Abstract: Treeline is sensitive to climate change. Forest gap and edge are important windows for the invasion of herbaceous species. Research on distribution patterns of herbaceous species in forest gaps and forest edges of treeline ecotones could help explain important ecological processes. We selected a forest gap (elevation: 2350 m) and a forest edge (elevation: 2300 m) as plots(5 m×5 m) in a treeline ecotone of Wutai Natural Reserve. Twenty-five quadrats (1 m×1 m) were set up in each of both plots, within which the locations of six dominant species (Hierochloe glabra, Anemone rivularis, Plantago depressa, Polygonum viviparum, Potentilla freyniana, and Taraxacum mongolicum) were recorded. Complete spatial random process (CSR), heterogeneous Poisson process (HP), and Poisson cluster (PC) were used to simulate the spatial patterns of the six species at different scales. The results showed that: (1) Aggregated sizes of the six species in forest gaps were broader than those in the forest edge, with those of Polygonum viviparum and Anemone rivularis were broader than other species in both plots. The aggregated sizes of Taraxacum mongolicum and Plantago depressa were narrower than other species in both plots. The most common aggregation occurred on 0-40, 100-140 and 200-230 cm. (2) For both forest gap and edge, HP simulation and significance tests showed that micro-habitat differences between plots had no significant effect on species distribution with broad ecological amplitude. However, the distribution of Hierochloe glabra was significantly affected by micro-habitat differences in forest gap and edge due to ramet growth. (3) Results from PC simulations and significance tests showed that seed dispersal significantly affected species distribution in the forest edge. Seed dispersal around maternal individuals often occurred at 0-50 cm scales as affected by gravity. At the scale of >100 cm, species with special dispersal modes or structures affected their dispersal distance. Additionally, species with special structures could reach 250 cm with the help of strong winds.

Key words: Arid-highland of loess plateau, Different mulching, Soil water, Soil tentpetatute. Soil nutrients