European old-growth forests are rare and confined to remote geographical areas. However, these forests are currently undergoing a revival of interest. Due to their structural and compositional characteristics, they provide valuable ecosystem services through their exceptional carbon storage and biodiversity hosting capacities. These mature forest ecosystems are mainly characterized (i) by the presence of large (and supposedly old) trees, on which rare dendromicrohabitats have developed, and (ii) by a large amount of diversified dead wood. The maturity reached by these forests suggests the ancientness of forest cover, which provides additional quality to the ecosystem, particularly at the soil level. However, the ancientness of the forest cover, i.e. the uninterrupted duration of the wooded state, is difficult to evaluate from direct observation or from the analysis of cartographic documentation alone, which does not always allow us to go back beyond the middle of the 19th century. We hypothesize that the age of these stands is at least several hundred years old, independent of anthropogenic management and practices. Moreover, based on our historical knowledge of Pyrenean forests, we hypothesize that human practices (pastoralism, various removals) have potentially influenced the historical trajectories of these forest ecosystems, which are now free of strong pressure, but still bear this heritage that we need to characterize.
The objective of this internship will therefore be to test these two hypotheses based on the analysis of wood charcoal found in natural soils. Wood charcoal has proven to be an efficient proxy to evaluate the age of forest stands at the Holocene scale and to detect opening episodes (fire disturbances, pioneer species) of varying importance that may have influenced forest trajectories. The intern, after a period of training in wood anatomy and anthracology, will be in charge of studying charcoal from six pits randomly dug in three forest stands located in the Haute-Garonne (31), the Bois-Neuf (Saint-Mamet commune) and Burat (Marignac commune) forests, and in the Hautes-Pyrénées (65), the Barrada fir forest (Gèdre-Gavarnie commune). They will also contribute to the construction of pedoanthracological reference materials for old forests (dead wood, stages of degradation).
The results could be compared to those obtained in old beech (Fagus sylvatica L.) and fir (Abies alba Mill.) forests in the Romanian Carpathians where a similar study is being conducted. Ultimately, this internship should contribute to a better understanding of the long term history of old European beech-fir forests.
Associated research program:
The internship proposal is part of the ANR JCJC BENDYS (« The last European old-growth (« subnatural ») fir-beech forests: a loNg-term and global stuDY for their better understanding, conServation and management), which focuses on the European old-growth forests of the Romanian Carpathians and the French Pyrenees.
This internship will be part of task 1 of this project, which aims to describe the ecological legacies of past natural (climate, extreme events) and anthropogenic (human harvesting) disturbances on the trajectories of forest ecosystems (structure, diversity, degree of maturity and openness) since the last post-glacial forest re-conquest (about 10000 years ago).
Supervision and host structure:
The trainee will be hosted in the GEODE laboratory (CNRS UMR 5602), located at the University Toulouse 2 Jean Jaurès. The candidate will be trained and co-supervised by Vanessa Py-Saragaglia (CNRS research fellow), Mélanie Saulnier (postdoctoral researcher) and Marie-Claude Bal (teacher-researcher attached to the laboratory).
All analyses will be performed on the PANGEME platform of the GEODE laboratory (anthracology-dendrology platform and sedimentology platform).