Mapping the effects of knots on loblolly pine lumber
Wright, Stephen Louis
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Loblolly pine (Pinus taeda) plantation rotation lengths have decreased due to the implementation of intensive forest management. Lumber extracted from younger plantations will tend to have lower stiffness (modulus of elasticity (MOE)) and strength (modulus of rupture (MOR)) than lumber from older plantations. This study analyzed the knots of dimension lumber sourced from intensively managed 24 to 33-year-old trees harvested from the Lower Coastal Plain in Georgia. The aim of the research was to develop a rapid method to evaluate knots and develop models that predict lumber stiffness and strength. The methodology involved image evaluation using a semi-automated process using K-means clustering to identify the knots from the clearwood. For each piece of lumber, a rectangle was overlaid on to each knot with the summed rectangle areas divided by the total surface area of the lumber to calculate the knot area ratio (KAR). Lumber stiffness was best modeled using KAR and specific gravity; the linear model had a R2 of 0.69 with RMSE of 1.29 GPa. The variation in lumber strength was best described by KAR and MOEdyn which yielded a R2 of 0.53 with a RMSE of 8.47 MPa. Significant differences were found in MOR when lumber was classified into three failure type categories: in clearwood (43.8 MPa), at a single knot (37.1 MPa), and at a combination of knots (32.4 MPa).