Influence of Thinning and Pruning on Southern Pine Veneer Quality

Abstract

This paper presents the effects of intensive pine plantation management on veneer yields, veneer grade distribution and veneer MOE as measured by ultrasonic stress wave transmission (Metriguard). Veneer production trials were done at a commercial southern pine plywood plant to elucidate the effects of silvicultural treatments on veneer quality, yield, and modulus of elasticity. Forty-nine trees, totaling 1,312 ft³, were selected from an intensively managed, 50-year-old loblolly pine (Pinus taeda L.) plantation at the Hill Farm Research Station of Louisiana State University at Homer, LA. Trees were selected from each of four treatments, pre-commercially thinned (PCT), pruned (PRN), pre-commercially thinned & pruned (PCT&PRN), and control (CTRL)[no thinning or pruning]. Twelve trees were selected per treatment, except for the PCT&PRN treatment that had thirteen trees. Each tree was felled, bucked into a log 17-foot-long plus trim, transported to the plywood plant, scaled on the log yard, bucked into two 101.5-inch-long peeler blocks (butt and top), conditioned in a drive-in steam chest (vat), rotary peeled into 1/8-inch-thick veneer using the plant's normal production process, then dried in a veneer drier. The length and width of full- sized veneer sheets, full-length random width strips (including half sheets) and half-length fishtails and strips were recorded to establish veneer yields. Full-sized sheets were graded visually according to U.S. Product Standard PS 1-83 in the green condition and after drying to establish veneer quality and drier degrades [A, B, C, D, and U (Utility) grades were identified] and by a Metriguard veneer tester for MOE determination. Five Metriguard groupings were assigned as follows: G1 (0-435ms, 2.44x10⁶ psi), G2 (436-475ms, 2.17x10⁶ psi), G3 (176-525ms, 1.86x10⁶ psi), G4 (525-700ms), and G5 ( > 700ms). Only the G1, G2, and G3 groupings are used to produce laminated veneer lumber (LVL); hence, the G4 and G5 groupings were combined into a below grade category. When G1, G2, and G3 veneer classifications were combined, all intensive silvicultural treatments had a higher number of veneers qualify compared to the CTRL treatment in both butt and top blocks. Also, the number of veneers qualifying for LVL production in the top blocks exceeded that in the bottom blocks for all treatments. It is also interesting to note that the percentage of G1, G2, and G3 veneers in the top block exceeded that in the butt block in all treatments except the PRN treatment. Compared to the CTRL treatment, the PCT and PRN treatments had slightly faster average sound transmission times in veneers produced from both butt and top blocks, which corresponds to stiffer veneer. However, these faster transmission times did not significantly alter the MOE range (G-Rating). The percentages of qualifying G1, G2, and G3 veneers were about equal in each treatment, but the intensively managed trees produced more G-grade qualifying veneers. The top blocks produced more G-grade qualifying veneers in all except the pruned treatment. The average Metriguard grade for all treatments was G2. The relationship of MOE to visual grade is the subject of a future paper.

Citation

Gibson, Mark D.; Clason, Terry R.; Hill, Gary L.; Grozdits, George A. 2002. Influence of Thinning and Pruning on Southern Pine Veneer Quality. In: Gen. Tech. Rep. SRS–48. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station. pg. 165-169