Mountain Soils - Mountain Geography: Physical and Human Dimensions - page 312

HISTOSOLS
Histosols, bog or peat soils, form where drainage is poor, typically in depressions and
areas where water accumulates from seeps or springs. The predominant characterist-
ic of Histosols is an abundance of mosses and partially decomposed plant remains at
the surface; these vary in thickness from a few centimeters to over a meter. The min-
eral matter of the soil is generally derived from the erosion of upland slopes, and the
transition from the mineral to the organic material is abrupt. The mineral soil is fre-
quently mottled with orange and bluish gray, due to the lack of soil aeration. Bog soils
are strongly acidic, with a pH of 4.0 to 5.0. By definition (Soil Survey Staff 2010), His-
tosols do not contain permafrost within a meter of the surface. If permafrost is present,
it contributes to poor drainage and the accumulation of sedges and mosses. Bog soils
are intrazonal because they develop under locally restrictive conditions. They are found
in all mountain areas except deserts. Bog and peaty soils are particularly abundant in
the oceanic mountains of Europe (Montanarella et al. 2006). With their high organic
matter content, Histosols are important for carbon storage in the world's mountains.
Arid Mountain Soils
In arid regions, increasing altitude frequently presents the apparent paradox of deeper
soils, more plant and animal species, greater biomass, and higher productivity than in
the lowlands. As discussed in Chapter 3, this is because moisture increases with alti-
tude. Forests often occupy intermediate elevations in semiarid mountains and display
both upper and lower timberlines, the lower timberline due to lack of moisture. Many
mountains in dry areas provide “islands” of greater moisture. Tropical examples include
Kilimanjaro and Mount Kenya in East Africa and the west slope of the Andes in Peru,
Bolivia, and northern Chile. Midlatitude examples include the Australian Alps, the Cau-
casus, various ranges of the Trans-Himalayas, the Rockies, Great Basin ranges, and the
east slopes of the Cascades and Sierra Nevada. Such intermediate-altitude forests do
not occur in the drier subpolar regions because temperatures are too low for forest
growth.