Species recruitment in alpine plant communities: the role of species interactions and productivity

P>1. It is not clear how local and regional processes influence plant species recruitment. Local abiotic factors are predicted to constrain recruitment under harsh environmental conditions and low productivity, whereas the role of seed availability may be more important at intermediate productivity. The role of establishment limitation (local interactions) is predicted to increase under high productivity due to competition. 2. This study examined the effects of local biotic interactions, such as competition and facilitation from the resident vegetation, on alpine plant species recruitment, and investigated whether the role of species interactions depended on productivity. All naturally emerging seedlings were recorded in plots with intact vegetation and where vegetation had been removed, in a natural low-productivity alpine Dryas heath and in plots where productivity had increased after fertilizing. 3. Positive effects of vegetation removal on seedling emergence suggested that competition from neighbour vegetation may have an important role for recruitment in alpine plant communities. The role of competitive release increased with productivity. Productivity increased short-term, but not long-term seedling recruitment, likely due to increased competition from re-growth over time. There was no effect of productivity on species richness recovery after vegetation removal. 4. There was a positive relationship between neighbour species richness and seedling density in the low-productivity plots, but not in the high-productivity plots. Local seed production was the major seed source in both parts of the heath, but in the high-productivity plots, the high abundance of a few species in the species pool was more important for seedling recruitment than species richness. 5. Synthesis. Competition may play a significant role for plant species recruitment in environmentally harsh habitats of low productivity, where abiotic factors or facilitation traditionally are predicted to be more important ecological filters. Climate warming and increased nitrogen deposition may result in higher productivity of tundra plant communities, which may increase the role of competition, and the identity of neighbour species may become more important for recruitment than species richness.