Out on the east fork of New Mexico's Gila River, the endangered Gila trout is getting help from adjacent landowners who are setting aside 48,000 acres in several land trusts to protect its habitat by preventing development.

At the same time, on the shores of Chesapeake Bay, 206 properties totaling more than 38,000 acres of fragile estuary habitat for migratory birds and marine life, like the short nose sturgeon, have been permanently set aside using legal tools like land trusts and conservation easements.

It's all part of a huge new boom in conservation of private lands in which landowners voluntarily give up rights to develop their land - often in return for tax breaks, but also to save rugged landscapes they love.

Private land set aside for conservation grew 54 percent from 24 million acres to 37 million acres- an area larger than New England - between 2000 and 2005, according to a recent study by the Land Trust Alliance, a Washington-based umbrella group of local, state, and national land conservation groups.

National groups such as The Nature Conservancy were key in this push for preservation. But the biggest drivers for growth were volunteer local and state land trusts, whose protected acreage doubled from 6 million acres in 2000 to 11.9 million acres. Meanwhile the rate at which those associations were saving land tripled to 1.2 million acres a year between 2000 and 2005.

"People are not sitting around and waiting for a Washington bureaucrat to solve the problem of strip malls in their own backyard - they're forming land trusts," says Rand Wentworth, president of the alliance.

Land trusts are nonprofit groups that assist in setting up conservation, agricultural, and other land-preservation easements and then act as land stewards. Over the five-year period, their numbers leaped by nearly a third to 1,667, the study shows. The focus of such trusts varied widely with 39 percent protecting natural areas and wildlife habitat to 38 percent for open space and 26 percent wetlands and water resources. Others focused on preserving farms, local parks, and urban gardens.

The single largest such deal saw 763,000 acres of Maine's Pingree forest protected by a 2001 conservation easement now overseen by the New England Forestry Foundation, preserving the shorelines of many pristine lakes.

Even though land conservation during the five-year period grew faster than sprawl, that's no reason for complacency, Mr. Wentworth says.

"Sprawl is breathing down our necks in the communities in which we live," he says. "We need these community land trusts with urgency."

Funding from government agencies for land acquisition has dropped significantly in recent years. But state and local bond issues in which the public votes to fund land purchases has been booming.

The public is voting solidly to increase taxes in order to preserve land, Wentworth notes. In 2006 alone, 133 ballot initiatives nationwide from California to Georgia, New Jersey, Texas, and North Carolina raised $6.7 billion in public funding for land conservation.

Residents of Austin, Texas voted in November to spend more than $50 million to buy open space, says George Cofer, executive director of the Hill Country Conservancy, a land trust. Much of that will go to preserve land critical to recharging local aquifers the city depends on for drinking water.

Indeed, much of the impact has occurred in the western US, which saw an 89 percent jump in land preservation from 2.7 million acres in 2000 to 5.2 million acres in 2005 - the nation's biggest.

Taxes are a key issue driving the phenomenon. With property values soaring, taxes on ranch land near Austin has soared for family ranchers. That has left some with the option of selling land to pay taxes - or lowering taxes by permanently setting the land aside from development.

"One rancher who put 5,700 [acres] in conservation recently told me, 'you saved not just my ranch, but my family,' " Mr. Cofer recounts.

In other parts of the West, ranchers face the prospect of selling family land just to pay estate taxes. But a growing number are choosing land-trust easements that diminish the land's value, but also chop estate taxes.

The Wyoming Stockgrowers Agricultural Land Trust, for instance, only got going around 2000, but now has more than 20 ranches and 50,000 acres in easements. Another 20,000-acre ranch will soon be added.

"Probably the biggest thing we've got now is wealthy people coming in and buying intact ranches and some building tract houses," says Ogden Driskill, whose 10,000 acre ranch surrounds two-thirds of majestic Devil's Tower National Monument.

He desperately wants to keep the view around it uncluttered. So he's pitching fellow ranchers easements to fend off the trend toward chopping up ranches into 40-acre pieces with houses.

Fortunately for him, western land trusts could see a banner year in 2007. That's thanks to a tax break for farmers and ranchers that preserves their land approved in August 2006.