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Trees feeling stress of the summer sun

Lower than average rainfall impacting trees



Some Whistler trees are stressed out.

It has been drier than usual this summer and that is causing drought and making some area trees vulnerable, according to Whistler arborist Paul Duncan. It also makes the surrounding forest more vulnerable to wildfire.

According to Environment Canada, it is too soon to say if this will be one of the driest summers on record in the municipality, but June and August (so far) were quite a bit drier than normal.

June saw 35 per cent of the normal amount of precipitation. July was fairly typical with 85 per cent of normal precipitation, but August has been very dry with about 1.5 mm of precipitation so far this month. The normal for August is 47.5 mm.

But trees are feeling the pain already.

Trees handle drought differently depending on the species, area, soil texture and other variable conditions.

In terms of species, the western hemlock is particularly susceptible.

"If you open up a forested area and it has a lot of hemlocks on it, you will often see them perishing from drought stress," said Duncan, who owns Garibaldi Tree & Landscape.

Thin-barked trees, such as aspen, birch and cottonwood are also more susceptible.

More established indigenous conifers —pine, fir, spruce — are better able to withstand a moderate degree of summer drought, but, prolonged drought stresses all trees, Duncan said.

Across the board, trees in areas where there are new developments are showing more stress, because the trees don't take well to the transition combined with drought.

Thin soil also makes all trees more susceptible.

Duncan said one of the Whistler areas seeing the most overall tree stress is Emerald Estates, where there isn't a lot of soil to begin with.

"That is where you will see the lodgepole pine getting really stressed because they just don't have the moisture in the soil," he said.

Signs of a tree that is too dry include wilted and scorched leaves and obviously dry soil at the base. To check the soil, dig down about 15 to 20 cm. The soil should feel cool and a little moist.

Healthy trees usually have new leaves or buds, some twig growth and no sign of dead leaves at the upper part of the tree.

Trees that are too dry are often more susceptible to insect attack, such as pine beetle.

Duncan said a telltale sign of the pine beetle are the little "pitch tubes" — popcorn-looking blobs of resin on the trees trunk — which mean the tree is trying to rid itself of the pest.

Most people think to water their plants and shrubs, but assume mature trees can be left to nature, but that isn't the case with extended dry periods, Duncan said.

Trees should be watered deeply, but not frequently — three to five cm of water per week, depending upon the texture of the soil.

All trees need to be properly mulched as mulch helps keep soil cool in the summer.

Healthy, hydrated trees are also less vulnerable to wildfire and so protect humans and property.

In addition to irrigating trees and plants, Duncan recommends getting vegetation away from the home.

"In terms of cleaning up around your house, getting rid of the fallen matter on the ground, raising the canopy on the trees, cutting trees back and removing trees that are within two or three metres of the house," he said.

He said starting from scratch, planting deciduous trees, such as maples, which are less flammable, makes sense.

For more information on landscaping in a FireSmart way, go to and search "firesmart."


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