Every year, falling trees or branches cause tragic deaths, injuries, and tens of millions of dollars in property damage. Fearing for their lives, some homeowners think they should get their trees taken down. But if the tree is healthy, this isn’t necessarily the best course of action. Just one large tree might add thousands of dollars to your property value, or it could save you hundreds of dollars each year in air conditioning costs. Not to mention all the benefits a lovely tree brings to your quality of life.
Our article, "How to Spot a Dangerous Tree," shows some of the more obvious signs of a tree with problems. They are easy to understand and can be seen with the naked eye. Some conditions we describe indicate that your tree has a problem that should addressed by a professional arborist immediately. We also show you some trees where the "problems" aren't problems at all, but rather normal and natural occurrences that don't pose a threat to the tree at all.
Make sure to view all the images for each "zone" by clicking on the dots below them.
Caution! Do not substitute this short article for getting the opinion of a professional! An experienced certified arborist can spot trouble that the untrained eye will not see, and can give you advice that goes well beyond the scope of our article and, probably, your own knowledge.
How to Inspect Your Tree(s) Using the “Four Zone Approach”
To inspect a tree thoroughly, examine all four of its "zones":
Zone 1: The tree as a whole, seen from a distance;
Zone 2: The ground under the tree, including the visible roots and ground around them, and the first three feet of the trunk;
Zone 3: The trunk -- the main vertical stem(s) of the tree;
Zone 4: The crown -- the branches and leaves, including where the branches connect to the trunk, and each branch all the way out to its tips.
Leaning TreeWhen this tree falls, it will probably split the house in two.
Dying trees--BeforeNotice how thin the leaves are at the top of the trees. There may be clues at the base of the trees that tell you why they are dying.
Dying trees--AfterWhen all the leaves in a tree turn brown during the growing season, the tree is dead.
Tree too close to houseThe limited area for roots and for trunk growth creates problems for the tree and the house.
Lightning strikes a big treeSometimes lightning kills a tree, but not always. Wait about six weeks to see if the leaves start to turn brown. If they do, your tree is a "goner." If the leaves stay green, have the tree checked carefully for structural damage.
Two pine treesWhich one is dead? The tree on the left does not have green needles. It is dead.
Dead top in oak treeA tree has a serious problem when it starts to die from the top down. Have it checked out immediately.
Zone 1: The tree as a whole
From a place where you can see the whole tree at one time, take a long look. Focus on the entire tree, rather than its individual parts.
- Is the tree leaning? What is it leaning toward? Has this lean been there for a long time? Is it leaning more than it was a day, week, or month ago? Is the tree leaning in an easterly direction? Trees that lean toward the east are more vulnerable to falling because most of the winds come from the west.
- Can you see any big dead branches? Are there a lot of dead branches, or just a few? Are they on the lower part of the tree? Only on one side of the tree?
- Are there sections of the tree where there are no leaves at all? Does the tree have a thin leaf cover? Are the leaves dropping much earlier than from other trees of the same species nearby? Do the fallen leaves look unusual?
- Are the branches dying back from the tips?
If the answer is “yes” to any of these questions, your tree may be in the process of falling over, sick, imbalanced, or dying. Get the tree evaluated immediately by a Certified Arborist. Better to be safe than sorry.
Split trunkIt is important to pull back ivy on double-trunk trees to look for splits or cracks.
Cracking trunkThis tree is in the process of breaking apart.
Decayed baseThe base of this tree is rotting, and the tree should be removed.
Frass (sawdust)The sawdust (frass) at the base of this tree tells you that the tree is being attacked by insects.
Mushrooms that attack trees - 1Inonotus is a fast-growing and deadly fungus.
Mushrooms that attack trees - 2Ganoderma shows up on hardwood trees and is a sure sign of decay.
Mushrooms that attack trees - 3Armillaria is also a fast-growing fungus.
Mushrooms that attack trees - 4Another cluster of armillaria, this one growing in a large clump.
Mushrooms that attack trees - 5An old inonotus dryadeus fungal body.
Cavity at the baseYou wouldn't know that this hole is as deep as it is without probing it with a long rod or stick. This tree needs to be tested with a Resistograph to find out how extensive the decay is.
