Something Else To Worry About: Droughts Can Make Tree Branches Break Off Spontaneously

Trees wilted by drought near Colchester, Vermont this
month. Another hazard was highlighted in
British Columbia: Repeated droughts can cause
trees and branches to spontaneously break off.

In British Columbia on July 31, a mother and her five month old son died when a tree fell on them while they visited a beach at Cumberland Lake Park campground on Vancouver Island. 

On August 10, also on Vancouver Island in British Columbia, a woman was injured when part of a large tree fell on her.  

In both cases, there were no storms, no strong winds. In both occasions, it was a gleaming, bright sunny day. 

So what happened?

It might have been drought. Per CTV News in Canada:

"A tree physiologist said that several years of repeated drought in British Columbia mixed with heat stress increased the likelihood of branches breaking off and this could even happen on a 'perfectly calm day' without any breeze."

Chances are the trees that caused the British Columbia tragedies had something else wrong with them besides drought. But the dry weather could have been a tipping point. Cumulative droughts tend to weaken trees more than one-offs, so that could have been a factor as well. 

Here in Vermont, the drought hasn't exactly been good for trees, especially those that turned brown, yellow or completely wilted in places where the soil has completely dried out. Examples include the now-sad, wilted, brown trees and bushes you see on the ledges along some of Vermont's Interstate highways. 

However, the risk of tree branches suddenly breaking off for no reason while you're at a state or local park are pretty low. But drought does appear to up the chances of that happening, at least a little. 

Vancouver Island has had repeated droughts in recent years, though the island is not currently especially dry for summer. 

Peter Constabel, a professor of biology at the University of Victoria, said he has seen branches of maple and oak trees just break off and fall on calm days during recent droughts.  

Per CTV News again: 

"It's just hot and dry for a long time, and the branch just breaks off. It's really kind of counterintuitive,' said Constabel, adding that the water in the cell walls in the old helps stabilize a weakened tree. 

Simon Fraser University biological sciences professor Jim Mattsson said he had recently witnessed big branches fall from a Douglas fir on Burnaby Mountain 'If some had been hit by that, that could be quite serious,' said Mattsson, adding that a prolonged period of drought can wear down even a Douglas fir, which is usually very drought-resistant."

Droughts reduce photosynthesis and growth, cut energy and sugar reserves and degrade defenses. All this creates a chain reaction that increases the risk of insect and fungal diseases, causing trees to rot inside.

That inside rot inside, increasing the risk of the tree or large branch breaking or falling over. 

Trees in urban settings are most at risk due to compacted soil, less access to water and hotter temperatures in a city's heat island. 

Climate change can make droughts worse, long lasting or more frequent, so this is an issue that will always be there. And it might get more frequent. 

Trees also lose leaves during droughts. That's why you see a lot of leaves on the ground here in Vermont even though it's only August, not October.  Trees try to conserve water during droughts by dropping leaves.  The fewer leaves on a tree, the less water they need. 

It's too soon to tell whether all this will have any effect on our fall foliage season.