WASHINGTON — When storms strike, one of the biggest concerns that some people in the DMV have is falling trees. A survey of residents in Fairfax, cited this as a concern on a recent environmental survey. If winds are strong enough, trees may be uprooted landing on cars or homes. Also, if grounds are saturated from rain and there are strong winds, the combination could make it easier for some trees to fall.
Is the wind strong enough to make my tree fall?
Estimates strength of wind versus potential impacts can be found using a Beaufort number. The Beaufort Wind Scale goes from 0 to 12 and estimates potential impacts on land and sea. It was created by Britain's Admiral Sir Francis Beaufort in 1805. He developed the scale to help sailors estimate the winds.
Overall, trees can withstand wind, but the health and type of tree play a role. Winds of 39 to 46 miles per hour are strong enough to break twigs and small branches. Stronger winds 47 to 54 miles per hour could cause damage to chimney covers, roofing tiles, small twigs and broken branches are also likely, based on the Beaufort Wind Scale.
Typical wind speeds that can be strong enough to knock over a vulnerable tree are between 55 and 63 miles per hour on the Beaufort Wind Scale. Damaging wind from violent storms can uproot even the healthiest trees, as some of these winds could be upwards of 100 miles per hour.
However, Daniel Coy, Urban and Community Forestry for Maryland's Department of Natural Resources said that it's not just about the wind when it comes to trees falling. It's about several variables including the health of the tree, proximity to other trees, even whether or not the trees have leaves on them.
"Evaluating a tree's risk of falling is very complicated and given the impacts of tree failure, one should not guess at their stability," Coy said. "There's no set wind speed that will take a tree down because all trees are different and have grown to adapt to the winds that they have been exposed to, but sometimes, like when an adjacent tree is removed the amount of wind that a tree receives can increase significantly," Coy explained.
How can I tell if a tree is going to fall?
Experts at Jenkins Restorations noted that you should watch for signs of trees that are compromised such as broken branches, missing bark, fungus on roots, or cracks in the trunk. Coy said the best time to prevent a tree from falling is before the storm, by making sure the tree is healthy and cared for.
"Factors like rot, fungi, and just if the trees have leaves on it increase the likelihood of failure in wind. In general, if one is looking at a healthy tree and normal wind, should include normal seasonal storms, there shouldn't be much concern for failure."
Coy said that having leaves on a tree could make it more prone to failure in wind, because the leaves almost act like a sail on a boat when exposed to wind.
"The leaves of a tree make up a lot of the surface area of its crown, so when the wind blows, it applies pressure mostly to the leaves," Coy said.
For trees that lose their leaves seasonally, there's not as much wind pressure.
"There's a lot less wind pressure applied to them when the leaves are off, which in turn means that any particular tree will need higher winds to bring it down when its leaves are off," Coy explained.
After a tree falls
After tree falls, safety is a big issue. Coy recommends calling in an expert, like a certified arborist to help with removal and clean up. Those impacted should be careful to avoid electrical wires that may have come down with the tree. Coy said pressure could be trapped in branches and logs. And while rare, he said to be mindful of the smell of a gas leak.
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