6
The Properties of Agroecosystems
Gordon R. Conway
Introduction
Agroecosystems are ecological systems modified by human beings to produce food,
fibre or other agricultural products. Like the ecological systems they replace, agro-
ecosystems are often structurally and dynamically complex but their complexity
arises primarily from the interaction between socioeconomic and ecological proc-
esses. Hitherto studies of agroecosystems have tended to concentrate on the flows
and cycles of energy and materials (see reviews in Frissel, 1977; Loucks, 1977;
Lowrance et al, 1984). While these have furnished valuable insights they have
captured only a part of agroecosystem complexity and have had relatively little
impact on the theory and practice of agricultural development. In this chapter I
suggest that agroecosystems can be characterized by a limited set of dynamic prop-
erties that not only describe their essential behaviour, but can be used normatively
as criteria of agroecosystem performance and hence can be employed in the design
and evaluation of agricultural development projects, at all levels of intervention.
Agroecosystems as Systems
Although the concept of the ecosystem is long standing (Tansley, 1935), it is often
difficult to identify and characterize ecosystems in nature. Their boundaries are fre-
quently obscure and sometimes ecosystems appear to be no more than random clus-
terings of weakly interacting populations. Indeed, there has been some dispute as to
whether natural ecosystems are true cybernetic systems, that is, have clearly defined
goals and are steered towards realizing these goals by pervasive feedback control loops
and communication networks (Engelberg and Boyarsky, 1979; McNaughton and
Coughenour, 1981; Jordan, 1981; Knight and Swaney, 1981; Patten and Odum,
1981). Nevertheless, there can be little doubt that the transformation of ecosystem
to agroecosystem produces well-defined systems of a cybernetic nature.
Reprinted from Agricultural Systems vol 24, Conway G R, The properties of agroecosystems, pp95–
117, copyright (1987), with permission from Elsevier.