Trees enduring heat and drought can lead to devastating outcomes

As the summer heatwave intensifies, trees across British Columbia are facing increased stress, with the potential of losing their lives within a year or two. The hotter temperatures are particularly challenging for Douglas fir, lodgepole pine, and western red cedar, which are more vulnerable to uprooting and inflammation due to repeated droughts and heat stress.

In urban settings, trees are even more at risk due to exposure to the sun, compacted soil, and weaker root systems compared to their counterparts in natural environments. Hikers are advised to be cautious, especially when passing maple trees and western cedar, as these species are susceptible to falling branches during drought.

Professor Jim Mattsson from Simon Fraser University's biological sciences department has observed the impact of dry spells on trees, explaining that they can weaken trees by reducing photosynthesis, growth, and energy reserves, lowering the production of chemical defenses. This vulnerability makes trees more susceptible to insects and fungal diseases, causing them to rot and potentially topple over.

The water in the cell walls of the wood helps stabilise a weakened tree, but if the drought continues, it can cause branches to break off. In a striking example, a mother and her five-month-old son were tragically killed by a falling tree at Cumberland Lake Park campground on Vancouver Island on July 31.

Professor Peter Constabel, a biology professor at the University of Victoria, has also witnessed the consequences of the drought. He has seen photos of fallen trees with signs of rot, and has observed branches of maple trees and oak trees falling off on the University of Victoria campus, even on a windless day.

On Aug. 10, another incident occurred at Pipers Lagoon in Nanaimo, where a woman was badly injured when part of a large tree fell on her. Constabel cautions that even professional arborists may not be able to predict which trees will fall during a drought, making it crucial for everyone to exercise caution.

While British Columbia is currently experiencing normal conditions, the repeated droughts of the past years have taken a toll on the trees. Even the usually drought-resistant Douglas fir can be weakened by prolonged periods of dryness. Mattsson, who has recently observed a big branch fall from a Douglas fir on Burnaby Mountain, warns that these weaknesses can make trees more susceptible to falling, even on a calm day.

As the summer continues, it is essential to be aware of the risks posed by stressed trees and to take necessary precautions when enjoying the outdoors.