120 Agroecology and Sustainability
In the transformation the great diversity of wildlife in the original natural system
is reduced to a restricted assemblage of crops, pests and weeds (Figure 6.1). There
is a strengthening of the biophysical boundary of the system, a bund is created
around the rice field, for example, which makes the boundary less permeable. The
basic ecological processes – competition, herbivory and predation – still remain,
but these are now overlaid and regulated by the agricultural processes of cultiva-
tion, subsidy, control, harvesting and marketing. Recognizable system goals
become apparent that are sought through human social and economic cooperation
and competition. One consequence is that the system boundary acquires a socio-
economic dimension. It is this new complex agro–socio–economic–ecological sys-
tem, bounded in several dimensions, that I call an agroecosystem. At least in
cybernetic terms, an agroecosystem defined in this way is more similar to an indi-
vidual organism than it is to a natural ecological system.
The most widely recognized agroecosystem is the crop field conceptualized in
Figure 6.1, or the livestock paddock. But if agroecosystems are defined so as to
include both ecological and socioeconomic components, then we can envisage a
classical hierarchy of such systems (Figure 6.2). At the bottom of the hierarchy is
the agroecosystem comprising the individual plant or animal, its immediate micro-
environment, and the people who tend and harvest it. Examples where this exists
as a recognizably distinct system are the lone fruit tree in a farmer’s garden or the
Figure 6.1 The rice field as an agroecosystem