Mountain Soils - Mountain Geography: Physical and Human Dimensions - page 306

FIGURE 6.4 Generalized pattern of changes in pH (solid line) in soil over time. (A) Soil developed
through time in the Indian Peaks regions, Colorado Rockies, showing percentage of organic mat-
ter as dashed line (Mahaney 1970). (B) Soil development on Mount Kenya, Kenya (Mahaney
1990), showing organic carbon as dashed line and nitrogen as dotted line.
Major Kinds of Mountain Soils
Mountain soils exhibit considerable local-scale diversity, and mountains occupy diverse
positions with respect to Earth's environments. What is true of a moist, protected mead-
ow does not hold for an exposed ridge. Soil development slows as altitude increases
in most humid midlatitude areas, but rates of soil development may increase with alti-
tude in arid and tropical mountains. In midlatitude humid mountains, temperature is
the primary limiting factor; in desert mountains, the increase in precipitation with alti-
tude may more than compensate for decreasing temperature, and conditions for soil de-
velopment may become more favorable than at lower altitudes (Whittaker et al. 1968;
Messerli 1973). In the humid tropics, decreasing temperatures with altitude slow rates
of decomposition and leaching, so more organic material accumulates at the surface
and more nutrients are retained in higher-elevation soils (Coûteaux et al. 2002).
Adding to the problem of great diversity of mountain soils is the fragmented nature
of our knowledge about them. Much of what we know comes from isolated research car-
ried out in widely separated areas. Generally, less is known about desert and tropical
mountain soils than about midlatitude humid mountain soils; and detailed soil maps are