Trees are remarkable in their ability to self repair when subjected to trauma. But even with the amazing ability to compartmentalize and seal-off injury, trees will eventually fail, die and fall. They are unable to escape from their environment and thus cannot avoid the dangers and threats from forces of nature and human related pressures.
Tree ownership brings with it the responsibility to manage each tree to minimize risks associated with environmental hazards and aging. Following these three simple rules will make for safer trees; (1) systematic inspection, (2) treating problems quickly, (3) removing a tree when it's risk outweighs its value.
The Tree Examination
Maintaining a tree health issues is a fairly simple process and should be done slowly and systematically. Pick a spot where you can see the entire tree and on a day with appropriate weather and sunlight conditions. That inspection should include these three major tree sections - the crown (branches and foliage); the trunk (tree stem); the roots (within the critical root zone). Printing my quick guide How to Check a Tree's Health can help with this and also be used for note-taking.
Some sources suggest a tool kit to use including binoculars, trowel, rubber mallet and a yardstick. This is certainly appropriate but, in my opinion, not really necessary. Using these tools can give clues that yield information to one who knows how to interpret those clues. I have found that most serious problems can be readily found without the kit by any observant tree owner. I will now describe the most serious conditions. You should try to identify the tree species group (oaks, elms, birches, etc) as they have unique risks and tolerances to certain conditions.
Tree Conditions of Major Concern
Defective root conditions: Roots can become defective by a failure of the soil and by root failure. It is important to know the difference. Soil failure happens when soil particles lose the the ability to hold the root system in place. Saturated and waterlogged soils combined with high wind can cause this. Serious saturation problems may call for a drainage correction.
Obviously, root failure is a major defect to contend with. Roots that are severed, decayed or otherwise damaged can cause failure. Check for large roots that have died, are decayed, have been cut or broken, or are confined, restricted or strangling the tree's main stem. Leaning trees may have a root problem and should be taken seriously when soil is "mounding" opposite the leaning side.
Multiple trunks: Tree failure can occur where a tree forks at or near the ground. Inside that fork, a weak union is possible and can cause the union to separate. Not all unions are problems. A solid union is when there is a well developed "u" and/or where there are upturned ridges between trunks, stems and branches. Problems are more likely when stem unions are cracked, decayed and has included bark (ingrown bark between two trunks).
Weak branch attachment: Finding weak branch attachments will take a little more time and keener observation skills. These attachments usually occur where older limbs have broken off and where sprouts have developed off these breaks. As the weak limb sprouts grow larger, they gain weight and can fail at any time. Signs of a weak branch attachment are included bark at the branch union, branches that grow off topping cuts, branches with abrupt 90 degree bends, species with a tendency for branch failure (hackberry) and where a branch is as large as its attached stem.
Cavities and decay: Decay is in every tree and introduced at the point of an injury. It is caused by a fungal infection which causes the breakdown of wood cells and overwhelms the ability of the tree to compartmentalize that particular area. Cavities develop as the wood deteriorates and may be visible on the outside or in an unseen interior section. Signs of decay include mushrooms and conks, loose bark, dead branch stubs, trunk bulges, ants and nesting holes.
Hangers and Suspended Branches: Hangers are limbs that have broken but remain attached to another limb or broken off the tree stem. A suspended branch is one that is detached but "hung up" in the living material. These aerially suspended branch hazards should be taken seriously and removed, especially if there is property and potential traffic below. The removal of hangers should be carefully completed and any remaining part of a live branch removed using proper pruning methods.
Cracks: Cracks can occur at the point of a major fork or where a tree flaw undermines the structure. Cracks can form from traumatic stress and usually separates along the wood grain. They are of major concern when they occur along the main tree stem or on major branches and when long and deep. Signs of a crack needing attention is one running deep and long, is opposite or connected to decay/cavity or among multiple cracks.
Deadwood: Some deadwood is seen on most trees in one form or another. and more easily identified during the growing season. Obviously, the tree safety hazard issue increases as the size of the branch or limb increases. Again, if you have targets that can be harmed under the tree, removing deadwood should be done as soon as possible. Deadwood also could mean that the tree has a health issue. Dying limbs and branches often indicates root damage on that same side.
So You Know The Problem! Now What?
Most of these problems will take major tree work if not corrected when the tree is very young. An aging tree becomes more and more massive and outgrows the ability of the owner to do the work safely. You should only attempt to do the work required if the tree is small, easily handled and in reach of the ground. Attempting tree work yourself may cost more than you bargained for and get you hurt too boot!
Always get a second opinion on your evaluation. There are professional arborists in the business that will gladly help you in the decision making process. Their cost may be well worth the expense and prevent a weekend job that could conceivably turn into a tragic mistake. Try visiting the International Society of Arboriculture's web site to find a certified arborist in your area.