Solène Brasseur's thesis “Impacts of forest management and water constraints on natural regeneration in Mediterranean forests: in situ and ex situ application to Quercus pubescens Willd.”

Mrs. Solène Brasseur, doctoral student at IMBE (team Functional ecology: from socio-ecological systems to molecules), will publicly defend his thesis work on Tuesday 23 June 2026 at 9am in the INSPE amphitheatre at the Saint Jérôme Faculty.

Pour les personnes qui ne pourront pas se déplacer ce jour là, ne loupez rien et suivez la soutenance à distance !

In front of a jury made up of :

• Margarida TOMÉ: Rapporteur (PR - Universidade de Lisboa, Instituto Superior de Agronomia, Lisboa, Portugal)
• Lluís COLL: Rapporteur (PR - Universidad de Lleida, CTFC, AGROTECNIO, Lleida, Spain)
• Philippe BALANDIER: Examiner (DR - INRAE, UMR PIAF, Clermont-Ferrand, France)
• Estelle FOREY: Chair of the Jury (PR - University of Rouen, ECODIV USC INRAE, Mont Saint-Aignan, France)
• Anne Bousquet-Mélou: Thesis supervisor (PR - Aix Marseille University, Marseille)
• Mathieu Santonja: Thesis co-supervisor (MC - Aix Marseille University, Marseille)

Summary of work:

Mediterranean forests are shaped by water constraints and nutrient limits, as well as by millennia of human exploitation and management. They are multifunctional systems that perform regulatory functions, promote biodiversity and provide cultural ecosystem services, while meeting a high demand for wood and non-wood forest products. In the context of climate change, it is essential to ensure their long-term resilience. Sexual regeneration (from seed) plays a central role in this respect, as the seedlings, genetically recombined, are subject to natural selection and can give rise to individuals better adapted to their environment. However, since the beginning of the 21st century, the process of sexual regeneration has faced major challenges: recruitment is insufficient, and the young seedlings that emerge have low survival rates and reduced growth.

In order to encourage natural regeneration, forest managers already encourage the opening up of the canopy by thinning. However, key questions remain, notably about the intensity of thinning needed to guarantee both seedling establishment and long-term growth. To address this issue, this thesis investigates the direct and indirect effects of canopy opening on the natural regeneration of Quercus pubescens Willd. The first two chapters examine the effects of a thinning gradient (ranging from 0 % to 100 % of basal area harvesting), implemented in March 2022 in an old Mediterranean coppice of Q. pubescens (70 to 80 years since the last harvest), on vegetative and sexual regeneration pathways for 2 to 3 years. We are also focusing on the effects of the main factors influencing seedling establishment and growth (light, water stress and competition) under semi-controlled experimental conditions.

Our results reveal a trade-off between seedling establishment and growth along the thinning gradient. We observed higher densities of seedlings from seeds under a closed canopy (i.e. one that retained its buffering role), suggesting that seedling establishment processes are very sensitive to water stress. Conversely, a more open canopy favoured the growth of established seedlings and stimulated vegetative reproduction (higher rejection and growth rates), highlighting the central role of light availability in growth processes. Under semi-controlled conditions, we also demonstrated a negative effect of competition - particularly from grasses - on seedling growth, an effect that is attenuated under a denser canopy. Overall, these results suggest that moderate thinning (around 50 % of harvested basal area) represents an appropriate management compromise. We emphasise the need to move beyond production-oriented approaches towards multifunctional forest management that fully integrates the diversity of ecosystem services and ensures successful sexual regeneration. Maintaining essential forest functions requires more adaptive and balanced management strategies.

Key words : Climate change, Mediterranean forests, Sexual regeneration, Thinning, Experimentation in situ, Experimentation ex situ.