TheImprovement ofTropical and Subtropical Rangelands

106 IMPROVEMENT OF TROPICAL AND SUBTROPIOAL RANGELANDS
soil taxonomy was bued primarily on soils from temperate regions,
its use in tropical areas may be problematic.
In addition to the FAO/Unesco soil grouping and soil taxonomy,
several other soil clusification schemes are in use in nonindustrialized
countries. The relationships and main features of several of these
are outlined by Beinroth (1975), Buol et al. (1980), Butler (1980),
Camargo and Palmieri (1979), Conant et al. (1983), Jacomine (1979),
and The Soil Survey Staff (1975).
Landform and Relief
Characterizations of landform and relief are necessary to the
evaluation of a site because of their influence on climate and soil conditions.
In many instances, the relation ofplant survival to landform
and relief is very close. At a minimum, general landform and relief
should be quantified at a macro level.
In general, an area should be divided into "warm" and "cool"
sites on the basis of aspect and slope combinations. So-called warm
sites in the northern hemisphere are oriented, in a clockwise direction,
from southeast to northwest, while "cool" sites are oriented
from northwest to southeast. Of course, this situation is reversed in
the southern hemisphere. Within a particular aspect class at a given
latitude, slope is important when orienting a site to the sun. More
gradual and steeper slopes receive less intensive sunlight than do
"intermediate" slopes; the hottest and often the driest sites are those
that most directly face the sun on a summer day. The amount of B0­
lar radiation received on a site is closely related to other factors (for
example, precipitation, temperature, and soil moisture) that, individually
or collectively, influence the choice of species, establishment,
and the growth of plants.
The position of a site on a slope can also determine the growth
potential of an individual plant species. High, convex surfaces, which
are frequently subject to wind erosion and weathering, tend to be
drier and (in dry climates) warmer than is average for an area.
Conversely, low, concave surfaces, on which soil tends to accumulate
rather than erode, are generally moister and cooler than average.
Midslopes are typically intermediate in these characteristics.
Knowledge of the terrain of a site may be helpful in selecting
the most appropriate method of revegetation. For example, level to
gently rolling lands are preferred in many instances because ground
preparation, if necessary, can be more effectively accomplished with