Winter storms that coat everything in layers of luminous ice leave a very beautiful but dangerous calling card. We know ice-covered trees are susceptible to breakage from the added weight. But if you take a look around, how do you know which trees are more likely to give in to the devastation of ice layers?
“There are a number of growth features that increase a tree species’ susceptibility to breakage in ice storms,” said Tchukki Andersen, BCMA, CTSP* and staff arborist with the Tree Care Industry Association. “Among them are: included bark, decaying or dead branches, increased surface area of lateral (side) branches, broad crowns or imbalanced crowns, and fine branch size.”
Included bark results from in-grown bark in branch junctions. This is a weak connection and increases the likelihood of branch breakage under ice-loading conditions. “As an example,” says Andersen, “Bradford pear branches are known to break during ice storms; this is because they commonly have included bark in branch junctions. In contrast, the Aristocrat pear has few branches with included bark and sustains less damage during ice storms.
Decaying or dead branches are already weakened and have a high probability of breaking when loaded with ice. The surface area of lateral branches increases as the number of branches and the broadness of the crown increase. With an increased surface area, more ice can accumulate on lateral branches; the greater ice load results in greater branch failure.
Many broad-leafed tree species, when grown in the open, form broad crowns (decurrent branching), increasing their susceptibility to ice storms. Examples include Siberian elm, American elm, hackberry, green ash, and honey locust. Trees with imbalanced crowns are also more susceptible to ice damage. Generally, though, susceptibility can vary greatly depending on the time of year, geographic location and overall health of the tree.
When planting a new tree, you should have a clear understanding of the size that tree is expected to grow. Is it too close to a house? The overhead wires? The sidewalk? Proper tree placement, away from structures, will reduce property damage. Trees should not be planted in locations where growth will interfere with above-ground utilities – branches that grow into power lines and fail during ice storms create power outages and safety hazards.
Trees pruned regularly from a young age should be more resistant to ice storms as a result of removal of structurally weak branches, decreased surface area of lateral branches, and decreased wind resistance.
After storm damage has occurred, hazardous trees and branches require immediate removal to ensure safety and prevent additional property damage. Trees that can be saved should have broken branches properly pruned to the branch collar (stubs and flush-cut pruning result in weakly attached sprouts and future insect and disease problems). Loose bark should be cut back only to where it is solidly attached to the tree. A split fork can be repaired through cabling and bracing.
Tree species resistant to ice damage reduce tree and property damage from ice storms.
Ice-resistant trees include:
Kentucky coffee tree
Swamp white oak