All states now allow for the imposition of conservation easements on land, which essentially prevent the land from being developed (at all, in the case of wild lands; for non-agricultural uses, in the case of agricultural lands). Why would landowners voluntarily allow conservation easements to be imposed on their lands? One big reason is to earn tax reductions that are applicable to lands subject to such easements. In most, if not all states, lands that ordinarily are taxed at their highest and best use (for development) will be taxed only at their existing use if subject to conservation easements. Agricultural lands, which are already taxed based on existing use, still benefit from lower federal inheritance taxes, if they are subject to conservation easements.
The rub is that in virtually every state, the tax benefits of conservation easements apply only if the easements are perpetual. This principle, which is clearly specified in the text of just about every statute authorizing conservation easements, was recently tested in the Supreme Court of New Hampshire, in the case of Manchester Water Works v. Town of Auburn (the slip opinion is available here). In that case, the Water Works granted a conservation easement to the Society for the Preservation of New Hampshire Forests, a qualified land trust organization, which covered 460 acres of watershed it owned to protect water supply. However, the conservation easement expressly reserved to the Water Works the right to terminate on 30-years notice. The Water Works then applied for a tax abatement, based on the conservation easement.
The courts, including the Supreme Court of New Hampshire, rejected the tax abatement request because the conservation easement really just amounted to a self-imposed restriction that could be enforced by the land trust against the Water Works only so long as the Water Works chose not to terminate.
This case makes clear that conservation easements must be truly in perpetuity to earn tax benefits, under existing law. Whether the law should require perpetuity for tax benefits is another - completely legitimate - question. Forever is a long time, and circumstances do change. See, e.g., this NPR story on a dispute over efforts to amend or terminate a conservation easement. Courts sometimes amend property interests such as subdivision covenants and charitable trusts - which are also presumed at the outset to be perpetual - under the doctrine of changed circumstances. Arguably, conservation easements should fall into the same category. Even so, there seems good reason for the courts to require that the makers of conservation easements to intend them to be perpetual at the time they are imposed.
Hat tip: Preservation Law Digest