Genetic variation in wood specific gravity from progeny tests of ponderosa pine (Pinus ponderosa LAWS.) in northern Idaho and western Montana

Green and oven-dry alcohol-toluene extracted wood specific gravities ((x) over bar = 0.39 and 0.46 respectively) were assessed from a total of 60 open-pollinated ponderosa pine (Pinus ponderosa LAWS.) families at 21 years from seed grown in progeny tests in northern Idaho and northwestern Montana. The trees in the Montana tests averaged higher green and oven-dry specific gravities (0.40 and 0.48 respectively) compared to those from the Idaho tests (0.38 and 0.44 respectively).There was wide variability in moisture content, but the families with the highest and lowest green specific gravities tended to rank high and low respectively for oven-dry specific gravity. Family x site interactions were significant only for green specific gravity in the Idaho tests. Growth data (height and diameter) and specific gravity were not significantly correlated at any of the test sites. Pilodyn densitometry was, with one exception, weakly, but significantly correlated with green and oven-dry specific gravity on an individual-tree basis. Use of the Pilodyn is not recommended for through-the-bark measurements with young ponderosa pine. Individual tree and family-mean heritabilities were lower for green specific gravity than for oven-dry specific gravity for families from both sets of tests. These results are likely associated with variation in moisture content. Moisture and extractive content averaged 109% and 4%, respectively, of the extractive-free, oven-dry weight of the cores across all samples. Heritability estimates for green and oven-dry specific gravity were consistent with findings for other coniferous species. Estimated gains in specific gravity from ten and three percent family selection ranged from 0.0095 to 0.0339 (about 2.5% to 7%) and 0.0153 to 0.0406 (about 4% to 8.5%) respectively. Specific gravity of core segments from the pith to the outer rings did not differ significantly from each other in any of the tests although in samples from three of the fourtest sites, mean specific gravity of the inner core segments (pith to ring 5) was higher than either of the two outer core segments (rings 6 to 10 and 11 to the outermost rings). At 21 years from seed, the trees in this study had probably not completed the transition to production of mature wood.