Hélie has magnificently defendedhis M.Sc. thesis in geosciences on 11th June. 
Thesis title: Eco-chemical variability of Corsican black pine (Pinus nigra) wood: ecophysiological response to wildfires and climate over the past 300 years.
His defence occurred at the Dept of Geology at the Ecole Normale Supérieure Lyon.
His opponent was Dr. Tu Thanh-Thuy Nguyen, Sorbonne University, Paris.
Hélie was co-supervised by François Fourel (CNRS) and myself, with the contribution of Jean-Christophe Domec (Bordeaux Sciences Agro). We wish him the best as he pursues his life's project.

Thesis abstract. In Mediterranean ecosystems, the intensification of wildfires driven by climate change could deeply alter the tree response. A few studies have used isotopic proxies to investigate the physiological points of this response. We here propose a method to assess the interaction between fire, climate and tree physiology on fire injured trees using isotopic proxies over a 300-year timescale. Forty-one fire sequences were analysed using EA-IRMS to measure the carbon and nitrogen isotopic compositions of Corsican black pine wood (Pinus nigra ssp. laricio) after resin extraction. The isotopic trends followed did not reveal variation in response to fire. However wood 𝛿13𝐶 and 𝛿15𝑁 are sensitive to climatic changes. Therefore, Corsican black pine appears highly resistant to fire. Despite deep fire scars, investigated trees did not, on average, modify neither their intrinsic water-use efficiency (iWUE) nor their nitrogen nutrition strategies in response to fire. Since 1960, climate change has been associated with a highly significant increase in iWUE, related rising atmospheric CO₂ concentrations and increasing spring and summer temperatures. In contrast, 𝛿15𝑁 exhibits a declining trend, reflecting a slight long-term decline in soil nitrogen availability driven by repeated wildfires. This trend has become increasingly marked since 1920, indicating that declining soil nitrogen availability may be reinforced by reduced symbiotic exchanges between black pine and decomposer mycorrhizal fungi.