In this section the following words have the meanings indicated. “Easement” means an interest in land that: is conveyed or assigned in perpetuity or for a fixed period of time to the Nature Conservancy or to a government or unit of a government; and limits use of the land to preserve the natural open character of the land. “Natural open character” means an area of great natural scenic beauty, open space, natural conditions, or present use that: enhances the present or potential value of adjacent development; or maintains or enhances the conservation of natural or scenic resources. Any land subject to an easement shall be assessed on the basis of its value as required by this subtitle, but the value shall be adjusted by the effect of the easement on the land. The Department shall adopt regulations establishing the value of land assessed under this section.