Storm Damaged Trees: Prevention & Treatments (Coder, 1995)

The Fredericksburg area has had severe winds the last several days.  I found this great article about storm damaged trees, prevention and treatments.  After reading this information and determine you would like a certified arborist to evaluate and  recommend a treatment plan, please give Goodfellers Tree and Excavating a  call at 540-710-9665 or visit our website http://www.goodfellertreeco.com/ and complete the "I need an estimate" section.

Storm Damaged Trees: Prevention & Treatments

Kim D. Coder 

Professor Silvics/Ecology 

Warnell School of Forest Resources 

The University of Georgia

March, 1995

Thousands of shade and street trees are lost every year to wind, ice and lightning. Historic, rare, and specimen trees, especially when landscapes are designed around them, are valuable. These trees can become major aesthetic, financial and social losses in storms. This publication summarizes information to help you understand and prevent storm damage to trees. It also lists resistant species of trees to plant, types of tree storm damage and treatments, and lightning protection systems information.

Definitions

Trees are biologically engineered to adjust to "wind loading." Wind loading is a straight wind from one direction applied evenly over the stem, branches and tree leaves. "Wind release" is the removal of wind loading when the crown and stem snap back into a normal position. In any wind there are gusts and calms. These alternately load and release the tree. Under normal weather conditions, trees sway in the wind. Movements in the wind initiate changes in the woody material developing in the stem.
If a wind continues to come from one general direction all the time, hardwood trees develop extra strength on the side of the tree toward the wind. In conifers, like pine, extra strength is built-up on the side of the tree opposite the wind. If the winds are not strong enough to blow the tree over, the tree will develop a trait known as "wind firmness" over several growing seasons.
Wind firmness is directional. Trees growing under a constant strong north wind are easily damaged by a strong east wind. Fortunately, most open-grown trees develop good wind firmness in all directions over the years. Wind firmness is developed over time in response to wind.

Storm Damage

There are six main types of storm damage to trees: 1 ) blow-over; 2) stem failure; 3) crown twist; 4) root failure; 5) branch failure; and, 6) lightning. Each type is the result of a complex and interactive mix of tree problems and climate.

1. Blow-over--The tree is physically pushed over by high winds. There is little biological adjustment available for a tree (or people) to make to hurricanes, down-drafts or tornado winds. The wind force on the aerial tree portions is too great for the wood structure. Past tree abuse, poor maintenance, pest problems (like fusiform cankers on pine or root rots on hardwoods) predispose the tree to storm damage by weakening the wood architecture.
2. Stem Failure--Trees do not heal wounds. Trees can only grow over old wounds and seal them off. This results in a tree carrying in its wood every injury it has ever had. These old injury sites, and the old and new wood around them, are structurally weaker than normal solid wood. These damaged areas can quickly fail under an constant wind loading and release. Pest damage, weak wood around old wounds, new wounds, and failure of the tree to adjust to wind conditions can lead to stem failure under heavy wind loading and release.
3. For trees with heavy crowns, abrupt wind gusts and calm periods can lead to stem breakage from release. As the wind load is quickly released, the tree moves back into an upright position. If the mass of the crown moves too quickly when released, the inertia of the moving crown may move too far in the opposite direction leading to stem damage and breakage.
4. Crown Twist--Tree crowns are the leaves and supporting twigs and branches. Trees are never perfectly symmetrical in every direction. Many trees, through past abuse or poor maintenance have lopsided crowns. More wind loading on one side of the crown than on another produces a twist (torque) on major branches and the main stem. Over time the twisting effect can be biologically adjusted for within the new wood. Stem twisting will magnify weaknesses around old injuries and the stem will split or branches collapse.
5. Root Failure--There are two types of tree roots: fine, absorbing roots and woody, structural roots. As their names imply, absorbing roots have a massive surface area, but are weak. Structural roots are woody, have a relatively small surface area, but are strong. Both types provide anchorage for a tree.

The primary roots growing from the bottom of the stem (root collar) play dominant roles in holding the tree upright while conducting water, essential elements and nutrients. If roots are constrained, diseased or damaged by construction, or as the top of the tree becomes larger, greater stress is put on the roots. Pulled or snapped roots cause trees to fall or lean.
6. Branch Failure--Branches are poorly-attached to the main stem. A branch is stuck on the side of the stem each year by a small layer of stem wood called the branch collar. The branch collar surrounds the branch base. The woody material from the branch enters the stem and turns downward. This structural arrangement allows the branch to be flexible and disposable. The stem can shut off the branch when the branch becomes a biological liability to the tree (Figure 1.)


