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Abstract. One of the most common locations for the aboveground portion of a tree to fail is at the junction of two or more codominant stems. Due to the frequency of failures at this point, a study was undertaken to get a better understanding of the mechanical strength of this point and to determine if included bark reduces the strength of the union. Eighty-four codominant stems were removed from 26 felled maple trees. These crotches were securely anchored and split apart using measured force. Breaking force varied from 64 to 2,363 kg. The regression line produced from the comparison of stem diameter and force required for breaking the union when there was no included bark was Force = Diameter * 613 - 1388, r^sup 2^ = 0.92. When only those unions with included bark were analyzed, the regression line was Force = Diameter * 537 - 1285, r^sup 2^ = 0.76. There was a significant difference between the regression lines (p < 0.05). Codominant stems that have bark trapped in the union are significantly weaker than those that do not have bark included. The differences appear to be greater with smaller-diameter stems than with larger stems.
Key Words. Pruning; cabling; bracing; tree failure; Acer rubrum.
One of the most common locations for the aboveground portion of a tree to fail is at the junction of two or more codominant stems. Matheny and Clark (1994) state that codominant stems with included bark do not form connective tissues between stems and are prone to failure. In earlier studies, there were indications that included bark did make these junctions weaker (Smiley et al. 2000). Due to the frequency of failures at this point, this study was undertaken to get a better understanding of the mechanical strength of this point and to determine if included bark reduces the strength of the union.
MATERIALS AND METHODS
Twenty-six red maple (Acer rubrum L.) trees were harvested between June 1999 and July 2001 at the Bartlett Tree Research Laboratories in Charlotte, North Carolina, U.S. Eighty-four codominant stems were removed from the felled trees, leaving at least 45 cm of stem on either side of the crotch....