Dendroécologie comparée du sapin blanc (Abies alba) et de l'épicéa commun (Picea abies) dans une vallée alpine de France

Abstract

A comparative dendroecological study was carried out in an alpine valley of France (Haute-Tarentaise, Savoie) to analyze the climatic influence on the radial growth of the silver fir (Abies alba Mill.) and the Norway spruce (Picea abies Karst.). Ten populations were sampled at three altitudes on two exposures (North and South). For each population, a chronology of ring-width indices was standardized with a 7-year weighted moving average and with a residue chronology by autoregressive modelling. Then, correlation functions were calculated between growth indices standardized with both methods and climate with an iterative process (bootstrap). The climatic window used here covers 3 years, with mean monthly data of precipitation and temperature. The summer is the most important period for the spruce, which shows a transition along the altitude. This species is successively sensitive to drought at the lower level (year n of ring formation), sensitive to the previous hot summer (n - 1) at the intermediate level, and sensitive to the cold the same year (n) at the upper level. Fir growth is favoured by a rainy previous summer (n - 1) and a hot summer n at the highest altitude on northern slopes, with a difference between northern and southern slopes stronger than for spruce. The interspecific comparison reveals that the fir uses soil water more efficiently and is thermophile, whereas the spruce is more sensible to summer drought. The influence of the year preceding ring formation appears with both methods of standardization and seems to show a real physiological effect.