关键词: 正相互作用, 斑块状植被, 幼苗密度, 物种多样性, 相似性

Abstract: The seedling stage is the most fragile and critical stage of the plant life cycle. The aim of this study was to determine whether existing dominant species could serve as nurse species to play a positive role in improving seedling establishment and survival on a loess slope where soil erosion is a serious problem. Three typical plant communities (Bothriochloa ischaemum, Sophora viciifolia, and Artemisia gmelinii) in the hill-gully region of the Loess Plateau were selected for in-depth analyses. For each community, the species composition, seedling densities, species diversity, and their relationship with the standing vegetation in two microhabitats (plant patches and bare land patches) were surveyed and analyzed. The results showed that: 1) the seedlings represented 52 species belonging to 22 families. Most seedlings in the B. ischaemum, S. viciifolia, and A. gmelinii communities belonged to the Poaceae, Leguminosae, and Poaceae family, respectively. Perennial herbs made up the largest proportion of seedlings. 2) Seedling density, seedling species diversity, and similarity indexes showed similar trends in seedling and standing vegetation. The values of these indexes were higher in vegetated patches than in bare land patches. In vegetated patches, the highest seedling density and species diversity index were in the A. gmelinii community; the lowest seedling density was in the B. ischaemum community; and the lowest species diversity index was in the S. viciifolia community. In the bare land patches, the communities could be ranked, from highest seedling density and species diversity index to lowest, as follows: A. gmelinii community>S. viciifolia community>B. ischaemum community. The similarity index between seedling and standing vegetation was less than 0.5 in both microhabitats of the three plant communities, indicating that the seedling and standing vegetation of each community were extremely dissimilar or moderately dissimilar. 3) These results show that adult plants of the three dominant species can play a positive role in the regeneration of seedlings in the surrounding area, and the strength of this positive interaction differs among species. The results indicate that all three plant species can serve as nurse plants to improve seedling survival, but that the positive interaction may weaken and turn into a competitive relationship as the seedlings grow, so that there is little similarity between seedlings and standing plants.

Key words: positive interaction, patched vegetation, seedling density, species diversity, similarity