TheImprovement ofTropical and Subtropical Rangelands

SITE EVALUATION 97
The natural procel!l8 of change in the composition of an ecosystem
is referred to as succession. Successional changes take place
in response to natural or man-made influences in the environment.
So-called primary succession happens on newly exposed areas, such
as landslides or sand dunes, whereas secondary succession occurs
after the previous vegetation has been destroyed or disturbed by fire
or agricultural practices, for example. In many areas of Africa and
Asia, a disclimax (a climax maintained through disturbance) has
been established through savanna burning and heavy use pressure
by livestock. In any case, natural ecosystems evolve from essentially
bare areas to more or less stabilized types of dominant vegetation
through a series of successional stages.
The current successional stage of a site being considered for
improvement should be characterized. Some individual plant species
grow better when in competition with existing vegetation on sites
in the early stages of succession. Other plant species survive and
grow with existing vegetation on sites in later stages of succession.
Through recognition of the current successional stage, the species to
be planted and managed can be better matched with the successional
condition of the site, thereby enhancing the probability of continued
growth.
Knowledge of successional patterns is gained, in general, from
analyses of systematic, long-term observations of cyclical processes
by astute ecologists. These analyses are difficult where successional
change is orderly, and they are next to impossible where the changes
are erratic. Nevertheless, the potential for the improvement of a
site is put in a proper ecological perspective when analyses provide
approximations of the current successional condition with respect to
the range of successional stages that characterize a site.
A SYSTEMS APPROACH TO SITE EVALUATION
A systems approach should be adapted in a site evaluation for
assessing potentials for range improvements. Otherwise, the effort
might simply be a collection of discrete, often incomplete, and generally
unrelated exercises in measurement.
A systems approach to problem solving, regardless of its nature,
generally involves a holistic study of the interacting elements that
function simultaneously for an explicit purpose, emphasizing the
connections among the various parts that constitute this whole. The
interacting elements of concern function in "driving" the ecosystem