Abstract:

Spatial distribution patterns of plant populations is fundamental to ecology. Primary communities have become rare in the steppe because long-term overgrazing has led to serious degradation of the steppe ecosystems and requires further investigation. The most widely distributed grassland across the Eurasia steppe region is the Stipa grandis community. At present, there are well-preserved primary S. grandis communities in the steppe region. We chose the primary S. grandis community and long-term overgrazing community of S. grandis, and applied an O-Ring function combined with null models to analyze the spatial pattern of S. grandis. The results showed that the spatial pattern of S. grandis was overdispersed in the primary community at the small scale, while it was clustered in the long-term overgrazing community. These results indicate that competition was the main interaction in the primary community, while positive interactions dominated in the long-term overgrazing community. Therefore, these results verified the stress gradient hypothesis and proved that long-term overgrazing altered population spatial patterns.

Key words: point pattern analysis, O-Ring function, stress gradient hypothesis (SGH), replicate sampling, population, primary community, long-term overgrazing