Faced with climate change, the upset face of the French forest

It is robust, has seen revolutions and storms, but the French forest is today facing the unprecedented challenge of climate change, which is going faster than the capacity of trees to renew themselves and is changing its face.

A forest that grows but suffers

The French forest is extremely diverse, tropical or temperate, coastal, plain or mountain, and covers nearly 26 million hectares.

In mainland France, the forest represents 17.1 million hectares, or 31% of the territory: it continues to grow but has seen its mortality increase by 54% over the past ten years, according to the National Institute for Geographic and Forest Information.

The forest is a victim of drought and virulent attacks by xylophagous insects such as bark beetles in the spruce beds of the Grand Est. It is also more vulnerable to fires.

France ranks 4th among the most forested European states, behind Sweden, Finland and Spain. It has the 3rd stock of European timber behind Germany and Sweden, with a volume of standing timber of around 2.8 billion m3, according to the National Forestry Office (ONF).

It is the most diversified, with 190 species of trees, of which more than 65% hardwood (mainly oak) and the rest softwood (pine, spruce).

All trees suffer. The most affected are the spruce, eaten by bark beetles; beech and ash, which wither for lack of water; and Scots pine.

This forest is 75% owned by 3.4 million private owners, the 25% of public forest being managed by the ONF.

The shock in Overseas too

The overseas departments have 8.7 million hectares of forest, mainly located in Guyana where the tropical rainforest – public – is the largest reserve of French biodiversity.

Its renewal is likely to slow down in the face of the drop in precipitation, which will accelerate the evolution of certain areas into dry tropical forest.

By the end of the century, it will also be threatened by the rising waters in certain coastal areas, affecting the mangroves in particular.

A carbon sink in peril?

Forests, the second carbon sink after the oceans, mitigate climate change.

How? During photosynthesis, the tree captures gaseous carbon (CO2) present in the atmosphere through the stomata, pores located on the surface of the leaves.

In summary, it stores as it breathes. It is his exhaustion that is causing the slowing down of his ability to sequester. The release of carbon is sudden in the event of a fire, the combustion immediately releasing the stock, and more progressive in the event of decline.

Citepa, the body mandated to carry out the French inventory of emissions, noted between 2019 and 2022 an average drop in storage “of 2.1% per year”. A trend that will accelerate with a reduction trajectory of -4% per year between 2029 and 2033, according to an anticipation of the National Low Carbon Strategy.

The forest is therefore still a net carbon sink (estimated at 17.1 million tonnes of CO2 equivalent in 2021) but it works less well.

A third of the forest is already considered to be in “climate discomfort” and “sensitivity to fire” will concern half of the territory in 2050, according to the ONF.

A whole ecosystem to protect

The forest provides many services: it is home to 80% of terrestrial biodiversity, filters air and water, stores carbon, reduces soil erosion, provides wood for construction, the paper industry and heating.

The ONF estimates that “within 50 years, half of the French forest could have changed its face”. Its natural adaptation mechanisms “are on average 10 times too slow with regard to the foreseeable rapidity of climate change”: we can therefore no longer count on natural regeneration, which today allows nearly 80% of stands in public forests.

The plantations will therefore increase, favoring “the diversification of species”: by assisting the “migrations” of trees more adapted to a dry climate, from south to north (such as the pubescent oak or the maritime pine), and by importing species, such as the Atlas cedar.