In the case of the disposal of timber held for more than 1 year before such disposal, by the owner thereof under any form or type of contract by virtue of which such owner either retains an economic interest in such timber or makes an outright sale of such timber, the difference between the amount realized from the disposal of such timber and the adjusted depletion basis thereof, shall be considered as though it were a gain or loss, as the case may be, on the sale of such timber. In determining the gross income, the adjusted gross income, or the taxable income of the lessee, the deductions allowable with respect to rents and royalties shall be determined without regard to the provisions of this subsection. In the case of disposal of timber with a retained economic interest, the date of disposal of such timber shall be deemed to be the date such timber is cut, but if payment is made to the owner under the contract before such timber is cut the owner may elect to treat the date of such payment as the date of disposal of such timber. For purposes of this subsection, the term “owner” means any person who owns an interest in such timber, including a sublessor and a holder of a contract to cut timber.