Geography Reference
In-Depth Information
rare, even for midlatitude mountains. On most world soil maps, mountain areas are pro-
visionally labeled “undifferentiated.” But despite the heterogeneity of mountain soils
and our lack of detailed information about them, their general nature under similar en-
vironmental systems can be predicted with a fair degree of assurance. National and in-
ternational efforts to develop soil classification systems demonstrate common soil char-
acteristics and relationships across the globe.
Soil Classification
A number of systems for identifying, classifying, and mapping soils have been imple-
mented over the years, but none has achieved global acceptance. Many of the ideas
about soil development originated in Russia. The Russian soil classification system was
based on the fundamental assumption that soil development accompanies the develop-
ment of vegetation as controlled by climate. Therefore, given enough time, regions with
similar climates and vegetation should support similar soils, regardless of differences in
parent material or topography. Vegetation and soil were thought to develop contempor-
aneously, each reflecting greater complexity through time until eventually achieving a
dynamic equilibrium with climate. This stage of development was considered “climax”
vegetation with “mature” soil profiles. No major changes were thought to take place
beyond this point, and those that did occur were considered to be fluctuations within
the context of a steady state, rather than directional. The similarity of soils under north-
ern boreal forests across vast expanses of terrain supports the assumptions of the Rus-
sian system.
Today, we recognize that static systems rarely exist in nature because wind, human
activity, fire, climate fluctuations, and other processes change environmental condi-
tions. Nevertheless, we recognize that some soils represent long-term climatic and
vegetative conditions. For example, “prairie soils” (Mollisols in the U.S. taxonomy,
chernozems in Russia) exist in areas supporting prairie grasses, Alfisols and Ultisols in
areas supporting broadleaf deciduous trees, and Spodosols (podzols in Russia) in the
boreal forest. In mountain regions, soil mapping usually shows zones that correspond
to the vegetation as it changes with increasing altitude. These are considered “mature”
soil types created by the long-term presence of similar vegetation in the absence of cli-
mate change. Such zonal soils theoretically occupy typical sites with good drainage on
gentle slopes. Soils at many locations within these broad regions do not match the zon-
al soil types, however, because of site-specific conditions. Soils that differ because of
local factors such as drainage, rock type, and topography are called intrazonal; those
on surfaces too young for full soil development are called azonal (Jenny 1941). In many
mountainous landscapes, intrazonal and azonal soils occupy more territory than zonal
soils.
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