What You Need To Know About Sudden Branch Drop
When a large, heavy branch falls from a tree without any warning (sometimes with devastating consequences), people always ask why. And they also always ask whether it could have been predicted and prevented.
The truth is, that even though we are professionally trained and highly experienced arborists, there are some things we don’t know about trees. In fact, no-one knows. It’s one of Mother Nature’s inexplicable anomalies. Why does a branch unexpectedly fall from a mature and seemingly perfectly healthy, stable tree in calm conditions?
What we know
We do know that some types of tree are more prone to sudden branch drop such as Ficus (Moreton Bay Fig), Beech, Oak, Sycamore, Elm and Eucalyptus. Some of the Elm species and the Eucalypts including River Red Gum, Sugar Gum, Spotted Gum and the Narrow-leafed Peppermint are particularly susceptible.
The season and the age of a tree also seem to be contributing factors. Ageing trees are more susceptible and sudden branch drop is more likely to happen in the heat of summer (which is why the syndrome is also sometimes called ‘summer branch drop’). We also know that branches that fall are typically heavy lateral ones with lots of foliage which extend beyond the main canopy.
In most cases, the limb shears off some way down from the point of junction with the main tree trunk – and the break is usually clean.
We also know that there are generally no warning signs with sudden branch drop. The tree appears healthy, with no visible cracks or colour changes and no evidence of stress, so it’s impossible to predict if or when this unusual phenomenon will happen.
What we think
While the causes of sudden branch drop are uncertain, there are some common theories.
The first theory is that high humidity and therefore excess moisture within the canopy of the tree weakens its structure, causing the branch to shear. Another suggests that insufficient water – even going back to the early years of a mature tree – could be behind the phenomenon. In other words, when a tree has lots of foliage and can’t get enough nutrients and water to meet all its transpiration requirements, it aborts a limb.
Other hypotheses include bacterial issues within the wood, tissue shrinkage and microscopic changes in the cell wall structure, but the truth is, they are only theories. We think the causes probably include a combination of environmental conditions, the age, health and of course, species of the tree – and our best recommendation is if you have large, mature trees under your care, it’s a good idea to have them inspected.
One of the things that a professional arborist may recommend is having the tree pruned to open up its canopy and reduce the risk of high humidity. They may also cut back any riskier branches to reduce the likelihood of them falling.
And of course, the healthier the tree, the better. That’s why we always recommend that people run a consistent programme of mulching, fertilising and deep watering their trees to ensure optimum health.
When there’s one, there may be others. A tree that has lost a limb without warning may be susceptible to further drops, so it’s important to get professional advice on the future health and wellbeing of the tree (particularly if people or property are at risk).
Here in Australia, sudden branch drop is not uncommon and that’s because we have so many Eucalypts. They’re native to our wide, brown land and we have almost 800 species! Our arborists in Perth have extensive experience with this syndrome and would be very happy for a friendly, obligation-free chat about any concerns you may have about your trees’ health. Please contact us on 08 9249 4077 or get in touch.
