Prognosis for Recovery of Storm Damaged Trees

Ice storms damaged millions of trees in Missouri during the winter of 2007. While crews have been working for weeks to clean up broken and fallen trees and branches, the scope of the damage is so massive that most trees will be left to recover as they can without human intervention. Given the rarity of such wide spread ice damage, it is diffi cult to predict the long term effects on landscapes and forests. However, it is possible to make some generalizations about the effects of storms on trees.

Ice storms cause several types of tree injury. The most obvious and most serious type of damage is breaking or splitting of the main trunk and massive branches. This most often occurs on large, mature trees and on trees like silver maples that tend to form branches that grow at a narrow angle with the trunk. While this type of damage may not cause rapid tree death, it exposes large areas of wood to decay organisms. Over ensuing years, decay can progress rapidly, making the tree increasingly susceptible to further storm damage. Also, loss of photosynthetic leaf area associated with large branches tends to weaken the tree and limit the movement of carbohydrates to the roots. This, in turn limits the ability of the tree to produce callus tissue to cover over (compartmentalize) wounds and to resist attack by insect and disease pests. Large old trees with major damage to the trunk and main branches may decline fairly rapidly. Other, more vigorous trees may recover quickly and live for decades, serving as assets to the landscape or forest. A rule of thumb often mentioned by tree experts is that a tree that has lost less than 50 percent of its branches stands a reasonably good chance of recovering to the point that it will remain an asset rather than becoming a liability.

Another type of ice storm damage is bending over. Small trees of many species can be bent nearly to the ground from ice load. In some cases, trees appear to straighten back up within a few months. In other cases, they may have a portion of the trunk that remains nearly horizontal and the top will begin to grow upright. Sometimes, longitudinal splits or cracks associated with bending are not obvious, but may serve as entry points for insects or disease organisms. Many hurricane damaged pines in Louisiana that seemed to be recovering were killed by bark beetles the year after the storm. In the landscape, it is often possible to mechanically straighten bent trees by guying or staking. It may even be possible to right a tree that has been partially uprooted during a storm. However, once severely bent, most trees will be more susceptible to storm damage in the future, especially if they can not be restored to near vertical.

The most common type of ice damage observed in the Springfield area is breakage of small and mid sized branches. In many cases, about half of the branch has snapped, leaving a significant part of the branch still attached to the trunk. Most trees can recover from this type of injury fairly well. Although this damage may lead to decay within the broken branch, the tree can often prevent the decay from spreading to the main trunk by forming a barrier of wound tissue. Also, lateral branches may grow from the remaining portion of the original branch to produce new foliage in the open region of the tree’s crown. Thus, while the tree may look odd for a year or two, it may be diffi cult to tell the tree was damaged a few years later.

As previously noted, it is somewhat diffi cult to predict how many of the storm damaged trees will respond. Therefore, unless they represent obvious hazards, it may be wise to wait for a year or two before removing trees that appear to have been hard hit. Some trees that look hopeless, may recover surprisingly quickly. If it becomes obvious that some damaged tree are moving from the asset to the liability column on your landscape balance sheet, keep in mind that tree work is dangerous. Hire a professional to work on large trees or branches.

Chris Starbuck
StarbuckC@missouri.edu