Timber grown and harvested from industrial tree plantations, tree and agro-forestry farms may be exported without restriction in quantity of volume, and if the exported is the same person or firm qualified and allowed to export logs, such timber from plantations/farms may be exported exclusive of the quantity or volume authorized. Provided, That the rentals on the forest land and the forest charges on the plantation timber shall have been paid: Provided, further, That, the export of the plantation timber shall be covered by a certificate to export issued by the Department Head on a yearly basis: Provided, finally, That the Department Head may at any time review the exportation of timber harvested from the plantations/farms and either reduced or totally suspend the export of such plantation timber whenever public interest so requires