[LUM#21] We Won't Go to the Woods Anymore
For a long time, storms have posed the greatest threat to France’s forests. But over the past twenty years or so, another threat has loomed over their future, forcing us to face a painful reality: not only will the forest not help us combat climate change, but worse still, this change is already killing it.
“We are seeing a 50% increase in tree mortality and a decline in tree growth. Based on current projections, by the end of the century, the forest in southern France could give way to a wooded savanna. In the north, competition for water will thin out the stands,” notes Isabelle Chuine, a researcher at the Center for Functional and Evolutionary Ecology1 and coordinator for the Academy of Sciences of a report on the state of French forests.
Drought is one of the first lethal consequences of climate change for trees (Climate Change and the Biosphere). “When it gets hotter, evaporation and transpiration from trees increase, so the water stored in the soil is released into the atmosphere more quickly, leaving them with fewer water resources available.” This trend is exacerbated by declining rainfall, which affects many regions of France to varying degrees.
Extensive damage
Equally linked to climate change is the increasingly frequent occurrence of early heat waves, as was the case in June 2019.“Even the Mediterranean forest, which is particularly well-adapted to such phenomena, has suffered considerable damage” (The fertility of the holm oak is not adapting to a drier world), the researcher recalls. The reason: the specific biology of these evergreen species, which do not shed their leaves in winter and produce new foliage later in the season.“This adaptation allows them to avoid late spring frosts. But if a heatwave strikes before the leaves have reached maturity, they won’t be able to withstand these temperatures as they would have in the middle of summer.”
Drought and heat waves trigger an immediate response in trees, whose leaves are equipped with stomata. These tiny pores open and close to capture the CO₂ essential for photosynthesis, but they also allow water to escape.“During a drought, the leaves close their stomata to conserve water. But in doing so, they no longer absorb CO2 and therefore cease photosynthesis,” explains Isabelle Chuine. If the drought persists, the leaves—and even the branches, or the entire tree, depending on the severity of the event—will die. The survivors will emerge weakened and become prime targets for pests and pathogens. Not to mention wildfires, which are also fueled by drought.
The laurels have been cut
Another threat is beginning to emerge: warmer winters.“In our latitudes, a tree produces new leaves and flowers in the spring, fruit in the fall, and then sheds its leaves,” the specialistexplains . This fall, in the Massane beech forest in the Eastern Pyrenees and in the Puechabon forest, scientists observed a massive burst of bud break in the fall. In 2015, massive blooms in the fall were also observed throughout France. “This is extremely risky behavior because these young leaves do not survive the winter, and the flowers do not produce fruit, which is a net loss for the tree. All these situations will become increasingly frequent by the end of the century.” (Understanding the multiple effects of climate change on the timing of leaf emergence) How can we even think about fighting climate change with forests that are dying?
French forests currently store nearly 3 gigatons of carbon, but the carbon sink they represent has been cut in half in just over a decade,“and if we look region by region, many are no longer carbon sinks.” The political response so far has been an increase in harvesting, in other words, logging. “ The national low-carbon strategy in France was built on the idea that, since the forests were going to die anyway, it was better to harvest them and store the carbon from the trees in long-lasting wood products, then replant more resilient species.The problem is that only 3% of the harvested wood is currently being turned into long-lasting wood products .”
Life-size
Another approach is to let nature take its course. Diversifying the tree species and genetic makeup of forests to make them more resilient is one possible solution.“No one really knows if we’ll be able to preserve the forests as we know them in certain regions. Because we failed to anticipate this situation despite warnings from scientists, we are now conducting a real-world experiment,”concludes Isabelle Chuine.
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What would the profile of France’s mainland forests look like?“They cover roughly 30% of the country and are three-quarters privately owned, ” explains Isabelle Chuine.“Two-thirds are hardwoods, compared to one-third softwoods.” Among the most common species areoak “and even very old oaks,” beech, and spruce in the northeast, as well as maritime pine, which is very prevalent in the Landes region—now France’s largest forest area.
French forests are characterized by their composition of even-aged stands.“It’s a centuries-old practice that has been added to the national inventory of intangible cultural heritage. It’s the image of a forest with tall trees of a single species, thick trunks…”Otherwise, one mainly finds coppice forests, which are shorter stands of trees that are often cut, or coppice-under-high-forest.
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- Cefe (CNRS, UM, IRD, EPHE) ↩︎