Agriculture Reference
In-Depth Information
same time, they are not dependent on expensive imported
agricultural inputs, and have very limited negative envi-
ronmental impacts.
More information on existing types of successionally
developed systems, especially those with perennial shrubs
and trees, is desperately needed. Urbanization and the
rapid move towards agroecosystem simplification and cash
cropping is threatening the existence of these systems,
especially in developing countries. We need to locate,
describe, and monitor existing systems that incorporate
traditional knowledge of the management of succession
and disturbance with selected agroecologically-based
improvements. Moreover, studies of such systems (e.g.,
Berkes et al., 2000; Altieri, 2002) require more institu-
tional support.
Perhaps the greatest value of agroforestry systems is
that they offer principles that can be applied to agroeco-
systems with few trees or none at all. By viewing all
agroecosystems as successional systems in which we
incorporate perennial species, appropriately introduce dis-
turbance, and promote recovery from disturbance, we can
make important steps toward sustainable food production.
The limits are set only by the kind of mature ecosystems
that would naturally occur in a region, and the human
component in the design and management of sustainable
alternatives that build upon such ecosystem models.
Regardless of whether they are grain systems or home
gardens, they must be dynamic, diverse, and flexible,
incorporating the important ecosystem characteristics of
resilience and resistance to disturbance, and the ability to
constantly be renewed and regenerated by the recovery
process of succession.
The more widespread implementation of practices
based on disturbance and recovery will involve consider-
able research. But it can lead to the development of an
agricultural landscape that is a mosaic of agroecosystems.
The need for high harvestable yields could come from
annual and short-lived perennial crops, grown in polycul-
tures of several species that are ecologically complemen-
tary and interdependent. In such systems, animals could
once again play important roles in nutrient cycling. Field
structure and organization could change over time as suc-
cession leads to a gradual conversion to long-lived peren-
nials. And incorporated into the disturbance cycle could
be a patchwork of rotations in which areas are allowed to
develop to maturity and their perennial or tree vegetation
harvested or recycled to open up parts of the agroecosys-
tem once again for annual cropping. In the end, a sustain-
able mosaic could be achieved.
TA B L E 1 7 . 5
Comparison of Plant Species in a 1240-square-
meter Home Garden over 2 Years in Cañas,
Guanacaste, Costa Rica
1985
1986
Species
71
83
Individuals
940
1870
Tree species
17
16
Food species
21
18
Ornamental species
23
31
Medicinal species
7
9
Firewood species
3
5
Spice species
0
4
Source: Gliessman, S. R. (ed.) 1990a. Agroecology: Researching the
Ecological Basis for Sustainable Agriculture . Springer-Verlag:
New York.
Mexico City, there is considerable demand and market for
a large variety of agricultural products, from basic corn
and beans to cut flowers. This demand is a stimulus to
diversify the local cropping systems, but it also puts pres-
sure on farmers to emphasize cash crops and abandon
many subsistence species. Those families that see an
advantage in combining both cash and subsistence crops
maintain the most diverse home gardens, while others shift
to mostly cash crops.
Although regional economic change has a clear
impact on home gardens, the link between the two can go
in the other direction as well. Where they exist, home
gardens tend to stabilize the local economy and social
structure by giving families a means of economic survival.
They act as a bridge between the traditional local economy
and the modern industrial economy, helping to buffer the
forces that encourage migration to industrial centers and
abandonment of traditional social ties. By offering the
possibility of local autonomy, economic equity, and eco-
logical sustainability, they provide important examples
that can be adapted and applied around the world (Méndez
et al., 2001; Major et al., 2005).
DISTURBANCE, RECOVERY, AND
SUSTAINABILITY
Agroforestry and home garden agroecosystems have been
examined in this chapter because of their usefulness as
models of sustainable agriculture. They incorporate a
range of desirable characteristics applicable and adaptable
to any agroecosystem. Manageable and productive, they
have the ability to respond to different factors or condi-
tions in the environment, to meet the needs of the inhabi-
tants for a great diversity of products and materials, and
to respond to external socio-economic demands. At the
FOOD FOR THOUGHT
1.
How similar or different are the ecological
impacts of human-induced disturbances in
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