Seedling demography in an alpine ecosystem.

Seedling establishment has long been believed to be rare on alpine tundra because of predicted life history trade-offs, the clonality of alpine species, and the harshness of the alpine climate. Contrary to the idea that seedlings are rare on alpine tundra, a 4-yr demographic study of seedlings at Niwot Ridge, Colorado, USA, found seedlings at high densities, particularly in wetter plant communities. Higher germination densities were associated with higher soil moistures both across communities and across time. Mortality of seedlings was highest in the first year and decreased in subsequent years. Species' abundances differed between seedling and adult populations. Many forbs that lacked vegetative reproduction were significantly more abundant among seedling populations, and many monocots and clonal forbs were more abundant among adult populations. In a comparison with published demographic rates, seedling recruitment and mortality rates of Niwot Ridge species fell above or within rates for a wide range of perennial species. Therefore, germination and seedling establishment stages are no more limiting to sexual reproduction in alpine plants than in other perennial plants.