Bending strength and stiffness of loblolly pine lumber from intensively managed stands located on the Georgia Lower Coastal Plain

Abstract

Loblolly pine is increasingly grown on intensively managed plantation forests that yield excellent growth; however, lumber cut from these trees often contains a large percentage of juvenile wood which negatively impacts strength and stiffness. Because of changing forest management and mill practices the design values for visually graded southern pine were updated in 2013 to more accurately account for the material properties available in commerce. This study was undertaken to assess the bending strength and stiffness of loblolly pine lumber from intensively managed stands located on the Georgia Lower Coastal Plain. Eight hundred and forty-one pieces of lumber sawn from 93 trees age 24-33 years were tested in four-point bending according to ASTM International standards. The No. 1 grade MOE 15 (11.9 GPa) was greater than the current (11.0 GPa) design value and comparable to the previous (11.7 GPa) design value. The No. 2 grade MOE 15 (10.6 GPa) was greater than the current (9.7 GPa) design value but slightly less than the previous (11.0 GPa) design values. The No. 3 grade MOE 15 (9.3 GPa) was between the current (9.0 GPa) design value and the previous (9.7 GPa) design value. Altogether, these results point to the MOE 15 mean values being reasonably comparable to the previous design values and currently meeting or exceeding the current design values for visually graded southern pine lumber.

An Acoustics Operations Study for Loblolly Pine (Pinus taeda) Standing Saw Timber with Different Thinning History

“…On average, these values dropped, making U.S. southern yellow pine (SYP) lumber less competitive on the international market. The reasons for these lower values were likely the acceleration of growth, coupled with earlier harvest, and perhaps, changes in supply patterns under a cyclic economy (Butler et al 2016). SYP is now harvested 10 to 15 years earlier than in decades past, resulting in a higher juvenile wood core and perhaps lower mean outerwood stiffness properties (Butler et al 2016).…”

“…The reasons for these lower values were likely the acceleration of growth, coupled with earlier harvest, and perhaps, changes in supply patterns under a cyclic economy (Butler et al 2016). SYP is now harvested 10 to 15 years earlier than in decades past, resulting in a higher juvenile wood core and perhaps lower mean outerwood stiffness properties (Butler et al 2016). As a consequence, the market appears to be in disequilibrium, with sawmills demanding better-quality material while forestry suppliers demand a higher dollar value for the additional growth necessary to reach previous stiffness values.…”

“…In response, some manufacturing facilities in the state of Alabama have gone as far as placing a specific age limit to ensure a higher-quality log. However, such a technique is inefficient because there may be some stands at a lower age that can meet Southern Pine Inspection Bureau SPIB stiffness values (Butler et al 2016). As such, a measurement system that could partition higher performing stands, regardless of age, could be helpful in the fight to transition the southern U.S. from a quantity-based market to a quantity-and quality-based market.…”

“…However, most improvements have already been made in other traits, and making improvements for stiffness will invariably lower gains in other traits (Via et al 2004). Additionally, in the event of significant genetic gains, the landowner may just lower the rotation age to improve profits, as has been done in the past (Butler et al 2016). The rotation age needed to meet design values can also vary by up to ± 10 years, depending on various genetic and environmental factors (Biblis et al 1993(Biblis et al , 1995.…”

“…To date, the instrumentation has been commercialized by acoustics manufacturers, but industrial use has not caught on in the United States. Historically, a lack of use of acoustics in the southeastern U.S. may be attributable to the high stiffness associated with southern pine grades (Butler et al 2016). However, with the recent change in U.S. southern pine design values, manufacturers are paying closer attention to the source of the raw material, in hopes of regaining product value through machine stress rated (MSR) grading.…”