19 Signs of Hazard Trees

Photos and Text - Copyright 2003 - 2008 by Mario D. Vaden

Pertaining to urban and rural property, and landscaping: trees should be inspected regularly. Prolonged tree problems are harder to correct. This list can enable a head start for recognizing problem trees. Also, visit our tree care album with several pertinent photos.

Realize that these are "signs" of hazards or problems "on the horizon", not proof. Suppose your maple tree has a leaning trunk, and an arborist already provided solutions for it. Then it may not be a hazard tree anymore. These are signs of potential problems that can be determined by inspecting the tree and it's environment. Especially if the evaluation is performed by a properly trained tree care professional. There are two ways to look at this too, from a community standpoint. The signs below are potential signs of hazards. When too many of these begin to accrue, then they become an indicator of the community's lack of tree safety practices.

1. MULTIPLE LEADERS OR TRUNKS.

Some trees have multiple leaders, like trunks - elm for example. Many times, the union of these, where they connect, are weak "V" shaped unions, instead of stronger "U" shape unions. These could allow the tree to split down the middle.

Cross-cut tree tops, from topping, are a potential sign of hazard trees. Sometimes, external decay fungi isn't visible, but the trees may be weak with rot. Often, sprouts emerge from the stubs.

Correction can include cabling the leaders together for structural suppot, or the removal of one or more leaders if it can be done without removing too much of the canopy. Improvement may include some moderate pruning to reduce “sail” (the total foliage that wind can apply force to).

Usually, larger leaders retain greater weight of wood and foliage. Therefore, weak "V" shape unions of larger leaders are potentially more dangerous than a similar weak union involving little leaders.

It's possible to have three or more leaders converging at one point in a similar weak fashion, producing weak side-by-side unions. If there are 3 leaders attached with weak unions at one point, it's imperative to cable them together before one of them is lost. If one breaks away, the two remaining leaders of the triangle will not be positioned properly for cabling. In a threesome of leaders, no two of them are directly across the trunk from another one. For effective cabling, either two leaders (only) must be directly opposite one another, OR, if there are three, then all three must be cabled to each of the other two leaders.

Sometimes, weak "V" shape unions are so weak, that they could be described as a convergence, rather than a union. Sometimes, these leaders may have separation between them, with a tiny gap of air between. Where an air gap is present, no bond exists.

2. LEANING TRUNK POSITION.

Check to see if a tree trunk has moved from a vertical position to a leaning position recently. Or, was it leaning before, but more now?

This is an example of a tree that is not a hazard tree. The entire trunk did not lean during one rain or wind event. The curve is gradual because its growing away from other trees in the group.

Gaps and fissures in the soil near the trunk, on one side of the tree, may be a result of the root system pulling loose due to lean. Some healthy trees will lean a little regardless, like the ones at the edge of a grove, leaning for light. When two trees are side by side, they may lean away from each other. Trees produce a hormone that can accumlate in cells on the shaded side of the trunk; elongating those cells. That "stretch" can produce a lean or curve - totally normal.

Likewise, trees can lean a bit more toward the south, or lean away from the side of a building. One clue for a potential hazard, is if the soil on one side of the tree has heaved upward from roots lifting soil. This heaving should be distinguished from the condition where soil has heaved around all sides of a tree.

That's because tree root systems and trunk flare can heave soil around the trunk perimenter as the tree matures and grows. On the other hand, trees can occassionally rock in multiple directions during inclement weather. It's the job of a trained tree professional to determine if the soil has heaved due to a problem, or in an acceptable fashion resulting form normal growth and expansion.

Solutions may include removal of the tree, staking and guying for support, and judicious pruning to reduce “sail” of foliage that wind can tug on.

Soil problems like drainage and compaction may need to be addressed. Also, the soil may need temporary covering, using a waterproof material, to prevent additional saturation from excessive rainfall in the days that follow.

3. WEAK LIMBS OR BRANCHES.

As with major leader unions, branches also, can be weakly attached when the union is 'V' shaped. A 'U' shape curve at the union is better. The 'U' shape allows layers of wood tissue to build-up. Some limbs may develop noticeable cracks from the weight of wind, snow, ice and even rain. Keep an eye out for poorly connected branches, where the attachment has cracks or disfigurement form bending.

