The classical definition of an ecosystem couples interacting living organisms and non-living components of the environment to form one physical system (Tansley, 1935) and grew from the recognition that definable and describable units existed in nature. Ecosystem analysis has been advanced by an improved understanding of how ecosystems are structured and how they function. Ecology has advanced from an emphasis on natural history to consideration of energetics, the relationships and connections between species, hierarchies, and systems theory. Still, we consider ecosystems as entities with a distinctive character and individual characteristics. Measures of human or nonhuman animal health, and the clinical analysis of factors that contribute to a definition of a state of health, provide useful analogs to the problems faced by environmental managers attempting to maintain the integrity of ecosystems (Schaeffer et al., 1988). As found in human/nonhuman animal health studies, disease states of ecosystems must be recognized before disease is of clinical magnitude. This paper discusses a comprehensive, systematic approach to ecosystem analysis based on identification and quantification of factors that define the condition or state of an ecosystem in terms of health criteria.
