Climate change: mortality in French forests has increased by nearly 80% in ten years

Louise Sallé with AFP / Photo credit: JULIAN STRATENSCHULTE / DPA / AFP 19:36 p.m., October 12, 2023

The French forest, hard hit by climate change, has seen its mortality increase by "nearly 80% in ten years", the National Institute of Geographic and Forest Information (IGN) announced on Thursday. In its national forest inventory, the IGN notes a "very strong increase in tree mortality" in metropolitan France, which rose to 13.1 million cubic meters per year between 2013 and 2021, while it stood at 7.4 million m3/year during the period 2005-2013.

"The forest area currently affected by dieback is equivalent to the cumulative area affected by fires over the last 35 years," the IGN said.

Proliferation of pests

The acceleration of the degradation of forest health is directly linked to climate change "manifested in particular by warmer temperatures and more frequent droughts than in the past". These changes encourage the proliferation of bio-aggressors, such as bark beetles, wood-boring insects that have decimated spruce stands in the Grand Est. The common spruce, the most resinous species taken in France for the quality of its wood intended for construction, "is now the first species affected by mortality ahead of chestnut and ash," says the IGN.

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The production of spruce wood, i.e. wood produced as a result of the growth of stands, is now "inferior to felling and trees dying", in particular because of the scale of "sanitary cutting" carried out "to limit the spread of bark beetles".

Tree growth slowed by 4%

In general, the study "shows declines in tree growth, including in places where water resources for trees are supposed to be the highest", which "is explained by stronger decreases in rainfall" in France. Tree growth has slowed. In volume, it has thus fallen "from 91.5 million m3/year in 2005-2013 to 87.8 million m3/year in 2013-2021, i.e. a significant decrease of 4%", according to the IGN.

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The suffering of the forest has reduced its capacity to absorb CO2, leading to the "slowdown of the carbon sink of French forests", which stands at 40 million tonnes of CO2 annually between 2013 and 2021. For the massifs affected by bark beetles, the net balance becomes "temporarily negative". Nevertheless, the forest continues to expand in metropolitan France and diversify. It now covers 31% of the territory with 17.3 million hectares, compared to 19% with 10 million hectares in 1908. The inventory was based on measurements collected from nearly 70,000 observation sites, following five field campaigns conducted from 2018 to 2022.