Heat, drought causing tree limbs to suddenly drop

WESTON, Mass. — Last week, an oak along Wellesley Street suddenly lost half its mass.

In Portland, Oregon, an oak tree recently shed a fifteen ton portion of itself — with no warning.

In both cases, no one was hurt or killed — but the potential was certainly there.

What the two coasts have in common this summer: heat waves that have just hung on and on. And that is likely contributing to the strange, unpredictable and ultimately frightening phenomenon — of trees suddenly losing limbs.

“I guess scientists don’t know exactly what causes the limb to suddenly break and fall off,” said Leo Simkins, a certified arborist and owner of Simkins Tree Service in Holliston.

While there are a few theories, Simkins believes it has to do with a lack of moisture in the tree itself.

“As cells in the wood start to dry out, they shrink and are less flexible,” he said. “It reaches that point where the flexibility isn’t there... and boom... it breaks right off.”

Simkins likens it to the difference between a board soaked in water, and used to construct rounded surfaces — such as with a canoe — to a dried-out piece of wood which, if bent, snaps.

While there is an element of unpredictability to such snapping, Simkins said a certain type of branch structure seems more vulnerable than others. That would be the long, horizontal limbs — especially those carrying weight at the end.

“In good conditions, that limb was able to hold that weight up and flex with it,” Simkins said. “But then, all of a sudden, a drought comes and you lose all that moisture in a branch. And it just can’t hold that up and flex with it.”

And, to be sure, Simkins said many trees are suffering dryness this summer.

“I would say this is one of the most extreme droughts I’ve seen in my close to twenty years in business,” he said. “We’re even seeing invasive species that normally thrive over our native species and they’re wilting. And you can tell the understory trees are suffering and the leaves are curled up. Everything is wishing for some water.”

The trees suffering most, he said: older, more mature ones.

“They lose a lot of their fine, root hairs,” Simkins said. “The root system is built up of different size roots. You have the big anchor roots, the smaller fine roots, then you have root hairs that actually absorb the water and nutrients. When it gets really dry out, the tree starts to lose those fine root hairs.”

Not only does that mean less water and nutrients getting absorbed, but the tree loses part of its anchorage to the soil.

“So what we also see in these big droughts is you’ll get a small windstorm that a tree could normally stand up in,” Simkins said. “But now a wind comes through and it uproots the tree because it just doesn’t have the holding capacity to the soil.”

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