Upon presentation of a statement for designating, measuring or estimating services specified in § 10.1-1132, the landowner or his agent shall pay to the State Forester within thirty days of receipt of the statement an amount not to exceed five percent of the sale price or fair market value of the stumpage so designated, measured or estimated. However, for the purpose of further encouraging the use of approved scientific forestry principles on the private forestlands of this Commonwealth, and to permit explanation of the application of such principles, the State Forester may, where he deems it advisable, designate, measure or estimate without charge the trees of a forest landowner on an area not in excess of ten acres.