Appearance of crowns and growth of trees in the last few decades in the border regions of Germany, France and Switzerland

L'article concerne les relations mises en évidence entre la croissance des arbres et l'état des houppiers dans les Vosges, le Jura (français et suisse), le Plateau suisse, quelques régions alpines suisses et italiennes, et les secteurs forestiers les plus importants du Bade-Wurtemberg. Les études reposent sur des données dendrométriques et des observations de houppiers recueillies sur des sites très nombreux. Ces relations varient fortement selon les arbres et les situations. Elles sont très marquées par la différenciation sociale au sein des peuplements. Il n'y a pas un seul mais de nombreux « états normaux » selon l'essence, l'âge, la station, les conditions climatiques et la gestion sylvicole. Il est montré le rôle capital de la pluie et la température,au cours de la période 1920-1986,dans le déterminisme des années ou des séquences d'années marquées par un accroissement très faible. Globalement,en particulier dans les stations pauvres et moyennes, on observe une nette augmentation du niveau de productivité, tant pour l'Épicéa que pour le Sapin. Ce phénomène pourrait impliquer une ou plusieurs des causes suivantes : amélioration de la minéralisation,augmentation du CO2 atmosphérique, meilleures conditions climatiques, meilleures pratiques culturales. Enfin les auteurs proposent divers objectifs de recherche et font des recommandations pour affiner les études dendroécologiques.The article deals with the relationships between the growth of trees and the condition of the crowns in the Vosges, the Jura (French and Swiss), the Swiss Plateau, some Swiss and Italiand Alpine regions and the most important forest sectors of Baden-Württemberg. The studies are based on dendrometric data and observations of crowns made at a large number of sites. These relationships vary greatly according to the trees and the conditions. They are greatly influenced by the social stratification within the stands. There is not one but many «  normal conditions » depending on species, age, site, climatic conditions and silvicultural management.The major role is demonstrated of rainfall and temperature, during the period 1920-1986, in the determination of years or series of years marked by very low increments. Overall, particularly on poor an intermediate sites, there is a clear increase in productivity level both for spruce and fir.This phenomenon could imply one or several of the following causes : improved mineralisation, increased atmospheric CO2, better climatic conditions, better silvicultural treatment. Finally, the authors propose various research objectives and make recommendations for the improvement of dendroecological studies

Debris-flood reconstruction in a pre-alpine catchment in Switzerland based on tree-ring analysis of conifers and broadleaved trees

Past debris‐flood activity on the forested fan of Torrent de la Greffe located in the Swiss Prealps was assessed from growth disturbances in coniferous and broadleaved tree species. The study of 186 tree‐ring sequences sampled from 44 Norway spruce (Picea abies (L.) Karst.) and 55 broadleaved trees from various species affected by past activity and the sampling of an additional 49 trees for the reference chronology allowed the reconstruction of 17 debris‐flood events since AD 1900. The spatial analysis of trees affected during particular events on the geomorphic map helped the identification of five breakout locations in the torrent and affected sectors on the fan. The coupling of tree‐ring analysis of coniferous and broadleaved tree species proved to be a valuable tool for the reconstruction of past events. Debris‐flood frequency in the investigated torrent (0.16 event yr‐1) is considerably lower than the frequencies reconstructed in most other catchments in the Swiss Alps. As material for the entrainment of debris floods is not always readily available, the torrent has to be seen as supply‐limited