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Revisiting Southern Yellow Pine ‘Design Values’ and the Quality of Lumber

The Q3 2015 Forisk Research Quarterly (FRQ) summarized recent research related to the strength characteristics of Southern Yellow Pine (SYP) lumber sawn from managed pine plantations. We addressed this topic originally in a February 2012 Forisk Blog post “Southern Yellow Pine ‘Design Values’: Likely Impacts of Changes are Overstated.” Two studies published this year support that original assessment.

Why is this topic important? Southern Pine Inspection Bureau (SPIB) design values materially affect the utility, applications and value of SYP lumber as a building material. In turn, SYP lumber value and demand affect pine sawtimber prices and timberland investments.

In the FRA Technical Release “Strength Parameters of Lumber Sawn from Loblolly Pine Plantations in Georgia’s Coastal Plain,” authors Joe Dahlen and Dick Daniels from UGA and Dale Hogg from Plum Creek Timber directly evaluated the strength characteristics of lumber sawn from intensively managed loblolly pine plantations. Tested trees were older than 24 years and grown on thinned plantation in South Georgia. The lumber, sawn into 2×4, 2×6, 2×8, and 2×10 dimensions, was kiln-dried and visually graded per SPIB rules. The trees produced No. 1, No. 2, and No. 3 lumber, most of which graded as No. 2. The mechanical properties and specific gravity of the lumber were comparable to or exceeded the original, pre-revision SPIB design values. The results indicate that lumber sawn from trees harvested from intensively managed pine plantations “should meet the design values for visually graded lumber at stand maturity.”

Plum Creek published a graphic that summarizes the tree growth and mechanical property results from a more detailed version of this study which the authors published in the in the European Journal of Wood and Wood Products.

A second study, “Impact of Age and Site Index on Lumber Quality from Intensively Managed Stands,” published by Southern Regional Extension Forestry, reports results of a 2001 International Paper study of how management intensity, site index and age affect lumber yield and quality. The authors – Don Ledford, Jim Rakestraw, John Paul McTague and Alastair Twaddle of International Paper and Joe Dahlen from UGA – focused on similarly aged forest stands that differed primarily in growth rate.

The study included trees harvested from different-aged stands in South Carolina. Lumber sawn from these trees was visually graded and tested to determine the modulus of elasticity (MOE, a component of stiffness) and modulus of rupture (MOR). While lumber quality improved with age, lumber sawn from faster growing trees produced a more profitable lumber mix for sawmills as they resulted in lower manufacturing costs and higher sales realizations. While the portion of No. 1 and No. 2 lumber was “slightly higher for slower growing trees,” the variance was “not sufficient to overcome the value loss due to lower lumber volume.”

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