How can we increase the resilience of our forests?

As climate change accelerates, our forests are increasingly subject to disturbances that could lead to their disappearance. A researcher from the University of Quebec in Outaouais (UQO) proposes a management method based on diversity and the introduction of species adapted to future conditions in order to increase their resilience and, as a result, preserve the biodiversity that they host.

“Forestry here and elsewhere in the world has always tended to simplify forests to emphasize the growth of a few commercially valuable tree species, while assuming that climatic and biological conditions would remain constant” , recalls Christian Messier, researcher at UQAM as well as the Department of Natural Sciences and the Institute of Temperate Forest Sciences at UQO.

“But with global warming, everything is changing. The climate is changing so rapidly that the trees don’t have time to move through the dispersal of their seeds. They are therefore less and less adapted to the new climatic conditions. In addition, trade with China and Europe has contributed to the introduction of increasingly prevalent exotic insects and diseases that kill trees. What we observe almost everywhere are forests in increasingly bad shape with increasing mortalities,” he points out.

If we want to keep forests healthy, Mr. Messier believes that we have to start planting, in different regions, species that are better adapted to future conditions and above all to plant a wide variety of species.

The researcher has developed an approach based on “functional diversity”, ie the diversity of functions that trees perform in the forest ecosystem and the diversity of abilities to react to different types of stress. His team has identified five major functional groups in Quebec, each of which includes trees with the same specific biological characteristics, such as drought tolerance, deep rooting allowing them to resist violent winds or rapid growth.

His team demonstrated that forests that contain species from different functional groups maintain a greater diversity of organisms and are less the target of diseases and insect pests due to the presence of natural predators. In addition, since the different species have complementary light, water and nutrient needs, there is less competition between them, which makes them more vigorous and better able to resist stress.

“After a forest cut, we try to plant or promote the regeneration of species from different functional groups, with the idea that the greater the diversity, the more we will have a forest that will be able either to resist, or to to regenerate following all kinds of disturbances, even those that we have not yet foreseen. If there are trees that die, there will be others better adapted to drought, high winds or new insect pests that replace them. We will have a resilient forest in the face of possible disturbances. This ensures that we have forests for the future and maintain habitats for biodiversity,” explains the researcher.

But doesn’t such an approach risk changing the landscape? It is possible, concedes Mr. Messier, who faces certain detractors who prefer that we keep our forests as they are today. “But if we preserve a forest with trees that are ill-suited to the coming climate and are starting to die…” he replies.

The approach he suggests is not to completely change the forests, but to create within the natural forest “more diverse islands containing species better adapted to the expected changes and which will be well connected to each other”. Then, if the surrounding forests begin to die back, there will be new, better adapted species that can come in and maintain a functional forest habitat for biodiversity.

“If, fortunately, the pessimistic predictions do not come true, the natural forests will continue to thrive, because the landscape and the ecosystems will not have been completely modified. In a way, we want to vaccinate the forest against the changes of the planet”, specifies the researcher who proposes to apply his approach to 5% to 10% of the territory.

Moreover, the new species he plans to introduce are not exotic trees, but species found in North America, particularly in southern Quebec. For example, in a forest in the Outaouais where drought is predicted to become more frequent, Mr. Messier laid out patches in which he planted drought-tolerant species, such as oaks, pines, hickories and Caroline’s charms.

Will we witness the emergence of new biodiversity in our forests? “Maybe in 50 years we won’t have the same species at any given point, because species that are able to move, such as insects, birds and mammals, will have migrated elsewhere, but there are will be new and we will have maintained biodiversity,” says the researcher.

“People may not realize it, but in the forests of southern Quebec, about 20% of biodiversity is made up of species that have been established for a hundred years. Without realizing it, the diversity that surrounds us has always changed and continues to change. But this time, the human-induced changes are ultra-rapid, and I think that with my approach, we are helping nature to adapt to a speed of change that is uncommon,” he argues.

Mr. Messier first validated his development concept using simulation models to see how it evolves in the face of possible disturbances caused by climate change and potential epidemics of insects and diseases. Now all that remains is to put it to the test in the field. Eight major Canadian forestry companies have agreed to fund a Canada-wide project to adopt this approach in different forests across Canada.

“We intend to test our approach with the First Nations and the people who live in the region where it will be applied, in order to take their needs into account,” emphasizes the researcher.

This approach has also been well received in Europe, particularly in Germany, Belgium and France, which have experienced extremely dry summers in recent years. “Almost 30% of the trees in certain regions of Belgium and Germany have died of drought. We are developing approaches to reforest these forests with various species belonging to different major functional groups to ensure that no matter what disturbances occur, a forest habitat will survive,” says the researcher.

Mr. Messier will present his project to the general public as part of COP15.

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