The Agroecosystem Concept - Agroecology: The Ecology of Sustainable Food Systems - page 31

convention followed in this text is to use an agroecosys-
tem's spatial boundary (explicit or implicit) as the dividing
line between internal and external. In terms of inputs
supplied by humans, therefore, any substance or energy
source from outside the spatial boundaries of the system
is an external human input . Even though the word external
is redundant with input , it is retained in this phrase to
emphasize off-the-farm origins. Typical external human
inputs include pesticides, inorganic fertilizers, hybrid
seed, fossil fuels used to run tractors, the tractors them-
selves, most kinds of irrigation water, and human labor
supplied by nonfarm residents. There are also natural
inputs, the most important of which are solar radiation,
precipitation, wind, sediments deposited by flooding, and
plant propagules.

Sustainability in agriculture can only come from
understanding the interaction of all components of the
food system. Therefore, this text lays the groundwork
for developing a food-system perspective from which to
view all questions of agricultural sustainability. This
perspective pays attention as much to the people in agro-
ecosystems as it does to the ecological conditions on the
farm. It takes into account the large amounts of energy
and materials that are integral to the processing, trans-
portation, and marketing that take place in the human
“food chain.” It pays attention to the equity issues of
hunger, food security, and access to good nutrition and
diet. It weighs the impacts of globalization in the
marketplace and in farm communities, and sees producers
and consumers as actively connected parts of a single
system.
The agroecosystem concept and the science of agro-
ecology provide a foundation for examining and under-
standing the interactions and relationships among the
diverse components of the food system (Francis et al.,
2003). A grounding in ecosystem thinking — wherein a
complex web of interacting and independent parts con-
tribute to the emergence of a sustainable whole — allows
a framework for integrating social, economic, political,
and ecological perspectives to take shape. It is the goal of
the chapters ahead to establish this grounding in ecological
thinking, apply it to agricultural systems, and then to
broaden the scope of agroecology to include all compo-
nents of the food system.

S USTAINABLE A GROECOSYSTEMS

The challenge in creating sustainable agroecosystems is
one of achieving natural ecosystem-like characteristics
while maintaining a harvest output. Working toward sus-
tainability, the manager of any particular agroecosystem
strives as much as possible to use the ecosystem concept
in his or her design and management. Energy flow can be
designed to depend less on nonrenewable sources, and a
better balance achieved between the energy used to main-
tain the internal processes of the system and that which
is available for export as harvestable goods. The farmer
can strive to develop and maintain nutrient cycles that are
as “closed” as possible, to lower nutrient losses from the
system, and to search for sustainable ways to return
exported nutrients to the farm. Population regulation
mechanisms can depend more on system-level resistance
to pests, through an array of mechanisms that range from
increasing habitat diversity to ensuring the presence of
natural enemies and antagonists. Finally, an agroecosys-
tem that incorporates the natural ecosystem qualities of
resilience, stability, productivity, and balance will better
ensure the maintenance of the dynamic equilibrium
necessary to establish an ecological basis for sustainability.
As the use of external human inputs for control of agro-
ecosystem processes is reduced, we can expect a shift from
systems dependent on synthetic inputs to systems
designed to make use of natural ecosystem processes and
interactions and materials derived from within the system.

FOOD FOR THOUGHT

1. What kinds of changes need to be made in the

design and management of agriculture so that
we can come closer to farming in “nature's
image”?

2. It seems that for modern agriculture to be sus-

tainable, it has to solve the problem of how to
return nutrients to the farms that they come
from. What are some ways this might be done
in your own community?

3. The concept of ecosystem stability is one that

is currently under much discussion in ecology.
Some ecologists claim that there is no such
thing as stability in ecosystems, since change
is constant and disturbance inevitable. Yet in
agroecology, we strive for stability of agro-
ecosystem structure and function. How is the
concept of stability being applied differently in
these different contexts?

A GROECOSYSTEMS IN C ONTEXT : T HE F OOD S YSTEM

Agroecology finds its most immediate applications at the
farm or agroecosystem level, where it can effectively deal
with production, short-term enterprise economics, and
environmental impacts in the immediate vicinity of the
farm. But each farm or agroecosystem is part of a much
larger system, a global network of food production, dis-
tribution, and consumption called the food system .

4. As a consumer, how do your choices affect the

global food system?