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Title:	Effect of initial planting spacing on wood properties of unthinned loblolly pine at age 21
Author(s):	Clar, Alexander III; Jordan, Lewis; Schimleck, Laurie; Daniels, Richard F.
Date:	2008
Source:	Forest Products Journal, Vol. 58(10): 78-83
Description:	Young, fast growing, intensively managed plantation loblolly pine (Pinus taeda L.) contains a large proportion of juvenile wood that may not have the stiffness required to meet the design requirements for southern pine dimension lumber. An unthinned loblolly pine spacing study was sampled to determine the effect of initial spacing on wood stiffness, strength and specific gravity (SG) at 8, 24, and 40 feet up the stem of chipping-saw loblolly pine grown using competition control and fertilization at planting plus fertilization at midrotation. Seven spacings ranging from 6 by 8 feet to12 by 12 feet were sampled. Analysis of the effect of spacing at each height level showed significant differences in stiffness, strength, and SG among spacings at 8 feet, but did not vary significantly with spacing at 24 or 40 feet. Stiffness at 8 feet of trees planted at 12 by 12 feet was 12 to 14 percent lower than that of trees planted at 6 by 8, 6 by 10 and 6 by 12 feet because the 12 by 12 trees were growing rapidly in response to fertilization and less competition and thus contain a larger diameter of juvenile wood characterized by wide microfibril angles and lower stiffness. Average weighted whole stem wood stiffness and strength decreased only 6 to 7 percent when spacing increased from 6 by 8 feet and 12 by 12 feet, and was not significantly different at the 0.05 level. Estimated stiffness, strength and SG at 8, 24, and 40 feet decreased significantly with increasing tree height because of increased juvenile wood in the upper stem.
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