Animal holeSomething has been digging -- an animal lives here! Animal holes can indicate extensive decay.
Missing bark on trunkThe missing bark on this tree, along with the mushrooms growing on it, tell us that this tree is dead and decaying.
Girdled rootGirdling roots are not good for trees because they cut off the water flow to the trunk and canopy. Often they can be pruned, depending upon their size and how much they wrap around the tree,
Uprooting TreeA quick scan around the base of this tree tells you that it is in the process of uprooting.
Zone 2: The ground under the tree, including the visible roots, and the first three feet of the trunk
There are two types of tree roots. The most visible are the large anchoring (structural) roots, which hold up the tree. The smaller and invisible absorbing roots provide the tree with water and nutrients from the soil. Even a tree that appears strong and vibrant with foliage can have serious root problems. Examine the base of the trunk and the ground around the bottom of a tree. It’s here that you may find your first evidence of root problems or other hazards.
- Pull back any ivy, mulch, or ground cover and look closely where the trunk meets the ground. If you see cracked or raised soil, the tree may be in the process of uprooting.
- Do you see fungus (mushrooms) on or near the tree's roots or trunk? Fungus is a strong indicator of root or trunk decay. And when a tree’s anchoring roots are rotting, decayed, or cut, the tree is at risk of falling over. If too much of the trunk is decayed, it can buckle or break.
Uprooting, root rot, and decay at the base of a tree can be very dangerous situations which require immediate attention. Call a Certified Arborist to help you determine whether the tree needs to be removed or whether it's safe to leave it standing.
Other things to look for in your Zone 2 inspection:
- Deep cavities (openings in the tree) near the ground are a bad sign. The tree could collapse if the trunk is missing too much wood at the ground.
- Are there dead branches on the ground? If so, there will likely be more up in the tree, especially if your tree has never been cleaned out by a tree care professional. Hesitate before you walk under the tree if the ground is littered with dead branches. An arborist will usually spot dead branches you didn’t notice.
- Do you see coarse or fine sawdust (also called "frass") at the base of a tree? If so, the tree is either hosting a colony of carpenter ants, or it is getting attacked by borers (small beetles). If there are carpenter ants, you've got a problem, as these insects only nest in dead wood. A borer invasion will usually kill the tree, though in some species it may be possible to save the tree if the insects are caught and treated early on. When you see frass, call a Certified Arborist to find out why it's there and what it means for your tree.
- Raised sections or cracks in the driveway or sidewalk caused by a tree's roots pose a risk to pedestrians. These need to be repaired so people don't trip or fall. Consult a Certified Arborist to learn how you can save your tree's roots while addressing the problem.
Burl on the trunkA burl is an abnormal growth usually found on the trunk. In general it doesn't hurt the tree or indicate weakness.
Slime fluxSometimes trees "bleed" something other than sap. If the stain is extensive, call a Certified Arborist.
Lightning scarCall a professional if you see a long scar like this on your tree.
Fusiform cankerFusiform canker is a fungus on pine trees that can cause them to break. Call a professional if you see one.
BulgeThis tree is trying to strengthen a weakened area with extra wood. If you see this on your tree, there will most likely be a fusiform canker on the other side.
Pitch tubesPine trees will try to drown attacking beetles with pitch tubes made of sap. Pitch tubes can be different colors (rose on left, amber on right). If you see these on your tree trunk, it usually means the tree will have to be removed.
Woodpecker damageThese trees are showing the work of a pileated woodpecker (left) and a yellow-bellied sapsucker (right). The pileated woodpecker is going after insects in decayed or dead wood; this tree is probably hazardous. The sapsucker is opening a hole for sap in live wood; the tree is probably okay.
Trunk cavityThe hole created by an old pruning cut (like this one) sometimes allows decay to enter the trunk. The cavity could be large even if the hole is small. This tree required an "aerial" inspection to assess the cavity.
Fungus on upper trunkWhen fungus grows where two trunks meet, there is usually weakness below the surface. This situation requires immediate professional attention.
Zone 3: The trunk
The trunk holds up the tree and supports the massive weight of its branches. Inspect the trunk thoroughly.
- Cavities can be dangerous, depending on their size, where they're located on the tree, and how deep they are. If there is a cavity above eye level, a "climbing" inspection may be needed to find out how deep it is and if there is decay.