Weak "V" unions in Flowering Plum from poor tree selection and inadequate routine pruning. The dark vertical linear areas are included bark that became pinched within, performing no structural strength Another photo on this page, of a split sweet gum, shows the the damage that this weakness can produce.

Bending can cause compression and bulging or wrinkles on one side, and stretching or tearing on the other side. Branches that have sprouted around the edge of pruning cuts, can be weakly attached. And branches that sprouted from the top of a tree which was topped, may be weakly attached.

Some insect larvae that live on trees, trigger lumps of pitch, potential clues that they were active in the tree. Larvae like these can damage and weaken limbs, especially if the chewing was on the top side of the limb. When lumps of pitch are present, structural strength of the tree is as important to consider as is insect eradication.

Consider pruning and guying. If the removal of a large limb would eradicate too much foliage from the canopy, it may be prudent to cable a weak limb for support, if the results are safe.

Some special needs may justify guying a weak branch instead of removing it. One example would be at a country club, where removal of a large limb can drastically alter difficulty of a golf hole (where the limb is a desired obstacle).

4. HOLLOW POCKETS, CAVITIES AND DECAY.

The white and orange growths on this Sitka Spruce are indication of wood decay. Here, the growths are in exposed dead wood, not through the bark (which can occur too). This tree is located near the "largest" Sitka spruce shown in an image below. The cavity here, is about 30% of the tree's trunk circumference. If a cavity was larger, like 50% of the trunk circumference, removal is a higher priority..

Inspect trees for peeling bark, hollow cavities and conks (or mushroom / fungi resembling growth) on the bark. Mushrooms (or fungi) may be a sign of decay, especially if the origin of the growth is from within the wood as opposed to the extremity of the bark only. Each of these conditions can indicate some kind of weakness. Sometimes the tree needs to be removed, and many times it can be preserved. Peeling bark can be due to disease, mechanical injury, sunburn and lightning, to name a few causes.

The decision to preserve or eradicate trees with cavities on the trunk, is best left to someone like a Certified Arborist or Consulting Arborist. The percentage of the trunk perimeter occupied by a cavity (or even dead dry wood) is critical. A cavity that goes 52% of the way around a tree trunk, is incomparable to a cavity that goes 15% of the way around a trunk.

The more of the circumference occupied by a cavity or decay, the greater the potential hazard.

Options may be removal or preservation of the tree, based on the advice of a properly trained and experienced arborist.

The solution will vary according to the type of the tree, as well as the location and size of this weakness.

If the tree will remain, drilling holes to drain cavities, may damage a tree's natural defensive barriers. Likewise, carving, grinding or sawing material from decayed pockets may also damage a tree's established defensive barriers.

Loose material that can be easily scooped away with gloved hands, should be fine to remove.

5. HISTORY OF THE TREE ZONE - BAD HISTORY.

Has the tree been topped? Have you or your neighbors applied herbicides. Has the grade of the soil been changed, like fill soil for example? Have roots been damaged or cut, possibly from trenching or concrete work? Have new plants or a lawn been installed near the tree in the recent past? Were other trees removed, increasing the intensity of available sunlight? Have any treatments been done in the area - non-tree-related - such as treating for moss on a roof or driveway?

Largest Sitka Spruce in the USA, near Seaside. The deck is for pausing the history of foot traffic that causes soil compaction.

Is there evidence of lightening or sunburn damage? Has heavy equipment or livestock, been moving across the soil within the dripline (compaction)? Could farming practices, even plowing from decades ago, have caused subsurface compaction (tillage pan)? Is the tree of a particular genus and species with a history notorious for problems?

Certain changes during the life of a tree can rightfully introduce serious concerns about how safe a tree is. Evaluating the history of a tree's environment can be complex, and is best left to trained professionals.

The options to deal with a bad tree care history, will vary according to each bad condition, each bad practice and each bad choice that occurred in the past. If any remedies shall occur, those solutions are dependent upon gathering as much information as possible. The hazard sign of bad history, overlaps other potential signs of a hazard tree.

