Geography Reference
In-Depth Information
they are retained, while silica is soluble under these conditions and easily transported
downward.
FIGURE 6.7 The general decrease of soil pH with altitude in the La Sal Mountains, Utah, a semiarid
region. (From Richmond 1962: 89.)
In humid tropical mountain soils, soil organic matter increases with increasing alti-
tude (Buytaert et al. 2011). In the lower montane forests of New Guinea, at 2,500 m,
the ratio of organic matter in the soil is 4:1, compared to 0.5:1 in adjacent lowland trop-
ical forests (Edwards and Grubb 1977). At higher elevations, leaching decreases, the
accumulated organic material provides a ready source of nutrients, and nutrients are
depleted less rapidly. As a consequence, tropical mountain soils commonly have a high-
er nutrient content than lowland soils (but see Grubb 1977 for examples of lower nu-
trient content in upland tropical soils). Additional reasons for the greater nutrient con-
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