Mountain Soils - Mountain Geography: Physical and Human Dimensions - page 301

ago). Similarly, in the limestone Alps of northern Austria, tropical soils formed during
the late Tertiary (20-30 million years ago) and were uplifted later. They now exist as soil
relicts at an altitude of about 2,100 m (Kubiena 1970). In such cases, the complexity of
environmental effects can be very great because the soils are exposed to a variety of
environmental systems during uplift. Furthermore, uplift causes temperature and mois-
ture regimes to change. Uplift of the Peruvian Andes caused landscapes to pass from
arid conditions in the lowlands through humid conditions at intermediate altitudes, and
eventually into a cold, arid environment at the highest levels (Garner 1959). Such vari-
able conditions have the potential to create polygenetic (multiple causes) soils and land-
scapes.
Biological Factors
The plants and animals affecting soil range from microorganisms to macrofauna, herb-
aceous plants, and forests. A handful of fertile soil is filled with living things, predomin-
antly fungi and bacteria. Organic matter, including living organisms (biomass) and well-
decomposed remains of living things (humus), usually makes up less than 10 percent of
the volume of soil, but is very important in the physical and chemical processes of soil
and provides nutrients for soil fauna. As they feed and respire, soil microbes release
compounds, including carbon, stored within the soil organic matter. In this way, these
unseen microorganisms help regulate the planet's geochemical cycles.
More than any other factor, vegetation gives the soil its distinctive character. In par-
ticular, vegetation controls the amount and kind of organic material added to soil. In
grasslands, the aerial parts of plants die each year, adding organic matter from the top,
while roots add organic matter below the surface. In forests, trees, even evergreens,
lose their leaves. Certain evergreen leaves are tough, leathery, and inherently slow to
decay, especially under the cool temperatures of high altitudes (Aerts 1995). Where
people have replaced forest vegetation with pasture grass, the soil adjusts to differences
in organic matter and in physical and chemical inputs. Deforestation followed by pas-
ture establishment in the Alay Range in Kyrgystan caused soil phosphorus concentra-
tions to increase (Turrion et al. 2000). In a comparison of soil conditions under pasture
and lower montane forest in northwestern Ecuador, Rhoades and Coleman (1999) found
pasture soils to be wetter and denser than those under nearby mature or second-growth
forest. In the Scottish uplands, afforestation with pines decreased soil pH (increased
acidity) and reduced the turnover time of organic matter (Grieve 2001).
One of the sharpest soil boundaries is that between forest and grassland. In many
areas, timberline has advanced or retreated, indicating either climatic change or some
other modification, such as by fire, disease, or human intervention. Evidence in the fab-
ric of the soils may allow researchers to reconstruct the former timberline (Molloy 1964;
Reider et al. 1988; Carnelli et al. 2004). Soils above treeline may preserve profile char-
acteristics (Earl-Goulet et al. 1998), stable carbon isotope ratios (Ambrose and Sikes
1991; Byers 2005), or wood charcoal (Di Pasquale et al. 2008; Talon 2010) that indicate
the earlier presence of forest.
Much remains to be learned about the effects of animals and other organisms on
mountain soils. Microfauna and microorganisms are less abundant at higher altitudes
(Tolbert et al. 1977; Margesin et al. 2009), although some, including protozoa and nem-