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Historically, our part of Illinois has been more prone to ice storms than the northern or southern part of the state.  Based on over 50 years of weather data from the Illinois State Water Survey, our area of Illinois (including Springfield, Bloomington and Champaign) is likely to have an average of 5 days of freezing rain per year.  Whereas the rest of our state will only receive an average of 3-4 days of freezing rain. 

Last week, we experienced freezing rain accumulation of about one tenth of an inch in my area of rural Monticello, along the Sangamon River.  Ice storms, by the meteorological definition, occur when ice accumulation is 0.25 in. or greater.  Larger ice accumulations (greater than 0.5 inches), can produce heavy damage in trees, especially when combined with wind.  So, what can you do to protect your property from ice storm damage?

Unfortunately, there is nothing we can do about the weather; ice accumulation will occur inevitably.  In order to assess potential property damage from ice storms, it helps to evaluate each large tree in your yard for potential “targets”.  Are there power lines under a large tree canopy?  Do significant limbs extend out over your home’s roof or the roof of other structures?  Do you have high value landscaping under the canopy of a shade tree?  If your tree is solitary specimen, with no would-be targets beneath it, perhaps the damage potential to ground level targets is little or none.

Professional arborists are training to assess the structural integrity of trees.  These tree experts use the many outward signs a tree provides to identify areas of internal defect and instability.  Arborists can often identify limbs with internal cracks and other weaknesses from patterns of bark, wood growth, or branch angle at the trunk.  Pruning can remove significant weight from the tips of limbs with weak branch unions (or other defects) to reduce the load upon weak or defective areas in the tree canopy.  In combination with pruning, limbs can be cabled or braced to provide addition support for a suspect branch union. 

Regular pruning should be part of any plant health care plan, especially for large, high-value shade trees around your property.  Pruning will not only keep your tree healthier, but also provides the best available preventative care for any type storm damage, including ice storms.

Wood fiber varies greatly among tree species.  Within the field of arboriculture, there is a significant body of research assessing various characteristics of wood fibers among species.  We know which tree species have stronger or weaker fibers.  We also know which wood fibers tend to bend and which tend to break. 

Certain tree species, such as Siberian elm, silver maple, willows and many species of evergreen, are prone to damage from ice storms due to the characteristics of their wood fiber and structure.   Professional assessment and pruning to increase structural stability is essential for trees that exhibit high susceptibility to ice storm damage.

It is important to note that evergreens are especially susceptible to ice storm damage simply due to the fact that these trees have a much greater surface area for ice accumulation.  Since they bear leaves over the winter months, evergreens have a lot more material for ice to accumulate on when compared to deciduous trees.  To further complicate things, many of these species also have more brittle wood fiber, which is inclined to break as opposed to bend.  Therefore, it is especially important to assess evergreen trees with significant targets beneath them.

Although severe ice storms can cause substantial tree damage, they are relatively rare in central Illinois.  Areas in the Midwest typically experience a large ice storm once a decade, so it may not be necessary to carefully assess every tree on your property.  However, preventative actions such as pruning, mulching and other plant health care practices can make a weighty difference on your tree’s resiliency to ice damage.