AMES, Iowa — Stormy weather frequently damages trees throughout Iowa. In most cases, the extent of tree damage isn't due to the luck of the draw.
According to Richard Jauron, Iowa State University Extension horticulturist, certain tree species are much more susceptible to storm damage than others. For example, silver maple, Siberian elm, willow and green ash are quite vulnerable to strong winds. Oaks, lindens and sugar maples are less susceptible to storm damage. In addition to tree species, the age of the tree, its condition and maintenance history also determine the extent of storm damage. Large, old trees with a structural weakness, such as some trunk decay and those with narrow branch angles are particularly susceptible to damage. No tree species can withstand the fury of a tornado.
Assessing storm-damaged trees
Carefully examine trees to determine the extent of damage. Give immediate attention to trees that are hazards to people or property. If a power line is involved, utility company personnel are the only ones who should be working in the area. After the elimination of hazardous situations, individual tree care can be assessed.
Storm damage to a tree can vary from a few small broken limbs to complete destruction. Severe damage to the main trunk often warrants removal of the tree. Trees that have sustained major trunk damage are no longer structurally sound and may come down completely in the next storm. Trees that have the majority of their crown destroyed are probably not salvageable.
Caring for storm-damaged trees
When pruning damaged trees, use correct pruning techniques to minimize the size of the wound and avoid flush cuts. Remove stubs by pruning back to an undamaged side branch, main branch or trunk. Generally, pruning paints are not necessary. However, wounds that occur on oaks between March 1 and July 1 should be painted to reduce the potential transmission of the fungus responsible for oak wilt. When painting pruning cuts on oak trees, use a latex house paint rather than asphalt or creosote-based paints.
The pruning of large branches and damaged branches high in the tree canopy should be left to trained arborists. Cabling and bracing may be appropriate if the cost involved can be justified. Cabling and bracing do not save trees that have suffered extensive structural damage.
Tree removal and replacement
If tree removal and replacement ends up being your only alternative, Jauron recommends selecting tree species and cultivars with a sturdy reputation. Excellent maple species include black and sugar. Oak species for Iowa include white, swamp white, bur and red. Linden (both American and littleleaf), American hophornbeam and ginkgo are other possibilities. Selection of a sturdy tree species alone will not ensure a strong tree. Proper pruning when small is imperative.
ISU Extension publications contain additional information on caring for trees damaged during storms:
Managing Storm-damaged Trees – Sustainable Urban Landscapes (SUL 6); Choosing an Arborist (RG 214); Pruning Trees: Shade, Flowering, and Conifer – Sustainable Urban Landscapes (SUL 5); and Understanding the Effects of Flooding on Trees – Sustainable Urban Landscapes (SUL 1) can all be downloaded from the ISU Extension online store.