TheImprovement ofTropical and Subtropical Rangelands

108 IMPROVEMENT OF TROPIOAL AND SUBTROPIOAL RANGELANDS
Plants
The native plants that are growing on a site, if any, can be helpful
in describing the inherent productivity of the site and, from this
knowledge, the chances for a succeesful range improvement activity.
The occurrence of "key" plants can often be used to indicate site quality.
Also, knowledge of the productivity levels of native plants can
"index" levels ofproduction that might be expected from subsequent
range improvement activities. Observations of plants that can be
important in the evaluation of a site include, but are not limited to,
identification of the individual plant species (taxonomy), properties
of the individual plant species (for example, chemical composition
and particularly, the traditional WIes of the plants which indicate
important properties), groupings ofthe individual plant species into
communities, and vegetation-soil-terrain relations.
Of course, interpretations of individual plants and communities
ofplants must be undertaken in light ofthe on-site land-use patterns.
Use of plant resources as described above can be hampered by land
management practices that result in excessive utilisation of the plants
on a site. Because previous and current land uses may tend to
cloud the picture, the ecological impacts of these previous or existing
land use patterns on the plant resources must be well known and
thoroughly understood.
PlAnt IndiCAtor, Various key plants may be useful in analyzing the
capacity of a site for range improvement. To a large extent, the
presence, abundance, and size of these plants will often reflect the
nature of the ecosystem of which they are a part and, therefore, may
serve as indicators of site quality. However, the correlations between
"key" plants and associated site quality, which are generally based
on detailed ecological investigation, may not always be apparent.
Effects of competition among individual plant species, events in the
history of plant development (such as drought, fire, and outbreaks
of insects), and land management practices can weaken a plant ass0­
ciation to the point that it has little predictive value. Nevertheless,
in many situations, site quality is sufficiently reflected by plant indicators
to make use of the latter in an evaluation of a site for range
improvement.
Sometimes, the occurrence of plant indicators is combined with
abiotic components of the environment (for example, climate, soil,
and topography) in an attempt to describe more accurately the
quality of a site. The more factors that are taken into consideration,