applies to individual organisms as well as to national or regional economies, industries, and natural resources such as fisheries.

Ecological health describes the goal for the condition at a site that is cultivated for crops, managed for tree harvest, stocked for fish, urbanized, or otherwise intensively used. At these sites, integrity in an evolutionary sense cannot be the goal. Healthy land use, with or without active management, should not degrade the site for future use or degrade areas beyond the site. Soils, for example, should not be eroded or otherwise transformed to reduce future productivity (see Pimentel, 1993). Groundwater should not be depleted.

Land use should not have deleterious effects beyond a site; atmospheric contamination should not result in downwind effects, such as increased greenhouse gases or ozone depletion. Healthy sites should not release contaminants or eroded soils that degrade sites elsewhere. Using these two criteria--no degradation of the site for future use and no degradation of areas beyond the site--most modem agricultural and urban land use, for example, is not sustainable. Recognition of that reality is the foundation for recent initiatives for sustainable communities and sustainable agriculture.

Failure to protect the ecological health of intensively used lands is also unacceptable on scientific, economic, aesthetic, and ethical grounds. We have no choice but to develop a conceptual framework to define acceptable and sustainable uses.

These concepts are easily applied to small parcels of land. Scaling up to large landscapes presents a serious challenge. What proportion of a landscape should be protected under a biological integrity goal? The World Commission on Environment and Development (1987) recommended 12 percent, but that seems inadequate. Does that proportion vary among regional ecosystem types (e.g., desert, forest, or grassland)? Do water bodies, fragile sites, or sites with the highest biodiversity deserve the highest priority for protection?

Measuring Health and Integrity

Neither ecologists nor engineers have been especially adept at defining or measuring either ecological health or ecological integrity. The track record of freshwater management provides an instructive example. Human society depends on freshwater as well as the resources associated with freshwater and marine systems. Yet 55 countries now have populations that equal or exceed the ability of their national territory to provide an adequate supply of freshwater (Ozturk, 1995). Improved water conservation, treatment and recycling programs can delay the crisis, but growing human populations will keep society on a treadmill trying to keep up with expanding demand. Even where the supply of water remains adequate, resource degradation continues because society chronically undervalues the products and services provided by aquatic ecosystems.

Although rivers are in many ways the lifeblood of society, prevalent attitudes

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