Tree Safety

Published on 20 January 2026

Large Tree Limbs Dropping

It is not uncommon to hear of incidents when large, heavy branches fall from a tree without warning.  Sometimes these events have serious consequences.  A question that is often asked is "why", and whether it could have been predicted and prevented.

The truth is, that even professionally trained and highly experienced arborists are not always able to answer that question.  It is one of nature's inexplicable anomalies - why a branch unexpectedly falls from a mature tree, that is seemingly healthy and stable, and experiencing calm conditions.  However, when we do become aware of issues with trees on Council owned or managed land, Council actions tree inspections by suitably qualified professionals to ensure the tree will continue to be safe for people nearby.

Tree Facts

We do know that some types of trees are more prone to sudden branch drop, such as: Ficus (Moreton Bay Fig), Beech, Oak, Sycamore, and Eucalyptus.  Some of the Eucalypts are particularly susceptible, including: River Red Gum, Sugar Gum, Spotted Gum, and the Narrow-leafed Peppermint.

The time of year and the age of a tree also appear to be contributing factors.  Older trees are more susceptible and sudden branch drop is more likely to happen in the heat of summer - sometimes called 'summer branch drop'.  Branches that fall are typically heavy lateral branches with lots of foliage that extends 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.

There are often 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 is usually impossible to predict if or when branch drop will occur with certainty.

Why do limbs drop?

While the causes of sudden branch drop are not clear, there are some theories.

One theory is that high humidity and therefore excess moisture within the tree's canopy weakens its structure, thus causing the branch to shear.

Another theory suggests that insufficient water - even going back to the early years of a mature tree - could be behind the issue.  When a tree has lots of foliage and cannot get enough nutrients and water to meet all its transpiration requirements, it aborts a limb.

Other theories include bacterial issues within the wood, tissue shrinkage and microscopic changes in the cell wall structure.

It is likely that the causes probably include a combination of environmental conditions, the age, health and of course, species of the tree.

It is possible to mitigate some of these issues through inspecting the trees and undergoing appropriate intervention, such as pruning the tree to open up its canopy and reduce the risk of high humidity, or to cut back any riskier branches to reduce the likelihood of them dropping with serious consequences.  Any work done to trees should be undertaken with the knowledge of how to care for the trees - randomly hacking off branches without the appropriate care or knowledge can harm or kill the tree.

Keeping Safe

While we all appreciate the shade provided by trees and certainly having trees in our towns help to cool the local environment, there are a few considerations to keeping safe.

Avoid camping or sitting directly underneath trees with large branches.  Incidents involving injury and death to campers by falling branches are well documented.

While keeping your car cool in the shade is a good idea, avoid parking directly under branches that may drop.  This does not mean avoiding the shadow of a tree, as the shadow often extends beyond the canopy of the tree and is thus safe to park within the shadow.