Colonization processes on a central Alpine glacier foreland

Questions: What are the colonization trends in vegetated vs. bare-ground plots over a 10-year period in a central Alpine glacier foreland? What are the long-term effects of artificial seed addition to these plots? Location: Glacier foreland of the Rotmoosferner in the Central Alps, Obergurgl, Tyrol, Austria, 2380 - 2400 m a.s.l. Methods: A total of 40 permanent plots were established on moraines ice-free for 35 and 50 years on vegetated and bare-ground areas. Half of them were treated with a seed mixture in 1996 and 1997. Number and cover of the species were recorded in 1996 and from 2002/2003 to 2006. Results: Species richness doubled in the control plots and tripled in seeded plots on the 35-year-ice-free moraine. On the 50-year-ice-free moraine the increase in species number was more modest. Significant site, seeding and time effects were found. Seed addition had no effects in the bare-ground plots on the older moraine and low effects in those on the younger moraine. All plots showed significant changes in cover of single species. The pioneer species decreased significantly in both moraines, in the control as well as in the seeded plots. A disappearance during the next years is predicted. Conclusions: Colonization in bare-ground plots is limited by a lack of safe sites, whereas vegetated plots facilitate recruitment and establishment. Colonization on the glacier foreland is also dispersal limited. Seed addition enhanced the presence of already established species, and late successional species were newly introduced.