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Why are so many trees falling during storms?

A large tree fell in a yard at a home on Country Way in Scituate, after a strong storm the night before.
A large tree fell in a yard at a home on Country Way in Scituate, after a strong storm the night before.Jonathan Wiggs/Globe Staff

After downed trees from Wednesday’s storm led to widespread power outages across the state, arborists said Thursday that trees can be under stress for a number of reasons, making them more vulnerable to such wind events.

Climate change, droughts, storms, invasive species, and disease are just some of the factors that threaten the health of trees.

Drought has had a negative impact on trees across Massachusetts, according to Russell Holman, an arborist from Arborway Tree Care of Hyde Park who serves on the board of the Massachusetts Arborists Association.

“It’s not just a one-year drought,” said Holman. “They’re losing roots.”

Most of Massachusetts is currently under severe or extreme drought conditions, according to the US Drought Monitor. The monitor has reported that since 2000, the longest duration of drought in Massachusetts lasted 48 weeks, from June 2016 to May 2017.

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Holman said dry seasons from previous years have weakened the roots of many trees, leaving them more vulnerable to high winds. Higher temperatures are also causing certain trees to move further north.

“Climate change is having a huge impact on these trees," said Holman. “With the weather being the way that it is, there’s more stress on the plants. We’re seeing hotter temperatures in the summer that trees aren’t adapted for."

Pests and disease can also be detrimental to the health of trees. An invasive insect known as the emerald ash borer is “wreaking havoc on native ash trees,” Holman said.

On Wednesday, Holman was proctoring an arborist certification exam at the Elm Bank Reservation in Wellesley when the wind outside began to pick up, he said. He looked out the window at a large sugar maple tree and began to worry that it might fall victim to the storm.

“We all cringed,” he said. “We all get nervous when we hear weather like that’s going to happen.”

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Many trees suffered that fate late Wednesday afternoon, as wind gusts of more than 55 miles per hour were reported in locations across the state. Some gusts hit 70 miles per hour, officials said.

From Falmouth to Fitchburg to Foxborough, trees toppled to the ground. Some blocked roadways. Some fell onto cars.

It made for a busy day for Mike Lueders, an arborist at Lueders Environmental Inc., a company based in Medfield that specializes in tree maintenance and care.

Whenever meteorologists predict strong winds in the weather forecast, “we don’t like it,” Lueders said.

Lueders said the number of high-wind events in the last nine months has brought down many trees and the lack of rainfall hasn’t helped.

“Certainly drought is changing the structure of the wood, because the wood of the tree has less moisture in it,” he said.

Without enough water, the root systems of trees begin to atrophy and die. Less water in the soil also makes trees more susceptible to falling down, he said.

“When you take water out of the soil, it gets lighter and there’s less anchoring going on,” Lueders said.

Laws and policies that protect trees have also left us with taller trees that are more mature.

“We’re protecting more space, and trees are getting taller,” Lueders said. “As they get bigger, decay occurs in a heavier, taller tree.”

Trees on streets and in residential developments are more susceptible to being felled by powerful winds. Street trees may not have fully developed root systems, and a tree that is planted in soil that has been compacted by construction vehicles won’t have the same stability as a tree that grew naturally in the forest, he said.

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Trees that stand on their own are also more vulnerable to winds.

“In a forest of trees, the trees buffer each other. Each diffuses the wind,” Lueders said. “If you cut a hole in the forest ... the trees left behind have never been able to stand on their own like they would in a forest.”


Emily Sweeney can be reached at emily.sweeney@globe.com. Follow her on Twitter @emilysweeney.