Trees get wounded — some are caused by Mother Nature and some by people. Wounds are a big concern for trees; they interrupt and reduce water and nutrient flow, expose inner tissues to potential disease and insect infection and degrade the structural integrity of the heartwood. Aesthetically, they often reduce eye appeal for your customers. Tree wounds can be problematic in terms of overall tree health — but they can also be a major cause of stress for your clients. Needless to say, tree wounds are a foundational occurrence for arborists to focus on.

A tree wound closure in progress.

Wound types

Several categories and causes of tree wounds exist. Some of the more common ones include:

  • Pruning cuts: These are perhaps the most obvious wounds, but also the least understood by customers. Of course, they’re the result of the necessary arboricultural procedure of limb removal. Cutting off cankered, codominant or critter-damaged stems are of the most basic procedures that a tree service provider can make; the unfortunate outcome in some cases is the softening of tissues through decay or desiccation and overall weakening of the tree. Clean cuts made with sharp saws help limit the wounding, especially when made just outside the branch collar.
  • Storm damage: Storms roll through town in almost every season. Winter and summer tend to be the most common seasons to experience limb breakage, but ruling out storm damage in fall and spring is simply not being realistic. In summer, extreme winds tend to be the biggest cause of injury, with the effects of compression, tension and torsion causing limbs to break and requiring good arboricultural care to remedy the situation. In most cases, pruning is the best approach, as it removes unstable limbs and returns the tree to a solid entity in the landscape. In rare occurrences, cabling and bracing can also be temporary solutions to achieve stability. Such instances include target-free environments, when landscape renovations are in progress and historical celebrations. In all cases, repair work must be done according to ANSI standards and ISA-certified arborist guidelines.
  • Car accidents: Tree wounds made from being struck by a large, moving vehicle can be quite damaging, depending on the size and speed of the force being applied. As well, the shape and configuration of the front end of the car or truck is another consideration. Sharp or pointed bumpers and whether car parts are metal or plastic all factor into the equation. Generally, the most damage is done by a fast-moving, heavy-duty vehicle with a wide striking zone. The main cause for concern with auto accidents is the crushing and tearing of bark and conductive vessels, two very important parts of a tree. When these are struck they usually lose function, opening the tree to disease and insect invasion and reducing the movement of nutrients and moisture through the tree — this almost always happens at the trunk level, which impacts all other parts of the tree. In some cases, automotive fluids are deposited at the base of the tree. In large quantities, radiator fluid, engine oil and brake fluid can cause dieback of tree roots.
  • Vandalism and mower blight: Vandalism can range from a simple striking with a baseball bat or tearing of bark to the carving of initials in the trunk by young lovers. Mower blight is the repeated striking of the trunk by mowing equipment. Similar in consequence to a car accident, mower blight causes destruction of important protective bark and water conducting vessels of the tree, causing it to be stressed and lose function. Mower blight is best prevented than corrected. One prevention method is the installation of wood chip mulch, beginning 3 inches away from the trunk and extending several feet outwards into the landscape.
  • Planting errors: These types of injuries usually occur during the installation process, when roots are cut in order to fit the root ball into an inadequately sized planting hole. Training new employees to dig shallow and wide planting areas and to loosen, spread out and place tangled roots into the soil carefully goes a long way toward preventing this type of wound.
  • Utility line injury: Trenching to install sewer pipes or electrical lines causes major wounding of the root system of a tree. Severing of roots can separate a large portion of the root system from the rest of the tree, causing an instant ceasing of function. Again, prevention is the best remedy. Communication with utility companies before digging can sometimes result in the identification of a different route for placement or repair of cables, pipes and lines and should be attempted wherever possible.

Trees don’t heal

A common misconception among tree care company clients is that trees heal from injuries. It certainly makes sense on a basic level — after all, skin heals after you get scratches or cuts. Unfortunately, tree wounds don’t respond the same way as human bodies do. Instead, in response to the various types of wounds described above, trees produce new tissues to cover or compartmentalize the injured portions of the branches or trunk. The majority of the new wood grows from “wound wood,” located in the branch collar/branch bark ridge areas of the tree. If this tissue is removed in pruning, the closing of the wounds is greatly reduced or nonexistent.

Adding to the frustration of healing is the inherent capacity for various tree species to recover from wounding. Some are just better compartmentalizers than others, generally grouped into good, moderate and poor wound closers. Poplars and silver maple are in the poor group, while oak and crabapple do better than most. Many trees into the intermediate category, like linden and catalpa. Some species, like Osage orange and black locust, are good at resisting decay but not necessarily closing wounds.

Excessive winds can cause tree wounding in the limbs and shoots.

Steps to take

Customers always ask what can be done to alleviate the damage done by tree wounds. Pruning out the damage is an option, with the extent of the removal guided by local targets and capacity of the species to close wounds. Customers may also bring up the possibility of painting, tarring, cabling/bracing, fertilization, vitamins or mycorrhizae. This is a natural mothering/fathering instinct. Don’t deny it; go with it and turn this enthusiasm into a profit center for your business.

Instead of wound dressings, sell the client a plant health care (PHC) program, which does far more good for the tree than sealing it up with tar or paint, or even fertilization that encourages leaf growth at the expense of stress tolerance and root growth.

A PHC program that includes scouting, monitoring, mulching, soil testing, pruning and pest control (as needed) will capitalize on the customer’s desire to provide good care for their trees and provide beneficial products and services for the landscape.

Perhaps a silver lining to the cloud lies in finding a positive action, in that tree wounding may present the occasion to plant another tree nearby, especially if the injuries are extensive. Keeping PHC in mind, especially in terms of structural strength, disease resistance and sun/shade preference, the opportunity to install high-quality, sturdy specimens into the customer’s landscape is certainly one to be seized.