Sustainable Agriculture and Food: Four volume set (Earthscan Reference Collections)

122 Agroecology and Sustainability

milk cow in a stall, but it is possible to think of the individual plant in a crop
population or the animal in a herd in this way. The next level is the field or pad-
dock and the hierarchy continues upwards in this way, each agroecosystem form-
ing a component of the agroecosystem at the next level. Near the top is the national
agroecosystem composed of regional agroecosystems linked by national markets,
and above that the world agroecosystem consisting of national agroecosystems
linked by international trade.
Systems theory holds that the behaviour of higher systems in such a hierarchy
is not readily discovered simply from a study of lower systems, and vice versa
(Simon, 1962; Whyte et al, 1969; Milsum, 1972; Checkland, 1981). This has
important consequences not only for analysis but for agricultural policy and plan-
ning. It implies that agricultural development cannot be based solely, or largely, on
genetic engineering, or macro-economic policy, or even on farming systems
research. Each level in the agroecosystem hierarchy has to be analysed and devel-
oped both in its own right and in relation to the other levels above and below, and
this totality of understanding used as the basis of development. To achieve this is a
difficult task but is greatly helped by a common approach to analysis and, in par-
ticular, a set of well-defined common properties for each level in the hierarchy that
can be related to each other, within and between levels.

Agroecosystem Properties

Individual organisms can be characterized by the basic properties of growth and
reproduction, maintenance and survival (Table 6.1). In cybernetic terms the ‘goal’
of an organism is increased fitness and this is achieved through one of a variety of
combinations of high and low values of these properties. The particular combina-
tion present in an organism can be regarded as its life history strategy (MacArthur
and Wilson, 1967; Grime, 1979). For natural populations, communities and eco-
systems it is possible to define a similar set of system properties, consisting of (1)
productivity, (2) stability (constancy) and (3) resilience (as defined by Holling,
1973). In each case these refer to the numbers or biomass of individuals or species,
or some combination of these measures. Unlike individual organisms, though,

Table 6.1 The properties of ecological systems

Individual Population Community Ecosystem Agroecosystem

‘Goal’

System

properties

Fitness

Growth

Reproduction

Maintenance

Survival

(Fitness) —

Productivity

Stability

Resilience

— Social value

Productivity

Stability

Sustainability

Equitability

Source: Conway, 1982b.