Pedodiversity, connectance and spatial variability of soil properties, what is the relationship?

The concept of diversity and its measurement is becoming increasingly attractive to soil scientists. This theme is explored using a terrace chronosequence in the Henares River valley, NE Madrid. Pedodiversity was computed at different hierarchical levels (Great Group, Subgroup and family of Soil Taxonomy) using appropriate indices including abundance and the Shannon diversity index. Taxonomic pedodiversity, i.e., the diversity of soil types, increased with time (from low to high terraces) at high hierarchical levels but no clear relationship was found at family level. Richness-area analysis showed that a logarithmic function fitted data from the low and middle terraces, while the high terrace data could be fitted with a power model. The geostatistical analysis revealed a decrease in the variability of soil properties from young to old deposits. This study showed that, at the Henares site, diversity and spatial variability of soil properties are not synonymous concepts. Indeed, the terrace with the highest taxonomic pedodiversity at Great Group and Subgroup levels, showed a low spatial variability of soil properties. Also, the same terrace exhibited the lowest connectance values. A non-linear dynamical system approach can be useful to explain these apparently contradictory results.