Sudden Limb Drop in the Santa Barbara Area

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As recently reported in the news about oak trees in the Santa Ynez Valley and around Cachuma Lake (http://www.keyt.com/news/county-arborist-to-assess-droughtstricken-trees-at-cachuma-lake/27515862)

Sudden Limb Drop has become yet another issue surrounding the drought and its impact on trees. As outlined in Arboriculture: Integrated Management of Landscape Trees, Shrubs, and Vines (Harris, Clark, and Matheny 2004) sudden limb drop is generally used to describe a unexpected branch (or even a trunk) failure during the summer months on days that are hot and the air is calm.

Sudden Limb Drop Characteristics

Some conditions commonly associated with sudden limb drop include:

  • Hot, calm summer afternoons;
  • Branches more horizontal than vertical extending beyond the crown;
  • Breaks most often occur along the limb away from the attachment;
  • Usually observed in over-mature or senescent (slowly deteriorating) trees.

Although there are trees that have a high susceptibility to sudden limb drop (oaks, eucalyptus, sycamores, and pines) it can happen to any tree.  Breakage of the limbs occurs at 3 to 12 feet from the main branch attachment point on branches that are apparently sound with no visible sign of disease or decay.

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How Can You Assess The Risk?

If you have a tree with any limbs that extend over a building, a deck, a parking area or any area where people frequent, it is best to have a qualified arborist certified in risk assessment look at your trees.  A risk assessment includes an assessment of the overall health and structure of your tree and identifies the potential ‘targets’ (what the tree would hit if any part of it fell) to determine the best tree care actions.

Ways to Reduce the Potential for Sudden Limb Drop

Complete removal of a tree is not the only solution.  Branches that are questionable can be shortened, have the end weight reduced, have a supportive cabling system installed, or removed altogether.

The tree canopy can be opened up (thinned) to reduce the humidity within the canopy (one theory behind sudden limb drop).  Trees can be kept vigorous and healthy while maintaining a full, well-balanced canopy. Make sure you trees lack decay, trunk or branch cavities, excessive deadwood, or visible insect damage.  Healthy, well-maintained trees are less likely to suffer sudden limb drop.

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