The damage is impressive and heartbreaking. But don’t worry: the vast majority of trees will recover easily from the damage caused by this week’s ice storm.
First, when the ice has melted, the bent trees will rise. Broken branches will regrow quickly; in a few seasons, we will see nothing but fire. It is really only to trees with broken trunks — or uprooted ones — that we will have to say goodbye. “Our forest here in eastern North America is well adapted to icy conditions. All species have mechanisms that allow them to recover well. Unless they fall to the ground, of course,” says Christian Messier, scientific director of the Institute of Temperate Forest Sciences at the Université du Québec en Outaouais.
When frozen branches break and fall, it’s often “good news,” says Messier, who also holds the NSERC/Hydro-Québec Research Chair in Tree Growth Control. Indeed, by getting rid of this ballast, the trees restore their stability and are less likely to fall completely.
In general, trees that lose less than 30% of their leafy crown will recover quickly, without even their growth being affected. Trees that lose more branches—60%, for example—also have a good chance of surviving, but these individuals will be more vulnerable to disease and other hazards that may affect them.
“Trees have a squirrel-like strategy,” explains Messier. They always accumulate enormous reserves in their wood, in their trunk, in their roots, precisely in order to rebuild their tops following breakage or disease. Where you see a lot of fallen branches, I can guarantee you that in two or three years it won’t show at all. »
Prune large wounds
What to do with an injured tree? It is important to cleanly cut the large torn branches, the indentations that expose the heart of the tree to the outside world. “Gaping openings are more easily contaminated by fungi,” explains Jean Lamontagne, an entrepreneur from Quebec specializing in urban forestry.
This pruning does not need to be done right away: any time in the next few months will do. It is also recommended not to apply gum to the wound, as it can encapsulate moisture, increasing the risk of infection.
Not all essences are equal when faced with ice. The birch can bend a lot, but will still manage to get up without damage. Poplar is a naturally very brittle tree. The ash tree, if it is weakened by the borer, will break more easily. Due to their pyramidal shape, conifers are generally more resistant to sleet, but more vulnerable to strong winds.
After the great ice storm of 1998, Mr. Lamontagne went with a team from the Ministry of Forests to damaged sugar bushes to prune the broken branches. “These trees have lost height, yes, but they have finally recovered very well”, he observes 25 years later.
This week’s ice storm has nothing in common with that of 1998. At the time, we were talking about precipitation of up to 125 mm of freezing rain. Now we are talking about 25 to 30 mm of ice. Tree damage will therefore be contained, believe the two specialists.
City trees more sensitive
It should also be noted that trees in forests will do better than those in urban areas. “The forest is well made: the trees grow tight against each other, they hold each other back,” says Mr. Lamontagne.
In 1998, about 100 mm of ice rained down Mont Saint-Hilaire. Researchers from McGill University, who run a research station on this hill, found that 97% of mature trees had lost branches, and 35% had lost more than half of their crown. The recovery of this forest was quick: in just three summers, its canopy was restored.
In the city, trees are sometimes forced to grow askew due to buildings on their way to the sky. The pruning carried out by Hydro-Québec technicians can also tend to unbalance their shape, which makes them more vulnerable to ice.
Moreover, it is expected that incidents related to ice storms will become more frequent in our cities, because the trees there will be more and more numerous. In fact, most municipalities in Quebec hope to increase the extent of the canopy on their territory. There are good reasons for this: trees reduce heat islands, filter out some of the pollution and reduce the risk of flooding.
Mr. Messier, also affiliated with UQAM, has made this cohabitation with trees a line of research. In particular, he is developing a pruning protocol to be applied to young trees growing near electrical wires in order to avoid having to prune them when they reach maturity, which then makes them more vulnerable to the ice.