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In 2018, from Wisconsin to New Brunswick, balsam fir trees turned bright red and died on their feet without anyone understanding why. Although an insect and a fungus were suspected, no one responsible could be formally identified to explain what scientists call the sudden death of the balsam fir. In an article published this fall by the journal Frontiers in Forests and Global Changethree researchers who revisited the case offer a new suspect: climate anomalies that occurred in 2017 and 2018.
Two reasons pushed this team towards this path. “On the one hand, a phenomenon which occurs synchronously over such a vast territory leads us to suspect a climatic effect which manifests itself on a large scale. On the other hand, we know that the balsam fir is a species more sensitive to lack of water than the other trees with which it coexists,” explains the head of the study, Loïc D’Orangeville, professor in the Department of Science of wood and forest and researcher at the Forest Study Center at Laval University.
New Brunswick was particularly affected by the sudden death of the balsam fir in 2018. Aerial inventories carried out in this province revealed that 115 development sectors had been affected. In 15% of these areas, fir mortality was between 6% and 30% while it exceeded 30% in 3% of the areas.
The sudden death of the balsam fir would result from water stress that hits trees already engaged in the “death spiral” due to insects or diseases. (WISCONSIN DEPARTMENT OF NATURAL RESOURCES/Provided by Laval University)
To test the climate anomaly hypothesis, Professor D’Orangeville and his collaborators James Broom and Anthony Taylor, from the University of New Brunswick, collected monthly climate data for the period from spring 2017 to spring 2018 in the areas affected by sudden fir mortality in New Brunswick. They then compared them to those recorded in the same areas between 1950 and 2018.
The results? The 2017 fir growing season was characterized by unusually low precipitation and unusually high temperatures. In addition, the following spring, the depth of snow on the ground in April was higher than normal and temperatures in May were above average, two factors which would have contributed to the drying out of the fir trees.
“The prolonged presence of snow keeps the ground cold. The water there remains near the freezing point, which makes it difficult for fir trees to access. Under these conditions, water losses caused by high temperatures in the foliage cannot be compensated for,” explains Loïc D’Orangeville.
Interestingly, the same climatic anomalies were observed in 1986, another year marked by sudden and inexplicable fir die-off in New Brunswick. Using climate data from 2017 and 2018, the three researchers developed a model that makes it possible to locally predict the probability of fir mortality. “We tested our model using climate data from 1985 and 1986. The mortality projections from our model agree 95% with what happened on the ground,” summarizes Loïc D’Orangeville. Our model could therefore be used to predict which areas are likely to be hit by the sudden death of the fir during the year following an abnormally dry summer.”
“Our model could therefore be used to predict which areas are likely to be hit by the sudden death of the fir during the year following an abnormally dry summer. »
— Loïc D’Orangeville
If the climate is to blame, how can we explain the presence of dead fir trees alongside green fir trees? “Climatic anomalies affect all trees, but their repercussions are especially felt in trees already weakened, among other things by the action of insects or fungal diseases,” replies the researcher. Trees most often die from a combination of causes. The phenomenon by which a succession of events progressively weakens a tree is called the death spiral.
In forests and Christmas tree plantations
According to the researcher, this study is the first to document a case of massive tree mortality attributable to drought in the forests of eastern Canada, a region known for its abundant rainfall. Climate change models predict that the conditions that favor the sudden death of the balsam fir will occur more frequently in the coming decades, which does not bode well for the king of the forests.
The balsam fir likes humid conditions and that is why it is mainly found in the forests of eastern Canada. Its needs are the same in Christmas tree plantations. The warmer temperatures and drier conditions observed in recent years have affected fir producers to the point where some are considering the installation of irrigation systems, underlines Professor D’Orangeville.
“Due to projected climate changes, more monitoring of insects and diseases will be required, and more maintenance work to keep balsam firs healthy, which could have an impact on their selling price,” he says. -he. We could also see the replacement of the balsam fir by parent species more resistant to hot and dry conditions.”
