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CORVALLIS - The degradation of streams and riparian zones in the western United States is reaching near-crisis proportions, a new report suggests, and can often best be helped by simply leaving them alone to let nature heal the wounds - not by flawed, mechanistic attempts to fix the damage.

The placing of artificial streambed structures or stocking with hatchery fish are sad substitutes for solutions that really work, such as stopping the livestock grazing, dam building or logging activities that caused the problem, researchers say.

And some well-intentioned cures may actually be counterproductive, said J. Boone Kauffman, an associate professor of fisheries and wildlife at Oregon State University, and Robert Beschta, an OSU professor of forest hydrology, who co-authored a report recently published in the professional journal Fisheries.

A move towards holistic ecological restoration on a landscape scale is needed, they say.

"Riparian and aquatic ecosystems are currently being altered, impacted or destroyed at a greater rate than any time in history," Kauffman said.

Up to 90 percent of all natural riparian areas in the U.S. have been extensively altered and more than half of the nation's wetlands have been lost in the past two centuries, researchers said in the report. Low water flows, siltation, erosion, channelization, and pollution are common, while streams lose their abilities to support fish and wildlife, purify water, reduce flooding impacts and perform other functions.

Almost 85 percent of historical Pacific Northwest anadromous salmon stocks are either extinct, endangered, threatened or of special concern. And sometimes well-intentioned efforts to address these problems make them worse than they already are, the scientists said.

There are two approaches to stream health that work best, they say. The easiest is "preventive medicine," or maintaining intact ecosystems that have not yet been degraded. On such streams intervention should be confined to protecting the natural status quo, perhaps by using prescribed fire or preventing invasion of non-native species.

If restoration is required, often the first and most important step is simply to remove the problems - whether they be grazing cattle, loss of water due to agricultural or municipal demands, or some other major impact. Often this is all that's required to restore streams and riparian zones to health.

"Many riparian zones are capable of rapid recovery after human perturbations stop because the biota have evolved adaptations to survive and reproduce despite frequent natural disturbance," the scientists said in their report.

The potential for success with this type of "passive" restoration - and the potential for high costs and failure with more active manipulation - is such that the researchers recommend waiting 10 years or so after implementing the passive protective measures before considering more active steps.

Extensive reviews of fish habitat improvement projects in eastern Oregon concluded that cessation of livestock grazing was the single most effective approach to restoring salmonid habitats, Kauffman and Beschta said. Three years after cattle grazing stopped on one northeastern Oregon stream, the crown volume of alder trees doubled, willows tripled, and black cottonwood went up eight times.

And despite some suggestions of using livestock as a "tool" in riparian enhancement, there is no evidence that such grazing, under any management strategy, can accelerate riparian recovery more rapidly than total exclusion, they said.

If passive restoration approaches such as this are inadequate to restore natural processes, the scientists said that active measures should emphasize the return of natural elements which may have been lost from the ecosystem - reintroducing species such as beaver or native plants. Prescribed burning may play a role. Riparian forest manipulations that mimic natural disturbances can help. In more severe cases removal of artificial hydrologic barriers - roads, anchored structures, rip-rap, or dams - may be required.

A problem in many cases, the scientists say, is failure to appreciate the natural complexity of stream and riparian systems. In a disturbed ecosystem, some subtle but essential elements may be missing even though the stream or its banks appear fairly normal.

This is especially common in efforts to improve fisheries habitat. Gravel may be brought in and logs placed - but often in the wrong place where they would not naturally exist. A summary of instream enhancement projects through the Pacific Northwest showed little or no positive fisheries response to such structural approaches. And some nutritional or biochemical needs that biologists don't even understand may not be there. Fish populations continue to dwindle, huge amounts of money are spent, labor is wasted and public credibility lost.

Despite the obstacles, the need to protect, preserve and restore riparian zones is too important to ignore, the scientists argue. The social and political inertia which sustain existing land use practices must be challenged. The trend towards "engineered solutions" and projects with quantifiable results - numbers of logs placed, fish stocked - must be resisted. And nature must be allowed to heal itself.

"While we recognize that ecological restoration sometimes comes at a high cost, it . . . is an investment in the natural capital of stream and aquatic systems and, hence, the environmental wealth of the nation," they said in the study. "Restoring once-productive riparian and aquatic ecosystems in the western United States is in the best long-term environmental and economic interests of the nation."