Estimating the Age of Demarcation of Juvenile and Mature Wood in Douglas-Fir

In order to characterize trends and to estimate the age of transition from juvenile to mature wood in Douglas-fir, piecewise linear regression analysis was applied to the radial pattern of intra-ring characteristics found in increment cores of Douglas-fir trees sampled at breast height. The data were collected with X-ray densitometry. Average ring density of all trees along the radius showed an initial decline within the first ten rings from the pith, a rapid increase to about ring thirty, and a continued increase at a lower rate thereafter. Three main wood-density profiles were found among trees. Piecewise regression models were used successfully to characterize radial development of wood density and to determine the demarcation of juvenile and mature wood