Six months after the Gironde fires, the forest was cleared and studied

Six months after the extraordinary fires in the Gironde on July 12, nearly 30,000 hectares of forest damaged this summer are being evacuated of dead or damaged trees and thinking about the future is beginning.

Ecophysiologist Sylvain Delzon, an INRAE ​​researcher based at the University of Bordeaux, together with his team took samples of maritime pines in areas affected by the megafires in La Teste-de-Buch, Bassin Arcachon and Landiras and Hostens this summer. sector, south of Bordeaux.

The goal was to provide immediate “decision support” to the timber industry in particular: cut or keep?

“Where there was a ground or basement fire, the tree was found to have no cellular vitality at the base. Although it was still completely green, it would have died within 12 months. We recommended cutting it down.” explains.

For pine trees that are preserved at the base but have burned the green part (crown), it is possible to survive with “less than 70% damage to the crown”. In addition, vitality “decreases greatly”, notes Sylvain Delzon.

In production forests such as Landiras, all “forests” less than 10 years old have been destroyed, but for very old trees (25-45 years) the “survival rate” is “estimated at perhaps 25%”: “The bigger the trees” , more were saved”.

– “Quality” wood –

But “in La Teste-de-Buch and Hostens, the flames rose much higher. Even the 30m stands were completely burnt. Probably because there was more scrub: this dry matter produced very strong fires.”

The firewood of the affected large trees remained “of good quality” for exploitation “even if the wood was 100% burnt”, assures Sylvain Delzon.

According to him, since October, the cuttings cut in the old stands of Landiras “have been able to be sold by the operators as standard wood”.

Surviving trees, on the other hand, appear to be more sensitive to drought and “a little less productive” because the fires have damaged their vessels responsible for transporting water: “So they will have more trouble growing.”

However, the problem remains moderate because the thousands of hectares covered by the fire “will be almost all cut down within four years”.

In La Teste-de-Buch, in the state-run part of the forest, forestry machinery began harvesting firewood in September (the equivalent of ten years’ cutting in normal times) before the arrival of insects such as the bark beetle. , ends up killing the most weakened trees.

– Increase “genetic diversity” –

In the remote, private and non-production “user” section, old forest management rules make it difficult to make any decisions between authorities, owners and users, but drywood auctions (in lots) have been held here. December and tree recovery will begin shortly.

Among the five camps destroyed by fire, Les Flots Bleus, made famous by the films “Camp”, is in the midst of welcoming its first holidaymakers in early April.

Although the “States General of the Landes de Gascogne Forest” begins, Sylvain Delzon also looks after the restoration of the affected massifs.

In Landiras, private owners intend to replant maritime pine, but he recommends increasing the “genetic diversity” of the plots by planting several species of this species. This will promote resilience to climate change. The researcher also recommends “leaving as much hardwood as possible without interfering with the operation” to increase resistance to pests (insects, fungi).

In La Teste’s “user” forest, he recommends relying on “natural regeneration” as much as possible.

Sylvain Delzon, however, advocates “certain clearing”. “Not systematic”, to optimize biodiversity. But “smart”, to enter the firefighters and prevent the continuous formation of more than hundreds of hectares. In doing so, he suggests an alternation of “cleared and uncleaned areas”.

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