Xerosere

The rainwater combines with atmospheric carbon dioxide that corrodes the surface of the rocks and produces crevices.

These spores grow and form symbiotic associations, lichen, which act as pioneer species of bare rocks.

The shallow depressions in the rocks and crevices become filled with soil and topsoil layer increases further.

The spores of xerophytic mosses, such as Polytrichum, Tortula, and Grimmia, are brought to the rock where they succeed lichens.

As mosses develop in patches they catch soil particles from the air and help increase the amount of substratum.

The changing environment leads to migration of lichens and helps invasion of herbaceous vegetation that can out-compete mosses.

These climatic conditions favor growth of bacterial and fungal populations, resulting in increase in decomposition activities.

Early invasion of shrub is slow, but once a few bushes have become established, birds invade the area and help disperse scrub seeds.

Leaf litter and decaying roots weather the soil further and add humus to it making the habitat more favorable for growth to trees.

Many intermediate tree stages develop prior to establishment of a climax community.