6. CRACKED TRUNKS / SPLIT WOOD.

Cracks in tree bark can be totally natural and normal. Cracking or splitting or tree bark does not happen to all trees. Some trees, like beech, can have smooth bark for many years. But other trees, like Douglas fir, have bark that cracks (develops fissures), within 20 to 30 years. Cracks of fissures in the bark may be normal - maybe not, but bark fissures are not uncommon. This is one category of tree care, where familiarity with tree identification and developement are essential. Usually, visible cracks in the wood are not a good sign. If your tree's trunk - the wood - is cracked, a decision must be made to either preserve the tree, or eradicate the tree. Splits in the unions between leaders and limbs could fit in this category too.

This sweet gum split apart in my own neighborhood at the end of summer during light rain and wind. It had a weak V shape union. The weakness existed for a while. The dark stain in between shows that the trunks were not bonded. There was an air gap, and roots were growing in-between. If a cable was installed beforehand, or had the extra leader been removed just after planting, this damage could have been prevented.

The size and type of the tree can completely alter the action to be taking. A 5' tall laceleaf Japanese maple with a crack in it's 8" DBH trunk, is not comparable to a 30' tall noble fir with a crack in it's 22" DBH trunk.

The crack alone, may not be the reason to save or eliminate a tree. It's the combination of the tree's size and type, and size of the crack, that determine the action to take. Likewise, the location of the crack or damage.

The best option may be removal of the tree if the damage is severe. If the damage is minor, merely pruning a limb off, may do the job. Sometimes damage can be so minor that no parts need to be removed, allowing the tree to grow and produce more tissue.

Cabling, guying or the use of fastening hardware may be beneficial and required.

Final decisions and actions for cracks and splits are a task for a properly trained and experienced tree care professional like a Certified Arborist.

7. BROKEN OR HANGING TREE BRANCHES.

These are branches that cracked or broke, or "healed" poorly and are "dangling by a thread" so to speak. These may be alive or dead. Professional tree care providers, may refer to these as "hangers" at times. Even limbs as small as 1" in diameter can be harmful or lethal. It's amazing how much speed and force a falling limb can gather.

Extra haste should be made to remove these if they are located over playgrounds, sidewalks, benches and tables; areas where people linger for extended periods. A branch that is hung-up in a national forest tree off the "beaten path" is not comparable to a broken branch, suspended directly above a picnic table.

It's probably obvious to some people that dead trees are a sign of potential hazard. The presence of dead trees may present a hazard in a community. In addition, when dead trees are allowed to remain for a long time, they may indicate that some people don't realize the potential hazard.

In most cases, broken or hanging branches should be removed.

One possible reason for delaying removal, is the presence of wildlife, like a nest of birds held in place by the weak branch. Delaying removal for this reason would depend on the location of the tree and the degree of hazard.

If a limb removal need to be delayed due to wildlife, or any other reasonable exception, then signs, barricades and temporary fencing are an option to divert and warn people.

8. DEADWOOD IN TREES.

The name denotes that all of these branches are dead. Deadwood weakens with every day that passes, as its wood slowly decays or deteriorates. These should be removed before they fall. A limb can cause serious injury if it falls - especially if its water-soaked. Deadwood is often heavier in winter when wet, than in summer when dried out. These can fall during any season.

This is an incense cedar that some landscape company tried bracing in Lake Oswego, Oregon. See the space around the lower trunk? See how the trunk does not flare outward at ground level? The tree is rocking in the wind and pushing soil away from it's trunk. The larger this tree becomes, the more dangerous will be, unless problems are eliminated.

In spring, a dead wet limb can dry and shrink and dislodge, allowing it to fall. In summer, wind or small animals can dislodge limbs. In autumn, the weight of water from rain can bring limbs down, as moisture soaks into the dry wood, increasing its weight with accumulated water. In winter, snow, rain, wind, ice and animals, can all dislodge dead limbs. If a limb is large enough, it can cause great harm. Property damage from falling deadwood can be expensive too.

Deadwood is usually removed by pruning. This can be done any season of the year. On rare occasions, where deadwood is in riparian areas, or away from human activity, mandates may be present to leave the deadwood for wildlife. Excessive deadwood in the lower canopy of single trees, or groups of trees, can present a fire hazard.

