Integrated Pest Management

Is it is time to cut down a damaged tree

Cutting down a tree that is an old friend is an emotional as well as a financial decision, so how do you know when it is time.

Here I am only going to deal with trees that have sustained physical damage and not damage from such things as insects or disease.
There are no easy answers to this question, but I hope to offer you some useful advice. The decision to, or not to cut down a beloved tree needs to be made taking these and other factors into account.
1. Is, or was the tree otherwise in basic good health?
2. Is the tree, or can the tree be made safe?
3. How old is the tree and is it at the end of its normal life cycle?
4. Will this tree survive and for how long?
5. Do you love that tree enough to spend more on it then you would to take it down?

This old Maple has lost a major branch in the last storm.

Now we have to decide if it's time for it to come down.

1. Is this a healthy tree?

The answer to this is that this tree has been in relatively poor health for a while.

This is not really a question most people can answer for themselves so if you don't know get some professional opinions.
I don't want to get very deeply into what makes a tree healthy, that is a long subject for another day. So why do I say this is not a healthy tree?
Look at the structure of this tree, it has multiple leaders which make it not structurally sound.
Trees with multiple leaders like this one should be cabled as this is not the natural form of a tree and co-leaders frequently break in storms.
You can see in this picture the rot in other areas of the crown.
Though it is normal for some small branches to die each year, this tree has been loosing more than the normal amount of larger branches for years. I suspect that it has some disease such as Verticillium wilt that is causing some of the dead branches.
I am reasonably confident that the main stem is still sound, however only the use of a tool called an increment borer can tell if this is true.
For the purposes of this discussion we will say that the trunk is sound.
If the trunk was rotten and hollow it would end the debate, this tree would definitely need to be taken down.
The tree has no insect or disease problems that will kill it. A driveway was installed too close to this tree which damaged roots and is contributing to its poor health.

2. Is this tree safe?

Safety depends on the situation as well as falling branches. This tree is growing away from any house and far enough away from the wires that falling branches will not hit them. More branches will fall from this tree but are unlikely to damage anything or hit anyone.
This tree can be made reasonably safe by pruning and cabling, but due to its overall poor health more branches will die and will have to be cut off. No large tree is one hundred percent safe however healthy it looks.

3. How old is this tree and is it at the end of its natural life?

Each tree species has a normal longevity, so you will have to find out what tree you have and how long they usually live. If this were for example, a white birch, it would already have lived long past the expected maximum age. This tree is a Soft Maple and a healthy tree of this species would have many more years to live. I do not know how old it is my guess would be around 60-80 years. Trees growing in different conditions vary greatly in size so only the increment borer can tell you for sure how old a tree is.

4. Will this tree survive and for how long?

This tree will eventually die from this wound, but when? This is always a tough question as it depends on so many other factors. The growing environment, tree species, health of tree, weather, insects and disease. A good landscaper will tell you I don't know, but give you some Idea. This is what I would tell a customer. When a tree has lost a branch this size eventually rot will kill this tree. However; this could take a long time for a maple and you could get several years of enjoyment out of it. This tree could last another twenty or so years or could lose its battle to live next year. I would suggest planting a tree to replace it when it does die. Pruning, cabling, creating a bed with mulch and compost might extend its useful life. The tree will be more susceptible to insect, disease, drought or too much rain. You should be prepared and able to give it extra care if you decide to keep it.
To be specific as to why this tree will die of its wounds. Look at the size of the branch. As a rule if a branch is cut or falls off and it is more than one third the diameter of the trunk the wound will not heal, rot will set in and travel down the trunk. (Technically tree wounds don't really heal but the tree compartmentalizes the damage.) If the branch is ripped from the tree as this one was it may have also torn down the trunk and this will contribute to the speed rot kills the tree. Even if a tree did not lose a major branch like this one but a lot of smaller ones, the total of the crown loss should be no more than one third for a reasonable chance of survival. Naturally this depends on many things such as the health of the tree and if you clean up the damaged branches with clean cuts.

5. Do you love that tree enough to spend more on it then you would to take it down?

This is then the big question. From what we have discussed above we know that this tree is not really that unsafe due to where it is.
We know that it will die of its injuries.
We know that it is a long lived species and not at the end of its expected life cycle.
We think that we can increase its useful life by taking good care of it. We can't do anything about the drive over the roots.
We know that if we decide to keep it that this will be more expensive then taking it down.
Now we have four basic choices.
Cut it down.
Do nothing and just let it go.
Prune the damage then let it go.
Prune the damage, the other dead branches and do whatever else is needed to improve the life expectancy.
But I still have not answered the basic question. That is because it really can not be answered the same for everyone.
I will tell you what I am going to do. I do love this tree but I am also in the business of plant health and know that the prognosis is not great, nor do I have a lot of disposable cash. I will prune the damage, build a decent bed around it, give it some compost and hope it survives long enough for a new very much smaller replacement tree that I plant to grow up to a decent size.

Here are two more scenarios.

This tree has a sparse crown from repeated attacks of Tent Caterpillar. It has some dead branches but they are smaller than one third of the trunk size. I know this tree is in the woods and I will do nothing about it. But let's say this tree is in your front yard.
Pruning, improving the growing conditions and treating the tent caterpillar outbreaks would be worthwhile for this tree. With reasonable care this could be a nice specimen tree. It is a Black Cherry and has many good years left.

I cut off one of the two co-leaders of this tree.

This tree had two leaders. They were both healthy and about the same size. I cut off one of the leaders as this tree is in the woods and will end up a firewood tree. Note that the wood is sound where it was cut, and it is a clean cut. The remaining side of this tree will live for many years before rot eventually kills it. If this tree were in my yard and I wanted to keep it I would have had a cable put between the two leaders.