Pedodiversity in the United States of America

Little attention has been paid to analyses of pedodiversity. In this study, quantitative aspects of pedodiversity were explored for the USA based on the State Soil Geographic database (STATSGO). First, pedodiversity indices for the conterminous USA were estimated. Second, taxa–area relationships were investigated in each soil taxonomic category. Thirdly, differences in pedodiversity between the USDA-NRCS geographical regions were compared. Fourth, the possible mechanisms underlying the observed relative abundance of soil taxa were explored. Results show that as the taxonomic category decreases from order to series, Shannonʹs diversity index increases because taxa richness increased dramatically. The relationship between the number of taxa (S) and area (A) is formulated as S=cAz. The exponent z reflects the taxa-richness of soil ‘communities’ and increases constantly as taxonomic categories decrease from order to series. The “West” USDA-NRCS geographical region has the highest soil taxa richness, followed by the “Northern Plains” region. The “South Central” region has the highest taxa evenness, while taxa evenness in the “West” region is the lowest. The “West” or the “South Central” regions have the highest overall soil diversity in the four highest taxonomic categories, while the “West” or “Northern Plains” regions have the highest diversity in the two lowest taxonomic levels. The high diversity index in the “West” region results from high taxa richness while the high diversity index in the “South Central” region results from an evenness of taxa. As the taxonomic level decreases, the pattern of taxa abundance approaches a lognormal distribution. One of the key findings of this research is that at lower levels of soil taxonomic divisions (especially the series level), soil taxa increase continuously with increasing area, indicating considerable soil endemism in the USA (and likely around the world), a key consideration in conservation and preservation planning.