Trees are commonly wounded and the causes are many: broken branches; impacts, abrasions and scrapes; animal damage; insect attack; fire; etc. Wounds usually break the bark and damage the food- (phloem or inner bark) and water- (xylem or wood) conducting tissues.
Wounds also expose the inside of the tree to organisms, primarily bacteria and fungi that may infect and cause discoloration and decay of the wood. Decay can result in structurally weakened tree stems and unsightly trees and can shorten the life of a tree. Decay in a tree cannot be cured. However, proper tree care can limit the progress of decay in an injured tree.
Urban and suburban trees are more likely to have wounds and decay than trees in native stands because people cause most wounds.
These wounds are usually unintentional, such as automobiles, construction equipment, or lawn mowers bumping the tree trunk or surface roots, or improper pruning. Naturally occurring events, such as storms, fires, or damage by birds or other animals, may also cause wounds.
Trunk wounds that are not addressed could potentially be a hazard in the future.
Once a wound occurs, decay-causing fungi can enter the heartwood and the decay process begins. Trees have a unique defense. The wood around the wound begins to produce special compounds in the wood cells that set up a wall or barrier to isolate the infected area.
This is called compartmentalization. In a vigorous tree, new growth continues to form and add to the sound wood Once compartmentalized, discoloration and decay will spread no further unless one of the barriers is broken.
Tree Response to Wounding
Tree response to wounding or injury involves two processes: compartmentalization and the development of barrier zones.
Compartmentalization of the Tree Trunk Wound
When a tree is wounded, the injured tissue is not repaired and does not heal. Trees do not heal; they seal. Trees are generating organisms while animals are regenerating life forms. Animals repair, replace, restore and regenerate tissue from existing cells. Trees “wall off” injured and infected tissues and then continue generating new tissues.
If you look at an old wound, you will notice that it does not “heal” from the inside out, but eventually the tree covers the opening by forming specialized “callus” tissue around the edges of the wound.
After wounding, new wood growing around the wound forms a protective boundary preventing the infection or decay from spreading into the new tissue. Thus, the tree responds to the injury by “compartmentalizing” or isolating the older, injured tissue with the gradual growth of new, healthy tissue.
Tree Pruning Wounds
Proper pruning should be used to remove dead, dying and broken branches; to remove low, crossing or hazardous branches; and to control the size of the tree. However, pruning of any kind places some stress on the tree by removing food-producing leaves (if the branch is alive), creating wounds that require energy to seal and providing possible entry points for disease.
Pruning cuts should be made to maximize the tree’s ability to close its wound and defend itself from infection. When pruning, make clean, smooth cuts. Do not leave branch stubs. Leave a small collar of wood at the base of the branch. The branch collar is a slightly swollen area where the branch attaches to the trunk. Cutting the limb flush with the trunk will leave a larger area to callus over and a greater chance of decay organisms entering the wound.
Any tree pruning that is higher than a step ladder or on a branch bigger than your wrist should be left to professional tree care service providers. The damage you can do will not be immediate but, may cause long term issues with your tree’s health.
Tree Wound Dressings
Research indicates that wound dressings (materials such as tar or paint) do not prevent decay and may even interfere with wound closure. Wound dressings can have the following detrimental effects.
• Prevent drying and encourage fungal growth
• Interfere with formation of wound wood or
• Inhibit compartmentalization
• Possibly serve as a food source for pathogens
If you have a wounded tree the best thing to do is call a professional arborist or tree surgeon to have a look at your tree to address a remedy. You may be told that the tree will heal on its own or the tree care professional may offer a solution if the tree is in poor health caused by the wound.
When is a tree a hazard?
When a tree service inspection reveals a structural weakness, internal decay, or poor branching structure.
A tree becomes a hazard when there is a “target”
A target is something that could be hurt or damaged if the tree or limb falls. “Look up”, is our motto. If you are planning on placing a shed, playset or other outdoor feature, look up. If you see anything that concerns you, give us a call.
If decay or structural problems are suspected, contact a professional arborist. Trees located in areas where people frequent should be inspected regularly.
SIGNS OF POTENTIAL TREE HAZARDS
- Large dead or detached branches
- Cavities or decayed wood
- Signs of internal decay – mushrooms at the base of the tree or carpenter ants
- Cracks or splits in the trunk where branches are attached
- Many branches arising from one point on the trunk
- Roots that have been cut or covered
- Evidence that the tree was “topped” in the past
WHAT TO DO ABOUT TREE HAZARDS
If you have a tree wound you want to have inspected, call Quinlan Tree Service today. Lisa our office manager will be glad to set up an appoint to have Shane or one of our other tree care experts have a look.