The complex nature of the interrelationships between agricultural production and
the natural environment means that we are far from knowing which methods
and systems in dierent locations will lead to sustainability (Youngberg and Harwood,
1989). This seems to be a crucial issue in the debate, and leads one to ask,
how long should an agrosystem behave sustainably to be considered sustainable,
and how should sustainability be assessed? It is extremely dicult to determine
whether certain agricultural practices are sustainable or not. It is only in retrospect
that sustainable techniques can be truly identi®ed. The identi®cation of technologies
as sustainable today is questionable, since such identi®cation is based on hypotheses
regarding the sustainable management of natural resources, maintaining their productive
capacity through time. This implies that a constant process of monitoring
and reevaluation is required. In fact, there have been few attempts ``to characterise
the sustainability of speci®c agricultural systems''