Crossed by the LGV project, is the Ciron valley threatened?

• The Ciron valley is home to several protected species such as the otter and the European mink, or the pond turtle.

• The oldest forest in France, a beech grove dating back 43,000 years, has been preserved there.

• It is impossible to quantify the impacts that the high-speed line would have, but "the watershed would be split into three parts" with consequences on the movement of species, points out the Ciron union.

"Lascaux or Noah's Ark of biodiversity" ... Scientists and naturalists have no shortage of formulas to underline the unique character of the Ciron valley (Gironde).

The site, which would be crossed in the middle by the LGV Bordeaux-Toulouse, is today at the heart of the debates on the GPSO (Grand Projet du Sud-Ouest).

But what is this valley of the Ciron, unknown to the general public?

Located south of Langon, this natural and still wild area is neither spectacular nor majestic: it is by taking the time to browse the river by kayak or on foot by its banks, to sink into its gorges. limestones, that the beauty of Ciron is revealed.

Between a prehistoric beech forest and an “exceptional” biodiversity, this valley has managed to preserve several elements intact for millennia.

Several protected species

97 km long, the Ciron has its source in the north of the Landes. After crossing the Landes de Gascogne plateau, and before flowing into the Garonne, the river continues part of its way under a gallery forest, in particular between Bernos-Beaulac and Villandraut. “There are several protected species there,” explains Morane Genet, an aquatic environment technician at the Ciron watershed union. "There is for example the European otter, the European pond turtle - a small freshwater turtle quite rare in France -, amphibians - frogs, toads, salamanders -, the European mink, species of bat ”, lists the technician.

The Ciron is also "one of the rare rivers that the catfish has not yet colonized, thanks to its freshness", underlines Michel Aimé, mayor of Sauviac and vice-president of the Community of municipalities of Bazadais.

An experiment is currently being carried out there with the Migado association, for the conservation of lamprey, directly threatened by catfish.

"We released lampreys in the Ciron just before their laying period, so that they reproduce and thus help them renew their population", explains Morane Genet.

"No Ciron, no Sauternes"

The Ciron owes its freshness, among other things, to its riparian forest - a plant formation that grows at the edge of watercourses - which retains the river water, mainly from underground water tables, at an average temperature of 14 ° C in summer. This same freshness generates morning mists at the end of summer, favoring the formation of the fungus

on the berries of the nearby Sauternes vineyard, which will give this sweet wine known all over the world. "No Ciron, no Sauternes", summarizes Olivier Douence, mayor of Pompéjac and president of the Ciron union.

This microclimate is also at the origin of another little-known peculiarity, since it has made it possible to maintain a beech forest for more than 40,000 years. Which makes it, quite simply, the oldest forest in France known to date.

“40,000 years ago we were in the middle of the ice age,” explains Alexis Ducousso, researcher at INRAE ​​(National Institute for Agronomic and Environmental Research). At that time, the trees were located in southern Europe, and beech rather in the south of the Iberian Peninsula, with perhaps a few refuges in northern Spain. The valley of Ciron was then only a vast tundra. But to our surprise, we discovered in the early 2010s that beech was present in this valley during this ice age, finding charcoal that we have been able to date back 43,000 years. "Genetically, these beeches are the same as those of origin, but they are on the other hand" different from all the other European populations "adds Alexis Ducousso,which specifies that the beech grove only extends over about thirty hectares today, and that it is necessary to preserve it.

"The first victim of the LGV will be the Ciron"

Could this biodiversity be threatened by the LGV?

In the community of communes of Bazadais, we are convinced of this.

"The first victim of the LGV, it will be the Ciron", cowardly, dryly, Michel Aimé.

The elected officials of the CDC of Bazadais adopted a motion on November 24, declaring themselves totally opposed to this project relaunched at the beginning of the year by the Prime Minister, and supported by most of the major regional elected officials of Nouvelle-Aquitaine and of Occitanie.

Our dossier on biodiversity

Of the 4,830 ha of landholding of the LGV, 845 ha are located in the Ciron valley, including 64 ha of wetlands, and 11 ha classified as a Natura 2000 site. Three viaducts should be built to cross the river, while the line would cross a total of 30 rivers and streams, tributaries of the Ciron.

The Ciron development union underlines that "the watershed would be split into three parts, by more than 70 km of new lines which follow the route of the river" while the famous railway triangle, part of the project which connects the line to Toulouse and the one towards Dax, would be located in Bernos-Beaulac, “one of the most preserved sectors sheltering many protected species.

"This town has already been heavily impacted by the construction of the A65 Langon-Pau motorway", recalls Olivier Douence.

The project "avoids the most sensitive sectors as much as possible"

The project's public inquiry declaration (DUP) highlights the efforts made at the environmental level to mitigate the impacts, with in particular 109 large wildlife passages over the 327 km of the route. "The definition of the route was carried out by avoiding as much as possible the most sensitive sectors", we still read in this DUP. "This is a pilot program of the" Avoid, Reduce, Compensate "approach", defends Étienne Guyot, Prefect of the Occitania region and coordinator of the project, who ensures that "all the recommendations of the Environmental Authority have been processed. "

"The problem, fulminates the mayor of Pompéjac, is that we, at the level of the rural communes, we make enormous efforts in our local urban plans to reduce the building land in order to limit the consumption of agricultural space and forest.

Today, we do not understand that such a project which will consume 845 hectares could land like that.

This project, it seems anachronistic, expensive, and frankly, it annoys a little.

"

The financial roundtable of communities for the GPSO project must be completed before the end of the year, before the Council of State decides by April 2022.

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