Pruning Damaged Trees

Damaged trees

Trees are resilient by nature and can generally withstand harsh weather conditions. They survive most winters without too much damage, and any damage sustained can be left to heal naturally without man's interference. Trees have the ability to compartmentalize and seal their wounds by forming woundwood (callus tissue). However, Mother Nature alone cannot repair the extensive damage caused by severe winter storms.

Consider Your Abilities

Before the first cut is made on any pruning job, make an honest appraisal of your pruning ability. Most property insurance policies do not cover trees damaged in storms, so you are on your own as far as the costs of clean-up and repair go. You may consider saving yourself some money by doing everything yourself; however, you may not have the necessary equipment or knowledge to do the job safely and without causing further damage to your trees, and possibly yourself. For safety's sake, never attempt the removal of very large limbs or entire trees without being absolutely sure that you have enough experience to safely complete the job. It is best to leave dangerous situations to professionals who have the necessary skills, equipment and liability insurance to deal with such hazards.

Damaged trees

Be careful how you select a contractor. Your local classified ads and yellow-page listings are full of qualified tree cutters, but mixed in with those are people quite willing to attack your trees at a price that may seem too good to be true.

Professional tree experts know all about the biology of trees and won't prune a branch without a motive – there's a good reason for what is cut and how it is cut. Arborists are experts in the tree pruning field, but foresters, forestry technicians, biologists, ecologists, horticulturists, loggers and land-clearing contractors may also be consulted for other tree issues (such as disease and clearing). You should make sure that the professional you hire to do the job is not only experienced but also certified in your province or state, has the proper equipment and has liability insurance to cover injuries suffered while repairing trees on your property. As further precautions, you should verify any references given and obtain more than one written estimate of the work to be carried out.

In any case, if a tree company advertises topping as a service, or uses climbing spikes to prune live trees, please do your trees a favor – call someone else! Topping, as well as the use of spikes on a live tree, is harmful to trees.

Practical Repairs

Since the full impact of the damage caused by any storm may not be seen for several years afterward, it may be difficult to properly make any predictions or assess long-term effects. It may be prudent to take a "wait and see" approach, and give trees a chance to recover on their own. Besides, wood debris is beneficial to the survival of the forest as it provides essential nutrients to be recycled for continued growth.

Homeowners should start by dealing with the trees that are close to buildings and work their way out. On large properties it is practical to prune and repair only injured trees that are close to the house. Unless distant trees pose a hazard to roadways or power lines, they can probably be left alone.

Various tree pruning tools


If you want to do your own pruning, consider your tool inventory. Wounded trees will further benefit when the right pruning tool is used for a particular pruning task. Trying to cut a branch that is larger than the recommended maximum size for any particular tool not only damages the tool, but can also cause torn and disease-prone plant tissues.

Whatever tools you choose to use, ensure that they are sharp and clean before starting any pruning exercise. Dull tools may cause more damage in the long run. Properly sanitized tools prevent the spread of disease, although there is less chance of spreading disease when pruning during the dormant season. Pruning tools can be sterilized in a solution of 1 part bleach to 10 parts water, then thoroughly dried.

Some basic pruning tools include:

  • Pruning Shears. Use them on branches up to 1/4" thick ? about the thickness of a pencil.

  • Loppers. Use these on branches up to 2" thick. Capacity depends on the size and design.

  • Pruning Saw. Any saw will cut branches with diameters equal to or less than 1/2 the length of the saw blade.

  • Pocket Knife. Used for cleaning and shaping the wounds.

  • Pole Pruners. These are pruners on a 6' to 18' pole, allowing you to cut branches up to 1-1/4" thick (some may come with a pruning saw) while standing safely on the ground.

  • High-Limb Chain Saw. This non-powered saw is used to saw high branches while you remain standing on the ground.

  • Chain Saw. Handy for cutting large branches into manageable pieces.

  • Safety equipment. Chain-saw chaps, hearing protectors, eye protection and gloves are the most basic when working with chain saws.

  • Hard Hat.

Knowing When and What to Prune

Because trees are dormant in the winter, and the cold weather makes it less likely for disease to spread, it is a good time of the year to prune damaged trees. Also, because the framework and form of the tree are easy to see in winter, appropriate changes and corrections are plainly visible and not obscured by foliage.

Despite the devastating look of damaged trees, resist the urge to rush into a pruning frenzy. Keep in mind the "wait and see" approach, as it will take an average of three years for trees to recover naturally or by corrective pruning. Taking care of any situation that poses an immediate safety hazard is the first priority. Cracked tree trunks and branches touching or threatening utility lines must be dealt with first, and are tasks better left for professionals. Any cosmetic repair that does not pose an immediate safety hazard can be dealt with after the growing season gets underway. Many other pruning measures can even wait until the following year.

As a general rule, no branch should be pruned without a reason. Although the damage caused by storms creates the temptation to overprune, the objective of pruning should be limited to the removal of what is hazardous and structurally weak; the natural form of the tree should be maintained as much as possible.