- Cracks and splits in the trunk are extremely dangerous. If there is a crack or split in the trunk, the entire tree could fall or break apart at any time.
- Missing bark (or areas where bark is falling off) usually signals a dead section. Look for places on the tree’s trunk where there is no bark, the bark is falling off, or the bark is discolored. Missing bark can also indicate a surface wound, infection, or a fungus attack.
- A long streak of missing bark coming down the tree usually means the tree was struck by lightning. It's possible that a tree can recover from this, but if the leaves turn brown after several weeks, the tree has died.
- When ants and beetles attack, they leave very fine, light-colored sawdust (“frass”) that is easy to see. Ants cutting into decayed wood leave coarse shavings. Pine bark beetles attacking a pine tree leave “pitch tubes” that resemble marble-sized balls of light-colored sap.
- Trees with 2 or more trunks sometimes crack and split where the trunks connect. Strong connections appear as a “U” shape; weak connections resemble a tight “V” shape. Sometimes a tree adds layers of wood over the trunk connection to strengthen a crack. After a windstorm, look at the connection in the tree where the trunks meet. Use binoculars if the connection is high up. If there is a lightly colored line that contrasts to the natural dark bark color, you are probably looking at a fresh crack. The tree may be in the process of splitting apart. Consider this situation an emergency.
If you see any of the above conditions in your tree, call a Certified Arborist immediately to determine if your tree is stable enough to leave standing or whether it should be removed.
Sparse leaf coverWe showed this image as an illustration for a Zone 1 inspection. It also falls into a Zone 4 inspection. Look at how sparse the leaf cover is in the crown of these trees.
Broken pine branchThis broken branch is easy to spot because of the differently-colored (dead) needles.
Cracked branchThis branch was loaded with mulberries. The weight of the fruit caused it to break.
Dead branch (with detail)The fungus on this dead branch over the street tells us that the branch can break at any time.
NestsYou might not realize that a nest is in a tree until whatever built it lets you know it's there. Here, this hornet's nest was hidden by big magnolia leaves. Listening as you inspect your tree often reveals what you didn't see!
Weak branch unionThis branch was decayed where it attaches to the tree. It should be removed before it hurts someone or something.
Widow makerA widow maker is a branch that is broken but hasn't fallen to the ground; it can come down at any time. We know this branch is broken because of the brown (dead) needles.
Zone 4: The crown
The crown includes the leaves and all the branches that extend out from the trunk.
One of the most common and obvious dangers in a tree's crown is dead wood. Dead branches are easy to spot in a hardwood tree. If the rest of the tree still has green leaves, the dead branches are the ones with brown leaves or no leaves at all. A pine branch that has recently died will have brown needles; if it's been dead for a long time, it won't have any needles.
Branches that have been dead for a while won’t have any bark on them. These dead branches break easily. They should be removed carefully so they don't fall on someone or something. A hardwood tree that has many brown leaves on it in winter is probably dead (except for American beech trees, which hold on to their dead leaves until early spring.)
Look for broken branches, especially after a strong storm. On some trees you may not know that a branch is broken until about a month later, when the leaves turn brown.
Pockets of decay or rot sometimes exist on the upper side of a branch, where they are invisible to a ground observer. A “aerial” tree inspection by a Certified Arborist in which he climbs the tree may be required. This is especially true when there are large branches that extend over the house.
Be proactive. Follow the guidelines below to protect yourself, your family, and your home.
- Inspect your trees often!
- Get your trees checked immediately if you see -- or think you see -- any of the warning signs mentioned in our four-zone inspection.
- A Certified Arborist should check large trees regularly, every three years at a minimum.
- Get your trees checked more frequently during extreme weather cycles, such as long periods of excessive rainfall or drought.
- Look at your trees after serious weather events, such as a very strong wind, overly excessive rain, or an ice storm. When you walk around your house, look carefully at your roof, too. Roof punctures caused by falling branches can lead to terrible water damage inside your home.
- Get your trees pruned by a professional arborist to remove any weak, broken, cracked, or dead branches. Have this done at least every three years or when you notice them. This will help keep your trees safe, healthy, and beautiful. And remember--don't allow any tree trimmer to climb using leg spikes!