9. SUSPENDED, DETACHED LIMBS OR TREE TOPS.

Sometimes limbs and tree tops break loose and only fall a few feet, getting caught in the remaining parts of the tree, or in other trees. Sometimes they are hard to spot. Espcially the green ones that just broke off after a storm. And in winter, the broken living branches or tops, can stay green for weeks, possibly a couple of months.

This is a close-up of a conk. In fact, there is a second one below. When these conks are visible on the outside of a tree, it's evidence of decay and weakness inside. The conk stems-from the inside. Conks grow with age. The larger the conk, the older it is. A large conk yields silent testimony that decay has been inside the tree for a quite a while.

Spend plenty of time viewing your trees from different angles as you look up and down throughout the entire canopy. Check your trees to make sure the tip of the leader, or tips or leaders, are still intact. If your tree is missing the skinny little leader tip, or even a section fo the tope, that may be a clue, or specific evidence, that a top is hung-up somewhere. If you are familiar with the tree, and it's broken top is not on the ground after a storm, it has to be somewhere.

The stronger the storm, the further the broken tree parts can travel. Winds with speeds like 40 to 100 miles per hour, can carry limbs or tree tops into nearby trees, even to other properties. If you are certain that a tree lost a large top, leader or limb in a storm, be sure to locate it.

Suspended or detached tree limbs need to be removed from the canopy of whatever tree they are in. At times, this can be dangerous, even for a skilled arborist; climber.

When a real threat exists of a detached limb hitting a climber, another solution should be sought. One potential solution includes a bucket truck or high lift machine.

Detached limbs present a different situation or work environment from typical pruning for maintenance. Ground workers for tree services, should be informed of this hazard before the work crew moves near the tree. This hazard may present a special communication need for a job site safety meeting.

10. LARGE DIAMETER TRUNK OVER SMALLER.

Some trees are grafted, one variety on another, and there will be a variance of trunk diameter, large over small (like is common with cherry, japanese maple or crapapple). Usually, the taper of tree trunk diameter is gradual, with only a slight bit of taper as the eye moves it's view up the trunk. Except maybe, the base of a giant sequoia, which may widen dramatically at the base. Even so, a sequoia tree's trunk taper, is smaller diameter over larger diameter. And, the increased girth of a Sequoia trunk, as it flares down and outward into the soil, is a gradual widening of the trunk flare. But, what if your tree has, for example, a 12" diameter trunk up to 5' above the ground, and then immediately at 5' and 1" above the ground, that trunk has an 18" diameter?

Deodar Cedar girdled by twine. The trunk is enlarged above the twine. One sign of a developing hazard.

Why is that? What is that? Sometimes a wire, rope, cable or other material, was left on a tree. Then, as it grew, the bark and tissue engulfed the material wrapped around the trunk. What happened during that time, is that the roots sent nutrients up through the inner xylem, or wood tissue, to the leaves. Then, the leaves made food from those nutrients, feeding the top, but not the roots. That's because food from the leaves and photosynthesis, moves downward in the phloem, just under the bark. And with that layer (just under the bark) "strangled" or constricted, the flow of food to the roots come to a halt. In this case, the trunk, limbs and leaves above the girdled area get fed, but the trunk and roots below the girdled area starve. It may take several years for a tree like this to die. Each year it gets weaker, and can become more hazardous. The top gets bigger and heavier, but the lower trunk supporting it stays almost the same size while slowly starving to death and getting weaker. In reality, the entire tree is being weakened, but the upper trunk usually builds more wood tissue, whereas the lower trunk barely expands. Eventually, the ailing lower trunk and root region of the tree weakens the upper part of the tree, and it's system fails.

This kind of damage is either going to produce a weakened region in the trunk or associated problems like dead limbs. If the tree is not decayed and hazardous when we find a condition like this, it's almost innevitable that it will be dead and hazardous in the near future. Only a few trees or species of trees seem to survive girdling by naturally grafting a bridge of tissue. But if a tree is girdled, and the trunk diameter is differing above and below the girdle, it's doubtful that it's overcoming the problem.

If, by some chance, a girdling wire, rope or hose, is not completely embedded in the trunk, try to remove it by severing the material. Pliers may be needed. This practice neccessitates that bark, cambium and phloem tissue are not ripped away, leaving another damage of near equal magnitude.

