General Introduction - Integrated Assessment of Health and Sustainability of Agroecosystems - page 10

spatial heterogeneity and biological diversity (Toledo, 1990). Self-sufficiency is only
crucial to sustainability in more or less closed systems. Open systems that have many
avenues for the flow of energy and materials among them can collectively achieve
sustainability through trade-offs, maximizing the use of renewable resources and
minimizing the use of nonrenewable ones within each system. Those products that
are too costly (economically, environmentally, or socially) to produce within one
unit are obtained from another, in a process of mutual exchange.
Other health attributes include vigor, resilience, integrity, and adaptability. The
vigor of a system is simply a measure of its activity (Costanza et al., 1998). Resilience
refers to the system's ability to maintain its structure and behavior in the presence of
stress (Holling, 1986). Cairns and Dickson (1977) identified four properties of eco-
systems that determine their stress recovery characteristics: vulnerability, elasticity,
inertia, and resiliency. They defined vulnerability as inability to resist irreversible
damage. Elasticity is the ability to recover after displacement of structure or to a
steady state closely approximating the original, while inertia is the ability to resist
such displacement. Resiliency is the number of times a system can undergo the same
disturbance and still snap back. If a system is able to maintain its organization in
the face of changing environmental conditions, then it is said to have integrity (Kay,
1991). Organization of a system refers to the number and diversity of interactions
between its components (Costanza et al., 1998). Integrity is therefore a composite
property, tying together other characteristics such as stability, resilience, and vigor.
Adaptability has been defined as the ability to undergo adaptive changes in response
to change in the environment (Ho and Saunders, 1979).
1.4.3 A s s e s s m e n t A n D i m p l e m e in t A t i o in
Agroecosystem health assessment and implementation are carried out in five itera-
tive steps: (1) describing the system of interest; (2) identifying the owners, actors, and
customers; (3) setting or naming the goals and objectives of the system; (4) identify-
ing and implementing feasible and desirable changes; and (5) monitoring appropriate
indicators and reassessing the situation (Bellamy et al., 1996; Waltner-Toews and
Nielsen, 1997). The agroecosystem health approach is complicated by three main
conceptual dilemmas. First, agroecosystems, like all complex phenomena, can be
viewed from a variety of perspectives, yet none of these can be labeled as right or
wrong or as good or bad. For example, a systemic description from an economic
perspective would not necessarily be analogous, comparable, or equivalent in any
way to that reflecting an ecological perspective of the same agroecosystem (Waltner-
Toews et al., 2000).
The second dilemma emanates from the fact that agroecosystems are holarchical
systems (Allen and Hoekstra, 1992). Each level is a holon; that is, it is simultaneously
a whole with its own emergent properties, comprised of smaller wholes, while itself
a part of a bigger holon. Conceivably, health and sustainability at a level, say n , of a
holarchy depends on trade-offs and balances among the holons in its penultimate
layer ( n − 1), implying that some holons may need to be unhealthy or unsustain-
able within specific spatiotemporal bounds to maintain the health and sustainability
of the overall system. The third dilemma is that agroecosystems seek to optimize