These images made the rounds on social networks.

The photos and videos of the flames visible from some of the most touristy beaches in the Landes region made an impression on Sunday July 17. 

The monster fires that have been ravaging the Gironde for seven days have come just a few kilometers from the famous and very touristy Dune du Pilat, departmental authorities confirmed on Monday July 18.

The prefecture has also decided to prohibit “navigation on the western part of Lake Cazaux-Sanguinet” which is barely ten kilometers from the dune.

Fire, continued pic.twitter.com/QAoKqqwmHg

— Mathieu Cavada (@MathieuCavada) July 13, 2022

“Carbon bomb exploding”

But this is only the most visible part of these fires described as historic for the region by several media, including Le Monde. 

These fires have already ravaged 14,000 hectares of vegetation in just one week.

“This means that these fires, in a single department, have burned almost half of the surface which is, on average, ravaged by fires each year throughout the territory [30,000 hectares]”, underlines Dominique Morvan, professor of fluid mechanics and specialist in fire dynamics at the University of Aix-Marseille.

The Landes forest was stormed by two main fires of exceptional intensity.

The first, near the Arcachon basin, extends over a perimeter of 9 km by 8 km and has already removed 4,200 hectares of vegetation.

The second, even more powerful, is spreading further inland, around the town of Landiras, and has ravaged nearly 10,000 hectares of forest.

In both cases, these fires far exceed what is called in France a “great fire, which is characterized when at least 1,000 hectares have burned”, specifies Dominique Morvan.

For the moment, the urgency is to protect individuals and buildings threatened by fires.

But this devastating passage of the flames in the immense Landes pine forests will inevitably leave traces.

It will have an impact on biodiversity, soil quality, the local economy, and, potentially, on the climate, like the fires that ravaged Australia in 2021.

Indeed, “if global warming explains why forest fires are always more intense and frequent, these fires can also, in turn, accelerate the rise in temperatures”, recalls Thomas Smith, specialist in forest fires and their impact on climate at the London School of Economics.

When tens of thousands of hectares of pine forests go up in smoke, it's a real “carbon bomb that explodes”, recognizes Jonathan Lenoir, researcher at the CNRS and specialist in forest management.

The pines of the Landes release into the atmosphere all the CO2 stored for decades.

But if this effect caused a lot of ink to flow at the time of the fires in Australia, it will be less marked concerning the fires in France... even if we add to it the other fires which broke out in southern Europe these last days.

“It is certain that this net contribution of CO2 in the atmosphere will have an impact, but it will not be measurable” on the scale of all the other greenhouse gas emissions, notes Jean-Baptiste Filippi, researcher at the CNRS which participates in the forest fires project of the University of Corsica.

An economic cost for the region

It could be, however, that these fires lead to a local increase in temperatures in the medium term.

The multiplication of fires means that “it is the best adapted plantations that will survive”, assures Jean-Baptiste Filippi. 

This forest Darwinism argues that the vegetation that will grow back naturally is probably more and more of the Mediterranean type.

A landscape which would then become closer to the maquis of south-eastern France, “which provides less plant cover, evaporating less water and therefore producing less freshness”, sums up the researcher from the University of Corsica.

The disappearance of thousands of pines will also undoubtedly have “an economic cost”, warns Dominique Morvan.

The Landes pine forest – which covers one million hectares and represents the largest artificial forest in Europe – has been exploited for decades by the paper industry, the chemical industry, carpentry and the energy sector. with the development of biomass. 

“The economic loss will be calculated both in terms of the number of trees destroyed, but also in terms of tourist impact”, adds Dominique Morvan.

The Landes pine has become an international symbol of southwestern France.

Because of the fires, the region could also be exposed to an increased risk… of flooding.

“If you have abundant vegetation, it will absorb rainwater, but when the land is dry, there is a risk of soil leaching, i.e. the water is not absorbed and drags the ground with it”, sums up Dominique Morvan.

The dangers of forest monocultures

The short-term outlook is therefore quite bleak.

But over a much longer time – around half a century – “these fires can represent an opportunity”, assures Thomas Smith.

The shortcoming of the pine forest in the face of the risk of fire is "that it is a monoculture decided at a time [before the 1970s, editor's note] during which the question of global warming was absent from the debates", adds Jonathan Black.

Forests with a single type of plantation “are those where fires spread the fastest, which means that the Landes pine forest has always been a matchbox waiting for the spark of global warming to catch fire. ”, adds the CNRS researcher.

The latter hopes that the fires of 2022 will raise the awareness of decision-makers in order to integrate a little diversity into these forests.

"Today we are paying for the broken pots of forest management errors in the Southwest", he regrets.

To start again on a good, more resilient basis, “it is necessary to promote more heterogeneous plantations, even if it means letting the forest grow back naturally”, concludes Jonathan Lenoir. 

But we can also have smarter forest management, says Thomas Smith.

Thus, “in the United Kingdom, there are very well documented proposals to surround, for example, pine forests with plantations of conifers, which are more resistant to fires”, he notes.

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