Joint interview: on the road to biodiversity

The development and maintenance of the road network have been associated with revegetation initiatives for forty years now. These practices are constantly changing to meet environmental challenges, but also to involve all project stakeholders, and to include other environmental issues such as carbon intensity reduction and the circular economy. In this interview we explore the current major trends and new prospects with Anaël Mayeur, PhD student at AgroParisTech working on the lab recherche environnement’s Research & Solutions programme, and Nicolas Durvaux, Végéneration project manager at VINCI Autoroutes, an initiative which won the VINCI Environment Award.

What are the current major trends and new prospects that are opening up through your project?


Anaël Mayeur: Plants were long considered to be a mere technical resource to serve humans, then as an aesthetic element that boosted the acceptability of planning projects. Now, they could be a way to integrate constructions into their environment more fully, provided that we consider their characteristics in greater detail. This is the subject of my doctoral research project, which focuses on the composition and study of the herbaceous seed combinations that promote biodiversity while continuing to meet the conventional technical challenges of revegetation.

The aim is to obtain seed mixes with a greater diversity of species than those commonly sold and used in large-scale developments, with a view to attracting small animals and pollinators in particular, but also to establishing competition against invasive exotic species. Some mixes are made up of seeds from the Végétal Local brand, the idea being to have sufficient genetic diversity for these species to enjoy enhanced resilience in the face of climate change, and a reduction in the use of inputs for their healthy growth.


Nicolas Durvaux: During the construction phases for new sections, we rolled out large-scale revegetation plans for the surrounding areas, with more than 17 million trees planted, as well as major sowing operations. We are currently working on maintaining this and incorporating new challenges such as abolishing the use of agrochemicals and applying reasoned mowing. We hope to promote and increase the potential for renaturation of the available green areas.

In addition, we have also observed that our need for mineralised operational surfaces has dropped by around 30% (around the operations centre, coating platforms, etc.) alongside technical and organisational developments. The opportunity arose to propose a renaturation of these spaces by demineralising unnecessary surfaces.

Renaturation raises questions regarding the creation of functional natural environments. Which levers do you use to achieve this?


Nicolas Durvaux: As the projects are smaller in size than those during the construction phases, each site needs to be engineered individually. Following the soil analysis phase, our partnership with the French Office National des Forêts enables us to conduct a study of several technical renaturation approaches for each plot. These approaches combine conservation measures of the existing sites such as meadows and hedgerows, the planting of local tree species that can adapt to climate change, and the creation of wetlands. For each project, these different approaches optimise the creation of natural areas and are approved by our in-house experts with a view to assessing the impact of feasibility, ecological interest and repercussions on maintenance.


Anaël Mayeur: To follow on from what Nicolas was saying, the composition and selection of seed mixes to be sown are part of the engineering work to be rolled out on every type of site. As part of my project, mixes with different functions are tested. Some are designed to be competitive against invasive exotic species, with others are intended to cover the plots quickly after being sown or to attract pollinators.

Let’s remember that the creation and upkeep of a site’s functions also depend on environmental factors that are not always under our control. It is therefore a good idea to preserve pre-existing natural elements where possible.

When a sowing operation is required, the use of wild and local seed mixes means that we can rely on species’ natural resilience to adapt to the changes in their environment. In this way, we give the better adapted plants a greater chance of survival in the event of disruptions. This leads to a sustainable population of plant species. We are in a long-term approach aimed at maintaining the newly created plant communities, and therefore their functions.

Both of your projects incorporate short supply chain development objectives in different ways. Which opportunities and obstacles have you come across?


Anaël Mayeur: Having a stock of wild and local seeds requires a sector with a wide range of skills and stakeholders. The technical pathway from collection to planting is complex and calls for local stakeholders with sound knowledge of the local area. We predict opportunities for the creation or specialisation of companies within this market, in addition to partnership opportunities for developers and stakeholders in this budding sector. Such partnerships would improve project acceptability and would also give rise to high-quality products and advice, in tune with the local conditions which planning projects must face.

Although the study of the social and economic factors is still in its infancy, two major obstacles to the widespread adoption of this approach are becoming apparent. The first concerns the cost of seed purchases, which may be prohibitive in comparison to mass-produced seeds. However, the removal of inputs and the reduction in seed quantities may offset these excess costs, for equivalent results (this remains to be demonstrated). The second obstacle concerns the supply of wild and local seeds. As the sector is still in its early development, not all regions are covered when you need to find a producer able to fulfil large orders, for example in the event of motorway construction and the creation of related compensatory areas.


Nicolas Durvaux: Short supply chains are primarily used in the deconstruction of mineralised sites. For the first project, we contacted local associations who were looking for materials. For the second project, we want to work with Granulat+® to optimise material recycling. Their presence across France means that chains can be shortened and recycling reduces the footprint of resources.

Our second ambition for short supply chains is to work on renaturation projects with local companies and building sites that bring the unemployed into the workforce. In addition to the pride of managing these projects in their local areas and seeing them grow, there is also the ambition of training new stakeholders in these approaches.

Lastly, the third challenge concerns the need to support local seedling creation sectors by conducting these projects with local plant species. This means planning future developments with a vision spanning several years.

Which stakeholders must be brought in to roll out your approach as widely as possible?


Nicolas Durvaux: The primary stakeholders are naturally project managers. We have to prove to them the benefits for biodiversity and convince them to agree to long-term projects.

These projects are rooted in local areas. Sometimes, local elected representatives wish to get involved by sharing the ambition or drive to support local employment, for the project’s completion or the arboriculture sector.

As some projects may need to extend their scope to include potentially workable land for certain types of agriculture, we must also foster dialogue upstream with chambers of agriculture and local farmers, to work with them to design projects that can meet the twofold environmental and sustainable production objective.


Anaël Mayeur: To second what Nicolas has said, it is necessary that project managers are involved as early as possible in the design phases so that plant requirements are planned ahead, to discuss the challenges they represent and to define the share of the budget that will be allocated to this. This can facilitate access to material by leaving stakeholders in the production sector the time to obtain a sufficient quantity to meet demand.

More generally, it is important to raise awareness among all stakeholders who use seed mixes, whether as part of the management of the sites operated, the construction of new developments or environmental restoration sites, so that the functions and importance given to plants on these sites can be reconsidered. Taking an interest in the origin of plants and the composition of commonly used seed mixes could play a part in improving the integration of projects in the current environmental challenges that local areas face.


For further information, you can watch the replay of the the Research & Solutions webinar on “The revegetation of road infrastructure” with Anaël Mayeur and Nicolas Durvaux (in French).

On the same subject
Anaël Mayeur
PhD student
AgroParisTech - Université Paris Saclay
Revegetation has long been a strategy used by planners to meet operational needs such as soil stabilisation and landscape aesthetics. Today, it is valued for its potential to contribute to restoring biodiversity,
Learn more
Practitioner group
Bertrand Ney Rooftop at AgroParisTech
The benefits and costs related to green infrastructure in cities need to be better understood through assessment tools that measure environmental impacts, for example, carbon emissions due to the transport of substrates,
Learn more
Reconciling nature and the city, a highly artificial environment, is an art that is practised from the scale of the building to that of the suburban territory, including that of the neighbourhood.
Learn more