Taxonomic structure, distribution, and abundance of the soils in the USA

Abstract

In this paper, we report the taxonomic structure, the spatial distribution, and relative abundance of soils in the USA. In the analysis, we used the STATSGO (1997 version) database, which contains information on 11 orders, 52 suborders, 232 great groups, 1175 subgroups, 6226 families, and 13 129 series. The analysis of taxonomic structure showed that the numbers of taxa in any category were distributed unevenly in relation to taxa present at the next higher category. This uneven distribution becomes more pronounced in the lower categories of the hierarchy. In addition, there is a trend for taxa to produce only one, or a very small number, of taxa in the next lower category at the lower categories of the system. The analysis of the spatial distribution of taxa showed that 10 662 (51.2%) out of 20 825 taxa exist only 1 Major Land Resource Area (MLRA), indicating that most soil taxa are not widely spread, and are specific to particular combinations of state factors. The area abundance of soil taxa is asymmetric with most taxa in a category having relative small area extent. Five (2.1%) great-groups, 37 (2.1%) subgroups, 417 (6.7) families, and 827 (6.3%) series had total areas less than 10 km2, and were defined as rare taxa. Among the rare taxa, four (80%) rare great groups, 36 (97.3%) rare subgroups, 378 (90.6%) rare families, and 750 (90.7%) rare series were found in only 1 MLRA. The portion of rare soils might be much higher because not all the soils are included in STATSGO because of their too limited area. The spatial and area abundance analyses of the soils provides a perspective useful for discussions on the preservation of soil resources in the USA, a topic whose importance is likely to grow in conjunction with increasing interest in global biodiversity and more intense uses of the world's soil resources.