Friday, January 2, 2009

Landscape - Assessing Deciduous Trees for Potential Limb Failure

Limb failure in trees is a common problem during the winter with snow and ice loads and heavy winds. The following is some information on assessing deciduous trees for potential limb failure.
  • Limb or branch failure is the most common form of failure for deciduous trees.
  • Begin the inspection with the attachment of the primary limbs with the stem. Codominant stems are a very common structural defect. This occurs when the stem divides into two equal diameter upright limbs. These limbs do not have a strong attachment and usually develop long lines of included bark. Strong winds will often separate these weakly attached limbs.
  • Limbs or branches with narrow branch angles behave similarly as codominant stems because they have large areas of ingrown bark that weakens the structure. Check for limbs with ingrown bark in narrow branch angles. These are the most likely to fail.
  • Topping and lion-tailing also reduce the structural integrity of the canopy. Topping occurs when limbs or branches are headed back. The pruning wound generally creates long decay columns as well as producing a proliferation of weakly attached watersprouts.
  • Lion-tailing occurs when long limbs are stripped of their interior branches. The loss of these leaves and supporting branches decreases the flow of food transported to the limb which can result in less taper, thus less structural support.
  • Assess limbs and branches for damaged or diseased areas. This includes decayed areas, cankered sections, borer damaged branches, bark cracking, and physical damage to branches.

Information taken in part from "Hazardous Trees: What You Don't Know Can Hurt You!" by John Ball, Ph.D., South Dakota State University, Brookings, South Dakota

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