SOIL CHRONOSEQUENCES, SOIL DEVELOPMENT, AND SOIL EVOLUTION - A CRITICAL-REVIEW

Soils chronosequences are valuable tools for investigating rates and d irections of soil and landscape evolution. Post-incisive chronosequenc es are the most common type of chronosequence. They are found in many landscapes, including sand dunes, glacial moraines, landslide scars, o ld pasture, burnt landscape patches, old mining areas, lava flows, all uvial fans, floodplains, river terraces, and marine terraces. They reg ister pedogenic change over time-scales ranging from years to millions of years. Soil chronosequences help in testing rival theories of pedo genesis. Traditional soil formation theory sees a soil developing prog ressively under the influence of the environmental state factors until it is in equilibrium with prevailing environmental conditions. This d evelopmental view of pedogenesis is supported by the classic soil chro nosequence studies. A new evolutionary view of pedogenesis, which was prompted by the omnipresent inconstancy of environmental conditions an d the notions of multidirectional changes and multiple steady states ( as predicted by non-linear dynamics), proposes that environmental inco nstancy and non-linear behaviour in soil-landscapes lead to soil evolu tion, rather than to soil development. Soils 'evolve' through continua l creation and destruction at all scales, and may progress, stay the s ame, or retrogress, depending on the environmental circumstances. Some recent soil and vegetation chronosequence investigations support an e volutionary view of pedogenesis. Ic is concluded that soil chronoseque nces are still potent instruments for pedological investigations and t hat they have a starring role to play in the testing of pedological th eories. (C) 1998 Elsevier Science B.V. All rights reserved.