Page "Soil retrogression and degradation" Paragraph 1

At the beginning of soil formation, the bare rock out crops is gradually colonized by pioneer species ( lichens and mosses ).

They are succeeded by herbaceous vegetation, shrubs and finally forest.

In parallel, the first humus-bearing horizon is formed ( the A horizon ), followed by some mineral horizons ( B horizons ).

Each successive stage is characterized by a certain association of soil / vegetation and environment, which defines an ecosystem.