Juvenile-mature wood demarcation in loblolly pine trees

Specific gravity data from loblolly pine (Pinus taeda L.) trees in a region-wide thinning study in southeastern United States were used to determine the age of demarcation between juvenile and mature wood. Segmented modeling, iterative solution, and constrained solution approaches were used to estimate the demarcation age. The results indicated that the age of demarcation between juvenile and mature wood occurs at approximately 11 years of physiological or cambial age (i.e., number of rings from the pith). Constraining the slope of the mature wood equation to a non-negative value lowered the demarcation age typically to less than 10 years. Within-tree variation in the age of demarcation was minor, suggesting that the use of the demarcation age estimate at breast height is adequate when quantifying the proportion of juvenile wood in a tree. Variations in the age of demarcation along the stem due to thinning effects and physiographic region did not show consistent trends. Trees in the Coastal Plain, however, tended to have lower ages of demarcation than trees from other areas.