Densitometric studies on the wood of young coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)

X-ray densitometry was used to investigate some environmental and genetic influences on wood formation in young Douglas-fir trees growing in the Pacific Northwest. Sampling methods were determined from sectional analyses of even-aged stems and eleven growth-ring width and density variables were measured in several trials to elucidate' some of the causes of variation. Breast height increment core samples were shown to giveve a good representation of stand properties and juvenile-mature correlations for a 40-year-old crop confirmed the validity of determining intra-ring density parameters on young material. Increment core samples from the Co-operative Douglas-fir Provenance Test (5 locations; 5 provenances/location) were used for both gravimetric and densi-tometric analyses. The major components of variation were found to be stand location and the individual tree effect. Provenances consistently accounted for less than 5% of the total variation. Genotype-environment interaction was shown to be small for all properties measured with the exception of the intra-ring density range. Between sites, earlywood widths were more variable than latewood widths, but latewood density properties (mean latewood and ring maximum densities) were more variable than those for earlywood (mean earlywood and ring minimum densities). Earlywood and latewood parameters varied independently of one another. It was suggested that genetic control was weak at the provenance level but strong for individual trees. Regression analyses using growth-ring components and monthly weather data for the outer five rings at each site uncovered some highly significant effects which helped to explain the observed year-to-year variation. Density variables were less affected by weather conditions than earlywood and latewood widths. An examination of eight ramets from each of ten 13-year-old clones revealed highly significant differences in all eleven intra-ring parameters. Heritability estimates for individual growth rings showed a regular increase with tree age, and latewood properties (width, density and ring maximum density) were found to be under strong genetic control. On a clone-mean basis, density was not related significantly to growth rate, so that vigour and density properties could be selected for independently. Crown phenology (flushing and shoot growth characteristics) was not strongly correlated with growth-ring parameters, although there was an indication that early flushing may be associated with higher latewood density. A study of four parent trees and their control-pollinated progeny proved unsatisfactory due to lack of adequate replication and atypical stand conditions, but nevertheless provided a vehicle for discussion of problems involved in assessing plus-tree wood quality and narrow-sense heritabilities. The combined results were discussed in terms of the genecology of Douglas fir and the implications for forest management and utilization.

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