Des résultats du projet ANR Bendys avec Dynafor au colloque anthraco2023 à Porto (Portugal)

2 communications orales sur les résultats récents sur les charbons de bois collectés dans le cadre du projet ANR Bendys ont été présentées au 8ième colloque international d'anthracologie qui a lieu du 29 août au 2 septembre à Porto (co-organisé par CIBIO-InBIO-BIOPOLIS et le musée d'histoire naturelle et des sciences de l'université de Porto). Pour en savoir plus: https://anthraco2023.weebly.com/ et https://anr-bendys.cnrs.fr/

1°) Py-Saragaglia V., Saulnier M., Larrieu L., Ladet S., Brun C., Burri S., Danu M., Maisonhaute T., Galop D. (2023) The beech-fir forest, the baseline forest ecosystem in the mountain belt of temperate Europe: questioning a myth

Abstract : The conservation of old-growth forests has regained international attention because of their crucial role in mitigating climate change and in providing refuge areas for biodiversity. The problem, however, is which forests should be prioritized for preservation and what should be done to ensure that other forests evolve to resemble high-value forests. Many agree here that the reference state should serve as a benchmark and guide management so that the forests furthest from that state come closer to it. For the European montane belt, it is commonly admitted that the reference forest is a mature fir-beech forest (Abies alba Mill., Fagus sylvatica L.) with yew (Taxus baccata L.). Palaeoecological and archaeological records provide a longer temporal perspective to address issues of naturalness, maturity, and ancientness, and thus shed light on the gap between these forests and a near-natural (reference) state. Through the analysis of charcoals from soils and charcoal kiln platforms we have attempted to better characterize the Holocene trajectory and sub-recent dynamics of these forest formations in two mountain areas: the Romanian Carpathian and the French Pyrenees. Our results from 6 stands, 3 in each massif are consistent with post-glacial forest recolonization processes known on a regional scale and species successions that followed the last glacier retreat. The temporal depth provided by our study in two disjointed massifs reveals a common trajectory during the late Holocene where the establishment of the fir-beech mixed forest resulted from a close co-construction between the life history of tree species and the development of pre-industrial societies. Considering the high heritage value of these forests inherited from human-nature interaction, it deserves to be considered in its own right and as a reference to be reached and preserved in the European montane level.

Keywords: European old-growth forests; Reference state, Charcoals, Carpathian and Pyrenean Mountains

2°) Parrilla S., Moret P., Stagno S., Saulnier M., Pescini V., Larrieu L., Valladares L., Brustel H., Py-Saragaglia V. (2023) The use of subfossil insects as a complementary tool for pedo-anthracology studies in old-growth forest soils

Abstract : The development of soil charcoal analysis has made it possible to reconstruct forest trajectories at the local scale, thus overcoming the main shortcoming of palynology. However, the presence of charcoal implies the occurrence of a forest fire in the past, which provides only a partial picture, at a given time, of past trajectories. It is therefore essential to look at other indicators. Insects, composing a large part of forest biodiversity, can be valuable proxies for (1) canopy density, (2) forest composition, (3) the presence of old trees or bark debris, and (4) the occurrence of disturbances. However, while the study of subfossil insects is common in peatlands or glacial deposits, it has almost never been conducted in soil archives. This study therefore aims to test the combination of insect and charcoal analysis in soils to reconstruct the trajectories of ancient forest ecosystems and assess their ancientness and naturalness.

We sampled soils from three old-growth forest sites located on the northern slopes of the Pyrenees. We dug two pits in each stand to collect soils and extract and analyse both insect (n=1134) and charcoal (n=1203) remains. The distribution of both types of remains in the soil layers is similar, limited primarily to the upper levels, suggesting progressive burial over time as well as taphonomic processes. Twenty wood charcoals were radiocarbon dated, and the probability intervals cover a long period from the Mesolithic to the present, whereas radiocarbon dating of eleven insect remains provides only modern to contemporary dates, but their low carbon content may have induced a rejuvenation of their dating by several centuries. The insects thus provided additional data on forest trajectories in historical periods and confirmed the multi-century ancientness of the three studied old-growth forests.

Keywords: Old-growth forests, insects, charcoals, soil archives, forest trajectories