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

Green and oven-dry alcohol-toluene extracted wood specific gravities ((x) o ver 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 fro m seed grown in progeny tests in northern Idaho and northwestern Montana. T he trees in the Montana tests averaged higher green and oven-dry specific g ravities (0.40 and 0.48 respectively) compared to those from the Idaho test s (0.38 and 0.44 respectively). There was wide variability in moisture cont ent, but the families with the highest and lowest green specific gravities tended to rank high and low respectively for oven-dry specific gravity. Fam ily x site interactions were significant only for green specific gravity in the Idaho tests. Growth data (height and diameter) and specific gravity we re not significantly correlated at any of the test sites. Pilodyn densitome try was, with one exception, weakly, but significantly correlated with gree n and oven-dry specific gravity on an individual-tree basis. Use of the Pil odyn is not recommended for through-the-bark measurements with young ponder osa pine. Individual tree and family-mean heritabilities were lower for gre en specific gravity than for oven-dry specific gravity for families from bo th sets of tests. These results are likely associated with variation in moi sture content. Moisture and extractive content averaged 109% and 4%, respec tively, of the extractive-free, oven-dry weight of the cores across all sam ples. Heritability estimates for green and oven-dry specific gravity were c onsistent with findings for other coniferous species. Estimated gains in sp ecific gravity from ten and three percent family selection ranged from 0.00 95 to 0.0339 (about 2.5% to 7%) and 0.0153 to 0.0406 (about 4% to 8.5%) res pectively. 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 sample s from three of the four test sites, mean specific gravity of the inner cor e segments (pith to ring 5) was higher than either of the two outer core se gments (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 prod uction of mature wood.