Janna Beckerman, Extension Plant Pathologist
To paraphrase Hobbes*, life for Minnesota trees is often cruel, brutish and short. In addition to bitter winters (with damaging ice and heavy, wet snows) and scorching summers, trees have to contend with storm damage for all but the coldest months. Most of the time, damage consists of a few broken branches. However, severe weather may result in severe damage, such as splitting of branches or even stem forks, trunk breakage, or uprooting. These injuries not only result in a change in the appearance of the tree but a dramatic change in the home landscape, as well. Tree health and tree appearance go hand in hand. Injury of any sort increases a tree's susceptibility to insect or disease attack. For this reason, it is important that damage is properly treated and repairs be made to maintain tree health. Although many types of damage may be treated by the homeowner, large trees, or severely damaged trees may require the services of a tree specialist.
Recognizing the Damage:
Uprooted Trees One of the most dramatic images that appear in the wake of thunderstorms is that of the uprooted tree. And, it's easy to diagnose! Although this has been said many times by many agencies, it bears repeating: If the tree is large, it cannot be saved and should be removed promptly. The scenario isn't as clear for smaller trees (less than 25' tall) and if 1/3 to 1/2 of the tree's roots are still in the soil. Although costly, for a valued tree, it may be possible to straighten the tree, and then brace it using guy wires or cables. Significant cost may be incurred if cranes or other equipment is needed to pull the tree upright. Remove soil from beneath the root ball to place the roots below the existing soil grade level. Backfill the soil to stabilize the tree (Do not plant too deeply!) and water to remove air pockets. Place guy lines to the trunk at approximately two-thirds of the height of the tree and to anchors 12 to 15 feet from the base to hold the tree in place until it is established. For more information, see Staking and Guying of Trees at: http://www.cnr.umn.edu/FR/extension/urbanforestry/stakeandguy1.htm
Lightning
Tall trees, like cottonwood growing in open locations are very susceptible to lightning strikes. Lightning strikes on trees are a common sight during the summer months when thunderstorms occur. Symptoms of lightning damage include trees that burst into flame or explode (easy to diagnose), bark that is usually stripped off the tree in a spiral fashion, or extensive root damage as the lightning has exited the tree (not easy to diagnose). Lightning has been known to kill trees immediately; others, even though damaged extensively, will continue to grow. Further confounding a diagnosis of lightning injury is that trees may appear normal immediately following the strike but die soon after for no apparent reason, although this occurrence suggests that root damage due to the lightning strike resulted in tree death.
Treatment of lightning-damaged trees depends on the severity of the strike. Again, evaluate the damage and decide if it is necessary to remove damaged limbs. Because it may take weeks for all the damage to develop, delay any repairs (unless hazard is involved) for at least 6 months. Because tall trees are predisposed to lightening strikes, you may wish to install a lightning rod as a preventative measure to guard against future strikes.
Even if lightning damage isn't obvious immediately after the storm, the voltage from lightning striking one tree can "jump" to adjacent trees if their branches are touching or if they're located close to each other (within 20 feet). Common symptoms of lightning jumps include sudden wilting, leaf death, prolific leaf fall, or sudden death, and can occur on trees several feet or trees away from the lightning strike.
Rating the Damage
Most storms only inflict minor damage, with little or no permanent damage to the tree. However, certain trees consistently fail in these storms, and include some of our most common street trees, like silver maple and green ash, in addition to willows and poplars. These rapidly growing trees are particularly susceptible to storm damage and homeowners should avoid planting these trees close to homes or utility lines. If these trees are already growing in these locations and are showing signs of weaknesses, homeowners may wish to consider removal to eliminate any chance of damage to their homes. Current research done in Rochester, NY, evaluating the effect of preventative pruning to prevent damage to trees did not show a significant differences for storm failure between pruned and non-pruned trees!
Spring storms, although potentially just as severe as summer storms, usually produce less damage to trees that haven't yet leafed out. Branch and tree failure rates are higher when foliage is present on the tree, or if the tree had a previously unidentified structural defect. Severe damage consists of large broken branches, split crotches, and splintering or splitting of the trunk. Trees like this need to be quickly evaluated to determine if they are hazard trees (To do so, read the US Forest Service Publication "How to Recognize Hazardous Defects in Trees at: http://www.na.fs.fed.us/spfo/pubs/howtos/ht_haz/ht_haz.htm )
What do you do if a tree is severely damaged? The first step you need to take is evaluate the type and nature of the damage. Are there cracks, split branch unions, splintering or topping? A beloved spruce will recover from topping but will take decades to recover, and will probably never obtain the pyramidal form one expects from spruces. Before doing anything, objectively analyze the tree, the site and the situation. Be sure to take into account what species of tree it is, how old it is, where the tree is growing and the value it adds to the property. Sentimental value should not be overlooked, but taken only as part of the total equation in determining if a tree is worth saving. Sentimental value must also be weighed against the possibility of additional damage occurring to the tree in future storms, or the tree becoming a hazard. Finally, remember that any injury is a potential infection court for future disease! If you are not sure about what to do regarding your tree's fate, consult with a professional arborist, urban forester or other tree service professional to obtain a second opinion.
