Evaluation of small-diameter ponderosa pine logs in bending

Ninety-nine roundwood bending specimens were tested over the course of seven months beginning in early 2002 at the College of Engineering and Technology at Northern Arizona University in Flagstaff, Arizona. These specimens were taken from 5.0- to 12.7-inch diameter at breast height ponderosa pine trees cut during the summer of 2001 from Unit 16 of the Fort Valley Ecosystem Restoration Project located in wildland-urban interface of the Coconino National Forest. The specimens were sorted into two groups as a function of processing: hand-debarked logs known as tapered specimens and machine peeled logs known as uniform specimens. Each group of tapered and uniform logs contained both butt and tip specimens. This work provides evidence of relationships between juvenile wood and roundwood strength and stiffness. Failure mode in bending was also affected by juvenile wood. This work also shows that processing a tapered log down to a uniform log of constant diameter reduces bending strength and stiffness, while increasing the percent juvenile wood in the cross section. Regardless of processing, butt logs in bending were stronger and stiffer than tip logs.