Using artificial soil mixtures to restore dry Mediterranean sub-steppe grasslands in quarries
About this good practice
The quarry on the Crau alluvial plain in southern France, known for its unique "coussoul de Crau" vegetation and semi-arid steppe habitat, addresses habitat restoration post-quarrying as required by law. This 500 km² plain, rich in silica-limestone gravel essential for road construction, produces 150,000-200,000 tonnes of sand and gravel annually, with 10% of the output being inert waste used for site redevelopment.
The practice involves removing and reusing about 300,000 tonnes of surface materials to restore the "Coussoul de Crau" habitat. Around fifty trials, each covering 1,250 m², used 850 tonnes of mixed materials per trial, combining inert industrial waste and soil from former orchard surfaces. Challenges include the scarcity of original soil and the evolving nature of Mediterranean dry grassland restoration. The approach now mixes orchard soil with quarry substrate to recreate the habitat, with trials showing that a 50-50 mix of raw quarry material and topsoil is optimal for species richness.
The project builds on Julie Chenot's dissertation and operates under the CIFRE national fund agreement (public research laboratories and business), with support from the ANRT (public-private intersectorial network for French research) and the GAGNERAUD company. It aims to return the site to agricultural or pastoral use by 2030, supported by ongoing academic supervision and funding for Chenot's PhD work.
Resources needed
Julie Chenot, a researcher supervised by university professors, conducts a thesis funded by the CIFRE scheme (€100,000 over 3 years).
1 quarry foreman and 1 manager prepare the experimental area.
1 loader operator and 4 people guide and prepare soil mixes, seeds, and sowing for the plots.
Evidence of success
Although the plant communities were a long way from the reference grassland after five years, the substrate mixes tested quickly established a sub-steppe type vegetation with many Poaceae species that will enable the quarry to be redeveloped pro-actively. In terms of inert waste recovery, this includes approximately 300,000 tonnes of soil from the stripping process and at least 300,000 tonnes of residual inert waste from the quarry process (operating licence until 2030), i.e. 600,000 tonnes.
Potential for learning or transfer
This practice is transferable as many areas face soil shortages for ecological restoration after quarrying. Mixing soil with inert quarry material increases substrate volume and balances the composition, favoring target species and reducing non-target species. Adaptable to different climates and soil conditions, this method is especially relevant to the steppe areas of southern Europe.
-Alleviates soil scarcity
-50% topsoil+50% inert quarry waste mix offers a good compromise, favoring target species and reducing non-target species
-Sowing Brachypodium reduces non-target species richness but also the coverage of target species, creating a physiognomy close to reference grassland
-Longer monitoring could refine treatments
The success of this practice led to the deployment of this soil mix on green roofs, supporting vegetation without watering. The experiment has been implemented on a new building at the University of Avignon and will be used on another building near Marseille in 2024.
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Good practice owner
You can contact the good practice owner below for more detailed information.
Société des Carrières de La Ménudelle (SCLM) Groupe GAGNERAUD