Figure 1. Branch collar where stem and branch join.
Heavy loading (as during an ice storm) puts great stress on the branch collar area. Over many years, a tree will adjust to this stress, but ice storms or downbursts that occur only rarely will leave the branches unprepared and susceptible to tearing downward along the stem or snapping. The branch collar area can also be weakened by "included bark." This material is bark from both the expanding stem and branch. Where the branch and stem expand against each other, bark can be surrounded and overgrown inside the branch collar area. Included bark leads to weaker structure and a place for pest attack. This is why forks (called co-dominant branches) are structurally weak. These weak areas can easily fail in a storm (Figure 2).

Figure 2. Codominant branches or forks are bad for tree support. Splitting can easily occur due to a weak crotch area that can contain included bark (bark that has been grown around.

7. Lightning--Lightning damage is a life-threatening situation. Lightning either moves in a narrow line down the branches, stems and roots, or along a wide pathway encompassing the entire tree cylinder. Lightning directly destroys tree tissues by electrical disruption and heat. Steam explosions down the stem, in a wide or narrow band, show where the electrical current has moved through the tree. Massive root damage can remain unseen.

Damage caused by lightning leads to extensive water loss which is also life-threatening. Pests quickly attack a lightning weakened and damaged tree. For example, the Southern pine beetle quickly destroys a lightning struck pine.

Preventing Storm Damage

    There is no way, except for complete enclosure, to protect trees from all storm damage. Trees are not adapted to worst-case storms only to our average wind climate. Listed are several things to minimize the main types of storm damage:

1. Let trees adjust to the wind environment. Tight staking and guying from the time of planting holds a tree in place while preventing internal adjustment to wind loading. Always stake and tie the tree loosely where the stem can move and bend in the wind. Keep ties in place for a few growing seasons to insure a well-established root system. Continue to loosen and eventually release the ties. The support stakes can be left in place to protect the stem from mechanical damage. After five to seven years, remove all tree support. The tree will continue to grow and adjust to its new environment.
2. Practice proper pruning techniques by cutting branches before they become larger than one inch in diameter. The branch collar should not be damaged (Figure 1). The branch collar is part of the stem and, if damaged by poor pruning, provides an avenue of attack into the main stem for pests. Proper pruning minimizes a number of structural problems that occur in association with new wood growth around a pruned branch.
3. Eliminate codominant branches. Prune forked branches and branches that arise opposite each other on the stem early. Cut one side off now to prevent losing the whole tree later if it splits in a storm. In trees with opposite branching patterns, such as ash or maple, proper branch training is essential for a long-lived, storm resistant tree.
4. Keep trees as healthy as possible with timely watering and proper fertilization. Healthy, vigorous trees adjust more quickly to changes in the environment, are more wind firm, and react more effectively to damage.
5. Do not overfertilize the tree with nitrogen or overwater the soil. This can increase the crown surface area and/or decrease the rooting area. This type of biological change makes the tree susceptible to storm damage.
6. Eliminate lopsided crowns. Prune branches to produce a reasonably symmetrical crown. If more than 70 percent of the crown is on one side of a mature tree, consider tree removal and replacement. Guying and bracing branches are last-ditch efforts when a tree has to be saved in spite of itself.
7. Remove or treat pest problems, like branch cankers, to minimize potential damage. Do not over-treat tree hollows. Do not remove decayed wood from hollows unless it falls away in your hands. Cleaning hollows can lead to further internal damage. Cover the opening to hollows to allow the tree to grow over the opening, prevent animals from expanding it, and to keep water from running in.
8. Keep the tree growing upright with one main stem. Prune away branches that compete in height with the main stem. Eliminate branches with tight or narrow crotches.
9. Install lightning protection systems on historic, rare, specimen or recreational area trees. Consult a qualified arborist or urban forester to insure adequate design. Lightning protection systems are covered in detail later in this publication.
10. Continue to promote wind firmness by not overcrowding trees and by proper guying and bracing. A tree must always be able to move in the wind. Do not keep a tree tied into position with tight cables. In a stand of trees, slowly remove trees over a number of years to allow wind firmness to develop in the remaining trees.

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