Growth stress versus capillary tension in relation to trunk splitting in Fraser fir Christmas trees
Hart, C.A. | Hinesley, L.E.
A study was conducted to determine why some harvested Fraser fir (Abies fraseri (Pursh) Poir.) Christmas trees develop longitudinal splits on the lower portion of the trunk (butt), typically beginning just under the bark and progressing both inward to the pith and upward. Cracks apparently do not appear in trees kept with their butts in water. Excessive drying was suspected, but the moisture content (MC) of split trunks was well above fiber saturation. A 60-tree study was conducted to examine MC, splitting, and capillary tension in the sap stream. Tree butts were enclosed in plastic bags to ensure that drying was only from the foliage. Average capillary tension was initially below the wood tensile strength of the species (180 psi), and increased to levels substantially above that strength as the trees dried. Capillary tension was concluded to be the cause of the splitting. These findings have interesting implications regarding distortions and warpage, normally attributed to growth stresses, that can occur during the sawmilling of planks. Further research in this area is needed.
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