The French forest is badly affected by climate change. It has seen its mortality increase by “nearly 80% in ten years”, announced this Thursday the National Institute of Geographic and Forestry Information (IGN). In its national forest inventory, the IGN notes a “very sharp increase in tree mortality” in mainland France, rising 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 accumulation of areas affected by fires over the last 35 years,” underlines the IGN. The acceleration in the deterioration of the state of health of forests is directly linked to climate change “which is manifested in particular by higher temperatures and more frequent droughts than in the past”.
A “decline in growth” of trees
These changes favor the proliferation of pests, such as bark beetles, wood-eating insects which have decimated spruce populations in the Grand-Est. Norway spruce, the resinous species most harvested in France for the quality of its wood intended for construction, “is now the first species affected by mortality ahead of chestnut and ash”, indicates the IGN.
The production of spruce wood, i.e. the wood produced due to the growth of stands, is now “lower than the cuts and the trees which die”, in particular due to the extent of the “sanitary cuts” carried out “to limit the spread of bark beetles. Generally speaking, the study “shows declines in tree growth, including in places where water resources for trees are expected to be highest,” which “is explained by greater declines of precipitation” in France.
Less ability to absorb CO2
Tree growth has slowed. In volume, it thus went “from 91.5 million m3/year in 2005-2013 to 87.8 million m3/year in 2013-2021, a significant drop of 4%”, according to IGN. The suffering of the forest has reduced its capacity to absorb CO2, leading to the “slowdown of the carbon sink of French forests”, which amounts to 40 million tonnes of CO2 annually between 2013 and 2021. For the massifs affected by the bark beetles, the net balance becomes “temporarily negative”.
Nevertheless, the forest continues to expand in mainland 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 carried out based on measurements collected on nearly 70,000 observation sites, The result of five field campaigns carried out from 2018 to 2022.