Proponents of conservation easements, an increasingly important tool to protect land from development, won a critical victory late last year which they say makes the legal agreements harder to break in the future.

Months of legal maneuvering ultimately resulted in a settlement that prevented new housing on a tract of Eastern Shore farmland with an easement held by the National Trust for Historic Preservation.

The prospect that the the trust might allow development had sparked intervention by the Maryland attorney general’s office, the Eastern Shore Land Conservancy, The Nature Conservancy, and others who feared the precedent could destroy the value of easements in the future.

“I’m relieved with the end result,” said Rob Etgen, executive director of the Eastern Shore Land Conservancy. “I think we really have avoided a disaster for land use and land conservation. The end result is that conservation easements will be stronger.”

The case involved Myrtle Grove, a 160-acre, 18th century plantation in Talbot County, on which the National Trust held a conservation easement since 1975. The plantation was bought by Washington developer Herbert Miller and his wife, Patrice, for $3 million in 1989.

In 1994, the Millers approached the Trust seeking to amend the easement and to develop eight residential lots — the maximum that would have been allowed under the area’s zoning. The Millers contended they wanted to develop the property to help raise money to pay for renovations to historic structures on the site, a project that was costing hundreds of thousands of dollars.

The National Trust initially agreed, but rescinded the agreement after a more serious review. That reversal prompted the Millers to file suit in the District of Columbia Superior Court for breach of contract. Later, Maryland Attorney General J. Joseph Curren Jr. filed a suit to uphold the easement.

In December, the case was settled when the National Trust agreed to pay the Millers $225,000 in damages. In addition, the National Trust agreed to the installation of a wildlife pond on the property, and both parties signed an agreement upholding the terms of the original easement and requiring the state attorney general to consent to any future amendments. Both the Millers and the Trust said they were satisfied by the resolution.

Etgen said failure to uphold the easement would have been a “disaster.”

First, he said, the public would have lost confidence in easements as a way to protect the land. In addition, states and the Internal Revenue Service could have argued that if easements were not perpetual, they had no value, and owners who placed land in easements might no longer be entitled to the tax breaks they often get for giving up development rights.

“The foundations of conservation easement law, and the incentives around them, could have been broken,” Etgen said.

That spurred both Etgen’s organization and The Nature Conservancy to intervene and support the state’s position. Several other organizations and individuals supported their efforts.

“After their initial mistake, the National Trust fought aggressively to uphold the easement.,” Etgen said. “Although the settlement payment was unfortunate, the result was positive in that the attorney general’s important enforcement role was clarified and land trusts everywhere were reminded of the seriousness of their duty as holders of conservation easements.”

Easements have been seen as an increasingly effective tool in protecting land from development. Typically, a nonprofit land trust or other organization purchases development rights from a landowner, and the easements are usually backed by a state agency. Landowners who give up their development rights are often eligible for tax benefits.

Nationwide, the number of nonprofit land trusts is growing rapidly and the amount of land they protect has doubled in the past decade. According to a survey last year by the DC-based Land Trust Alliance, 4.7 million acres are protected by locally based trusts nationwide — an area larger than Connecticut and Rhode Island combined. Another 13 million acres are held or protected by larger national trusts, such as the Nature Conservancy.