TheImprovement ofTropical and Subtropical Rangelands

32 IMPROVEMENT OF TROPIOAL AND SUBTROPIOAL RANGELANDS
the tropics similarly affect the exploitation and management ofrange
resources.
RANGE CLASSIFICATION
Range management issues are usefully considered within the
context of ecoclimatic zones. In this report, these zones are defined
largely on the basis of land potential and moisture availability (Pratt
and Gwynne, 1977). Within the tropics, five such zones can be
distinguished:
1. Humid to drJlsu6humid (moi.ture indez not Ie.. than -10).2
This zone is characterized by forest and derived grasslands and bushlands,
with or without natural glades. The greatest potential is for
forestry (perhaps combined with wildlife and tourism), or intensive
agriculture. The natural grasslands of this zone require intensive
management for optimum production. Approximately 0.8 hectare
is required per livestock unit, depending upon the related grassland
association. s In this zone, approximately 2.5 livestock units are
required to support one subsistence pastoralistj hence, 2 hectares
are required to support each individual. The maximum population
density per km 2 is about 50 pastoralists (see table 1-1).
2. DrJl su6humid to .emiarid (moi.ture indez -10 to -90).
The vegetation of this zone includes moist woodland, bushland, and
savanna. Forestry potential is low. However, the agricultural potential
is relatively high, soils and topography permitting, with emphasis
on lea farming. Large areas are generally under range use and, with
intensive management, can carry 1 livestock unit per 1.6 hectares.
Approximately 3 livestock units are required to support 1 subsistence
pastoralist. Thus, 4.8 hectares are required to support 1 individual.
The maximum density of pastoralists would be approximately 21 per
km 2 • Regular burning is an important management tool in this zone.
3. Semiarid (moi.ture indez -90 to --If). These are areas
with marginal agricultural potential, which in some regions is limited
to rapidly maturing grains. The natural vegetation is characteristically
dry woodland and savanna. This is potentially productive
rangeland. Approximately 3.5 hectares are required per livestock
unit, except where dry seasons exceed 6 months. The corresponding
human carrying capability is 7 individuals per km 2 • Animal
husbandry is limited principally by the encroachment of woody vegetation
and, in some locations, by leached soils. In many areas,