• deterministic uncertainty;
  • pedodiversity;
  • soil geography;
  • spatial variability

The spatial variability of soils, and thus pedodiversity, can in many instances be linked to measurable, observable variations in environmental factors that control and influence pedogenesis. In addition to these extrinsic factors, recent studies have emphasized the possibility of deterministic chaos, dynamical instability, and divergent self-organization in pedogenesis and soil landscape evolution. These are intrinsic factors, operating within apparently homogeneous landscape units and independently of observable variations in environmental controls. In most soil landscapes, both extrinsic and intrinsic factors are relevant. A method for assessing their relative importance is developed here, based on soil richness-area relationships. A power function relating the number of samples and the number of soil types is a good description of the richness-area relationship for an eastern North Carolina study area. This case study shows that intrinsic variability within homogeneous landscape units is more important in determining the total pedodiversity of the study area than is the extrinsic variability associated with measurable differences in topography, parent material, and vegetation/land use.