Missions

The composition of the Mediterranean vegetation is the result of long-lasting effects of fire, and land use. For the next decades, climate in Mediterranean region is expected to be 25% warmer over the year than the rest of the planet with up to 40% warming peak in summer. These increasing heatwaves in combination with drought and land-use changes (decrease of grazing or protected lands, both increasing tree connectivity) are likely to increase fire risks, longer fire seasons and more frequent, large, and severe fires2 than today. This could result in the reduction or change of key habitats, modifying species dynamics across the Mediterranean region at short (years) and long (centennial) timescales. Therefore, understanding the processes shaping plant communities under fire became a core challenge in ecology and conservation science in Mediterranean region.
Recent advances in the application of species traits, to assess the functional structure of communities, have provided an approach that responds rapidly and consistently across taxa and ecosystems to disturbances. In fire prone ecosystem, such as the Mediterranean basin, the plant strategies to resist or to be resilient to fire lead to plant functional uniqueness. Yet the long-term response of critical plant traits and functional diversity to fire activity compare to the response of plant traits to climatic and edaphic conditions commonly studied, is still unknown despite the recent and ongoing increase of fire frequency and intensity.
More specifically, the postdoctoral fellow will address these two main objectives, (1) assessing the effects of fires on vegetation dynamics and plant trait distribution, and (2) quantifying functional diversity, its long-term dynamics in response to both fire frequency and fire intensity, and its future regarding expected climate change in the Mediterranean area. S/he will identify (i) potential tipping-point in the composition of vegetation in response to fire, and (ii) processes of functional diversity dynamics through time to ultimately reveal the vulnerability of the vegetation to fire

Activités

This project will use sediment core records from five basins (Pantelleria, Tourves, Cavallo, Etang de l'Aulne and Etang du Pourra) located in the northern Mediterranean basin. The records cover the last ~12,000 years (the Holocene), which include stable climate conditions the past 7000 years to test the effect of fire regime changes.
To model the dynamics between fire regime and vegetation, the postdoc will use a spatially explicit mechanistic approach at the landscape scale (LandClim model). LandClim includes a local model simulating forest succession and a landscape model simulating disturbance processes such as fire, human land use and herbivores. LandClim operates over long-time scales (centuries) and a spatial extent large enough to encompass disturbances ranging from landscape to region (up to about 100 km2), but with sufficiently fine resolution to capture local physiographic variations (25 x 25 square metre). The modelling approach is used (1) to refine the vegetation composition from genus level obtained from pollen to species level, and (2) to test mechanistic factors such as light competition, drought and fire on past vegetation dynamics.
The sites are distributed from the northern climatic conditions of Mediterranean area on the French continent to the dry and warm climate of the Italian island of Pantelleria, allowing a great variation of Mediterranean climate. The dryness and warmness of this island is offering a unique opportunity to test the response of Mediterranean biodiversity and functional diversity in conditions that have not been experienced by the continental flora so far. The species list and the fire regime are those taken from the sediment core records studied in parallel by a PhD student. The species assemblages simulated by the model are evaluated against the pollen assemblages with the estimate of the fit to the reconstructed data per time period. Once the species list validated, the outputs of species biomass serve to focus on plant traits response to long term fire regime changes.
To extend the results to the Mediterranean basin, the postdoc, the PhD and B. Leys will compute average trait values at the genus level of taxa present in palaeo-community derived from reconstruction and at the species level of modelled vegetation community. The focus is on 1) six functional traits determining plant fitness, which represent major axes of ecological strategy for growth, survival, reproduction and fire resistance (SLA, LDMC, max Height, wood density, LNC and seed mass) derived from the TRY database and the BROT database; and 2) the CSR strategies from Grime. The functional diversity will be studied through each of the traits considered separately, as well as for all the traits simultaneously. The comparison of these two approaches will make it possible to understand the existence of interactions between traits of different natures: morphological, physiological trade-offs, or functional adaptation strategies

Compétences

PhD in quantitative ecology, or biostatistics
Use to long term datasets and temporal ecology
Good level in statistics
Excellent skills in R software and large datasets
Good skills in C++ and modelling, knowing LandClim will be a plus
Writing and oral communication
English spoken, written
Autonomy and initiative
Openness to teamwork, collaboration

Contexte de travail

This postdoctoral fellowship is part of a 4-year ANR project in which master's students and a PhD student will interact together. This project is collaborative with researchers from French and Australian universities, and makes a strong link with the managers of the natural parks of the Etang du Pourra and the Domaine de Ranquet as well as the Etang des Aulnes

Contraintes et risques

This subject includes no fieldwork, work progress related to the advancement of the PhD and the master results as well as self-motivated investigations. The work is made 100% on computer for data analyses and modelling.