Trees With Holes – Causes, Hollow Effect, Dangers & Fixes

What is a hole in a tree called? A tree hollow.

You’re probably reading this article because you need answers to your hollow tree problem. If you do, this article provides you with all the answers you seek.

Here, you’ll find details on the causes of hollow trees, how to remedy the situation, and possible risks (if any at all) associated with this condition.

Tree Hollow: Definition, Hole Causes, And Safety Issues

Whether you’re faced with a hollow in your trees or tiny holes in it, all such situations can be problematic as they can affect tree health.

We’ll be discussing the causes of holes in trees and appropriate fixes to cover such holes. This will prove highly beneficial to the overall well-being of your trees.

What Causes Holes In Trees?

To fully understand tree hollow and its impact, you’ll need to understand the cause(s) of such a condition.

These spaces always look unnatural hence the need to investigate and provide appropriate fixes. Tree hollows can be caused by different factors, including bird and insect activity.

Tree hollows may also result from natural causes, as you’ll soon find out. Any of these causes above could lead to creating spaces or holes, which may require action on your part.

Let’s briefly discuss each of these conditions for a more detailed understanding.

  • Insects

The causes of holes in your trees could partly be due to insect activity.

These insects are borers who bore through your trees to lay their eggs. These holes can be very tiny or a bit larger depending on the size and type of insect.

The most notorious of these include bark beetles, clearwing moths, dogwood borer, banded ash borer, lilac borer, peachtree borer, flathead appletree borer, bronze birch borer, and lesser peachtree borer.

Others include red oak borer, redheaded ash borer, locust borer, cottonwood borer, twig girdler, southern pine beetles, and shothole borers.

All of these pests drill through your precious trees for various reasons.

The targets for most tree borers are weak or stressed-out trees. Tree weakness and stress are caused mainly by pruning injuries, insufficient water supply, and environmental stress, among others.

The Larger the Insect, the Bigger the Holes

Whenever insects drill through trees, they leave holes behind. Now, the size of these holes will depend on the size of the insects.

As expected, more giant insects drill bigger holes and vice versa. Your trees suffer over the long term as such holes in both bark and sap effect and hinder the transportation of food and water.

So, you want to take action, whatever the size of the hole is.

We’ll be discussing the various fixes shortly to implement whenever you find these holes on your tree.

  • Birds

Birds aren’t left out of the party when excavating holes in trees.

These birds either target dead trees or the dead limbs of living trees. The goal is to create a nesting cavity in which they can lay and hatch their eggs.

Birds known for this digging activity include woodpeckers and northern flickers. In the case of woodpeckers, different species are known to be active diggers or excavators of wood.

These include red-bellied woodpeckers, downy, red-headed, and pileated woodpeckers.

The action by birds in excavating a tree won’t damage the tree itself. However, the problem lies in the injuries inflicted on the trees.

Such injuries are points through which diseases and other destructive insects can enter the tree.

Causes of Tree Hollows In Trunks

Hollows are common occurrences on some trees. These are cavities that could have a more expansive space within.

Hollows may be formed due to natural causes and are mostly found on tree trunks.

A hollow may result from a tree dropping its withered or dead limb.

Space previously occupied by the dead limb becomes a point through which this cavity might form. Hollows serve as homes for a variety of wild creatures, including birds.

Such cavity-nesting birds include tree swallows, eastern bluebirds, eastern screech owls, and American Kestrel.

Others include white-breasted nuthatches, tufted titmice, Carolina chickadees, purple martins, and house wrens. This isn’t much of a problem compared to other types of holes in trees.

  • Bird Activity

Whenever you find a hollow on a tree, a bird may have excavated it. Certain bird species are notorious for such type of activity.

They include multiple species of woodpecker birds, as well as northern flickers. Whenever such excavation is done, it seeks to achieve a purpose; creating a nesting space.

Apart from the potential stability issues such excavation is likely to cause, it also exposes the tree to possible diseases which gets in through the wound or opening created.

However, the activity of birds in creating tree hollows is only one possible answer to why there are hollows on your tree.

  • Insect Activity

Insect activity could also be a possible reason you have a hollow on your tree. Certain insect species have mouthparts that are well adapted to bore through wood.

Most of these don’t feed on the tree but simply boreholes to lay their eggs.

Healthy and strong trees aren’t as vulnerable as those stressed out. So what exactly are stressed-out trees? These trees are mostly those most affected by environmental stress or having a short supply of water.

They’re also trees whose stress condition is due to injuries caused by pruning activity.

As these insects focus on wounded areas, their burrowing activity creates a hollow. This becomes more pronounced over time.

Examples of burrowing insects include peachtree borer, clearwing moths, banded ash borer, dogwood borer, and lilac borer.

Others include southern pine beetles, locust borers, and cottonwood borers. Others are red oak borers, shothole borers, twig girdlers, and bronze birch borers.

