ABSTRACT
The previous chapter has been concerned with soil formation under present environmental conditions, but in all parts of the world, environmental conditions have changed through time, and soils very often reflect these changes. The magnitude of environmental change can vary greatly. For example, a broadleaf forest may experience a change in the relative proportions of its component species, which would represent a minor environmental change in terms of pedogenic processes and the resulting soil characteristics. In contrast, an area whose climate changed from warm and dry to cold and humid would be likely to experience a major pedogenic transformation. There can also be great differences in the length of time over which environmental change occurs; some changes may be rapid, for example those resulting from vegetation clearance or artificial drainage may be complete in less than a year, whereas others, particularly major climatic change, may occur over thousands or even millions of years.