What Is Recoverable

A tree's ultimate fate will be determined by the degree of damage it sustained. If it lost less than 25% of the canopy, it will probably recover. If the main trunk has snapped in two, it should probably be removed at a later date, unless the tree is very rare or you want to keep it for nostalgic reasons (e.g., a tree that was planted to celebrate an event such as a birth). Deciding what to save and what to discard is both a science and an art. The science part is usually black and white - to prune or not to prune. The art lies in how you sculpt what remains of the tree to achieve the best long-term result.

An example of a Y junction split beyond repair.

Dealing with Major Damage

Although total tree removal is recommended in several cases, it is a task that can wait for warmer weather, when it will be easier to assess a tree's overall health. The removal of a tree may be a consideration under the following circumstances:

One of the arms of a Y junction on the trunk has started to split away and is beyond saving.
  • When the entire top is broken off (see photo above)

  • When the weight of the ice has caused the trunk to split most of its length

  • When one of the arms of a Y junction on the trunk has started to split away and is beyond saving (see photo at right).
Proper pruning and repair of Y junction.

Minor Crotch Damage

In theory, Y junctions should never be allowed to develop when trees are young; however, in practice, many trees are left to develop branches with narrow angles of attachment and tight crotches. Such junctions are weak, lead to the development of included bark and make trees vulnerable to damage. However, when one side of a Y junction breaks, it is often possible to save the other side and make it become a dominant central leader. Where the Y junction split is small, a 45° diagonal pruning cut (see Figure 1) may be made to remove the weakened limb.

To strengthen a weakened joint, a cable can be joined from A to B. Branch on the right should be removed at points C down to D if junction at E is starting to split.

Multi-Stem Damage
Trimming back to lateral branch.

If the tree or shrub has suffered multiple damage to stems or main branches, the damage can usually be corrected by cutting branches back to a lateral branch or bud. The correct order and positioning of cuts for the removal of large branches is described below in "A Three-Step Cut".

Wrong ways to remove a large branch.

Wrong ways to remove a large branch

A) Do not allow weight of branch to rip branch from trunk.

B) Do not leave a stub.

C) Do not flush cut and removed branch collar.

Correct pruning cut on small branches.

Correct pruning cut on small branches

It is important to always cut the smaller branches back to an outward growing bud. This reduces the likelihood of crossing branches and overcrowding crowns. For shrubs or trees that flower on last year's wood (e.g., lilac, mock orange), pruning to correct form can wait until after flowering.

Correct method for limb removal.

A Three-Step Cut

Proper pruning ensures proper healing. To encourage proper healing, avoid cutting into the branch collar, leaving long stubs, or cutting between buds. Ideally, a branch should be pruned at the branch collar – the area at the base of a branch that looks like a turtleneck. The terpines (in conifers) and phenols (in hardwoods) located in the branch collar protect the tree from invading pests and diseases. Cutting past a branch collar gives a tree little defense against marauding insects and fungal infections.

A large branch is heavy and can tear the bark if it is cut back incorrectly. Before pruning a large branch, it is necessary to reduce its weight by cutting a portion of the branch first.

  1. The first cut is made underneath the branch, halfway through the branch, away from the trunk.

  2. The second cut is made from the top, slightly away from the first cut.

  3. The final cut is made outside the branch collar. The surface should be smooth so that water cannot penetrate.

Trees that Bleed

Birch and maple trees pose an additional challenge. Due to their copious sap flow, these two species will bleed profusely from wounds (caused by either pruning or storm damage) that occur prior to or during peak sap flow periods. If at all possible, wait until the trees have leafed out and the sap is no longer flowing before doing any further pruning.

Because excessive bleeding will result in loss of nutrients, it is not advisable to tap any tree for syrup the year it sustained storm damage.

Crown Damage

Trees that suffered damage to their crowns can be pruned by cutting the stem at a 45° angle below the break and just above the first live branch. This angle of cut will prevent water from entering or pooling in the affected area.

Broken leaders

Broken Leaders

If a break occurs in the upper parts of the canopy, your choice of action depends on the type and age of tree. A conifer with a damaged central leader (a single straight stem) may be pruned and trained to form a new central leader. Cut the broken leader back to a strong healthy side branch. Gently bend the side branch vertically and secure in place with a suitable brace. Cut back branches below this to encourage the new leader to develop strong upward growth. In fact, soon after the original leader is removed the tree will naturally start to develop a new one. You may wish to wait a season or two to see if a single dominant leader develops. Then your job is to ensure that it remains dominant by cutting back the competing branches.

Repairing central leader damage.
Straightening bent trees

Straightening Bent Trees

Young trees and trees with slender stems are prone to bending under the weight of ice from an ice storm. Many of these flexible trees may have their crowns frozen to the ground. Generally speaking, it is best to leave bent trees to return to their upright positions on their own. Releasing the branches in cold weather can cause more harm than good as bark can be damaged and essential buds may be accidentally removed in the process.

