TheImprovement ofTropical and Subtropical Rangelands

98 IMPROVEMENT OF TROPICAL AND SUBTROPIOAL RANGELANDS
processes. By its very nature, a systems approach to designing a
comprehensive site evaluation involves several disciplines, including
meteorology, soil sciences, and biology.
It may be impractical (or unnece88&ry) to measure all ofthe parts
of an ecosystem in a particular site evaluation because, in many
instances, only a relatively small number of limiting components
may be related to the IlUCcea of the range improvements. With a
systems approach, however, the probability ofoverlooking important,
possibly constraining, attributes will be greatly lessened.
EVALUATION or ABIOTIC AND BIOTIC COMPONENTS
A site evaluation focuses upon two broad sets of components:
nonliving (abiotic) components and living (biotic) components. Climate,
soil, landform and relief, and water resource are abiotic components;
plants and animals of all forms, including humans, are biotic
components. The objectives of the proposed range improvement
project or program, the complexity of the ecosystem being evaluated,
and the completeness of the available relevant knowledge will largely
determine the intensity of the effort to be undertaken in evaluating
these abiotic and biotic components. Details of measurement and
sampling techniques may be found in Avery (1975), Bell and Atterbury
(1983), Brown (1954), Cain and de Oliveira (1959), Carmean
(1975), Child et al. (1984), Conant et al. (1983), Jones (1969), Lund
et al. (1978), Lund et al. (1981), National Research Council (1962),
Schemnitz (1980), and Soil Resources Inventory Group (1981).
Abiotic Components
Reasons for evaluating specific abiotic components of a site are
discussed below. Techniques commonly used to quantify these components
are briefly described.
Climate
Climate can be defined as the total complex of weather conditions
and its average characteristics and range of variation over an
appreciable area of the earth's surface. Conditions over an extended
period of time are usually taken into consideration. Weather, in tum,
comprises a set of atmospheric conditions at a specified point in time
and, therefore, refers to events. Climate is basic to an ecosystem because
of its significance in soil development and plant productivity.