Assessing Internal Hurricane Damage To Standing Pine Poletimber
Keywords:Storm damage, poletimber, toughness, tension strength, FIA damage class
Two test methods were used to assess type, location, and degree of internal stem damage to standing pine poletimber (5.0-8.9 in. diameter at breast height, DBH) caused by Hurricane Hugo. A total of sixty trees [15 from each of the four Forest Inventory Analysis (FIA) damage classes] were taken from three sites in the Francis Marion National Forest. Internal damage was expected in the form of ring shake and compression failure. Five stem sections (A through E) were taken from each tree at different heights. From each section, specimens were cut from four quadrants (Tension, Compression, Left, and Right) relative to the wind direction during the storm for toughness and tension perpendicular to the grain testing. A total of 2,147 toughness specimens were tested. A total of 273 specimens were tested in tension perpendicular to the grain. The dependent variables analyzed were toughness, tension strength, and specific gravity with FIA damage class as the whole plot factor.
Although there was an increasing trend in toughness from Damage Class 1 through 4, analysis of variance showed damage class not to be a significant effect on toughness. Stem section and quadrant were found to be significant on toughness. Much of the variation in toughness due to stem section may be attributed to the effects of juvenile wood differences with tree height. Also a high occurrence of reaction wood in Quadrant C (side of the tree away from the wind) would contribute to lower toughness strength. Similarly, specific gravity (SG) values showed an overall increase from Damage Class 1 through 4. Specific gravity of Damage Classes 1 and 4 was found to be significantly different. Statistical analysis showed no apparent relationship between damage class and tension strength perpendicular to the grain.
The lack of evidence for internal damage is relatively unimportant compared to the evidence of change in the wood properties from the formation of reaction wood. In leaning stems (FIA Damage Classes 2, 3, 4), reaction wood should continue to form. In straight trees, reaction wood formed in the two growth seasons following the storm, but it is unclear whether it will continue to form. The results lead to the conclusion that stands with leaning stems should be harvested and replanted.
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