Pedodiversity analysis at large scales: an example of three fluvial terraces of the Henares River (central Spain)

This paper presents the results of the application of richness and diversity indices and the fitting of four probabilistic distribution models to a soil chronosequence developed on the fluvial terraces of the Henares River (NE Madrid) as a means to analyse the soil mantle evolution of the valley during the Quaternary. Richness–area relationships were also investigated. Calculations were performed considering individuals (i.e., pedons) and the area covered by a given soil type, at different hierarchy levels of the USDA taxonomic classification (Great Group, Subgroup and family) as well as for diagnostic horizons. Abundance of Great Groups and Subgroups (richness or pedorichness) increases from low (young) to high (old) terraces. It has also been found that the higher the detail in the classification, the higher the pedodiversity values. Diagnostic horizons accounted for the genetic pedodiversity; its value decreases with soil development in the first meter of the solum; this trend changes with increasing observation depth. Therefore, genetic pedorichness and pedodiversity increase in this example with the age of geomorphologic surfaces. However, an appropriate quantification of the genetic diversity should consider the entire solum depth. It is also shown that pedodiversity increases with the area considered. On the other hand, the fit of sampled areas to the probabilistic distribution models used by ecologists is less conclusive. Regarding richness–area relationships, the low and middle terraces fitted a logarithmic function, while the high terrace fitted a power model, in agreement with the ecological literature on biotaxa–area relationships.