GENETIC-VARIATION IN THE AGE OF DEMARCATION BETWEEN JUVENILE AND MATURE WOOD IN DOUGLAS-FIR

Variation in the age of demarcation between juvenile and mature wood based on wood density was studied in 180 Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) trees. Ring density profiles were generated from X-ray densitometry of increment cores from each of 3 randomly selected trees from each of 30 wind-pollinated families (parent trees) grown in 2 replication blocks. The families represented 10 provenances (3 families per provenance). Two boundary points were determined: the age at which a significant change occurred in the slope of the density-age relationship (using piecewise regression techniques), and the age at which species average density was reached. The period of juvenile wood production ranged from 11 to 37 years among the trees sampled. Most of the variation was among trees-within-plots; however, significant differences among families-within-provenances indicated that the period of juvenile wood production for this population of Douglas-fir was under appreciable genetic control.