Everyone loves trees, and we love even more older trees, because we know how long it takes for a tree to grow to maturity. That makes it difficult for us to take down a tree. We don’t want to kill something beautiful and old, but we do want to protect our homes and families – and trees can become dangerous. Because nobody wants to take down a tree when it isn’t necessary, there are steps we can take to decide when a tree should be taken down, and when it is safe to leave it, or perhaps fix a problem with some tree surgery. It always makes sense to keep a tree if you can, so let’s consider how to make that difficult decision smartly and avoid doing something that doesn’t need to be done.
Equally, you might have a tree that is a hazard, but you don’t realize it – until it is too late. It pays to keep an eye on your trees, so that you can recognize a problem. Let’s consider then, how to decide if a tree should be removed.
Do I Need a Permit?
In many countries today it can be difficult to remove a living tree from your property. To preserve the tree cover in cities and towns, you might need a permit from your city, or face a fine. Across much of the United States this is not true, and many states and cities have no restrictions on cutting down a tree on your own land. This is changing, especially in larger cities, where preserving the urban forest is a priority. So in Chicago and Atlanta, for example, you do need a permit, and there are rules on what you can, or can’t, take down. It is best to call your town or city and find out. If you use an arborist, they will know the rules and get the permit for you.
What About Neighbors?
Sometimes a neighbor will want you to remove or trim a tree, perhaps because it blocks light from their home. Or you might want to get rid of a neighbor’s tree that is causing you problems. In most cases the law is clear on this. If it is on your property, it’s yours. So a tree hanging over a property line can be trimmed back to that line, but no more. Equally, the parts of a tree on your property are yours. This is why, when planting trees, it is always best to stay well inside your property line. Otherwise a neighbor can remove branches right back to the trunk, and of course if you plant right on the line, the tree could become a big legal dispute.
Is This Tree a Dangerous Tree?
To answer the question, ‘Should I take down this tree?” we need to make a decision about it. A tree that should be taken down is called a ‘danger’ tree, or a ‘hazard’ tree. To be a hazard, you need two things – a defect, and a target. In other words, when a tree falls in the forest, is anyone underneath? A dying or dead tree in a forest is not usually a hazard, because there is nothing that we care about for it to hit. Indeed, dead trees in forests are part of the natural cycle, and a good and natural thing. Equally, a tree next to a home may be in good health, but if a large branch hangs over the roof, there is a big target, should that hanging branch be likely to fall.
Targets for Trees
What are likely targets for trees? Homes are obvious ones, and a tree landing on our house is a serious matter. Even a relatively small branch can break a chimney or make a hole in a roof, that in turn could let in water and cause further damage. Garages and outbuildings could also be damaged. Parked cars are another costly potential target. Garden structures, like walls, fences and pergolas are also possible targets, or a tree could end up inside your pool, damaging it. Roadways, driveways, paths, and other paved or hard surfaces can also be damaged by a falling tree or large branch and they can be costly to repair.
Worst of all, of course, is a human target. A surprisingly large number of people are injured or even killed by falling tree branches, which can obviously fall during storms, but can also drop suddenly during calm weather. Recognizing trees that present that kind of danger is obviously important.
The Target Zone
How close to the tree does a target need to be? You might think that once you are outside the area beneath the branches you are safe, but that is not true. Imagine a circle drawn around the tree. Estimate or measure the height of the tree (there are some simple ways to do this, which will be the subject of a future blog). Trace a circle with a radius of 1½ times the height of the tree. The area inside the circle is the potential target zone, where limbs or the whole tree could land. If the ground is sloping, you need to add extra distance on the downhill side of the tree, perhaps as much as the height again, if you allow for the danger of parts of the tree rolling after they fall.
Identifying Tree Defects
For a tree to land on a target, there must usually be a ‘defect’, something about the tree that makes it a danger. It is never possible to identify hazard trees with absolute, 100% certainty, but knowing about, and looking for, defects in your trees is a valuable way of reducing their hazard. There are several important defects that make a tree a hazard:
A Dead Tree
A dead tree is always a hazard, if it has a potential target.
A crack all the way through a tree, where you can see light, is a serious defect. So are cracks where there is decay inside, or a cavity. The larger the part of the tree that is cracked, the more serious the defect. Small cracks, without decay, perhaps from a lightning strike, or frost on thin bark, are not usually serious.
Tight Branch Unions
The union is where a branch forks or leaves a main trunk. A strong union is U-shaped, while a weak union is V-shaped. Tight unions trap bark as the branches thicken, creating a weakness. This can result in a branch breaking and often also tearing a strip of the side of the tree. This is why some formative pruning is a good idea with young trees, eliminating V-shaped unions while the branches are still young.
If there is decay inside a tree, this can be serious defect. The presence of fungi growing off the side of a tree often indicates decay, and if that tree has a target it should be looked at more closely. If you can, try to measure how much healthy wood is around the decayed area. If it is one-third of the radius of the tree, the defect is not usually serious – yet. If a tree is 2 feet across, the radius is 12 inches, and the healthy wood should be at least 4 inches thick.
These are areas of dead wood on the side of a tree, often hidden by dead bark. Particularly if there are fungi growing from them, these could be defects. If the canker is large, or at the base of the tree, it could be more serious.
Large dead branches or tree-tops, more than 10 feet long, or if there is decay, can make a tree defective. Consider though, that birds of prey often use dead treetops as lookouts, and owls nest in them, so don’t remove them if you don’t have to.
Leaning trees, or lifting roots
If a tree suddenly starts to lean, and even more if the roots are rising out of the ground, then it is clearly defective. Dead areas at the base of the tree indicate the potential for root damage, which may cause a tree to loosen and fall in a storm.
Add Them Up
The more defects a tree has, the more of a hazard it is. If you look at your tree and decide it has one serious defect, or several minor ones, have it assessed by a professional.