In a deal involving the largest conservation easement ever, the New England Forestry Foundation paid more than $28 million yesterday to protect 762,192 acres of forestland in Maine. In exchange for the money, which came from other foundations, a few millionaires, and more than 1,200 other individuals, the Pingree family will give up its development rights to the land, which covers an area greater than Rhode Island. The deal effectively prevents family members from subdividing the land for housing tracts, but they will still be able to log portions of the tract. The family’s logging operation is the only one in the country certified as sustainable by both the Forest Stewardship Council, an independent group, and the Sustainable Forestry Initiative, an industry program.