It can be very disconcerting to wake one random morning and find a branch that has fallen from one of your trees. Especially if it fell in the middle of summer on a calm, hot day with no wind. Aren’t tree branches supposed to fall during the winter when it’s really windy and rainy? A little spooked, you’re suddenly aware of ALL the trees in your yard and wonder when the next branch will fall!
Every summer, after several days of extreme heat, arborists will receives calls about broken tree branches. We get more calls about broken branches in the summer months then we do in the winter! This is such a common occurrence that it has its own name: Summer Limb Drop or Sudden Limb Drop.
Why Does It Happen?
Research over the years has led to lots of speculations but no definite cause. There is enough consensuses among arborists to believe water is a factor.
One theory suggests that on hot days, branches become lighter because the tree is transpiring water quicker than it can pull it up. Many SLD branches fall in the late afternoon, early evening, or early morning when there is a change in temperature. If a fog rolls in as the sun sets, or the overnight temperature reaches its lowest point in the early morning hours, the tree is able to pull up more water, weighting the lifted branch and causing it to fall back down and snap off. Or so the theory goes.
We also know that Sudden Branch Drop is more frequent in trees that have not been pruned in a number of years (or not at all!) and in trees with defects. However, many sudden limb failures have occurred in trees with no defects at all, which makes it really difficult for arborists to predict.
Can Summer Limb Drop Be Prevented?
Education is your first line of defense. Being knowledgeable about Sudden Limb Drop will help you understand and value the need for periodic inspection of your trees by a professional arborist and specifically one who is also a Tree Risk Assessor. An arborist will look for long branches that extend outside the canopy and that contain a lot of foliage at the ends, creating the perfect situation for SLD to occur. Minimize this by thinning the heavy foliage and if possible reduce the length of the branch back to a suitable lateral.
Sudden Limb Drop List of Common Observations
SLD is more likely in summer or early fall on hot, dry days with little or no wind
SLD is more likely in afternoons and early evenings
Deciduous trees appear to be more susceptible than conifers
Older oaks, maples, ashes, beeches, and elms are common victims of sudden branch drop
Mature trees with larger limbs are more susceptible than younger trees with small limbs
Horizontal limbs that extend outside the canopy are more susceptible than upright limbs
Affected limbs may appear healthy and show no signs of defects
Trees experiencing SLD on one occasion may be more likely to drop limbs in the future
If you are concerned about your tree or it has been several years since it has been pruned, please call and arrange an appointment with an ISA Certified Arborist.
By John Traverso, Traverso Tree Service