2024-02-02 21:06:24
How can we reconcile our need for trees in the city with the proximity of electrical wires? For more than a decade, researcher Christian Messier has been testing new pruning methods.
Reduction of heat islands, better water flow, benefits for human health: the services provided by trees in cities are countless. But the urban forest requires regular maintenance, in particular so as not to interfere with the electrical networks.
The Hydro-Québec Chair on the control of tree growth is conducting research to review current pruning practices, criticized by the scientific community for their lack of effectiveness and scientific basis. She saw her mandate renewed in February 2023, for the second time. Interview with Christian Messier, Chairholder and professor in the Department of Biological Sciences at the University of Quebec in Montreal.
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Photo: Annick St-Denis, ArbrenVil Chair.
Québec Science We know that proximity to trees can cause damage to electrical wires. And the pruning techniques used to reduce risks are questioned by numerous studies.
Christian Messier Indeed, Hydro-Québec would prefer not to have large trees under the wires, but we need them in cities for all kinds of reasons, notably to reduce heat islands. However, when we prune without taking into account the growth of the tree, as is currently done, it will grow back as quickly as possible. It produces numerous discharges [de nouvelles pousses] to maximize its light capture. The more we cut it, the more there is a need to cut.
QS How do you work at the Chair to improve these pruning techniques
CM We start from the idea that it is preferable to intervene earlier so that the branches grow spontaneously away from electrical wires, and to reduce the need for recurring pruning. A dozen years ago, we planted 400 tall trees in a field in Saint-Bruno. They belong to the 6 large functional groups of trees found in the city [ces groupes sont fondés notamment sur la silhouette de l’arbre, sa vitesse de pousse, le mode de dispersion des graines, etc.]. We test different pruning approaches before the tree reaches the height of the electrical wires, to see if we can prune while maintaining the biomechanical stability of the branches, to minimize the risk of falling.
QS What are your possible solutions?
CM We are testing several. The first, classic, consists of continually pruning the young tree so that it develops two main branches with an angle of 45°, in order to obtain a fork which “naturally” avoids wires. We also use a metal structure, which is left in place for 5-6 years, which mechanically induces an angle of 45°.
The third approach arises from my observations in the undergrowth. When trees seek light, they tend to reduce the growth of their terminal spire and instead grow sideways. For two years, we have been testing a sort of opaque fabric cap placed on the spire of the tree, which reduces the light received a little and encourages the tree to redirect its resources towards the lateral branches.
QS You are also banking on LiDAR technology, within the “Arbrenvil” project. What does it consist on?
CM In collaboration with the Quebec mobile mapping company Jakarto, we collect LiDAR data on trees in Montreal [les impulsions laser de l’outil permettent de numériser la géométrie de l’arbre]. The idea is to detect which trees really need to be pruned, to carry out targeted preventive interventions rather than systematically pruning all the trees on a street or neighborhood every 4 or 5 years.
We are developing artificial intelligence algorithms, with my colleague Marie-Jean Meurs, which will help us see which trees have a more fragile structure.
In this sense, the 2023 ice storm was a blessing for research, because we had just collected data on thousands of trees. Jakarto returned just after the storm to see which branches had fallen, and to try to determine in retrospect whether it could have been predicted. In the same way that we use technologies to do precision agriculture, I think we can also move towards high-precision forestry.
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