32 Pa. Stat. § 73
In case of the removal of said lands from the class known as auxiliary forest reserves, prior to the maturity of the timber, and without payment of the tax of ten per centum of the value thereof, as provided in section three of this act, the county commissioners shall, on notice from the commission, ascertain the amount of the taxes which would have been paid by the said owner on the original assessment, before the reduction provided for in section two of this act, adding legal interest from the date when each tax payment would have become delinquent. The said commissioners shall likewise ascertain the amount of taxes which have actually been paid upon the land in question, adding legal interest upon all such payments from the date when paid, and certify the result thereof to the county treasurer, who shall then proceed, in the manner provided for the collection of county taxes under general laws, to recover from such owner the difference between the two amounts, with costs. Such difference, so ascertained to be due as tax as aforesaid, shall be and remain a lien upon the land of such owner until payment shall have been made.
32 P.S. § 73