Mountain Soils - Mountain Geography: Physical and Human Dimensions - page 308

FIGURE 6.5 The pattern of soil orders in the United States shows strong relationships to climate
patterns. At this scale, local variations in mountain soils are not evident. (Based on USDA NRCS
information.)
Although still widely used, soil classification by vegetation cover has been criticized
in recent years because the terminology is imprecise, the soil characteristics are dif-
ficult to quantify, and the system has a strong genetic bias that many specialists find
limiting. As a result, a new system of soil classification, Soil Taxonomy, was developed
in the United States and also used by scientists in 45 other countries (Brady and Weil
2008; Soil Survey Staff 2010). It is based entirely on soil properties that can be determ-
ined by human senses or by instrumentation.
The U.S. Soil Taxonomy classification has 12 soil orders, subdivided into suborders,
great groups, subgroups, families, and series (Fig. 6.5, Table 6.2). Subdivisions are
based on analyses of chemical and physical characteristics from the entire soil profile,
rather than from surface samples. No soil order is specific to mountains; all can occur
in mountain regions. The initial soil taxonomy contained ten orders; then Andisols (vol-
canic soils) were added in 1989 and Gelisols (soils with permafrost within 2 m of the
surface) in 1996.
A major effort to standardize soil mapping across country boundaries was completed
by the Food and Agriculture Organization (FAO) of the United Nations and revised in
1988 (FAO 2003). The FAO soil classification has 28 major soil groupings, based largely
on environment. Because mountain environments consist of many microenvironments
(e.g., well-drained slopes, poorly drained depressions, alluvial deposits), most FAO soil
groups are present in mountain environments. Some soils, such as andosols ( Andisols
in the U.S. taxonomy) and podzols ( Spodosols ) are essentially the same in both the U.S.