Hot, dry summer takes a toll on trees

The hot summer weather and lack of precipitation is taking a toll on the urban forest in Calgary and will have consequences for years to come, an arborist warns.

Matthew Davis says this is the hottest summer he can remember since he started working as an arborist in the city in 2000.

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Heat reduces a tree's ability to hydrate itself, because pores on the bottom side of the leaves close up as temperatures rise, he explained.

Immediate signs of tree heatstress include wilted leavesor brown or rust spots on the leaves, but the full effects may not be seen for three to five years, depending on the tree species, Davis said.

"We'll start to see some interior deadwood, especially in evergreen trees and stuff like that where they start to give up on some of their branches due to the stress they're suffering through right now."

That in turn can make trees weaker and more prone to insect attacks and disease, he said.

Trees that are particularly susceptible to heat stress include "heavy feeders" that typically require more water, such as Calgary's poplars and Manitoba maples.

How to help

"Trees, just like any other plant, need water, and this year we've had almost none for the last 30 days or more," saidNikki Anguish, acting urban forestry lead for the City of Calgary.

She said the best thing people can do to help the urban canopy is water their trees.

Trees, within their first three years, requireabout 30 minutes of water every week at a very slow drip, which encourages good saturation of the soil, Anguish said.

After the first three years, trees should be watered for about half an hour every two weeks at the dripline, or the furthest point that the branches of the trees reach.

Davis said the best thing to do is water at night, when trees are better able to absorb water than they are during thehottest parts of the day.

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