Trees That Go Bad
Who is responsible when trees attack and how to mitigate risk
Thursday, August 6, 2020
by: Sarah Gaskin, Consulting Arborist at A Plus Tree, Inc.

Section: Trends and Tips

As a Consulting Arborist and lover of all things tree. I have wondered,

“Have I ever met a tree I didn’t like?”

And the answer is yes, yes I have.

I know it’s not the tree’s fault. At the heartwood of them, they’re good treeple. They can’t help where they were planted, what environment they’re exposed to, or what hides under their roots.

To live around trees is to inherently assume risk. Trees are living and dynamic, even the smartest of Arborists cannot assure you a tree will never fail. Yet, there are indicators and characteristics of a tree that can point to a higher level of risk or hazard. So, when a tree goes bad, whose fault is it? And how can we save our leafy friends from attacking?

Before we get into the blame game- we need to look at 4 things that could indicate a higher risk of failure, and what you can do about it.

Fractures and Cracks

Some fractures are superficial or even a characteristic of their species. The ones to look out for are those along attachments or appear to penetrate deep into the wood and compromise the strength of the tree or the limb.

Non-Structural Cracks vs Structural Cracks

What should you do?

If it's a major crack down the center of a tree or large limb, hit up your tree care provider and have them take a look and make the call.

Otherwise, be sure your trees are on a regular maintenance schedule- roughly every three years per tree unless pruned for clearance. You should also have annual assessments. It’s good to have them assessed in the fall to prevent failures and to be ready for winter months. Many of these issues can be mitigated by proper pruning.


One of the biggest concerns we get from a tree owner is, “My tree is leaning! Help!” Most of these alarms are false, and the tree has been growing that way. (This is called "Phototropism, where it grows toward the sunlight"). On a few occasions, the tree was actually slowly falling. So, how can you tell the difference?

Growing Toward Sunlight vs Disturbed Soil Around Roots

What can you do?

If the tree is leaning and appears to have been growing in that direction it's whole life, likely the roots have also developed in a way to account for the lean. With that said, a lean does inherit a bit more risk. It will never be as strong as a straight trunk. The best way to mitigate is to prune to keep weight off the direction of the lean.

If the tree is leaning and you DO see disturbed soil or lifting roots around the trunk, this often indicates root slippage and it's a major red flag. You should call your tree care provider to take care of that bad boy before it takes care of itself.

Mushrooms feed on dead organic matter. Which means the presence of mushrooms indicates some sort of decay. Some mushrooms can be beneficial, and others can be indicators that something very bad is happening. Like trunk rot or root rot. This is caused by a fungus that eats away at the wood

It’s important to know the difference. The entire structure of the tree may be compromised and at risk of falling over. Even if the canopy is fully green!

Beneficial Mushrooms vs Bad Mushrooms

What can you do?

Unfortunately, once the tree has root rot and the root system is decayed, there is no reversing it. An arborist can perform a root excavation to see how much of the root system is compromised. But most likely the mode of action is to remove the tree.


The strength, integrity, and risk of a tree is directly related to its structure.

Not all pruning is created equal. It's not like getting a haircut and it is not all about looks. Actually, the wrong type of pruning can ruin a tree. And the right type of pruning can set the tree on a great growth path, make it safer, AND save you from future pruning costs.

As part of our industry standards, there are 6 main types of pruning that have different techniques. We won't get into every type, but here's the list:

1) Clearance Pruning
2) Crown Raise
3) Crown Clean
4) Crown Thin
5) Crown Reduction
6) Structural Pruning

A good tree company should know the difference and should also not be carelessly cutting limbs.

Pruning your tree for clearance every year is the most minimal type of pruning and does little to address any structural issues the tree may have.

Structural pruning is talked about a lot less, but perhaps one of the most important techniques at the younger stages of the tree since it sets its growth structure for the future. The aim is to develop a main leader by shortening those around it that may compete with the trunk stem.

Good Structure (single leader) vs Bad Structure (multiple leaders)

What can you do?

When having your trees assessed, there should be a goal and strategy behind every pruning recommendation. If your bids come back to you and all the recommendations all say "Pruning" or "Trimming"? Well, that doesn't tell you much, and you may have a lazy tree company. Ask if they are addressing any structural issues, that will impress them.
Now back to the question I'm sure we all want to know the answer to.

When a tree does fail, whose fault is it?

I've got two words: due diligence.

In my experience, that is all the insurance companies care about. "Did you do your due diligence?"

When was the tree last pruned? If it wasn't, when was the last time a professional looked at it and did you have a plan for it?

If you have maintenance records on that specific tree, or you have records of recent assessment, then that usually satisfies the insurance investigation. The incident usually gets filed under the "Act of God" - an unforeseeable event.

This is why a tree inventory and a management plan is so important. I'm not talking about the old tree tagging systems that cost thousands of dollars and ends up in an excel spreadsheet. Nowadays, there should be an app for that. Ask your tree care provider.

Below is an example screenshot of the program we use, ArborPlus. It has all the details and work history of the tree. It has saved many of our clients from incurring costs by proving their due diligence.

Tree inventory example: Screenshot of property map overview  with tree locations. Different colors indicate different tree species.

Tree history example: Screenshot of tree with pruning history and upcoming recommendations.

To wrap it all up, here are the 3 things I'd like you to take-away:

1. Keep an eye out for all the indicators mentioned above. If you see any concerns, call your tree care professional and have them take a look.

2. Pay attention to your bids and ask questions! Not all pruning is created equal.

3. If you have lots of trees on your property and don't have a tree inventory or a management plan, consider getting one. Depending on your tree care provider, it can be an additional cost, or like us, it's included in our regular services.

That's all folks! Next time you stroll through your urban forest, I hope you look at your trees with more insight and understanding.
Leaf out.
Thank you to A Plus Tree, Inc, a 2020 BOMA San Diego Annual Supporting Partner, for providing this educational content!