SEED RAIN, SEEDLING ESTABLISHMENT AND CLONAL GROWTH STRATEGIES ON A GLACIER FORELAND

Seed production, composition of the seed rain. germination, and seedli ng mortality, as well as vegetative growth characteristics of common p ioneer plant species were studied on the foreland of the retreating Mo rteratsch glacier in the Swiss Alps. The frequency of diaspores trappe d in different successional stages was related to their dispersal mode and was highly skewed towards a few species. Plenty of diaspores well adapted for dispersal by wind are a precondition for the most importa nt pioneer species. Seeds from all pioneer species investigated had a good germination success, provided that the moisture content of the so il was high enough. However, requirement for seedling establishment di ffered among sites of increasing terrain age and among species. Only s pecialized pioneers such as Cerastium pedunculatum. Linaria alpina, Ox yria digyna and Saxifraga alzoides tolerate the cold and moist conditi ons near the glacier. However, these species are restricted to early s uccessional stages. Seedlings of Epilobium fleischeri are affected not only by the cold and moist conditions near the glacier but also by mo derately dry conditions on older sites, Availability of safe sites bec omes crucial for most species with increasing age of sites and with dr ier conditions. Most species playing a dominant role during early succ ession and persisting during later successional stages have a distinct ive ability to spr ead clonally and have a growth form with more or le ss widely spaced ramets: Achillea moschata, Cerastium pedunculatum, Ep ilobium fleischeri and Hieracium staticifolium. The growth strategy an d demography of the clonal E. fleischeri is presented as an example. T he life cycle of this species is characterized in succession by (1) th e colonization of safe sites by small seeds adapted for wind dispersal , (2) horizontal spread by clonal growth, and (3) the persistence thro ugh phenotypic morphological plasticity in later successional stages. Seedling establishment and clonal growth are thus complementary mechan isms in plant succession on recently deglaciated terrain.