In Sonoma County, the grape is king. But as California winemakers seek to capitalize on the popularity of their chardonnays and cabernets by spreading vineyards over as many acres as possible, they have steadily encroached on the rivers, streams and creeks that crisscross the scenic valley.

The rapid narrowing of the wooded corridors along these waterways worries wildlife specialists and environmental researchers, who say their studies show that these riparian, or streamside, lands play a complicated and vital role in the ecosystem, far beyond providing water for farmers and wildlife. But proposals to require wider corridors have run into heated opposition from vineyards.

"Vineyard expansion is costing native animals habitat needed for food, reproduction and seasonal migrations, and leading to increased erosion from barren riverbanks, and more sediment in streams," said biologist Jodi Hilty, of the Wildlife Conservation Society, who collaborated on a study that documented the streams' crucial role.

In many areas of Sonoma County, said Adina Merenlender of the University of California at Berkeley, riparian zones are now the only viable corridors linking undeveloped oak woodlands that serve as havens for wildlife in an increasingly fragmented landscape.

Although grizzly bears and wolves are long gone from northern California, said Andrea Mackenzie, general manager of the Sonoma County Agricultural Preservation and Open Space District, "the survival of other native animals like bobcats, foxes and coyotes could be threatened if vineyards are allowed to grow close to rivers and streams."

Streamside areas also support more than half of the reptiles and three-quarters of the amphibians in California. All told, 349 animal species rely on California's oak woodlands, most of which have creeks running through them -- and, in Sonoma County, vineyards growing along them.

Sonoma has already lost 70 to 90 percent of its riparian habitat, Mackenzie said. That worries biologist Caitlin Cornwall of the Sonoma Ecology Center, who says preserving broad corridors along streams produces dozens of benefits, including flood protection, good groundwater quality, and flourishing fish and wildlife populations.

Not surprisingly, proposals to require wider riparian corridors have triggered conflicts between environmentalists and vineyard owners.

At last count, Sonoma County boasted 190 wineries. More than 50,000 acres of grapes worth $375 million grow within its 52-mile-wide, 47-mile-long environs.

"With the value of vintners' collective investment in land here," said Jeff Lyon, a viticulturist at Gallo Vineyards, "we need to plant grapes on as much of that land as we can."

Wine growers have questioned the evidence marshaled by those pressing for wider corridors.

Nick Frey of the Sonoma County Grape Growers Association says that "the scientific basis to justify wide riparian setbacks, and the economic costs for landowners, have not been well considered. The setbacks will reduce farmers' income-producing acres and are likely greater than needed to filter sediment from runoff and preserve wildlife corridors."

To see how setback size affects wildlife, Hilty and Merenlender set remotely triggered cameras along 21 streams in six Sonoma County vineyards over two periods of several months in 1999 and 2000. Five corridors were "wide," with more than 2,200 feet on each side of a creek; seven were "narrow," with 65 feet on each side; and nine were "denuded," with vegetation covering 20 feet on each side.

The cameras showed that wide corridors were frequented by twice as many species as narrow or denuded corridors.

"Animals like bobcats, gray foxes and striped skunks were detected most often in wide corridors," Hilty said. "Native animals used wide corridors twice as much as narrow ones, and more than three times as much as denuded ones." Results were published in February in the journal Conservation Biology.

Sonoma County has a mandated vineyard stream setback of 25 to 100 feet on each side of a waterway, depending on its location. The widest setbacks are along the Russian River, home to the threatened coho salmon.

"With literally thousands of miles of streams here, we need to find a balance between vineyard expansion and riparian protection," said Greg Carr of the Sonoma County Permit and Resource Management Department.

A proposal under consideration by the Sonoma County Board of Supervisors would increase stream setbacks for non-agricultural development, such as housing, to 200 feet along the Russian River and to 100 feet on all other streams identifiable on a U.S. Geological Survey map. The required setbacks for agriculture, including vineyards, would be only about half as wide. In vineyards with a slope of more than 20 percent, and thus more likely to produce erosion, 100-foot stream setbacks would be mandated.

The wider setbacks being reviewed by the Board of Supervisors are about as wide as the "narrow" corridors in Hilty's and Merenlender's study, Hilty noted. "Even this setback size," she said, "is not enough. Large predators, for example, need extensive streamside territories in which to hunt."

"We have turned landscapes into obstacle courses, and that requires thinking differently about restoring connectivity," said biologist Thomas E. Lovejoy, president of the Heinz Center for Science, Economics and the Environment, a nonprofit policy institute in Washington, D.C. "If you make sure that streams have enough vegetation along their banks to control silt and other runoff from land, you can go a long way toward that connectivity."

Vineyard owners' reactions to the setback proposals have ranged from welcoming to quietly accepting to resistant.

At Gallo, Lyon did not respond directly to questions about the company's position. In March 2003, the company, one of the two largest land-owners in Sonoma County, reached a settlement with the county over complaints that vineyards at its Twin Valley Ranch had discharged sediments into waterways that flow into Porter Creek and then the Russian River. Gallo committed to more than half a million dollars in various mitigation projects.

Not far from Gallo land, as the bobcat roams, is Alexander Valley Vineyards, one of the places where Hilty placed her cameras.

Manager Mark Houser said, "Foxes, quail and even a mountain lion frequent Hoot Owl Creek, which runs through our property." While he, too, did not address the setback proposal directly, he said the vineyard's philosophy is that "while we're here to make a living by growing grapes, we're not here to scorch the earth in the process."

An aerial view of California's Sonoma County contrasts with an area alongside a vineyard that has been mostly denuded of vegetation.Expanding vineyards may threaten the habitat of some native animals.