The Chaux forest, the 2nd largest broadleaf forest massif in France, covers 22,000 ha of state and municipal forests. It flows across an alternation of silty plateaux (known locally as « platières ») and dales that drain into the Clauge and then the Doubs. It is classified as Natura 2000 under the European Birds and Habitats Directives. Of the 413 km of waterways running through the forest plots, only 88 km are permanent. Major drainage and correction work on these small watercourses was carried out in the 1950s and 1960s to dry out the areas to be reforested and improve farming conditions. 50 years later, the growing awareness of natural habitats and water management in forestry practices, as well as the environmental policy of the National Forests Office (ONF), have led the managing body to reconsider former practices and their subsequent repercussions : lowering of the watertable in the valleys, regressive erosion and increased summer drought with localised oak dieback.
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For adaptation to climate changes: increasing the resistance of forest stands to the risk of drought.
For the local area: improving water quality and groundwater levels, reinforcing water availability.
For managing natural risks: limiting erosion of the riverbed and banks by slowing down the flow and replenishing the plateaux (“platières”) with sediments.
For biodiversity: restoring the river continuity and its biodiversity
In May 2015, the ONF signed a partnership agreement with the Rhône Mediterranean Corsica Water Agency and the University of Franche-Comté to carry out restoration works on the upstream tributaries of the Clauge. These restoration works, on around 45 km of streams (three stretches of 15 km each), began in July 2015. They consisted in redirecting the flow into the former natural meanders of the stream. The work continued over the following summers. Three stretches of 15 km have now been completed.
• Complete filling in of drains and ditches in the upstream part of the streams at the edge of the plateaux
• Setting up of obstructions and counter-obstructions elsewhere to allow the streams to return to their old bed and/or create a new bed
The length of the streams has been approximately doubled. The project has also improved the taking into consideration of the streams in forestry operations and the search for alternative solutions to conventional service tracks in order to preserve the restored streams and avoid crossing them.
Scientific and technical monitoring to assess the results of the project:
• Scientific monitoring by the University of Franche-Comté: piezometric monitoring (changes in the level of the watertable) and monitoring of aquatic insects
• Dendrometry and forestry monitoring carried out by the ONF.
BENEFITS REGARDING TARGETED ADAPTATION ISSUES
• Low-water availability: a two-week extension of the period when water is available in the soil in late spring and autumn. In response, the time when the upper water table is present increases by about a month in both seasons, i.e., two months over the whole hydrological year.
• Erosion: the works lifted the riverbed, reducing current speeds and sediment transport.
BENEFITS FOR THE PROTECTION, MANAGEMENT AND RESTORATION OF BIODIVERSITY
• Increase in the number and quality of temporary wetland habitats
• Return of certain aquatic insects
• Increase in amphibian reproduction
• Effects on the forest stands have not yet been highlighted, due to the long reaction time.
OTHER BENEFITS ACHIEVED
The dune walk that has been created has notably helped to highlight these environments and raise public awareness through educational panels along the route. Today, all the urbanized neighborhoods are connected to the various authorized beach access points. Moreover, although the work carried out represented a significant investment, it helps to limit annual maintenance costs. Today, this maintenance, which costs the community around €10,000 to €20,000 per year, ensures the preservation and stability of 2.5 kilometers of dunes and the protection of the urban areas located just behind.
- Reduce drought risk
- Increase Biodiversity
Levers of success
• Concertation: the same organisation, the ONF, is responsible for both managing the forest and project management for the works, which facilitates exchanges between different units of the same agency, particularly concerning the tree-felling programme and the scheduling of restoration works.
Recommendations :
• Administrative procedures: take into account the time required for administrative procedures (Natura 2000 impacts, water law, and public inquiries).
• Technical expertise: develop the number of companies experienced in this type of work.
• Reproducibility: to expand and develop this project to enable the restoration of the 400 km of watercourses located in the forest massif so as to have a real effect on flooding, drought, and erosion, etc.
• Rhône Mediterranean Corsica Water Agency (80 %)
• ONF (The French National Forest Office) (20 %)
750,000 € exc. VAT
Hélène Gervaise
Natural Habitats Risk Project Manager – Water
ONF - The French National Forest Office
helene.gervais@onf.fr