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 © photo AgroParisTech, Le Monde

Project leaders: Sophie JOIMEL & Claire CHENU (ECOSYS)     Type of project: emerging project (2017-2018)

Partners

• BASC units: ECOSYS, ESE, SADAPT
• Outside BASC: LSE
• Non-academic: EXP'AU engineering office, ELISOL engineering office, Paris City Hall soil analysis laboratory

Faced with the development of urban areas and related environmental problems (e.g. soil sealing, air, water and soil pollution, habitat fragmentation), the urban ecosystem is now the subject of new societal expectations with an increasingly strong desire to reintegrate nature into the city¹. These vegetated surfaces are seen as one of the solutions because of the ecosystem services they can provide (e.g. water retention, biodiversity support, carbon storage)².

New forms of vegetation are emerging, such as green roofs, vegetable gardens or ornamental gardens, implanted on urban soils constructed from various materials, in particular organic waste from the city. Expectations are high with regard to these components of a green grid and the ecosystem services they could provide to the city, but this should not obscure the fact that the functioning of these natural spaces is still very poorly understood.

Although recent research programs (such as JASSUR Jardins ASSociatifs URbains) have focused on collective gardens³, the role of biodiversity support is currently very poorly known, especially for rooftop gardens⁴. Yet, biodiversity plays an important role in the functionality of urban ecosystems and the resilience of cities.

The "TROL" project therefore aimed to study the soils of green roofs and their capacity to support biodiversity. The knowledge of the plant and animal communities of these soils and the understanding of what determines them should make it possible to define how to optimize the ecosystemic service of supporting biodiversity in the city through the design and management of green roofs. The aim is to make the "mineral" city evolve towards a multifunctional city, able to face global changes.

We have studied the communities of plants, micro-organisms, micro-, meso- and macro-fauna living in 20 vegetable or ornamental roofs in Ile-de-France for two years.

The two types of roofs studied (extensive and vegetable roofs) © Joimel

Through a coupled taxonomic and functional approach to biodiversity, we identified two modes of colonization for springtails (soil bio-indicator organisms): passive wind dispersal - "flying" springtails - and colonization by compost inputs (Joimel et al., 2018). Rooftop connectivity with other green spaces, - brown screen - within the urban matrix is thus necessary for rooftop colonization by wind-borne soil organisms.

In addition, the characteristics of Technosols (constructed roof soils) have strongly influenced the animal and plant communities of organisms. While diversity levels (abundance and species richness) may be similar between different roof types, the composition of these communities is completely different between roof types, raising many questions about the functionality of biodiversity in these spaces.

Subsequently, the TROL project served as a lever for the creation of the SEMOIRS project (ADEME) on the evaluation of ecosystem services provided by the soils of urban micro-farms. Numerous perspectives on the evaluation of ecosystem services provided by soils in urban agriculture are envisaged.

==> A researcher explains the project and its RESULTS in VIDEO (LabEx BASC scientific days, February 2021)

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Publications 

> Joimel S., Grard B., Auclerc A., Hedde M., Le Doaré N., Salmon S., Chenu C. (2018). Are Collembola "flying" onto green roofs? Ecological Engineering, 111: 117–124. doi:10.1016/j.ecoleng.2017.12.002

References

1.Cheverry and Gascuel, 2009

2. Luederitz et al., 2015; Tzoulas et al., 2007

3. e.g. Joimel et al., 2019

4. Lin et al., 2015