There is no current "VALUE" per unit area. There may a may not be a current unit "COST" for that region. If not an appriaser would calculate it from current nursery costs, IF replacement is an appropriate method for the case. COST must be depreciated to get VALUE.
Treble damages is an award by a court of up to three times the value of a loss. The court not the appraiser calculates such punative damages. Whether or not they apply to trees in Montana is a quewstion for a lawyer.