On the other hand, leaving trees shackled to the ice throughout the winter may result in a trunk that remains bent out of shape, much like the result you obtain from shaping a bonsai with wires and braces. When the temperature is above freezing, you can try to gently free some of the branches from the thawing ice. Don't pull them out like weeds. What you want to do is gently ease the branches out. If the branch doesn't come out freely, it is best to wait a bit longer.

After the crown branches are free, leave them alone until warmer weather. On a warm day, before the buds break, ease the trunk up straight and use stakes or tie lines to hold it in position. Ensure that the staking allows some tree movement, as rigid staking can cause the tree to snap in high wind or make the tree too dependent on the staking. A plank can also be strapped to the trunk, like a splint, for temporary support. The tree may need support for up to 3 years before it is strong enough to stand on its own.

Torn branches

Torn Branches

Many trees may have suffered torn bark as the result of losing limbs during an ice storm. In some cases, the entire branch collar and a large area of bark may also have been removed. You may be tempted to remove these damaged trees, but given time and proper care, a healthy tree is capable of making a remarkable recovery. Trim and round out the loose bark with a chisel or knife to prevent water, insects and disease from entering the wound. Cut back jagged stumps to further encourage proper compartmentalization.

1) Branch torn away by tree. 2) Repair to wound.
Wait for the thaw before making decisions on bent, ice-covered trees. Over time, the trees may straighten naturally or with some assistance.

Assess the Damage

1. Wait

Wait for the thaw before making decisions on bent, ice-covered trees. Over time, the trees may straighten naturally or with some assistance.

llustration courtesy of LandOwner Resource Centre and Ontario Ministry of Natural Resources.

Prune the tree if it is healthy and if less than 25 per cent of the crown is damaged.

2. Prune

Prune the tree if it is healthy and if less than 25 per cent of the crown is damaged.

llustration courtesy of LandOwner Resource Centre and Ontario Ministry of Natural Resources.

Cut the tree if it has lost more than 25 per cent of its crown. Fast-growing species like silver maple, poplar and willow may survive. These species produce shoots (epicormic sprouts) when damaged or poorly pruned.

3. Remove

Cut the tree if it has lost more than 25 per cent of its crown. Fast-growing species like silver maple, poplar and willow may survive. These species produce shoots (epicormic sprouts) when damaged or poorly pruned.

llustration courtesy of LandOwner Resource Centre and Ontario Ministry of Natural Resources.

Peg grafting

Experimental Repairs

A tree that means a great deal to you may look like it has been damaged beyond hope. Instead of immediately cutting down the tree, wait until late spring and try your hand at grafting. Late spring or early summer is a good time of the year to try grafting, because the bark lifts easily from the sapwood. Grafting some scions (small branches) from the "old" tree onto a compatible rootstock may make it possible to recycle your favorite tree.

Because we cannot adequately cover grafting techniques within the scope of this bulletin, we recommend you consult a grafting book for more information. Exploring alternative techniques to pruning may make it possible for you to save more trees than you thought possible.

Tree Wound Dressings

Latest research shows that dressings (like paint) applied to cover wounds actually inhibit healing by trapping and protecting harmful organisms. Many experts no longer recommend the use of wound dressings as they have found that trees have their own protection mechanisms that will effectively close wound surfaces and ward off infectious diseases. However, when elm and oak trees are wounded during storms, thin coats of non-toxic tree wound dressings are still recommended to prevent Dutch elm disease and oak wilt.

Overpruning leads to the development of epicormic sprouts.

Epicormic Sprouts (water sprouts, lion tails, dog tails)

Many varieties of trees respond to excessive pruning by developing epicormic branches, or water sprouts. Water sprouts are, in essence, a defence mechanism that trees like elm, maple and poplar use to deal with injury. These unsightly masses of rapid growing vertical shoots come from the activation of latent buds. These shoots are not to be treated as permanent branches, however, as they are prone to breaking. Some of these will have to be pruned back in the fall, and in successive years, to ensure that only the stronger sprouts are left to develop into branches.

Safety First

  • Exercise caution when assessing the damage.

  • Approach damaged trees only if it is absolutely safe to do so.

  • Do not, under any circumstance, go near or touch a branch that is touching a power line.

  • Chain saws should be used only for cuts that can be made with both feet firmly on the ground. Never use a chain saw for overhead cuts.

  • Wear protective gear.

  • Do not work alone.

Proceed with Caution

While the job of cleaning up after an ice storm is an enormous one, it is not necessary to do everything at once. By slowing down your clean-up activities and thinking before acting, you may actually save yourself a lot of hard work. When in doubt as to what is best for your trees, read up on pruning or consult a professional. With careful pruning and patience, you may discover just how resilient trees really are.

Further Reading

  • Cavendish Encyclopedia of Pruning & Training, Christopher Brickell

  • How to Prune Trees, Peter J. Bedker, Joesph G. O'Brien, Manfred E. Mielke

  • Modern Arboriculture, Alex L. Shigo

  • The Pruner's Bible, Steve Bradley

  • The Pruning Book, Lee Reich

  • Tree Basics, Alex L. Shigo

  • Tree Pruning - A Worldwide Photo Guide, Alex L. Shigo
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