According to the amount of moisture present three successional patterns are recognised:
1. Xerarch Succession (Xerosere)
This type of xerosere originates on bare rock surfaces. Here the amount of moisture present is very little or not available to the communities. Succession in desert areas is an example of xerarch type. Xerophytes and animals like certain reptiles and burrowing mammals are examples of the xerarch community. The various stages are as follows:
(i) Custose Lichens Stage
The lichens are pioneers and they produce some acids, which bring about weathering of rocks. These lichens are then replaced by foliose type of lichens.
(ii) Folios Lichens Stage
This type of lichen can absorb and retain more water and help into the development of fine thin soil layer on the rock surface.
(iii) Mass Stage
The development of thin soil layer on the rock surface, especially in the crevices favours the growth of some such xerophytic mosses. Due to their death and decay, the thickness of the soil increases.
(iv) Herb Stage
Changed habitat favours the growth of some herbaceous weeds, which are chiefly the annuals, in turn being followed by some biennials and perennials.
(v) Shrub Stage
Due to much accumulation of soil, the habitat becomes suitable for shrubs, which start migrating in the area.
(vi) Forest Stage
Some xerophytic tree species invade the area. Further weathering of rocks and increasing humus content of the soil favours the arrival of more trees.