantly different among undisturbed communities (Kobresia pygmaea meadow, K. humilis meadow, Stipa purpurea steppe, Carex moorcroftii steppe), but significant differences (P less than 0.05) were observed for evenness and diversity indices among four undisturbed communities. Three indices significantly decreased from communities 100m (lightly disturbed communities), 200m (undisturbed communities), and 50m (severely disturbed communities) from the Qinghai-Xicang Highway, and three indices of severely disturbed communities were similar to that of 30m communities (extremely-severely disturbed communities). Diversity and richness indices peaked at intermediate elevations of 4720m in undisturbed communities and lightly disturbed communities, but were uniform in the severely disturbed communities and extremely-severely disturbed communities along with the increase of elevation.

²-Diversity decreased in communities at 30, 50, and 100-200m distance from the highway. This indicated that ²-diversity of communities was enhanced with the increase of disturbance for each grassland type in the study region. Both undisturbed and disturbed communities showed the same changeable bell-shaped trend with elevation increase, increasing from 4320-4620m, decreasing from 4720 to 4920m, and peaking at 4620 to ~4720m, indicating that elevation from 4620-4720m was a transition zone in permafrost region.