TheImprovement ofTropical and Subtropical Rangelands

TllB aoorAL aoNTEXT FOR RANGELAND IMPROVEMBNT 39
goyernmental management and control and economic difrerentiation
ueociated with commercialization-have led to a 1018 of plant cover
and required the development of goyernment revegetation programs.
To fully appreciate why this has occurred and how this proce. can be
revel'lled, we must first understand how human beinp have adapted
to specific environmentalsettinp.
PRODUCTION SYSTEMS IN TROPICAL AND
SUBTROPICAL REGIONS
The lands coDSidered here are thoee in which permanent, suatainable
crop production is not poaible because of soil and climatic
conditions. Theee regions have, however, supported substantial human
populations for thousands of yean. In these areas, people have
developed production systems adapted to the low and variable productivity
of these lands. In semiarid regions and marginal areas, one
can find many kinds of production systema-hunting and gathering,
agricultural, pastoral, and agro-pastoral systelDB. Pastoralism and
agro-pastoralism are probably the meet common production systems
in these regions; this is because domestic animals can convert vegetation
on land unsuitable for agriculture into food and fiber. In Asia
and Africa, agro-pastoral and pastoral societies take many forms.
The exact organization of these production systems is influenced
by local environmental factors, by history, by culture, by economic
considerations, and by level of technology. In addition to theee differences,
there are similarities that must be understood if successful
revegetation is to take place.Traditionally, people who live in semiarid
and marginal lands have relied on two Btrategiee-divenification and
mobility-to cope with the erratic and generally low productivity
of their lands. Mobility is perhape the most important characteristic
of theee production systems. By moving about, one can take
advantage of the spatial and seasonal variation of plant production.
In crop production, systems ofshifting and opportunistic cultivation
are examples of strategies bued on mobility. Land is cultivated for
lleVeral yean, and then it is abandoned to fallow and new land is
cleared. The shifting nature of cultivation permitted natural revegetation
processes to occur-provided that the fallow cycle was long
enough.
Livestock are particularly mobile. Not only can they move about
to "harvs- spane vegetation, but they convert grasses and shrubs
into U8eful products. They also can harvest perennial shrubs and