Ecosystem Health

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Ecosystem health

Ecosystem health is a new concept that ecologists are examining as a tool for use in detecting and monitoring changes in the quality of the environment , particularly with regard to ecological conditions.

Ecosystem health (and ecological integrity ) isan indicator of the well-being and natural condition of ecosystems and their functions. These indicators are influenced by natural changes in environmental conditions, and are related to such factors as climate change and disturbances such as wildfire , windstorms, and diseases. Increasingly, however, ecosystems are being affected by environmental stressors associated with human activities that cause pollution and disturbance, which result in many changes in environmental conditions. Some species , communities, and ecological processes benefit from those environmental changes, but others suffer great damages.

The notion of ecosystem health is intended to help distinguish between ecosystem-level changes that represent improvements and those that are considered to be degradations. In the sense meant here, ecosystem-level refers to responses occurring in ecological communities, landscapes, or seascapes. Effects on individual organisms or populations do not represent an ecosystem-level response to changes in environmental conditions.

The notion of health

The notion of ecosystem health is analogous to that of medical health. In the medical sense, health is a term used to refer to the vitality or well-being of individual organisms. Medical health is a composite attribute, because it is characterized by a diversity of inter-related characteristics and conditions. These include blood pressure and chemistry, wounds and injuries, rational mental function and many other relevant variables. Health is, in effect, a summation of all of these characters related to vitality and well-being. In contrast, a diagnosis of unhealthiness would focus on abnormal values for only one or several variables within the diverse congregation of health-related attributes. For example, an individual might be judged as being unhealthy because they had a broken leg, or a high fever, or unusually high blood pressure, or non-normal behavioral traits, even though they are "normal" with regards to all other traits.

To compare human and ecosystem health is, however, imperfect in some important respects. Health is a relative concept. It depends on what we consider "normal" at a particular stage of development. The aches and pains that are considered normal in a human at age 80 would be a serious concern in a 20-year old. It is much more difficult, however, to say what is to be expected in an ecosystem. Ecosystems don't have a prescribed lifespan and generally don't die but rather change into some other form. Because of these problems, some ecologists prefer the notions of ecological or biological integrity rather than ecosystem health.

It should also be pointed out that many ecologists like none of these notions (that is, ecosystem health, ecological integrity, or biological integrity). The reason is that by their very nature, these concepts are imprecise and difficult to define. For these reasons, scientists have had difficulty in agreeing upon the specific variables that should be included when designing composite indicators of health and integrity in ecological contexts.

Ecosystem health

Ecosystem health is a summation of conditions occurring in communities, watersheds, landscapes, or seascapes. Ecosystem health conditions are higher-level components of ecosystems, in contrast with individual organisms and their populations.

Although ecosystem health cannot be defined precisely, ecologists have identified a number of specific components that are important in this concept. These include the following indicators: (1) an ability of the system to resist changes in environmental conditions without displaying a large response (this is also known as resistance or tolerance); (2) an ability to recover when the intensity of environmental stress is decreased (this is known as resilience ); (3) relatively high degrees of biodiversity ; (4) complexity in the structure and function of the system; (5) the presence of large species and top predators; (6) controlled nutrient cycling and a stable or increasing content of biomass in the system; and (7) domination of the system by native species and natural communities that can maintain themselves without management by humans. Higher values for any of these specific elements imply a greater degree of ecosystem health, while decreasing or lower values imply changes that reflect a less healthy condition.

Ecologists are also working to develop composite indicators (or multivariate summations) that would integrate the most important attributes of ecosystem health into a single value. Indicators of this type are similar in structure to composite economic indicators such as the Dow-Jones Stock Market Index and the Consumer Price Index. Because they allow complex situations to be presented in a simple and direct fashion, composite indicators are extremely useful for communicating ecosystem health to the broader public.

[Bill Freedman Ph.D. ]