After the major fires of the summer, the question of the management of new plantations in the affected sectors arises.
In the South Gironde, work to remove the wood that is marketable is underway.
Maritime pine will be reinstalled as a priority, with hardwoods on the edge.
For the wilder forest of La Teste, Sylvain Delzon, research director at INRAE, recommends intervening as little as possible, deeming it only desirable to help regeneration in the most desolate areas.
The extraordinary fires of the summer have left Landiras and La Teste-de-Buch with desolate landscapes, amputated in total by more than 30,000 hectares of forest.
In the South Gironde, forest machines are at work at the moment to remove all the wood that can be marketed.
"It's a race against time against bark beetles [beetle insects] that get on weakened trees, explains Bruno Lafon, forester and president of the DFCI (defense of forests against fires) Gironde.
These pests reproduce quickly and will at some point prefer to attack green trees and this can be very dangerous.
The forestry sector is giving itself until March 2023 to cut down and evacuate as many trees as possible for the paper industry, the manufacture of pallets and, for some, the construction sector.
Diversify the South Gironde forest
Which species to replant?
The question will arise in a few months for the plots occupied by the youngest trees and within two years for those which housed adult pines (40 years old).
Of the 1,500,000 hectares of the Landes de Gascogne massif, there are approximately 500,000 hectares of hardwoods for a million hectares of maritime pines.
"Taking advantage of such damage to increase biodiversity is a good thing," says Sylvain Delzon, research director at the National Research Institute for Agriculture, Food and the Environment (INRAE) and at the University of Bordeaux. .
On the other hand, to say that we must increase biodiversity to fight against fires is heresy”.
According to this specialist in the forest ecosystem, the maritime pine is indeed the species most adapted to the sandy and nutrient-poor soil of the Landes plateau.
If it is necessary to maintain the deciduous trees already present inside the massif and provide some on the edge, it is above all to "allow [the forest] to have greater resilience against pests, but that will not allow fight against drought or fires", insists Sylvain Delzon.
Advocacy for maritime pine
Hardwoods, if they are for example more resistant than maritime pine to hazards such as the wind, are on the other hand more sensitive than maritime pine to fires.
Adult maritime pines have no branches up to 20 meters high and some have been saved from fire while hardwoods, with lower crowns, have been consumed.
It is therefore absurd to think that their presence in the massif will be able to strengthen resistance to fires.
"We need to think about the spatial planning of the forest, and on our side we are working on resistance, on how we can create more interesting varieties for the industry", highlights Alain Bailly, director of the Biotechnology Forestry division. advanced at the FCBA (Forest-Cellulose-Wood-Furniture) technological institute.
Cut to resist water stress, the maritime pine has also proven itself in terms of resistance to drought.
In conjunction with the National Forestry Office (ONF), INRAE has planted in Sanguinet "16 hectares of young pines of different species, reputed to be more resistant to drought (coming from Spain and Portugal for example), explains Sylvain Delzon.
We are measuring their mortality and we will be able to find out more within five years.
» Genetic diversity is to be favored to avoid betting everything on a species from the south which could be more sensitive to frost, for example.
A productivist drift?
"When the forest was replanted, the objective of Napoleon III and Brémontier was to clean up this space, reputed to be the "Landes desert", recalls Jean-Luc Gleyze, the president of the Gironde department.
But at the time, the pine was also planted with oaks, laid out on embankments, which we gradually abandoned in a more productivist logic.
» He also points to an increasingly sought-after profitability: « we started to exploit younger and younger pines, cut today at 30-35 years, whereas before we were up to 60 years old.
»
A change that has had effects on the entire industry, over time.
“You no longer have the small sawmills that once existed on the moor, and which had the merit of spreading a fine economic fabric in practically all the villages, he points out.
They have gradually closed in favor of large units.
Excessive monoculture is not conducive to the resilience of the forest, which is increasingly subject to climate change.
»
Supporting regeneration at La Teste
The situation of the so-called user forest of La Teste is quite different.
The massif, almost entirely ravaged by fires (7,000 hectares), plays a protective role to prevent the dunes from advancing.
Much older and more diversified, it is not exploited for forestry purposes.
The private owners of the woods can recover it for heating but not to trade in it.
“It would be a misinterpretation to cut and replant where all the trees are not dead, you have to let the area regenerate, believes Sylvain Delzon.
And, we could bring seeds where there has been no regeneration, as the ONF has been doing on the dune cordon for decades”.
No question of sending to La Teste the same gigantic machines as to Landiras, which would be disproportionate.
If the question of the evacuation of certain large trees arises, “we must keep the intervention to the strict minimum”, assures the researcher.
For him, there is an in-between to be found between a complete return to nature in this sector, while firebreaks and firefighter access appear essential, and a model of productive forest, as in the Landiras sector.
"It would be a solution for the ONF to be mandated by the State to ensure the management of this forest", suggests Sylvain Delzon, taking the model of the Hourtin nature reserve.
In the perspective of climate change where “the summer we experienced will perhaps be the average summer of 2050”, launches the researcher, it is important to learn lessons from these fires.
“We ask that the prefect lead the states general of the Landes de Gascogne forest, declares the president of the Department.
We will address issues of forest management, urbanization, firefighting... But we will also talk about replanting the forest, with what species, for what uses?
»
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