Ecosystem health is a metaphor used to describe the condition of an ecosystem. Ecosystem condition can vary as a result of fire, flooding, drought, extinctions, invasive species, climate change, mining, fishing, farming, logging, oil spills, and a host of other reasons. There is no universally accepted benchmark for a healthy ecosystem, rather the apparent health status of an ecosystem can vary depending upon which health metrics are employed in judging it and which societal aspirations are driving the assessment. For example, an ecosystem that is productive of fish at the expense of drinking water quality may be classified as healthy by consumers of fish and as unhealthy by consumers of water. Advocates of the health metaphor argue for its simplicity as a communication tool. “Policy-makers and the public need simple, understandable concepts like health.”  Critics worry that ecosystem health, a “value-laden construct,” is often “passed off as science to unsuspecting policy makers and the public.” 
History of the concept
The health metaphor applied to the environment has been in use at least since the early 1800s and the great American conservationist Aldo Leopold (1887 – 1948) spoke metaphorically of land health, land sickness, mutilation, and violence when describing land use practices. More recently, metrics for judging ecosystem health have been proposed, and environmental field assessments of rivers, lakes, seas, and forests  have employed the ecosystem health metaphor in relation to environmental parameters.
An ecosystem encompasses a complex and changing network of interactions among organisms, and it is not practical to measure most of these. However, if a human goal for the ecosystem is known (e.g., fish production) targeted measurements may provide an estimate of the “health” of the system for that purpose. For example, a vision for ecosystem health of Lake Superior was developed by a public forum and a series of objectives were prepared for protection of habitat and maintenance of populations of some 70 indigenous fish species. A suite of 80 lake health indicators developed for the Great Lakes Basin include monitoring native fish species, exotic species, water levels, phosphorus levels, toxic chemicals, phytoplankton, zooplankton, fish tissue contaminants, etc.
Ecosystem health advocates have also proposed benchmarking as healthy the historical ecosystem state “prior to the onset of anthropogenic stress.” A difficulty is that the historical composition of many human-altered ecosystems is unknown or unknowable. Also, fossil and pollen records indicate that the species that occupy an ecosystem reshuffle through time, so it is difficult to identify one snapshot in time as optimum or “healthy.” 
A commonly cited broad definition states that a healthy ecosystem has three attributes: productivity, resilience, and "organization" (including biodiversity). While this captures significant ecosystem properties, a generalization is elusive as those properties do not necessarily co-vary in nature. For example, there is not necessarily a clear or consistent relationship between productivity and species richness. Similarly, the relationship between resilience and diversity is complex, and ecosystem stability may depend upon one or a few species rather than overall diversity.
Other authors have sought a numerical index of ecosystem health that would permit quantitative comparisons among ecosystems and within ecosystems over time. One such system employs ratings of the three properties mentioned above: Health = system vigor x system organization x system resilience. Ecologist Glenn Suter argues that such indices employ “nonsense units,” the indices have “no meaning; they cannot be predicted, so they are not applicable to most regulatory problems; they have no diagnostic power; effects of one component are eclipsed by responses of other components, and the reason for a high or low index value is unknown.” 
Relationship to human health
Some authors claim that human health should be a criterion of ecosystem health, as human health would be expected to decline in the presence of ecosystems viewed as unhealthy. For example, destruction of wetlands to control malaria mosquitoes “resulted in an improvement in ecosystem health.”  This privileging of humans has been criticized as a conflict of interest in the sense that efforts to improve human health may occur at the expense of natural ecosystems, with human health improvements driving population growth, resulting in environmental damage. Disease and parasitism are normal in nature and promote ecosystem functioning, driving biodiversity and productivity, and parasites may constitute a significant fraction of ecosystem biomass.
Criticism of the ecosystem health concept and proposed alternatives
Criticism of the ecosystem health concept has included the following:
- Ecosystem health is in the eye of the beholder. It is an economic, political or ethical judgement rather than a scientific measure of environmental quality. Health ratings are shaped by the goals and preferences of environmental stakeholders. "At the core of debates over the utility of ecosystem health is a struggle over which societal preferences will take precedence."
- Health is a metaphor, not a property of an ecosystem. Health is an abstraction. It implies “good,” an optimum condition, but in nature ecosystems are ever-changing transitory assemblages with no identifiable optimum.
- Use of human health and well-being as a criterion of ecosystem health introduces an arrogance and a conflict of interest into environmental assessment, as human population growth has caused much environmental damage.
- Ecosystem health masquerades as an operational goal because environmental managers "may be reluctant to define their goals clearly.” 
- “Currently there are many, often contradictory, definitions of ecosystem health,”  that “are open to so much abuse and misuse that they represent a threat to the environment.” 
- The public can be deceived by the term ecosystem health which may camouflage the ramifications of a policy goal and be employed to pejoratively rank policy choices. "The most pervasive misuse of ecosystem health and similar normative notions is insertion of personal values under the guise of 'scientific' impartiality." 
Alternatives have been proposed for the term ecosystem health, such as to “express exactly and clearly the public policy and the management objective,” to employ habitat descriptors and real properties of ecosystems rather than to use a health metaphor. An example of a policy statement is “The maintenance of viable natural populations of wildlife and ecological functions always takes precedence over any human use of wildlife.”  An example of a management objective is "Maintain self-sustaining populations of lake whitefish within the range of abundance observed during 1990-99." 
Ecological health has been used as a medical term in reference to human allergy and multiple chemical sensitivity and as a public health term for programs to modify health risks (diabetes, obesity, smoking, etc.). Human health itself, when viewed in its broadest sense, is viewed as having ecological foundations. It is also an urban planning term in reference to “green” cities (composting, recycling), and has been used loosely with regard to various environmental issues, and as the condition of human-disturbed environmental sites. Ecosystem integrity implies a condition of an ecosystem exposed to a minimum of human influence. Ecohealth is the relationship of human health to the environment, including the effect of climate change, wars, food production, urbanization, and ecosystem structure and function. Ecosystem management and ecosystem-based management refer to the sustainable management of ecosystems and in some cases may employ the terms ecosystem health or ecosystem integrity as a goal.
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