SAINT-DENIS: Doubling of tree mortality in a decade, slowdown in growth and less absorption of CO2: faced with global warming, French forests are paying an increasingly heavy price in the face of global warming, a public body warned on Thursday .
According to the National Institute of Geographic and Forestry Information (IGN), “forest watchdog”, it covers 17.5 million hectares, or a third of the metropolitan territory: it is growing, but its condition is deteriorating , with repercussions on its role as a green lung.
Tree mortality increased from 7.4 million cubic meters per year between 2005 and 2013 to 15.2 Mm3 for the period 2014-2022, 0.5% of the total volume of trees in the forest.
The cause is increasingly unfavorable conditions for trees, favoring the proliferation of “bioaggressors” (fungi, insects, bacteria).
Added to this is “water stress”: “lack of water” or conversely “too much water, as is currently the case”, underlined Stéphanie Wurpillot, head of the service which carries out the inventory, during a press conference at the IGN headquarters in Saint-Mandé, near Paris.
Published every year based on data collected over the previous five years, the inventory also notes a slowdown in tree growth of 4% (between 2005-2013 and 2014-2022) and therefore a decline in their CO2 absorption.
Metropolitan forests absorbed 39 million tonnes of CO2 per year on average over the period 2014-2022, according to the inventory, compared to 63 over the period 2005-2013.
Densification
Despite this slowdown, the stock of CO2 it contains, and thus keeps out of the atmosphere, increased by 17% between 2009 and 2023.
The 11.3 billion trees counted by the IGN in 2023 represent a stock of 1.3 billion tonnes of carbon.
“Each hectare of forest today contains on average 81 tonnes of carbon in its living trees”, compared to 73 on average in 2009, according to IGN.
The increase at work is in fact much older and can be explained by the densification of the forest in recent decades. In 1981, the average stock was 58 tonnes of carbon per hectare, according to IGN.
According to figures published in May by IGN and the FCBA technological institute, the absorption capacity of forests has been halved in the space of a decade.
And a projection for 2050 estimated that “in the vast majority of (…) scenarios” studied, “carbon sequestration in forests continues to erode over the 2020-2050 projection period”.
Damage from deer and roe deer
Citepa, the organization mandated to carry out the French emissions inventory, noted between 2019 and 2022 an average drop in storage “of 2.1% per year”. A trend which will accelerate with a reduction trajectory of -4% per year between 2029 and 2033, according to an anticipation of the National Low Carbon Strategy.
Last month, experts from the High Council for the Climate expressed concern about the low absorption of CO2 in natural sinks, such as forests, after France, which aims for carbon neutrality by 2050, failed to respect its 2019-2023 climate objectives, in particular due to the less than expected absorption of forests and soils.
By counting the carbon contained in dead trees and the organic matter contained in the surface soil, the total reservoir of the forest ecosystem is estimated at 2.8 billion tonnes of carbon by the IGN.
The institute also presented a new indicator, called DEPERIS, intended to measure the health of trees, taking into account the presence of dead branches in their upper part. According to this indicator, 8% of forest trees are altered.
Another indicator aims to record the presence of large ungulates – deer, roe deer and other bighorn sheep – which can damage trees by grazing on the stems or bark, or by rubbing against each other. Such traces are present on 29% of young trees.
