Abstract:

Aims: Understanding the spatial patterns of vegetative populations is fundamental to plant ecology, as changes in spatial patterns can reveal past, present, and future processes that impacting the plant community. The study of population spatial patterns in natural communities has garnered increasing interest, particularly in the temperate steppe of China. In this region sheep overgrazing has degraded native grasslands since 1960s, decreasing production and biodiversity. In response, some primary Leymus chinensis communities have been preserved through enclosures that were established in 1979. Using both the primary L. chinensis communities that were preserved and the overgrazed L. chinensis communities, we aim to address two questions: (1) How do the spatial patterns of L. chinensis differ between primary and overgrazed community? (2) Is the L. chinensis aggregation intensity of the primary community lower than that of the overgrazed community?

Methods: Three 5 m × 5 m plots were established within the primary and long-term overgrazed L. chinensis communites with minimal variation in topography and environmental conditions, respectively. Within each plot, the location of each L. chinensis individual was recorded by integrating digital photographs into a geographical information system. To analyze spatial patterns of L. chinensis, we applied the pairwise correlation function g(r) and compared these to homogeneous and heterogeneous Poisson null models.

Results: In the primary L. chinensis community, L. chinensis exhibited a clustered pattern at small scales (< 0.71 m) and a random distribution at larger scales (0.71-2.50 m). In contrast, in the overgrazed L. chinensis community, L. chinensis exhibited a clustered pattern across all scales (0-2.50 m). When variations in the surrounding habitat (habitat heterogenity) were controlled for, the L. chinensis aggregation intensity of the overgrazed L. chinensis community was higher than the primary L. chinensis community at the small scale.

Conclusion: Grazing caused habitat heterogeneity, shifting the spatial pattern of L. chinensis as it developed from a primary to an overgrazed community. Furthermore, controlling for habitat heterogeneity revealed that the positive interactions caused by grazing stress increased the aggregation intensity of L. chinensis compared to the primary L. chinensis communities.

Key words: primary community, g(r) function, replicate sampling, grazing