Recent moraines constitute a worthwhile opportunity for studies concerning plant colonization, especially when the date of origin of the moraine is known. The moraine studied, roughly 34 years old, was in an early stage of plant succession. Plant communities were observed only on the boulders at the top of the moraine. They were always composed of a relatively small number of lichen species and with a low coverage of the rock surface. It is noteworthy that all lichen species observed lack asexual propagula and most of them are considered as being nitrophilous or ornithocoprophilous. In many cases, a close relation between the boulder size and the measured variables (specimen diameter, coverage, and number of species) has been noted, with maximum values for the biggest boulders. The hypothetical biological implications of the boulder size and the causes of the interspecific differences observed in the average diameter of lichens are discussed.
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