Upon receipt by the county commissioners of such certificate of the commission¹ it shall be their duty at once to place said surface land in the class established by section one of this act,² and keep the same therein until the trees growing thereon shall, in the judgment of the commission, become sufficiently large and suitable for merchantable forest products, or the land be devoted to other purposes: Provided, however, That the certificate of the commission shall not become operative to place said surface land in the class established by section one of this act² until the owner of said surface land has agreed, in writing, with the commission, to care for the trees growing thereon, according to the instructions and directions of the commission, up to such time as such trees become suitable for merchantable forest products; and if any such owner at any time fails to care for the trees growing on said land as agreed with the commission, and due proof thereof is made, the commission may remove said surface land from the class established by section one of this act.² In case of such removal, either through failure of the owner to care for the trees or on his expressed desire for removal before the trees shall have been cut at maturity and tax paid thereon, the county commissioners shall, on notice from the commission, proceed to recover from said owner, for the use of the county and township, by an appropriate action at law if necessary, the difference in the amount of tax which would have been paid by the said owner at the rates established for the years for which recovery is sought and the rate provided for auxiliary forest reserves, with costs of suit, to be recoverable from the time when such land was placed in the class of auxiliary forest reserves. And the commission shall remove said surface land from the class established by section one of this act¹ at any time that the then owner shall, in writing, notify the commission that he desires such removal. The commission may, in its discretion, at the time said surface land is placed in the class established by section one of this act,² require the owner to file with the commission his or its bond, of such kind and amount as the commission shall deem reasonable and sufficient to secure the obligations of such owner under this act.