TheImprovement ofTropical and Subtropical Rangelands

CRITERIA 'OR PLANT SELEOTION 199
disease, and desiccation. Hence, solutions to fuelwood scarcity are
increasingly being sought in diversified strategies, pouibly including
the establishment of woodlots, fuelwood production in agroforestry
systems, improved natural forest management, and more efficient
fuel utilization.
Windbreaks, She1terbe1t1, md LlTIng Hedges
Althoush windbreaks and sbelterbelts cannot alter regional climatic
conditions, they do change microclimatic conditions at the
ground surface by reducing wind speed and advective energy inputs
(the oasis effect). Shelter plants are thus able to reduce temperature
and potential evapotranspiration, which in turn reduces the water
demand of crops, natural vegetation, and animals. An added benefit
is the production of fuelwood and timber.
Traditionally, cut branches from thorn trees and shrubs are used
for fencing and corrals. In the tropics, these structures need to
be renewed frequently because of the destruction of the cut wood
by termites, thus resulting in substantial losses of native trees and
shrubs. The establishment of permanent live hedges composed of
local thorn shrubs could help solve this problem.
MaIntenance and ImprCWemeDt of SoU lertillt,
The role of trees and shrubs, particularly legumes (such as Acacia,
Pro,opu, Albina, Gliricitlia, and Leucaena), in maintaining or
restoring soil fertility has been documented for a number of agroforestry
systems: for example, with Acacia albitla in the semiarid
tropics of Africa, with Pro,opu cineraria in the Rajasthan Desert
of India, with Leucaena leMcocep1&ala in various countries of the humid
tropics, and with desert shrubs throughout the drylands of the
tropics and the subtropics.
Leaf litter, combined with the shading effect of the canopy, produces
a recycling of nutrients (N, P, Ca, K, Mg) brought from deep,
subsurface layers to the topsoil. As a result, yields of millet under
Acacia tJlhitla, Pro,opU cineraria, or other legumes are up to twoand-one-half
times greater than in open fields in otherwise similar
conditions (Charreau and Vidal, 1965j Garcia.Moya and McKell,
1970j Mann and Sazena, 1980).