After weighing the future of the tree, it may be decided that the tree is damaged beyond repair, that the cost to repair the tree exceeds the value of the tree, or quite simply, that the tree is too ugly to tolerate. In the case of large trees, remove the tree as soon as possible to prevent possible injury or damage.
Tree-tment
If you have made the decision to repair the damage to the tree, the next step is to decide if you can repair the tree yourself or if require professional assistance. Keep in mind that major repairs will require the use of ladders, climbing equipment and very sharp tools like handsaws and chainsaws. This is a dangerous combination on the ground and becomes even more so when working off the ground, and especially so if power lines are involved.
If you decide to consult an arborist, contact the Minnesota Society of Arboriculture, 115 Green Hall, 1530 Cleveland Ave. N., St. Paul, MN 55108, or check out their web site at: http://www.cnr.umn.edu/FR/extension/pages/, and click on "Certified Arborists." This listing of arborists in Minnesota that have attained the professional level of "Certified Arborist" through the International Society of Arboriculture includes a column that details the services they provide. For more information on pruning: How to Prune Trees (http://www.na.fs.fed.us/spfo/pubs/howtos/ht_prune/prun001.htm) Pruning Trees and Shrubs (http://www.extension.umn.edu/distribution/horticulture/DG0628.html)
Weak branch unions Weak branch unions where branches are attached to a tree by a narrow angle with included bark. Certain trees (dwarf fruit trees, elm and maple) have a greater tendency to produce these types of branches. This narrow angle branch can also occur when bark grows between the branches, inside the union. This included bark is lacking structural strength, and may act as a wedge, forcing the branch union to split. Research on tree damage in wind storms conducted at the University of Minnesota since 1994 has shown that multiple leaders with included bark attachments, or any branch attachment with included bark, are the most common, pre-existing conditions associated with branch failures.
Early identification of forking, and tree stabilization is recommended to prevent complete breakage. There are two methods of stabilization: Cabling and bracing. Cabling is really recommended as a preventative measure. Bracing is rarely recommended any more due to the invasive nature and potential to encourage decay. Neither is ever recommended if the split/failure has occurred. Both function to create artificial support for structurally weak or injured trees and branches. Mechanical supports like these lessen the likelihood of prevent crotch and branch breakage, and subsequent stem decay. It must be stressed that some structurally weak trees (green ash, silver maple, cottonwoods) do not benefit as much from cabling or bracing. If the split has just begun and is relatively even, split portions can be held together and secured by steel bolt or threaded screw rod placed through the split section. If the split is severe, and the split portions cannot be held together, remove the more damaged or weaker branch by proper pruning methods, such as the drop crotch cut [How to Prune Trees (http://www.na.fs.fed.us/spfo/pubs/howtos/ht_prune/prun001.htm)]
Such severe pruning will require additional pruning to improve the aesthetic appearance of the tree. Do not paint wounds unless the tree in question is an oak or American elm, and the damage has occurred during oak wilt or Dutch elm disease infection period. Although the theory behind these practices is sound, to date, there is no published evidence that preventive practices such as bracing, or cabling reduces the potential of branch failure due to storm damage. Finally, it must be stressed that a tree with an existing crack and bracing installed after the fact is just an advertisement for a high-risk tree, and a magnet for liability lawyers.
After the removal, repair and/or cleanup of storm-damaged trees, you may wish to add new trees to your landscape. For a list of storm resistant trees and more information of storm damage, read "Trees and Ice Storms: The development of ice storm resistant urban trees" (http://www.ag.uiuc.edu/~vista/pdf_pubs/ICESTORM.PDF) For more information on storm damage, go to: Storm Damage to Landscape Trees: Prediction, Prevention,Treatment
Storms over the urban forest For a tutorial on preventing storm damage:
Finally, we would be remiss not to mention the brief on flooding and trees. This brief can be found at: http://www.extension.umn.edu/projects/yardandgarden/ygbriefs/p465floodstress.html Thanks to Gary Johnson for websites suggestions and additional assistance. *Hobbes=philosophic, stuffed tiger, of Calvin & Hobbs cartoon strip see: http://www.ucomics.com/calvinandhobbes/1991/07/01/ Please check out the new diagnostics web pages at http://www.extension.umn.edu/projects/yardandgarden/diagnostics/
