How to tell if the tree looming over your house and in your thoughts is a hazard tree…
It’s big and it’s heavy, and it’s got the potential to put a major dent in your home and your finances…but is it truly a hazard tree? When should you worry? And when should you simply be grateful for the extra shade?
Trees lay across a roof after a windstorm
We at Sand Creek Tree Service are experienced in assessing hazard trees. That said, not all problem trees are readily detected. Sometimes the structural defects are hidden inside the tree or below the soil. Sometimes, a “better safe than sorry” approach is best. We’ll always discuss options with you, letting you make the final call when it comes to potential risks that are hard to quantify.
However, many hazard trees present signs of their structural weaknesses. Ultimately, a hazard tree is one in which the weight of a tree – or a part of the tree – exceeds the tree’s structural integrity (in a branch, trunk or roots). When assessing your tree for risks, we evaluate the likelihood of the tree failing, the environment that contributes to failure, and the target (the part of your property that would sustain damage).
There are seven general problems that point to your tree being a hazard tree: decayed wood, cracks, root problems, weak branch unions, cankers, poor tree structure, and dead portions of the tree. Decayed or rotting wood is often indicated by shelf mushrooms – a parasitic fungus – growing on the trunk. Cracks are often obvious and can be the result of lightning, frost, or other factors. Root problems might be evidenced by a bulging in the ground to one side of the tree, indicating that anchor roots are slowly losing their capacity to hold the tree in place. Weak branch unions can appear as a kind of seam in the bark, a sign of included bark. This means the branch is not fully connected to the rest of the tree; as the limb grows over the years and increases in weight, that union my fail. Cankers will look like a bulge or deformation in the trunk of your tree, meaning that the bark and cambium layer are dead and nutrients aren’t flowing through the tree as they should. Poor tree structure simply implies that your tree has grown in a direction or manner that makes breakage more likely. Perhaps the tree has a heavy lean, or maybe a horizontal branch has acquired too much weight. Finally, a hazard tree is most obvious when it is dying (dead top or branches) or completely dead.
Besides looking at these seven factors, we also assess the direction of prevailing winds in your area and which direction your hazard tree might fall. Another important factor to consider is the target. What will the tree damage when it falls? If you have a hazard tree without the potential to damage your property or injure anybody, we sometimes suggest letting nature takes its course. Trees that humans deem hazardous can make for important animal habitat. Think of all our local eagles and osprey that nest in snags.
If a potential hazard tree is regularly invading your thoughts, don’t hesitate to give us a call. It’s better to bring down a tree in a controlled manner – especially around people and structures – than to let your roof bear the brunt. And who knows, maybe your tree is perfectly healthy and willing to provide you and your family shade and birdsong for another fifty years. But a little peace of mind provided by a professional is always worth the effort.
Cankers are often quite visible, but cause and treatment aren’t always straightforward…
Cankers tend to be prominent. If your tree has a potentially hazardous canker, it’s hard to miss. Think of the tree version of a large, open wound or deformity, and you’ve got the visual idea of cankers. They may be ugly, but are they a problem? Maybe yes, maybe no. And maybe not quite yet.
An older callused canker on a paper birch. Photo courtesy Markus Hagenlocher via Wikimedia Commons.
Visually speaking, cankers are places on the trunk or branch of a tree where the bark is sunken or missing. They can lead to hazardous situations, creating weak spots where breakage can occur. Of most concern are cankers that affect more than 120 degrees of the tree’s circumference or cankers connected to other tree defects (e.g., cracks, weak branch unions, or cavities). Also of concern are cankers that are either directly facing or opposing prevailing winds.
Note the callus formed on the canker on this spruce tree. Photo courtesy Сыроежкин via Wikimedia Commons.
Cankers are typically caused by bark-inhabiting pathogens (usually fungal or bacterial), but sunscald and frost can also cause cankers by killing patches of bark. And while a wound on a tree (an improperly cut branch or a damaged place on the trunk) won’t directly lead to a canker, it can be the entry point for pathogens that will.
