N.H. Rev. Stat. Ann. § 230:30

The commission may include in their assessment of damages to the abutting owners, damages for the maintenance or planting, from time to time, within the limits of such highway, of such shade and ornamental trees and shrubbery as may be necessary in the opinion of the commissioner of transportation, for the preservation, improvement, or landscaping of such highway, and upon tender of such damages there shall be a public easement on such highway for such purposes and to protect, preserve and renew the growth thereon.