A mill study of the quality, yield, and mechanical properties of plywood produced from fast-grown loblolly pine

Due to the increasing demand for wood fiber as well as the desire to produce fiber using shorter rotation ages (30 to 35 years) efforts have been made to greatly improve the growth rates of the southern pines. Increased growth rate will make trees having four or fewer growth rings per inch common. Trees having these growth characteristics will contain a large core of juvenile wood, with its associated undesirable properties. The rapid growth rate will tend to produce wood that may behave like unbalanced construction when converted to solid products. This study, using loblolly pine trees ranging from 20 to 25 years of age, indicated that veneer cut from these fast-grown trees could be expected to be substantially lower in yield and grade than veneer cut from slower-grown trees of similar size. The greatest reduction observed was in veneer grade. The fast-grown trees yielded less than 1 percent of the net log input volume in grades better than C, while the control trees exceeded 20 percent. The recovery of full sheet veneers was also reduced. Plywood manufactured from veneer cut from these fast-grown trees had mechanical properties that were marginal for the species, especially in stiffness and modulus of elasticity. Bending strength was reduced, but to a lesser degree. Recovery and performance would be expected to improve with increasing tree age.

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