Seed rain, soil seed bank, seedling recruitment, and survival of seedlings on a glacier foreland in the Central Alps

Abstract

Summary Seed rain, soil seed bank, germination and the establishment of seedlings were investigated on a glacier foreland in the Central Alps on a 25 and a 40 year old moraine at 2380–2400 m above sea level. Spatial and temporal variability of the seed rain during the growing seasons of 1996 and 1997 was recorded, using seed traps sunk into the soil surface. The size of the seed bank was determined in a preliminary study for spring samples in 1996, using the extraction method. Seedling emergence and establishment were recorded within permanent plots during the growing seasons of 1996 and 1997, comparing vegetated and bare-ground plots. The results showed a high degree of inhomogeneity within the samples from each site. In general, the species composition of the seed rain, the seed bank and the seedlings resembled that of the present vegetation. Late-successional species were present in neither the seed rain nor the seed bank. They were also absent from the seedling cohorts. More seedlings were recorded on the vegetated plots compared to the bare-ground plots. Between the two moraine stages no significant differences in seedling recruitment were found; however, the species composition was different. Most of the seedlings emerged on safe sites, i.e. in the vicinity of already established plants and larger stones. Ca. 50% of all seedlings died before they could be identified. Mortality rates of the remaining seedlings were between 0% and 100% after two winters. The relatively high plant cover on the studied moraines suggests that an additional input of plant fragments from avalanches and streams has to be assumed. The speed of colonization and succession on the studied glacier foreland is relatively low compared to that recorded on other glacier forelands of the Alps, probably due to the scarce sources of propagules close to the youngest moraines.