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No legal approach is completely reliable, so often a few approaches operate in tandem to ensure that the goal is obtained. Conservation easements sometimes include a clause that transfers the easement from one land trust to another if the original land trust fails to properly enforce the easement. Sometimes conservation easements are acquired in lands that cannot be intensely developed under existing zoning. Possible reasons include:
- The cost of purchasing an easement tends to be less in areas where development is not expected (e.g., more landowners are willing to donate easements);
- Low-density zoning sometimes results from a community process that recognizes the same environmental or preservation reasons to refrain from development that motivate conservancies to seek an easement; or
- Transferable development rights programs may provide someone with the right to build additional units in a developed area in return for permanently refraining from developing a low-density area, with conservation easements being a common mechanism to ensure that an area is permanently preserved.
Even though the conservation easements preserve lands that would remain undeveloped anyway through zoning, the easements provide a longer term guarantee compared with zoning, which often changes in response to increased market demand.
Conversely, lands with conservation easements can be zoned for agriculture, conservation, or open space. Usually the easements do not encompass all the land in an area because some owners choose not to transfer their property rights. If a large portion of the land is already subject to conservation easements, however, localities are often reluctant to allow intensive development within the inholdings. Subdivisions in the middle of an agricultural area can have adverse effects on farming. Concentrating development within growth corridors decreases the cost of providing water, sewer, roads, and other services; and the owners have less of a reasonable expectation of being able to subdivide and develop their land in areas where development of other land has been prevented, than along the fringes of existing development.
These general principles would also apply to rolling easements. We briefly discuss five combinations: rolling easement zoning of land that is already subject to recorded rolling easements; rolling easement zoning of land subject to federal or state regulations that discourage shore protection; recorded rolling easements on land already subject to restrictive zoning; covenants on subdivided parcels of land where a developer has already conveyed a rolling easement on the entire development; and a combination of a conservation easement with a possibility of reverter.
Even if title to all of the property in an area is restricted with a rolling easement, rolling easement zoning can be useful. A private conservancy may need help enforcing the rolling easement; and local residents who see activity inconsistent with an eventual retreat may be more likely to contact their local government than complain to a land trust. Legal challenges to conservation easements and future interests in land sometimes succeed, in which case zoning can provide a legal backstop.
One way to combine rolling easement zoning with recorded rolling easements would be for the local government to identify lands whose titles are subject to a rolling easement, and create a new retreat zone which would be subject to rolling restrictions. Alternatively, if a significant portion of all lands in an area have recorded rolling easements, it may be appropriate for zoning to restrict shore protection in the entire area. Otherwise, as sea level rises, the shore could become a patchwork with some land protected and other land submerged.
This combined approach is not yet possible, both because little if any coastal land is subject to recorded rolling easements. We mention this option here because the potential for rolling easement zoning might be relevant when conservancies and governments consider recorded rolling easements.
A related option that may be practical sooner would be rolling easement zoning of lands already subject to conservation easements (which do not necessarily roll). A new zone could be created by identifying low-lying areas where most lands have conservation easements, and adding a retreat overlay zone (or adding additional zones to reflect a retreat as shown in Figure 8). Such an approach would probably be more practical for jurisdictions where new conservation easements roll, than in areas where shore protection is so valued by landowners that a waiver of the right to shore protection would be a deterrent to providing a conservation easement. 
Another example where rolling easement zoning would be particularly easy to justify would be lands where state or federal regulations already prohibit or discourage shore protection. Calvert County, Maryland's cliff retreat regulations, for example, prohibit cliff protection in areas where shore protection would threaten an endangered species protected by federal law. State regulations sometimes prohibit structural shore protection; zoning the adjacent lands for retreat could help to ensure that development is consistent with the existing state requirements. Similarly, development in existing nontidal wetlands is generally discouraged by federal wetland protection programs. Nevertheless, these areas are sometimes developed. Given the government interest in wetlands, subjecting nontidal wetlands to a rolling easement would be a compromise between prohibiting development and allowing development with shore protection.
If existing laws prohibit shore protection (or at least shoreline armoring), then landowners have a reduced expectation of a right to hold back the sea and will tend to be more willing to restrict their titles with a rolling easement than in areas where shore protection is not restricted. Therefore the willingness of landowners to transfer a rolling easement should be greater there than in areas where the right to hold back the sea is established. Yet an eventual relaxation of government regulations is possible; so recording a rolling easement can add additional certainty to the eventual shoreline migration.
