On succession in a saxicolous lichen community

The lichen flora was sampled at each of the five sites on a near-vertical gneiss rock face. The sites were ranked according to the degree of weathering of the rock surface and were taken to represent different stages in a succession. The succession shows an increase in species richness and diversity over time, although the proportion of the rock face unoccupied by lichens increases at the oldest site. The succession will be driven by allogenic processes, physical weathering of the rocks, facilitation, especially the effects of lichens on surface erosion, and by inhibition, through competition for space. At the oldest site mortality of lichen thalli becomes important continually opening up new areas of recolonization and maintaining community diversity. The succession may be described by four phases: (1) colonization, (2) growth, (3) competition and (4) senescence.