Whenever powerful storms blow through north Georgia, tree removal services and insurance companies often have plenty of work to do. When a tree branch fails or a tree becomes uprooted, clients often call the Extension office wanting to know why it happened and what went wrong. Examining storm-damaged trees can provide many insights into why trees fail during windstorms.
Two of the most common forms of tree damage during windstorms are limb breakage and wind-throw. Major limbs often fail when heavy wind loading occurs to multi-stemmed trees or trees with narrow, vertical branches. Branches and stems that grow close together are structurally weaker than branches or stems that grow at wider, more horizontal angles. Over time, included bark becomes trapped between narrow, vertical branches and stems.
As the tree becomes larger, this bark inclusion acts as a wedge, forcing the branches further apart. Eventually, the right wind comes along and pushes the branches or stems just far enough apart to split the wood. When planting new trees, select only those trees that have one main stem and wide branch angles (45 degrees or wider). Also, be sure to correct any narrow, vertical branches and co-dominate stems with proper pruning and training while the trees are young.
Soft-wooded, fast growing trees, such as willow, silver maple, ‘Bradford’ pear and edible pear species, tend to have very weak, narrow branches that grow vertically. These species are generally considered short-lived since they have a tendency to self-destruct around twenty years old. These species are also prone to wood rot and are often the types of trees with the most “failure” in windstorms. You should avoid planting these types of trees close to your house or near high traffic areas.
When trees blow over, roots and all, it is often referred to as wind-throw. Wind-throw is typically associated with trees that have shallow root systems. For example, in the recent storms we noticed many Leyland cypress trees that were wind-thrown. Wind-throw is also common when high winds are accompanied or preceded by heavy rains. When the ground is saturated and the soil becomes soft, trees are easily up-rooted.
Shallow root systems may be the result of compacted soils, shallow (frequent) watering, and limited soil volume adjacent to walls, foundations, driveways, sidewalks, and parking lots. Trees can also be uprooted and blown over because of root damage due to soil excavation, the use of heavy equipment over the tree’s critical root zone, or trenching for utilities. Avoid planting trees in areas that have limited space for root growth and protect trees from construction damage.
Many large, older trees develop internal wood rot, compromising the structural stability of the tree. Wood rot in landscape trees is often the result of poor pruning practices in the past, especially “topping” and other bad pruning cuts (such as leaving branch stubs) that create open wounds for extended periods. These open wounds allow water to penetrate the tree’s wood, which invites wood rot and wood decaying fungi. By the time you see conks or mushrooms growing on the tree trunk or root flare, then the tree is in advanced stages of decay and there is a concern for possible tree root or stem failure.
It takes years for infection and growth of the fungus in the wood to produce outward signs of conks and mushrooms. There is no cure for wood decay. When decay fungi are present, it’s only a matter of time before they compromise the strength of the tree’s stems or roots and eventually cause the tree to break or fall. With recent rainfall amounts and saturated soils, we recommend keeping a very close eye on these types of trees for any shifting of the root plate and soil cracks that might indicate impending root failure for as long as these trees remain standing. Eventual tree removal is recommended.
If you have big, old trees on your property, you should consider consulting a certified arborist regarding their soundness and stability. If a tree is determined as hazardous, a certified arborist will recommend removal or selective pruning to diminish the hazard. You can locate a certified arborist online at www.isa-arbor.com.
Paul Pugliese is the Extension Coordinator and Agricultural & Natural Resources Agent for Bartow County Cooperative Extension, a partnership of The University of Georgia, The U.S. Department of Agriculture, and Bartow County. For more information and free farm, lawn, or garden publications, call (770) 387-5142 or visit our local website at ugaextension.org/bartow .