Évolution de la croissance radiale du pin d’Alep (Pinus halepensis Mill.) en Provence calcaire (sud-est de la France)

Abstract

Global changes : climatic change, atmospheric CO2 rise and nitrogen deposition increase, are likely to have an effect on forest production. Dendrochronology offers the possibility to verify this hypothesis in natural conditions since tree-ring data can be interpreted as indicators of forest ecosystem productivity. Numerous studies of radial tree growth have been carried out, mainly in temperate and cold climate regions. However, the Mediterranean region appears particularly promising for researching the causes of the observed trends. Dendrochronological data used in this study come from 21 Aleppo pine stands located in South-Eastern France. Analysed variables are : minimal density, earlywood density, earlywood width, maximal density, latewood density, latewood width, and a tree growth index. Raw data are used for minimal and maximal density, whilst the other variables are standardised. Trends are detected using simple linear regressions over the period from 1950 to 1990. In contrast to the results published in the scientific literature, this study does not find out positive general significant trends regarding ring widths. However, this work shows an increase of earlywood density and a decrease of latewood and maximum density. These observations are coherent with some recent experimental results, suggesting that the increase of the earlywood density could be a consequence of CO2 increase, whilst the decrease of latewood density could be a consequence of the increase of nitrogen deposition. Moreover, these results show that the decrease of latewood density, observed by several authors for North and Central Europe, seems also to be pertinent for South Europe. This suggests the influence of a common factor to all these regions which could be the increase of nitrogen deposition.