Vertical stripes or strips of damage are a potential sign of a hazard tree. Lightning or sunburn can cause trees to loose vertical sections of tissue, potentially weakening the trunk and limbs.

If the trunk diameter variation is due to a graft, there should be nothing to be worried about. Although, in some cases, there may be a graft incompatibility where the upper and lower sections did not graft or fuse properly. Recognizing a graft incompatibility usually requires experience.

11. SCORCHED TOPS NEAR POWER LINES.

Trees can conduct electricity. In many cases, utility companies will come and prune trees away from power lines for you. If the tops of the trees are touching the dangerous lines, call your electric company, and keep children from climbing the branches. In fact, keep them and anyone else, away from the tree. Sometimes the tips trees get scorched by the electric current. If you see that condition (scorched tips near power lines) you need a trained pruning professional who can handle that kind of operation. This is not homeowner work, nor the work of many landscape or tree professionals. Its special skilled work. There are some tree services or arborists that are not trained to do this work.

Don't be deceived by the size of power lines. Big power lines are not always more dangerous than the ones that look small and skinny. Many skinny lines are not placed so high on the power poles without a reason. Don't expect that one type of tree is safer than another around power lines. A maple, cherry or birch can move the power as easy as a hemlock, fir or pine tree.

12. TREES THAT ARE DEAD.

It should be obvious to almost anyone, that a dead tree can be a hazard tree. But many people don't understand that dead trees can decay and weaken quickly. It may be because they have held lumber before (which is not alive) and formulated an incorrect correlation between that lumber and a tree. They may expect the tree to keep standing and remain firm and rigid just like a board in their shed, or like the treated wood fence post in their yard. But, dead trees, in the rain, wind, warm and cold, begin to decay and weaken. Often, heavy pieces come down in the winter, because weak wood soaks up rain water and becomes too heavy for it's weak point of attachment.

This aspect of trees and hazards, may become complicated due to the dead trees left in some parks and riparian areas for wildlife habitat. Sometimes, this leads to dead tree wildlife habitats being kept closer to areas where people are active.

If dead trees are kept near areas of human activity (for whatever reason), that kind of tree is going to need regular inspection. Trees like this have even been left on corporation properties where hundreds of employees walk by every day. Wildlife habitat trees in a human activity environment, can't be ignored until it eventually falls down.

Dead trees should be removed. If dead trees are habitat trees, they should be inspected yearly by a competent tree care professional, who can provide timely advice, or a warning.

13. TREES THAT ARE BEING PRUNED - AT THAT MOMENT.

Whether a tree is being pruned, or removed, consider it as a hazard tree. Accidents are possible. Wood pieces can become lodged and drop at any time. There are too many variables.

When your tree, or any other big tree, is being pruned by an amateur or a skilled professional, consider that tree as a hazard tree. Use caution whenever branches are being removed from a tree. Branches can land on an end, springing many feet from the landing zone. Limbs can be lowered on a rope, but that's not always the case. Little chunks of wood can get caught in the tree and fall at any time. Pieces of dead decayed wood can dislodge, and many are heavy enough to cause injury, even though they are dried out. Watching pruning is never a casual spectator sport. Observe from a safe distance, and let a pruning professional know you are in the vicinity. Standing next to a window when the tree being pruned is just outside the window, is not wise. Pets should not be secured under or near these trees, nor allowed to roam free in the area.

If you are a professional, pruning a tree near a house, and if people are in the window watching you, ask yourself if they should be standing there, or, if you should still be pruning while they are standing there.

When big trees are being pruned by arborists, communication must be maintained between the supervisor, climbers, ground workers, homeowners, and pedestrians. Spotters or barricades may be needed.

A property with adults or children on it, should be monitored regularly, to determine where everybody is at. Likewise with the workers, livestock and pets.

14. TREES WITH VERTICAL STRIPES OR STRIPS OF BARK DAMAGE.

Lightning, or sunburn, can cause linear or vertical strips of damage to trunks and limbs. Some trees can last for years if the damage is not too severe. But when the bark and tissue below it is destroyed - even if it's a skinny area - the wood beneath can become exposed or begin to decay.

