[PhD defence] 24/02/2025 - Hugo Fontes: "How can the concept of reference ecosystem be used to assess the success of creating temporary ponds in the Camargue?

Mr Hugo Fontes, a doctoral student at the UMR IMBE, EECAR team, IUT d'Avignon and at the Tour du Valat, Research Institute for the Conservation of Mediterranean Wetlands, will publicly present his thesis on Monday 24 February 2025 at 2pm at the Tour du Valat, Le Sambuc, Arles.

Laboratory

UMR 7263 IMBE - Mediterranean Institute of Biodiversity and Ecology EECAR

Composition of the jury

• Laila Rhazi, Professor, Hassan II Mohammedia University, Casablanca, Morocco, rapporteur
• Ana Rodrigues, CNRS Research Director, UMR CEFE, Montpellier, Rapporteur
• Renaud Jaunatre, INRAE Research Fellow, UMR LESSEM, Grenoble, examiner
• Elise Buisson, Senior Lecturer HDR, Avignon University, UMR IMBE, examiner
• Thierry Dutoit, CNRS Research Director, UMR IMBE, Avignon, co-director
• François Mesléard, Professor, Avignon University, UMR IMBE and Tour du Valat, co-director
• Patrick Grillas, Research Director, Tour du Valat, co-supervisor

Summary

Faced with the degradation of natural areas and the loss of biodiversity, ecological restoration is considered to be one of the major tools of biological conservation. This recent discipline is still the subject of controversy, particularly concerning the concept of "reference ecosystem", which is considered to be too fixist. However, it is now generally accepted that the definition of a reference ecosystem does not consist in freezing a representation of a past "ideal" ecosystem, but in exploring its historical and current variations. Despite these conceptual advances, methodological gaps still need to be filled in order to take better account of the variability of reference ecosystems when assessing the success of ecological restoration operations. To meet this need, we chose the temporary Mediterranean ponds of the Camargue as a case study, an ecosystem whose environmental conditions and plant communities are particularly variable, notably due to the intermittent nature of the aquatic and dry phases. Despite their conservation importance, Mediterranean temporary pools have been and continue to be heavily impacted by human activity.

In response, restoration and creation operations have been carried out and now need to be evaluated. As a first step, we have developed an indicator, the "Distance to References Communities Index" (DRCI), which compares a site or community undergoing restoration with a panel of reference sites or communities. This method considers each reference situation as a potential objective, unlike commonly used methods which consider an average reference situation as the optimum objective. DRCI is an integrative indicator that focuses on communities and uses an index of distance or similarity. It is particularly well suited to variable ecological systems such as temporary ponds. We then explored the spatio-temporal diversity of ponds in the Camargue, using all the old floristic data available and surveys carried out as part of this thesis in 27 reference ponds in April, May, June and August 2019 and 2020. The surveys found most of the species known since the 1950s, in comparable proportions. The contemporary ponds can therefore be considered as relevant reference ecosystems, comparable to the temporary ponds inventoried in the second half of the 20th century. Nevertheless, certain minor changes in the vegetation of the ponds can be interpreted as degradation, in particular the appearance of invasive exotic species and salinisation phenomena that may be linked to climate change.

Finally, we compared the vegetation of 25 ponds created in the 19th, 20th and 21st centuries (inventoried in April, May, June and July 2020) with that of 27 reference ponds. The plant communities (species composition and abundance) of the ponds created in the 21st century are quite distinct from the reference communities, unlike the communities of the ponds created previously. The communities in flooded conditions are closer to the reference communities than the communities in the dry phase. In particular, protected and threatened emergent species are generally absent from the pools created, unlike submerged macrophytes. The value of creating temporary Mediterranean ponds is therefore significant for aquatic communities, but remains limited for certain terrestrial and amphibious communities. The choice of reference model and measured variables can have a major influence on the results and conclusions of the assessment. Defining a reference model is tantamount to defining the objectives of restoration projects and therefore makes their assessment more or less flexible.

Keywords Reference ecosystem, Community ecology, Restoration ecology, Plant ecology, Temporary pond, Mediterranean