Foliose Lichen Stage - Xerarch
As mentioned earlier, the weathering of the rocks and the decaying of the crustose lichens results in the formation of soil on the otherwise bare rocks. The foliose lichens make their appearance on such spots on the rocks which have accumulated some soil. These lichens include Dermatocarpon, Parmelia and Umbilicaria. These lichens have large, leaf-like thalli, which overlap the crustose lichens. The latter are thus cut-off from direct light. This results in death and decay of the crustose lichens.
The mass of foliaceous lichens can absorb and retain more water to some extent. Wind and water-borne dust particles are trapped by these lichens. This helps in the further building up of substratum. All these processes result in the accumulation of more and more humus. The rocks are weathered by the acids secreted by the living and the decaying plants. The weathering of the rocks and the rapid addition of humus to it result in the increase in thickness of soil layer. Thus, a considerable change in habitat is brought about.