This text is part of the special Research section: climate issues
More intense and more frequent fires are just one of the many perils that threaten our forests, affected by climate change and increased international trade. Their resilience requires a new approach to planning.
The gigantic fires that ravaged different parts of Canada this summer captured the imagination. As of August 29, more than 15 million hectares of forest have burned, according to the Canadian Interagency Forest Fire Center, an area larger than Portugal and the Netherlands combined. According to the World Weather Attribution network, global warming has made extreme weather conditions (high temperatures, low humidity) seven times more likely, which have favored the spread of these fires in the east of the country.
Generally, boreal forests regenerate quite well after fire. However, climate change could put this capacity to the test by causing more intense and, above all, more frequent fires. “Let’s take the example of a boreal forest in Abitibi, which would suffer two major fires in 20 years,” says Olivier Villemaire-Côté, assistant professor in the Department of Wood and Forest Sciences at Laval University. Trees that began to grow after the first fire will not have had time to reach sexual maturity, which may result in a failure of natural regeneration after the second fire. »
Climate change can also increase the frequency and intensity of other events destructive to forests, such as high winds and icy episodes. In addition, other risks threaten them, notably insects and fungi. We have already seen the damage that can be caused by insects such as the emerald ash borer, a beetle from Asia, or Dutch elm disease, caused by a fungus.
“It is predicted that between 20 and 30 diseases or insect species could come back from the United States to us in the next 30 years and threaten up to 40% of our tree species,” warns Christian Messier, professor in the Department. of biological sciences from the University of Quebec in Montreal. So what we see with ash, elm and beech is just the beginning. »
Forests that are too homogeneous
Our commercial forests would be particularly vulnerable to these various risks due to their excessive homogeneity. “This is really the crux of the problem,” underlines Olivier Villemaire-Côté. Over the years, we have artificially reduced the diversity of several forests by always replanting the same species after logging, such as spruces or pines. If a pest came along and attacked one of these species, we could lose the entire stand at once. »
This trend towards homogenization comes partly from the industry, which tends to replant the trees it exploits commercially, but also from the laws and regulations which govern the forest. These require companies to replant species similar to those they cut, in order to ensure the sustainability of the resource over a period of 150 years. An outdated vision, according to Christian Messier and his colleague Olivier Villemaire-Côté, who both call for cutting and forest management to be used to maximize the diversity of species according to their ability to resist different risks. This is called functional diversification. Not only do we need to plant a lot more trees, we need to do it smarter.
Christian Messier is also beginning a vast five-year research project, funded by the Natural Sciences and Engineering Research Council of Canada, several forestry companies and provincial ministries. It will test its diversification approach at 21 sites across Canada. Its approach consists first of evaluating the forests to identify the species that make them up and the risks that threaten them.
This then makes it possible to select certain species that could be introduced to promote functional diversification. This could, for example, lead us to plant species that respond more effectively to forest fires, such as jack and red pines and poplar, in areas vulnerable to fire or to better distribute currently highly concentrated species across the territory. , such as sugar maples in southern Quebec.
We are not the only ones thinking about these questions. In Germany, in particular, years of severe drought have hurt monocultures of Norway spruce, the most important species for the timber trade in this country. It is now seeking to diversify its forests.
“We can no longer continue as before in Quebec and Canada,” warns Christian Messier. We need a very ambitious plan, otherwise we could see forests disappear entirely. »
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