I do a lot of work with land that may be in conservation so I hope you will find this answer helpful.
In New Hampshire, a parcel may be "in current use" if there more than 10 acres are undeveloped. Current use is a discount on the property taxes given to owners who keep their land undeveloped. There are a number of categories of current use designation. The property owner gets a larger discount if non-motorized recreational uses by the public are allowed or if the forest has a management plan.
If the property that you are interested in is just "in current use," then part or all of it can be withdrawn. If withdrawing only part, there would have to be at least 10 acres remaining undeveloped to qualify for current use treatment. Developed area includes all driveways, utility easements for a dwelling, excavated slopes and grades, the septic system, cleared area for the home and the 75 ft. diameter well radius.
On the other hand, if a conservation easement has been granted either to the town or to an organization like the Society for Protection of NH Forests, then the language of the easement document will govern. That easement may allow some land to be withrawn from the easement for residential development.
If you want to see what an easement deed might look like, you can follow this link http://www.nnerenmls.com/nne/maildoc/a007Ea2223.html
and then click the paperclip icon at the top to go to the documents. This property listing has a SPNHF conservation easement. on it. If the easement does not alow residential development, then the chances of taking it out of conservation are slim unless perhaps you had other more desirable landto trade. However, that would be entirely up to the holder of the easement deed. Chances are slim to none that withdrawal will be allowed.
Give me a call to discuss your specific situation. I will be glad to resaerch the details. 603/677-2154
Chuck Braxton, REALTOR GRI