One of the most successful land trusts is the Marin Agricultural Land Trust, which incorporated in 1980. By 1986 the Marin trust had secured only three easements, and three per year was the average thereafter. It holds easements on more than 38,000 acres, quite a change from the county's 1969 general plan that foresaw 125,000 people living along the Tomales Bay and in the Olema Valley. It seemed inevitable that under relentless market pressures commercial agriculture would give way to a landscape of ranchettes, small hobby farms or rural estates.

Livermore, California's premier wine region at the end of World War I, never recovered from the Depression and appeared to be headed for suburbia. The last two vintners, Concannon and Wente, seemed to have no other choice but to pick up and head to Monterey County. Sentiment in the city of Livermore turned to preservation, while Alameda County looked to urbanization. Directed by a judge, the two governments developed a joint program for South Livermore -- establishing a firm limit to urban growth with productive agriculture locked in place to the south.

A plan was created in which the development of land north of the boundary would pay for preservation of farmland just south of it. Builders of housing near the edge of town had to purchase easements in the farm zone. Fees collected from developers pay the Tri-Valley Conservancy, a land trust, to receive and administer these easements.

Today, 3,800 acres are held by the land trust and 24 new small wineries operate in the region, which includes Livermore, Pleasanton, Dublin, San Ramon and Sunol. The tangible rural edge gives way to a thriving urban landscape. No one would argue that the fixed rural landscape has been a boom for Livermore as well as the region's economy.

Central Valley Farmland Trust is a relatively new agricultural land trust, forming in 2004. It includes Sacramento, San Joaquin, Stanislaus and Merced counties. San Joaquin and Stanislaus counties mitigate for the loss of agricultural land. The trust holds easements on 10,000 acres of farmland and is looking to place its first conservation easement in Stanislaus County this year.

The Yolo Land Trust has operated since 1988. It holds conservation easements on 6,300 acres of farmland, open space and habitat. The Yolo trust works with Woodland, Davis and Yolo County to hold easements on agricultural land in "farm belts" designated in the general plans of the three entities. Yolo County requires that developers mitigate for the loss of agricultural land.

Farmland mitigation has become a significant impetus for conservation easements in Northern California, usually to offset the loss of prime farmland to development. Conservation easements are an important tool for protecting farmland and to demonstrate how voluntary land conservation can bring together willing landowners and experienced land managers.

Ferrari is president of the Farmland Working Group, a nonprofit organization formed in 1999 to advocate for farmland protection.