Agriculture Reference
In-Depth Information
DIVERSITY, STABILITY, AND
SUSTAINABILITY
2.
Explain a situation where lack of diversity in
one component of an agroecosystem can be
compensated for by greater diversity in some
other component.
Diversity in agroecosystems can take many forms,
including the specific arrangement of crops in a field,
the way that different fields are arranged, and the ways
that different fields form part of the entire agricultural
landscape of a farming region. With increased diversity,
we can take advantage of the positive forms of interfer-
ence that lead to interactions between the component
parts of the agroecosystem, including both crop and
noncrop elements. The challenge for the agroecologist
is to demonstrate the advantages that can be gained from
introducing diversity into farming systems, incorporating
many of the components of ecosystem function that are
important in nature, and managing such diversity for the
long term.
In part, meeting this challenge means determining the
relationships between the different kinds of diversity
presented in this chapter and the stability of the agroeco-
system over time. This stability should be understood as
both the resistance of the system to change and the resil-
ience of the system in response to change. Since each spe-
cies in the agroecosystem brings something different to the
processes that maintain both types of stability, an important
part of agroecological research is focused on understanding
the contribution each species makes and using this knowl-
edge to integrate each species into the system in the optimal
time and place. As this integration takes place, the emergent
qualities of system stability appear, allowing the ultimate
emergent quality — sustainability — to develop.
The most sustainable agroecosystems might be those
that have some kind of mosaic pattern of structure and
development, in which the system is a patchwork of levels
of diversity, mixing annuals, perennials, shrubs, trees, and
animals. Or the most sustainable systems might be those
with several stages of development occurring at the same
time as a result of the type of management applied. Such
systems might incorporate minimum tillage to allow a
more mature soil subsystem to develop, even with a sim-
pler aboveground plant system, or use strip cropping or
hedge rows to create a mosaic of levels of development
and diversity across the farm landscape. Once the param-
eters of diversity are established, the issue becomes one
of frequency and intensity of disturbance — which we
will explore in the next chapter.
3.
What is the connection between diversity and
the avoidance of risk in agroecosystems? Give
examples to support your viewpoint.
4.
What are some possible mechanisms allowing
a crop to produce a higher yield in an intercrop
than when planted by itself in monoculture?
5.
What are the main disincentives for farmers to
shift into more diverse farming systems? What
kinds of changes need to occur in order to pro-
vide the necessary incentives?
6.
What are some of the forms of agroecosystem
diversification that will best promote the success-
ful use of Integrated Pest Management (IPM)?
7.
Why are intercropping and agroforestry agro-
ecosystems more common in the tropics than
in the temperate parts of the world?
INTERNET RESOURCES
Agroecology in Action
www.agroeco.org
The website of Professor Miguel Altieri, at the
University of California, Berkeley, with ex-
tensive material on agroecological pest and
habitat management.
Cedar Creek Natural History Area and LTER
www.lter.umn.edu
An important Long Term Ecological Research
site (STER), directed by recognized diversi-
ty ecologist David Tilman, and with infor-
mation on long-term vegetation diversity
experiments and publications.
Farming Systems Research Unit, Center for Envi-
ronmental Farming Systems
www.cefs.ncsu.edu/frsu.htm
An excellent site located at North Carolina State
University, with projects and publications
focusing on management of agroecosystem
diversity.
The Land Institute
www.landinstitute.org
A well-known research and training center in
Salina, Kansas, which has focused on agro-
ecosystem diversity management through its
natural systems agriculture approach.
FOOD FOR THOUGHT
1.
Describe a pest management strategy that
builds on the theory of island biogeography.
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