Why did some trees topple in Saturday’s storm?

Jay Senter - July 26, 2017 7:54 am
The storm debris pile at Young's Pool in Overland Park had grown several feet high Tuesday. Photo via city of Overland Park.
The storm debris pile at Young’s Pool in Overland Park had grown several feet high Tuesday. Photo via city of Overland Park.

Since Saturday’s storm, many homeowners have been asking what made some northeast Johnson County trees prone to splitting or toppling over while others stood firm.

Dennis Patton, the horticulture agent at Johnson County K-State Research and Extension, said a variety of factors came into play to form “the so-called perfect storm that led to stately old mature trees falling over.”

Here are the variables that came into play:

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  • Saturated soils from recent rains. “Wet soil does not hold the roots as tightly as a dry soil,” Patton said. “[T]hink of the soil being slippery when wet. The roots move more freely. The other example would be pulling weeds from the garden. It is easier to pull out a weed by the roots after a rain when the soil is wet compared to dry soil.”
  • Strong winds causing movement, adding pressure. With bursts of 70-mile-per-hour winds, Saturday’s storms caused big swings of tree branches and trunks, with each gust adding pressure. “Each push and pull added stress to the roots,” Patton said. “Think of wiggling a post in the ground back and forth. It keeps working loose and eventually comes out.”
  • Water on leaves adding weight to the canopy. The torrential downpour that accompanied the storm soaked the thousands of leaves on each tree — and all that water added hundreds of pounds of pressure. “The canopy catches a lot of wind when dry but add the weight of wet leaves and this places more stress on the roots,” Patton said.
  • Weak root systems due to developed environment. Urban and suburban areas are not the ideal environment for trees. With shallow soils that have been compacted, trees can’t develop the deep, spread out root systems you see in undeveloped forest settings. “The root system is more shallow, closer to the surface,” Patton said. “Another factor [is] compromised roots from urban stress.”

Put the factors above together, and “at some point the weight and motion…wins out during a strong storm,” Patton said. “If you look at the trees that fell over the mound of soil uprooted was not that deep or wide.” (See below):

Photo courtesy reader Mark Read.
Photo courtesy reader Mark Read.
A downed tree in Overland Park. Reader submitted photo.
A downed tree in Overland Park. Reader submitted photo.

Patton also addressed the counterintuitive phenomenon of strong, hard-wooded trees like oaks suffering the most severe damage while weaker, soft-wooded trees like maples and ash mostly experienced relatively minor limb breakage.

“With the softer trees such as red maples, silver maples, ash and others the damage was limb breakage as they snapped off thus reducing the stress on the trunk and roots,” he said. “The wind broke out the limbs reducing all the factors described above. So the limbs breaking reduced the chance of being uprooted. In a calmer storm or not the perfect storm the oaks would have remained standing and the other soft wooded trees would have been all broken up.”

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