Jean-Louis Edouard

Seven centuries of avalanche activity at Echalp (Queyras massif, southern French Alps) as inferred from tree rings

The purpose of this study was to reconstruct spatiotemporal patterns of avalanche events in a forested avalanche path of the Queyras massif (Echalp avalanche path, southeast French Alps). Analysis of past events was based on tree-ring series from 163 heavily affected multicentennial larch trees (Larix decidua Mill.) growing near or next to the avalanche path. A total of 514 growth disturbances, such as tangential rows of traumatic resin ducts, the onset of compression wood as well as abrupt growth suppression or release, were identified in the samples indicating 38 destructive snow avalanches between 1338 and 2010. The mean return period of snow avalanches was 22 years with a 4% probability that an avalanche occurs in a particular year. On a temporal plan, three maxima in snow avalanche frequency were reconstructed at the beginning of the 16th and 19th centuries and around 1850, correlating with below-average winter temperatures and glacier advances. Analysis of the spatial distribution of disturbed trees contributed to the determination of four preferential patterns of avalanche events. The comparison of dendrogeomorphic data with historical records demonstrate that at least 18 events – six of which were undocumented – reached the hamlet of Echalp during the last seven centuries, but no significant temporal trend was detected concerning the frequency of these extreme events.

Climate/growth relationships in a Pinus cembra high-elevation network in the Southern French Alps

Abstract•IntroductionIn the context of climate change, assessing climate–growth relationships is of high importance in order to understand how forest ecosystems evolve and to test climate models at regional scale.•ObjectivesThis study aims to identify the climate variables that explain most of the variation in Pinus cembra radial growth at different spatial–temporal scales, response functions and moving response functions were processed on chronologies from a dense tree ring network. This original network is centred on the French Alps influenced by the Atlantic, Continental, and Mediterranean synoptic systems.•ResultsA spatial clustering pattern matching the latitudinal climatic gradient was observed in tree ring indexed chronologies and climate responses. The stationary response functions computed for each cluster-averaged population evidenced a thermo-dependent northern cluster (Cl1), a rainfall-dependent southern cluster (Cl3), and an alternative response for the intermediate cluster in between (Cl2). Since the late nineteenth century, the moving response functions indicate an increasing influence of winter precipitation for the northern and the intermediate clusters.•ConclusionConsidering the increase in temperature and reduction both of summer precipitation predicted by general circulation models and of the snow cover and duration in the French Alps, stone pine is likely to be exposed to stressful conditions during the twenty-first century.RésuméDans le contexte actuel de changement climatique, l’amélioration des connaissances concernant les relations entre le climat et la croissance des arbres est primordiale pour comprendre l’évolution des écosystèmes forestiers et tester des modèles climatiques à l’échelle régionale. Afin de déterminer les variables climatiques expliquant significativement les variations de la croissance radiale du Pin cembro à différentes échelles spatiales et temporelles, un vaste réseau de données dendrochronologiques a été utilisé pour le calcul de fonctions de réponse fixes et mobiles. Ce vaste réseau original est centré sur les Alpes françaises soumises à des influences climatiques océaniques, continentales et méditerranéennes. Les analyses en composante principale réalisées sur les chronologies indicées et sur les résultats des fonctions de réponse révèlent l’influence d’un gradient climatique latitudinal permettant d’identifier différents groupes de populations. Les fonctions de réponses calculées pour chaque groupe de populations moyennées mettent en évidence une dépendance aux températures des populations septentrionales (Cl1), une dépendance aux précipitations des populations méridionales (Cl3) et une réponse alternative d’un groupe intermédiaire Cl2). Depuis la fin du 19ème siècle les fonctions de réponse mobiles révèlent une augmentation de l’influence positive des précipitations hivernales pour les populations des groupes septentrionale et intermédiaire. Compte tenu de l’augmentation des températures et de la réduction à la fois des précipitations estivales prédites par les Modèles Globaux de Circulation et de l’épaisseur et de la durée de la couche nivale dans les Alpes françaises, le Pin cembro pourrait être soumis à une augmentation des conditions de stress au cours du 21ème siècle.

Utilisation d'un modèle biogéochimique en dendroécologie. Application au pin Cembro

Using a biogeochemical model in dendroecology. Application to Pinus cembra. Dendroecology, which is based on annual growth variable measure- ments, is in possession of data particularly well adapted to analyse the impact of global change on vegetation production. But the classical statistical methods of quantification of tree ring-climate relationship cannot take into account the effect of CO2 increase. Therefore, a biogeochemistry model (BIOME3) has been adapted to these data and then validated on Pinus cembra. The results indicate that the production is reduced by 14 % if only the climatic changes are taken into account. If both climatic changes and CO 2 increase are taken into account the production is increased by 62 %. The direct fertilisation effect of CO 2 increase will have more influence on the productivity than the indirect climatic effect.

A long-term tree-ring chronology over 796 years for silver fir (Abies alba Mill.) in Southern France

Abstract• Key message This paper presents ring width data of silver fir trees (Abies alba Mill.) from buildings and living trees from 1214 to 2009 in southeastern France. A 796-year chronology spanning the period 1214–2009 has been built. Data can be used for dating projects, paleoecology studies, and climate reconstructions. Dataset access is at https://hal.archives-ouvertes.fr/hal-01528324. Associated metadata is available at https://metadata-afs.nancy.inra.fr/geonetwork/srv/fre/catalog.search#/metadata/a74b4869-318c-458c-a5fe-f9ff44a5082c