TheImprovement ofTropical and Subtropical Rangelands

8 OVERVIEW
Improving rangeland is generally a costly process because of low
economic returns, relatively low productivity, fragility, site specificity,
and often capricious precipitation. For privately owned land,
it makes no sense to invest $50 to renovate a hectare of land worth
$5. To halt the siltation of dams, harbors, and rivers, and to slow
the vast loss of topsoil and avoid threat of devastating flash floods,
in most cases will require programs that encompass large areas and
are supported both by the government and by the local community
structure.
To overcome future starvation and malnutrition, either marginal
lands must produce more food or there must be a decrease in the
human populations relying on such lands. Revegetation is the critical
key to the renovation of many rangelands. A cover of vegetation
keeps the soil and water in place and decreases evaporation and
runoff. Vegetation creates a living barrier to runoff and erosion by
increasing percolation and soil storage of rainfall. It shelters the
soil from scouring and provides a barrier that slows runoff. Its leaf
litter absorbs water and protects the soil surface from rain and wind.
Roots and soil organisms help break up the soil, making it porous so
that water can infiltrate.
Revegetation is possible both by such natural procel8e8 as seed
dispersal by wind, birds, and other animals, or carried by seasonal
streams and f100dwatersj planting by human activity, deliberate or
unplanned also promotes new growth. Planned revegetation has two
components: (1) direct intervention by seeding or planting trees,
shrubs and grasses, using a variety of techniquesj and (2) management
interventions that serve to strengthen the role of natural
revegetation processes.
Strengthening natural regenerative systems, in addition to direct
planting methods, can be achieved in ..veral ways. The basic
objective is to add extra genetic material adapted to the ecosystem
to provide a greater range of material for multipurpoee use, and to
assist the system to regain its former productivity and resiliency.
For example, existing distribution mechanisms can be used, such as
planting a mixture of perennial legumes around degraded well-heads,
from which animals will spread them naturally (National Research
Council, 1981). Nomadic pastoralists supplied with seed will be able
to replant fodder shrubs and improve oasis systems with windbreaks
or living fences composed of fodder legumes.
Where grazing pressure can be reduced and regenerative mechanisms
strengthened, substantial regrowth is likely. The usual way