Cankers can either be annual or perennial. The annual ones are handled in a single year by a healthy tree, which grows a callus over the affected area. A perennial canker returns year after year, growing slightly bigger in the process. The pathogens attack the callus each year, meaning the tree has to start over again. These cankers often have the look of a target on the face of a tree, exhibiting concentric circles. Though these cankers may be visually unappealing, they are slow-growing, and you may be able to enjoy your affected tree for years to come.
What you really need to be concerned about is canker rot. This is when the canker is actually associated with fungi that is decaying wood inside the trunk of the tree. Thus, you have the combined issue of poor internal structure (from the rot inside the tree) and dead bark and tissues on the outside of the tree. Trees exhibiting canker rot are very hazardous and should be dealt with immediately.
Cankers come in all shapes, sizes, and can be from scores of different pathogens. Often, we can’t pinpoint how exactly the canker came about, but we can assess your tree and let you know if the canker is simply an eyesore or a true hazard.
For more information on cankers, the Forest and Shade Tree Pathology website is absolutely the best place to go…and it will make your head spin with all the scientific information they have to share. For an overview, go to their Cankers page, and to learn about specific diseases, go to Cankers on Parade.
If decayed wood is visible on your tree, is it always a hazard? How do you know if there is decayed wood that you can’t see?
As mentioned in our previous post, there are seven general problems that point to your tree being a hazard tree, and decayed wood is one of them. Hazard trees are definitely still on peoples’ minds these days with the pair of storms we sustained this summer. Many of us experienced tree loss and breakage – some with resultant property damage – and all of us (even the lucky ones who didn’t lose trees) are wondering which trees might go next. We’re only now, months after the fact, getting caught up on cleanup and precautionary tree pruning and removal related to the storms. Those wind events left major impacts on our properties and our psyches.
In order to answer lingering questions and assuage fears, we’ll cover all the different hazard tree indicators over the next few months. Today we’ll start with decayed wood. Decay is probably responsible for the largest percentage of tree failures (though, honestly, those windstorms blew a lot of conventional wisdom out the window; we saw many seemingly healthy trees simply uproot). While decay is not always visible from the outside, there are several reliable indicators of internal decay.
One indicator of decayed wood is rot fungi.
One indicator is the presence of conks, brackets or mushrooms sprouting from the tree. This is a definitive sign of internal rot and should be taken seriously, especially if the fungi appear on the trunk or visible roots. Different fungi signify different kinds of rot. White rot reduces wood’s stiffness, while brown rot (common in conifers) makes the wood more brittle. Soft rot can lead to both of these deleterious effects. All of these kinds of rot reduce a tree’s structural strength.
Open cavities also signify rot. It’s important to explore the depth of a cavity to determine the extent of decayed wood. However, it’s never advisable to fill the cavity with any kind of “strengthening” material or to excavate the decayed wood from the hole. More harm than good comes from both of these approaches. Sometimes – as with many kinds of decay – trees are able to compartmentalize the cavity, containing it and halting progress. Our interventions only hinder this process. With other kinds of decayed wood, a tree might attempt to outgrow it, adding more layers of strong, healthy wood to stabilize the weaker portions.
Carpenter ants and their resultant “sawdust” at the base of a tree are another good sign of decayed wood. Other potential signals are cracks, bulges, loosened bark, oozing, and both old and open wounds, all of which should be inspected further to determine the extent of possibly decay.
Sometimes, no sign of decayed wood is visible; even the canopy may appear full and green. However, if you have any reason to suspect there is silent decay going on inside your tree, share your concerns with us. We can talk about the history of the tree and its care and maybe even pound on the trunk from a few different places (something known as “sounding”) to get a sense for what might be gong on inside.
Decayed wood doesn’t always mean the tree must come out. Perhaps some selective pruning will mitigate dangers, or maybe a lack of targets (i.e., houses, outbuildings, landscaping, etc.) means the tree is free to live out its natural life. Ultimately, it’s up to you, the landowner, to make the final decision on the level of risk you’re comfortable with. On our own property, we live with a certain level of risk because we so value the big, beautiful trees circling our home.
If you have any concerns about decayed wood, don’t hesitate to give us a call. We’ll do our best to help inform you in your
