Variation in Decay Resistance of Southern Pine Sapwood

This study was undertaken to determine the decay resistance of sapwood of the most important southern pines: slash (Pinus elliottii var. elliottii Little & Dor.), shortleaf (Pinus echinata Mill.), longleaf (Pinus palustris Mill.), and loblolly (Pinus taeda L.) During the summer of 1968 three trees each of slash pine, shortleaf pine, longleaf pine, and loblolly pine, growing in Central Mississippi were cut and converted into lumber. Sufficient clear sapwood was retained from each tree to provide 30 blocks 1 by 1 by 3/8-inch. Decay resistance was tested using the standard soil-block method with Poria monticola Murr. (Madison 698) as the test fungus. Four inoculated blocks and one uninoculated test block for each of the 12 trees were incubated for 3 weeks; other sets were incubated for 6, 9, 12, 15, and 18 weeks. Weight loss was determined after conditioning to constant weight at 27,5?C. and 70 percent relative humidity. There were no significant differences between trees within pine species for any of the incubation periods. Difference in decay resistance was statistically significant only after the 9- and 15-week incubation periods. Application of the “t” test showed that after 9-weeks incubation, slash pine was significantly more decay resistant than shortleaf or loblolly pine (at the 5 percent level), and after 15 weeks significantly more resistant than shortleaf (at the 1 percent level) and loblolly (at the 5 percent level). Also, after the 15-weeks incubation period longleaf pine was significantly more decay resistant than shortleaf pine (at the 5 percent level). The overall tendency of the sapwood of longleaf and slash pine to show more decay resistance than shortleaf and loblolly pine is in agreement with the ratings given the heartwood of these species.

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