Sunburn damage can look similar to lightning damage and is usually exposed to south and west light, whereas lightning damage can run be in dense shade. This maple was one of 30 trees in a row all with sunburn. A result of no trunk protection after planting.

This is a potential sign of a hazard. The severity of the damage and decay will determine whether or not the tree is a hazard tree.

A good solution, is an inspection by a properly trained and experienced arborist, who can determine if the tree should be removed or saved; or pruned.

15. GAP OR SPACE AROUND THE LOWER TRUNK.

If a tree has a gap of air or space between the trunk and the surrounding soil, there may be a problem. In the warm season, soil around the tree's trunk can dry and contract, leaving a small hollow space.

Other times, the gap may be due to poor soil conditions or an inferior root system, allowing the tree to sway in multiple directions during windy or rainy weather - even when irrigation saturates the soil. These trees may not be leaning. That's why this sign is not included under the leaning tree sign.

As the tree rocks in every direction, the trunk pushes soil to the side, pushing-open an air gap that could be circular.

If the flare of the trunk is not detectable, and there is an air space around the trunk, that's even more reason to be concerned. This could be caused by planting the tree too deep, too much irrigation combined with poor soil drainage in winter, or a damaged root system.

If the tree is very large, and it was planted too deep, raising it's root system may not be possible. Lowering the grade around it is an option, but is frequently impractical. Removing the tree, or correcting poor soil conditions may be the best alternatives.

A good solution, is an inspection by a properly trained and experienced arborist, who can determine if the tree should be removed or saved. Corrective measures for soil or mulch conditions, or depth, may be needed.

16. FINE PARTICLES LIKE WOOD DUST, ON, OR BY THE TRUNK.

Some trees - willows for example - can be damaged by insects that chew or bore small holes and passageways beneath bark and in the wood. In time, the damage can lead to weakness or collapse. The dust or frass produced, is not similar to typical chainsaw chips. These fine particles are very small

A tree that's been weakened by this damage should be removed. If the damage is minimal, consider pesticide or biological treatments if any are available.

An properly trained and experienced professional should be involved.

17. EXCEPTIONALLY HEAVY CONES OR PLANT PARTS.

This is an infrequent hazard, because it's limited to a small percentage of trees like the Auraucaria.

One tree, found in Australia, is Araucaria bidwillii, the Bunya-bunya tree, with cones as heavy as 8 to 15 lbs, with sharp spines. This tree is dioecious, with male and female trees. Only trees with female flowers (that can be pollinated by a nearby male) will produce the massive and potentially dangerous cones, which develop high up in the canopy. New owners of property with these trees whould be warned by previous owners or plant collectors. This tree can be ordered, and will grow in parts of California and other states. Cone production in landscape situations exists, but is not common.

Other trees in the Araucaria genus may drop large cones, even for species with cones that are supposed to dissintegrate on the tree. I found reports of occassional cone drop from these. There is also the Coulter Pine with cones of 2 to 3 pounds, native from California to Mexico.

Other than removal, solutions include signs, fencing or covers and arbors over pathways.

18. CHARRED TREE TRUNKS & FIRE DAMAGE.

This sign will be limited primarily to regions where wildfires occur occasionally, or have occured in the past.

Instead of conks produced by fungi, this trunk with decay has fungi producing mushrooms with caps.

If trees are discovered on a property, with charred trunks - most likely from a forest or brush fire - be sure to inspect it. See if the bark is firmly attached. Is just the outside of the bark charred, or can charcoal chunks be removed? Is the foliage discolored?

Some trees may not be blackened, but may be damaged and even ooze pitch through the bark. The bark may be strangely spotted or colored on the fire side, and normal on side which faced away from the fire and heat.

Some trees can endure and survive many wildfires. But every tree that has been in a wildfire, should be inspected. If too much heat penetrates the bark, tissue can be damaged and the tree can deteriorate.

These trees should be checked periodically, especially immediately after a fire .

19. THE NAME OF CERTAIN TREES, PLUS THE AGE.

Sometimes, the mere mention of a tree's name can be a potential sign of hazards, based on previous problems known to be associated with the species. One example is Lombardy Poplar, notorious for large dead limbs when the trees age. Typically, the name can trigger suspicion when the trees are a bit older.