Is My Tree Safe?

A question I often get asked by my clients is “Is my tree safe?” Trees have evolved in a forest environment where branches can fall with little consequence.  They have not been designed like man-made structures and do not come with a tested breaking strain.  In some cases, it can be obvious that a tree is unsafe due to the presence of a significant defect. There are also some trees that in their present form represent a very low risk, such as new planting.  The majority of trees, however, fit somewhere between these two extremes.  This blog will help you understand why you might not always get a yes or no answer to the question “Is my tree safe?” from an arborist and why you shouldn’t always trust it if you do.  I’ll also add some tips on what to look for in your trees to help you form your own decision.

Robin Hoods Oak, Sherwood Forest, UK. Estimated to be between 800-1000 years old. Artificial props now support the heavy limbs.

Robin Hoods Oak, Sherwood Forest, UK. Estimated to be between 800-1000 years old. Artificial props now support the heavy limbs.

The most commonly used technique by Arborists to assess trees is visual tree assessment (VTA).  In VTA an arborist will look for certain tell-tale signs that can indicate dysfunction and a likelihood of failure in a tree.  It takes training and a lot of experience to become proficient at VTA so it is important that you know the person inspecting your trees in competent.  The benefit of VTA is that it is very low cost and does not harm the tree in any way.  Where VTA is lacking is that you cannot look inside the tree and this is where a fault might be hiding.  Having said that the tree often exhibits subtle clues on its surface about what lies beneath and a skilled arborist will be able to read them. 

Methods for looking inside the tree have been developed but they can often involve making small holes in the tree which can breach the tree’s natural defenses.  More recently non-invasive methods have been developed to “look inside” trees using sound waves and heat imaging devices.  These can be quite expensive and their accuracy can be effected by environmental conditions.

This tree failed during the 2018 Auckland storm taking down a power line to the house and blocking the footpath and driveway

This tree failed during the 2018 Auckland storm taking down a power line to the house and blocking the footpath and driveway

Trees have evolved to break under certain conditions, if they didn’t break they would fall over.  It is better for a tree that a branch breaks off in a strong wind or heavy snow than the whole tree falling over as it attempts to hold onto it.  If a certain branch in a tree is using more energy for its growth than it is making via photosynthesis from its leaves it will likely die off because it is “too expensive” for the tree to maintain.  These are just two examples of how trees self-manage. Both can lead to branches falling off the tree.  They are natural processes that the tree undergoes all the time.  Questions to ask are “how big are the branches, how likely are they to fall, and what will they hit if they do fall?”  Determining these answers is not an exact science and so you will often hear an arborist talk about likelihood of risk rather than a definitive answer.  The weather can play a very significant role in all of this too; even perfectly healthy trees can fail in strong winds. 

So, what can you look out for as a tree owner?  Below are a few items you can look for in and around your trees which may indicate that you should contact an arborist:

·         Fungal fruiting bodies (mushrooms) surrounding the tree or on the tree

·         Changes in the ground surrounding the tree – cracks in the soil, mounds or hollows, excavations near the base of the tree, very wet or very dry ground

·         Movement at the root plate of the tree

·         Loose or peeling bark

Fruiting body of a bracket fungus growing on a street tree

Fruiting body of a bracket fungus growing on a street tree

·         Rot holes

·         Cracks

·         Branches that appear to be dead

·         Broken branches

·         Abnormally yellow leaves

·         Lots of new shoots growing from the trunk of the tree

·         It can also be good practice to have your trees looked at by a professional following any strong weather conditions

If you are unsure about the condition of your trees it is best to contact a suitably qualified and experienced Arborist.