Soil Complexity and Pedogenesis

Abstract

This paper reviews recent developments in studies of soil complexity, focusing on the variability of soil types within soil landscapes. Changes in soil complexity are directly related to divergent and convergent pedogenesis and to dynamical stability and chaos. Accordingly, strong links exist between nonlinear dynamical systems theory and studies of soil complexity. Traditional conceptual models of soil formation emphasized convergence of the soil cover in the form of progress toward mature, climax soils. A view of divergence as a frequent occurrence rather than an occasional exception is more recent. Measurement of soil complexity is now firmly linked to field pedology. In addition to strong methodological links to pedometrics and soil geography, standard tools for assessing complexity include chronosequences and other historical approaches, relationships between soil properties and soil forming factors, and pedological indicators. Eight general pathways to changes in soil complexity are identified. Three are based on changes in soil-forming factors. These may increase or decrease complexity depending on whether the factors themselves are converging or diverging and the relative magnitudes of soil and state factor divergence. Three pathways are associated with local disturbances. If these occur less frequently than the relaxation time for soil responses, and if internal pedological dynamics are dynamically stable, then disturbance-induced complexity is reduced over time. Otherwise, divergence and increasing complexity occurs. Two additional pathways are directly related to dynamical stability of intrinsic pedological processes, which may result in decreasing or increasing complexity, either in concert with, or independently of, environmental controls or disturbances.