Take Time, Use Caution Pruning Injured Trees

The November ice storm left many of the region’s trees seriously damaged. It is important that we don’t further damage them as we cut out dead or broken branches.

For repairs of large trees it’s best to hire a certified arborist. The International Society of Arboriculture has set professional standards for arborists and administers a comprehensive test as part of the certification process. A list of ISA-certified arborists is available by calling WSU Cooperative Extension in Spokane at 533-2048 or Spokane Conservation District at 353-2120, or on the Web at www.ag.uiuc.edu/isa.

If you are going to make repairs yourself, limit your work this year to only repairing the injuries resulting from the ice storm and removal of dead wood. Save any other pruning on damaged trees until next year or later. There are two reasons for this:

1. Tree leaves will produce energy that these injured trees need to recover from the trauma of split trunks, broken limbs, etc. Energy that leaves need for development is stored in the branches. By removing undamaged limbs and their leaves this year, you are both increasing the trauma and removing a source of energy that wounded trees need this spring and summer.

2. Because portions of trees have been removed, newly exposed parts of trees will be subject to sun injury this year. This is particularly true for smooth-barked trees such as mountain ash and Norway maple. Sun damage will become another stress on injured trees. Normally, tree leaves shade tree branches. By removing undamaged limbs this year, you are removing a source of shade to newly exposed areas of trees.

Limiting your pruning to dead and storm-damaged wood will be difficult if it leaves asymmetrical or even silly looking (but structurally sound) trees. However, in the interest of long-term tree health, we must bite the aesthetic bullet this year and leave the trees with all possible sources of energy.

For those planning to repair their own trees, here’s a guide to pruning:

Removing broken branches: (Figure 1, Page 2) Cut broken branches (or stubs that are left) back to what is called the branch collar. The branch collar is that swollen or bulging tissue at the base of any branch where it attaches to a limb or main trunk. When a branch is correctly pruned, this collar will eventually grow over the exposed cut surface and prevent decay. Cut precisely to the outer edge of the branch collar. If you cut into the branch collar tissue, any decay will spread into the parent limb or trunk. If you leave any stub outside of the collar, the collar will not be able to close over the wound. If wounds fail to close, internal decay will result. (Branch collars look different on different kinds of trees. Some are difficult to see. Look at several trees in your yard to get a general idea of branch collar formation.)

If a large branch or the main trunk has broken: (Figure 2) In this situation it is necessary to make what is called a drop-crotch cut. This means you will cut a limb or the main trunk back to a side branch, as shown. The smaller branch should be at least a third of the diameter of the larger one being cut off for this method to be effective. Make the cut just above the branch bark ridge and continue downward at about a 45-degree angle.

If a branch has split but is not detached from another branch (or itself) or if the main trunk is split: (Figure 3) If the bark is intact, the two pieces may be rejoined and held tightly together, but do not wrap anything around the split sections to hold them together. This will only result in later strangulation of that branch or tree. Consult a certified arborist with experience in repairing this type of damage.

If there is not sound wood on either side of the split or if bark is no longer attached to one side of the split, remove the damaged section of the split at a slight angle down and away from the bottom of the split. Cut all splintered wood back to solid wood without unnecessarily enlarging the wound.

If a branch has torn out of a larger branch or trunk: (Figure 4) If more than a third of the cross-section of wood is gone, consult with a Certified Arborist to determine if the remaining portion is structurally sound. If less than a third of the cross section of wood is gone, there is little need to do anything. Pare back the edges of the wound only to remove loose, splintered or ragged edges. Do not unnecessarily enlarge the wound if the margins are relatively smooth.

Do not paint or seal wound surfaces. These substances do not aid wound closure or prevent disease entry. In some cases wound closure is delayed by their application.

Sterilize pruning tools when moving from one tree to another. Wipe blades with 70 percent isopropyl alcohol (rubbing alcohol) to prevent the spread of fireblight, bacterial canker and other diseases.

When removing a trunk or any branch that is too heavy to be supported by hand, make a three-step cut to prevent tearing bark (Figure 5.) Make the first cut at A about 12 inches from the trunk. Make the second cut at B on the outside of A. Make the final cut outside the branch collar (E-F). A cut at C-D would leave too much of a stub which may rot; a cut at G-H is a flush cut which may allow decay to enter the tree trunk.

MEMO: Text by arborist Rich Baker and WSU Extension Agent Tonie Fitzgerald; illustrations by WSU Master Gardener Dottie Bender.

The following fields overflowed: CREDIT = Rich Baker, arborist and Tonie Fitzgerald, WSU Extension Agent