Other culprits include flathead appletree borer and bark beetles.

  • Natural Causes Of Tree Hollows

Tree cavities may also be due to natural causes. They result from dead tree limbs that fall off, thus creating a hole at the point where the stem dropped off.

The hollow becomes a ready nesting site for different birds, including house wrens and white-breasted nuthatches.

Other tree cavity dwellers include Carolina chickadees, purple martins, American kestrel, tufted titmice, and eastern screech owls, just to mention a few.

Having identified the different causes of tree hollows, you’re left to decide whether a solution is needed or not.

Pros and Cons of Tree Hollows

Assessing the pros of hollow tree issues can be a bit difficult if you mostly view these for the problems they cause. To give you a better perspective of things, we’ve included the pros and cons of tree hollow.

Sometimes, tree hollows offer certain benefits, as shown below.

  • Tree Hollow Benefits

Cavities formed on trees can serve as a refuge for birds. This is especially true for hollows located higher up the tree. It offers birds and other wild creatures a ready nest to rear their young.

You may find certain trees close to or within water bodies. Aquatic animals may use cavities formed on such trees to lay their eggs.

  • Tree Hollow Downsides

Hollows tend to have more negative than positive impacts on trees. Trees with cavities near homes may serve as secondary nesting sites for certain pests until they get into your dwelling.

Such hollows also pose a structural risk as they’re likely to make a tree or its limb weaker.

The tree’s weakness becomes more evident during a heavy storm. The weak point created by the cavity is likely to cause the tree to give way. Such a tree or affected branches could come crashing down on your home.

In a nutshell, hollow trees become a safety concern for homeowners.

Fixing Holes On Trees

Having discussed the many causes of tree holes, it’s necessary to shift our attention to how you can fix such holes.

There are several ways to achieve this. One of them involves patching up the hole in a tree hole, using screening or a thin metal flap. Covering this with some plaster will serve the purpose.

The aim is to prevent any birds or animals from getting access to the hole. The tree can heal up and cover the gap when this is done. To prepare the spot for treatment, remove any water or rotted softwood.

Be careful not to remove any hardwood as you may be causing further problems.

  • Other Ways To Treat Holes

There are different ways to fix holes in your trees.

For this to be possible, get a tarp, silicon caulking compound, wood scraper, and expandable polyurethane foam.

You’ll need to place a tarp above the hole to keep out water. You can do this after or before filling the gap with silicone caulking.

You can remove such tarp after the silicone caulk gets dried.

Another method involves the application of expandable polyurethane foam. However, before this is done, consider scrapping the deadwood out.

Calling An Arborist

When holes are detected on your trees, it’s best to call an arborist.

This is the best strategy to adopt as they inspect the problem and determine its causes. These causes are treated, and preventive measures are implemented to forestall a repetition.

Sometimes, it’s okay not to do anything as long as the holes are tiny. However, you may want to find a solution to the continued tedious activity of insects. Stopping them early will save your trees from further damage.

Discuss any concerns you have about this problem with your arborist for professional recommendations. You stand a better chance of eliminating these tree-boring insects with the help of a professional.

Tree Hollows Don’t Suddenly Appear.

Tree hollows that form naturally take long periods to develop.

They do not suddenly appear but result from years of gradual changes. This is especially true for giant trees, which have more extensive cavities where birds and other wild creatures can nest.

A cavity that’s wide enough for animals to nest in may take several decades or up to a century to fully form. Such hollow may result from a fallen branch.

However, we must say that not all tree hollows take this long.

Those excavated by birds won’t take that length of time.

Does My Hollow Tree Pose a Significant Danger?

One of the things you need to figure out is how much of a danger your hollow tree poses.

Sometimes, there may be no cause for alarm for certain cavities. To better understand potential risks, it’s best to hire the services of an arborist to examine the hole.

Here, the structural support of the tree is assessed to determine whether it’s stable or not. A hollow that’s likely to affect the tree’s stability may require more drastic action like cutting down the tree.

Some expert help is needed to determine the extent of the problem.

Whenever you come across a tree cavity in your yard, it’s best to call for a professional assessment. Sometimes, you may take specific actions to fill up such holes.

Whatever the case is, listening to a professional will help.


As trees grow, they may develop certain unexplainable features that could raise many questions.

Tree hollows are among such features and are pretty standard. One of the most common fears is that hollow trees might die off.

Some hollows can be significant, as well as holes. Both of these have to do with creating unnecessary spaces on your trees. Holes are much tinier than hollows.

The sustained boring activity of insects and birds results in multiple holes, which eventually takes its toll on trees. You may begin to notice some browning which eventually worsens and leads to the death of such trees.

It’s necessary to take appropriate measures immediately after such holes are noticed.

In other situations, people may consider cutting down such trees.

We’ve provided some of the common fixes for holes in trees. Try any of these today.

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