Another near-term opportunity would be to obtain rolling easements on land where development is prohibited or restricted to very low densities. Low-density zoning such as Maryland's Critical Areas Act makes purchase of rolling easements relatively feasible because the cost of protecting 20 acres of farmland with a single home may be high compared with the alternative of farmland gradually converting to marsh.  Yet as long as shore protection is allowed, there is some risk that it will occur.
If a developer retains a recorded rolling easement on a parcel and then transfers the easement to a land trust or government agency, the rolling easement holder will be able to enforce the restrictions. By adding covenants with similar restrictions to the deeds of each parcel when the land is sold, members of the community will also have a right to enforce the terms. Like other combinations, this approach creates a legal backstop in case the land trust is unable to enforce the rolling easement. This approach can make negotiations more complicated if, for example, a land trust and a property owner agree to modify the requirements. On the other hand, engaging a community in the negotiations can ultimately increase community acceptance of the policy.
Shoreline migration conservation easements and possibilities of reverter have different benefits and risks. The trend in state law to restrict the possibility of reverter—if continued—could invalidate that type of rolling easement. Failure to properly enforce a conservation easement may enable a future owner to assert that the interest has been abandoned. The hostility of courts to forfeitures might lead a court of equity to refuse to order the removal of a home under a conservation easement even if the terms of the easement provide for such a removal. If shorelines erode more rapidly than expected, a possibility of reverter based on sea level might not transfer title until after an owner erects shore protection.
Subjecting a given parcel to both a conservation easement and a possibility of reverter would be more likely to achieve the particular conservation goal than either of these instruments by itself. In some cases, the tax consequences depend on the order in which these two transactions take place, in which case transferring the conservation easement before creating a possibility of reverter would be less vulnerable to having the tax deduction disallowed.
 Dana & Ramsey, supra note 19, at 35. Although these clauses are sometimes called reverter clauses, they are actually executory interests, but exempt from the Rule Against Perpetuities, which does not apply to transfers between two charities.
 James T.B. Tripp and Daniel J Dudek, Institutional Guidelines for Designing Successful Transferable Rights Programs, 6 Yale J. on Reg. 369, 373 (1989) and Juergensmeyer et al., infra note 312, at 451 (discussing Montgomery County, Maryland). But see id. at 447 (transferable development rights programs involve the recording of a covenant running with the land).
 Residents of the subdivisions often try to curtail some of the farming activities, which has led every state to pass right to farm legislation. Terence J. Centner, Governments and Unconstitutional Takings: When Do Right-to-Farm Laws Go Too Far? 33 B. C. Envtl. Aff. L. Rev. 87, 87–88 (2006).
 Calvert County Zoning Ordinance (revised, June 10, 2008), Article 8, Environmental Requirements: Section 8-2.02, Shoreline and Cliff Areas on the Chesapeake Bay, Patuxent River, and their tributaries. Available at: http://www.co.cal.md.us/residents/building/planning/documents/zoning/default.asp. Cited February 1, 2011. See also CCSP, supra note 3, at 219. Officials have recently decided to relax these rules so that most of the threatened homes will not be lost. See, e.g., Christy Goodman, Homeowners near Cliffs May Get Some Relief, Washington Post, October 27, 2010, and to provide financial assistance to others whose homes will be lost. See, e.g., Meghan Russell, Cliff Dwellers Sent Packing, Southern Maryland News, December 31, 2010
 Without a rolling easement, the nontidal wetlands may be converted to dry land and remain dry through shore protection. Alternatively, they may be placed off limits to development, and remain as nontidal wetlands until the year X, when they will be submerged and become tidal wetlands. With a rolling easement and a permit to develop, the nontidal wetlands would become dry land, but still convert to tidal wetlands in the year X.
 See, e.g., supra note 286.
 See supra note 149 and accompanying text , (discussing prospects for shore protection of lands where development is restricted by Maryland's Critical Area Act). See also Environmental Research Letters, supra note 14, Table S4.
 See infra note 443. Cf. also Alan F. Rothschild Jr., Planning and Documenting Charitable Gifts, 20 Probate and Property (American Bar Association 2006), (discussing a case where donating a conservation easement first and then donating a fee simple interest with a restriction would have resulted in much greater tax savings than the taxpayer's donation of the land with the restriction).
This page contains a section from: James G. Titus, Rolling Easements, U.S. Environmental Protection Agency. EPA‑430‑R‑11‑001 (2011). The report was originally published by EPA's Climate Ready Estuary Program in June 2011. The full report (PDF, 176 pp., 7 MB) is also available from the EPA web site.
For additional reports focused on the implications of rising sea level, go to Sea Level Rise Reports.