Everyone knows the now infamous story of the ice storm of 1998. For the thousands of Maine people who experienced the storm firsthand, the descriptions of the extensive damage to trees in landscape and forest settings need no repeating. But, as certain as the severe winter weather will yield eventually to spring, the task of cleaning up the downed trees and branches will shift to attending more closely to the damaged surviving trees. Although the methods used to help trees recover from the damage are rather limited, these few simple procedures, when applied correctly, can make a significant difference in tree health.

Damage Classes

The excessive icing from the storm resulted in several different kinds of damage to trees, and each damage category has specific, long-term consequences to tree health. The first and most severe damage occurs when the main stem, or central trunk of the injured tree, splits off or is broken. Larger, mature trees are most susceptible to this damage. Strength of the remaining stem is reduced immediately. In addition, research has shown that wood decay has a high probability of developing from injuries (areas of the stem where the bark has been removed and the wood exposed) of a size greater than 50 square inches. When secondary stems of multiple-stemmed trees are split away from the main stem, decay will almost certainly occur over time. The decay will further reduce stem strength and result in the tree becoming a potential hazard, especially when in a landscape setting.

The second damage category of bending generally occurs to younger trees of sapling size or smaller. Bending of the main stem will result in a "set" to the stem. The recovery of the tree to an upright position will depend on the degree of the bending, and the length of time the tree has remained in the bent position. Trees unable to recover become very susceptible to further damage from ice, or even snow loads, and to uprooting by wind.

The final, and generally least damaging category, is that of broken branches, where the break occurs at some distance away from the main stem. Broken branches will not usually threaten tree survival, unless they involve over 75 percent of the tree’s crown, or leaf supporting area. And, although decay may eventually develop in the broken stubs and proceed into the main stem, the process is likely to take several years, and should not threaten stem strength.

An individual tree may have any combination, or all the damage types described above. Trees with multiple injuries are especially at risk to declining health from decay and insect activity.

Effects of the Ice Storm

Damage to individual trees varies greatly, depending on a variety of factors. Size of the tree is important, as stated earlier. Old, large, heavy-limbed trees are highly susceptible to stem breakage, while saplings are more susceptible to bending.

Old, large, heavy-limbed trees are highly susceptible to stem breakage, while saplings are more susceptible to bending.

Differences in damage are also recognized between species. Species such as willow and poplar have comparatively weak wood. Branching habit also affects damage susceptibility. Conifer species with a sloping branch habit, such as hemlock and balsam fir, will tend to have less damage than those with more horizontal, or upright branching, such as white pine. As a group, hardwood (deciduous) trees tend to be damaged more than conifers.

Landscape or stand conditions affect damage levels. Open-grown trees with little side support are easily bent, while those in more dense stands tend to have more breakage. Here, however, tree size is again important. Some sapling-sized stands, even though dense, can receive significant bending damage. In some stands, these trees appear as "lodged," similar to a windblown field of grain.

What to Do to Help Trees Recover

The good news is that trees are well adapted to survive for long periods of time in spite of numerous and often severe injuries. The great majority of trees will survive, recover, and continue to provide the amenities we demand of them. However, in the depths of winter things look a lot worse than they are likely to be, given the tremendous resiliency of this resource. The best course of action now is to wait until late winter or early spring to conduct a damage assessment of your property. By waiting, there is less chance of removing a tree that has the potential to recover.

Pruning Properly

Follow "natural target" pruning methods when removing broken branches and portions of damaged stems. Natural target pruning is the removal of the branch at the branch collar, and not flush with the main stem (see illustration). Using this method, developed by scientists of the USDA Forest Service several years ago, results in less decay development. Wound dressings applied to the cut branch or other exposed wood don’t help reduce decay and are not recommended.

Natural Target Pruning

1. Locate the branch bark ridge (BBR).
2. Find target A—outside BBR.
3. Find target B—where branch meets collar.
4. Stub cut the branch.
5. Make final cut at line AB (with power saws make final cut on upstroke).

Do not:

• make flush cuts behind BBR

• leave living or dead stubs

• injure or remove the branch collar

• paint cuts

The best time to prune living branches is late in the dormant season or very early in spring before leaves form. Dead and dying branches can be pruned anytime. Use sharp tools. Make clean cuts. Be careful with all tools. Put safety first.

Topping trees results in a serious injury regardless of how it is done. Avoid it if possible by starting to prune early in the life of the tree to regulate its size and shape. If you must top cut, follow these guidelines.

Cut line DE at the angle approximately the same angle as the angle of the BBR. Do not leave a stem stub. Do not paint the cut. Know your safety limits—call professionals when the job is too big for you.

Staking and Straightening

Younger and smaller trees in landscape settings that are bent or leaning can be gently straightened by staking with a guy rope. Several products are on the market for supporting and guying recently transplanted trees, and many of these products would also be useful in rehabilitating bent trees. Take care to clearly mark the guy ropes or cables if near sidewalks, so they can be readily seen by pedestrians. If the stems have not been bent for an excessively long period of time, guyed stems should recover and assume a nearly vertical position again within a few weeks. For stems that have been bent for a long period, the guy ropes may need to stay in place until the end of the first growing season (mid-summer) after the storm.

What About Trees in Forest Stands?

The same principles used to help with the rehabilitation of landscape trees can also be applied to forest trees. However, if lots of trees are affected, such intensive treatment will be impractical. Practices for the removal of damaged or defective trees should be applied during the next timber stand improvement operation (and it may be sooner than originally planned).

Damage in larger trees of even moderate severity (less than 50 percent main branches broken) is not likely to result in degradation of the main stem for most timber products. However, diameter growth rate may be affected for several years, or at least until the crown foliage area is replaced. Decay of the upper stem portion may develop over time, but will probably not affect overall timber quality.

Large trees with stem damage should be salvaged before major losses from decay occur.

Similarly, forest stands of sapling-sized material that have been bent over may never recover to an upright position, in which case salvage will be the only real management option.

A Word of Caution

Safety is a primary concern when working with trees. Storms create untold hazards with many weakened and broken limbs in the upper crowns of trees. This material is a serious hazard to workers below, and only trained and properly equipped individuals should prune or remove damaged trees. Take special precautions when working in forest stands, even if the damaged trees are not the focus of activity.

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Source: "Recovery of Ice-Storm Damaged Trees," by William D. Ostrofsky, Cooperative Forestry Research Unit, college of Natural Sciences, Forestry and Agriculture, University of Maine, 1998. Reviewed by Jim Philp, Extension forestry specialist.

For more information on emergency preparedness, contact your county UMaine Extension office.

© 1998
Published and distributed in furtherance of Acts of Congress of May 8 and June 30, 1914, by the University of Maine Cooperative Extension, the Land Grant University of the state of Maine and the U.S. Department of Agriculture cooperating. Cooperative Extension and other agencies of the U.S.D.A. provide equal opportunities in programs and employment.