There are a number of different kinds of easements and protections for land, and they are all a little bit different. Some are private, and some a state programs and of course vary from state to state. What state are you in?
Here's what I'm aware of in NH and VT.
1) "Current Use", "Use Value", etc. These programs are state run and have different names in different states. They are designed to encourage land owners to keep their land in agricultural or forestry use, and do so by providing a significant property tax break. In exchange for the tax break, you agree to use the property in it's "current use". The deal is secured via a lien on your property and it carries thru to new owners. Often you can get out of these deals, but their is a "change tax" that you pay, so it creates a dis-incentive to development. Unfortunately, developers will often just pay the fee and chop chop chop.
2) Private easements, held by owner: You can place whatever restrictions you want on your property by way of an easement on the deed. You can prohibit sub-division, commercial use, building, etc. Typically these easements are placed on property when you sell it, thereby restricting the new owner. One isssue with such an easement is that only the Grantor (seller) can enforce the easement. For example, let's say your neighbor sells his property and prohibits sub-division in the deed. Down the road, the new owner builds another house and sells it off with an acre of land, thereby violating the subdivision restriction. You have no complaint because the restriction on the deed doesn't benefit you. Only the previous owner can enforce it, and they or their heirs may have no interest in doing so.
3) Private easements, held by a land trust: These are like (2), but the "rights" are conveyed to a third party who's purpose in life is to protect those rights. Now you have an organization owning the rights that you wish to restrict who's job is to monitor and prevent violations. I use the term "land trust" loosely, since there are all sorts of trusts with all different kinds of objectives. They can also be town conservation commissions, or other organization. If you are thinking of granting easement rights to an org, check carefully what their objectives are to be sure they are well aligned with your own.
Another important issue is how the easement in (3) is conveyed to the land trust. They can be donated or sold. A land trust is more likely to accept a donated easement rather than agree to buy one, but donating an easement can have an attractive tax benefit to the donor. The value of the rights being granted can be taken as a tax deduction, assuming the land trust is a 501C3 non profit, which pretty much all are. To get a land trust to buy an easement typically requires that the land being protected has broad public appeal and benefit, or is of critical importance to the mission of the land trust, such that money can be raised for the purchase.
Hopefullly this helps sort out the different replies you have and will get to the question.