A survey was made of the gravel left bare by the retreat of the Rotmoos Glacier, Obergurgl, Austria. Dating of the glacier recession and of the serai stages was estimated from the age of dwarf willows. It was found that humus in the soil was not necessary for colonization, and that, contrary to the general belief of ecologists, the first pioneers on the bare soil were spermatophytes (Saxifraga aizoides and Salix), and that the population of mosses remained very low until 5 years after the start of colonization. Lichens were absent for 13 years. It is thought that colonization began in the same year that the ice left the gravel. Dating therefore was estimated as the age of the oldest Salix plus one year.