Evaluating the bending properties of clear wood specimens produced from small-diameter ponderosa pine trees

The bending properties of clearwood test specimens produced from small-diameter pine trees were evaluated to provide a basis for determining how to better utilize this resource. Specimens (16 in by 1 in by 1 in) were processed from 57 small-diameter trees harvested from the Manitou Experimental Forest located near Woodland Park, Colorado. Trees were categorized into three groups, 20 normal disease-free trees harvested from dense stands typical of the region, 21 mistletoe-infested trees from similar stocking conditions, and 16 disease-free trees from more open growing conditions. Test specimens were tested in bending and data for 542 specimens were evaluated statistically using a nested design, considering both within- and between-tree variation. This analysis revealed that property variation was much greater transversely across the cross section than longitudinally along the length of the tree. Modulus of elasticity (MOE) and modulus of rupture (MOR) values were highest for test specimens from normal trees. Specimens produced from open-grown trees had significantly lower MOE and MOR values than specimens from both normal and mistletoe-infested trees. While mean MOE and MOR values for specimens from mistletoe-infested trees were lower in comparison to normal wood values, only the difference between mean MOE values was statistically significant. No significant differences existed in the mean specific gravity between the groups. There was not a linear relationship between specific gravity and either MOE or MOR; however, there was a weak linear relationship between sample growth increments per inch and both MOE and MOR, which may provide an opportunity for visually evaluating (grading) small-diameter trees.