Agriculture Reference
In-Depth Information
FIGURE 17.6 Cows crowding into the shade of a lone Ceiba pentandra left in a tropical lowland pasture in Tabasco, Mexico.
Trees can provide a number of benefits to pasture and grazing systems.
methods used to analyze multiple cropping systems apply
equally well to agroforestry systems.
Because of these effects, trees in agroecosystems are
a good foundation for developing the emergent qualities
of more complex ecosystems. They allow more efficient
capture of solar energy; enhance nutrient uptake, reten-
tion, and cycling; and maintain the system in dynamic
equilibrium. By providing permanent microsites and
resources, they make possible a more stable population
of both pests and their predators. In an agroforestry sys-
tem, all of these factor interactions can be managed to
the benefit of the associated crop plant and animals, while
at the same time lessening the dependence of the system
on outside inputs.
THE ECOLOGICAL ROLE OF TREES
IN AGROFORESTRY
Trees are capable of altering dramatically the conditions
of the ecosystem of which they are part (Reifsnyder and
Darnhofer, 1989; Farrell, 1990). The sustainable produc-
tivity of agroforestry systems is due in large part to this
capability of trees.
Below ground, a tree's roots penetrate deeper than
those of annual crops, affecting soil structure, nutrient
cycling, and soil moisture relations. Above ground, a tree
alters the light environment by shading, which in turn
affects humidity and evapotranspiration. Its branches and
leaves provide habitats for an array of animal life and
modify the local effects of wind. Shed leaves provide soil
cover and modify the soil environment; as they decay they
become an important source of organic matter. These and
other ecological effects of trees are summarized in
Figure 17.7.
DESIGN AND MANAGEMENT OF
AGROFORESTRY SYSTEMS
In an agroforestry system, farmers have the choice of how
many trees to include, how frequently and in what patterns
to remove them, and what kind of pattern of successional
mosaic to maintain. These management decisions depend
on the local environment and culture, as well as the nature
and proximity of markets.
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