Acquisition of rights and interest to a property to protect identified conservation or resource values, using a reserved interest deed. Easements can range from permanent to a multi-year period. A few states prohibit permanent easements. The largest federal programs using conservation easements on private lands are the Farmland Protection Program and the Wetland Reserve Program. Many state governments, especially in the northeast, and local government and nonprofits have been buying conservation easements on agricultural lands. Nonprofit organization have been very active in recent years. More than 1,250 land trusts around the country are using easements to protect about 2.6 million acres of land, according to a 2000 survey by the Land Trust Alliance.