Content area
Full Text
Southern pine lumber graded No. 2 and better generally sells for 45 percent more than lumber graded No. 3 or No. 4. Such a difference in dollar value will be increasingly important in future plantation management decisions as the timber industry experiences further declines in available natural stands and relies more and more on plantations. No existing decision models for southern pine contain the ability to include wood quality differentials in predicted volumes.
Initial planting density and thinning are silvicultural tools that can influence wood properties and, thus, the quality of lumber produced. This paper examines the effect of initial spacing and periodic thinning on the grade, strength, and volume of lumber produced at age 38 from loblolly pine (Pinus taeda L.) in southwest Louisiana.
Size and frequency of knots and volume of juvenile wood are important wood properties that influence the desirability of wood for lumber. Large knots and juvenile wood reduce lumber value because they weaken the lumber and make it more prone to warp, creating problems for manufacturers and consumers. Juvenile wood is a cylinder of wood surrounding the pith where xylem cells are formed by immature cambium. The prolonged influence of the apical meristem in the active crown is thought to be responsible for juvenile wood formation since, regardless of tree age, juvenile wood is formed in that portion of the stem that contains young live crown (17). The properties of juvenile wood and their adverse effects on product quality and yield have been reported by many researchers (2,3,16,21,24,26).
The number of years southern pines produce juvenile wood is more highly correlated with environmental factors that are associated with geographic location than genetic differences inherent among species (9). The duration of juvenility in planted pine is not influenced by initial spacing, but the diameter of the juvenile core is significantly correlated with initial spacing (9). Trees planted at wide spacings grow more rapidly during their early years than trees planted at close spacings, thus they contain a larger diameter of juvenile wood. Recent studies of the influence of juvenile wood on the strength of dimension lumber show that some lumber cut from the juvenile zone of young fast-grown plantation pine may not meet design requirements (12,15,18).
Early attempts to incorporate wood...