Any arborist worth their sawdust will tell you that trees have a greater tendency to break where structural defects are present, or during storms with high winds and precipitation.
…but then there is summer limb drop (SLD) — also known as ‘sudden’ limb drop which is equally appropriate.
This poorly-understood phenomenon defies conventional thinking about how, why, and under what circumstances tree limbs will break, or ‘fail’, as we say in the tree biz.
Imagine a warm summer day or evening with dry conditions and no wind. Suddenly (hence the name), a large lateral limb may creak, groan, or pop seconds before tearing off the tree and crashing to the ground.
The cause of summer limb drop has yet to be deciphered by science. There are several theories out there and many point to complex interactions between environmental conditions outside the tree and water movement inside the tree.
After limited scientific study and years of observations by tree experts, here is a sampling of what we think we know about this mysterious issue:
- 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
- Oaks are potentially the most susceptible species
- Mature trees with larger limbs are more susceptible than younger trees with small limbs
- Horizontal limbs 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
Here are a couple of links to more information on summer (or sudden) limb drop:
From the United Kingdom’s Arboricultural Advisory & Information Service
From the United Kingdom’s Quantified Tree Risk Assessment Training