ELEMENT ANALYSIS OF TREE-RINGS IN PEDUNCULATE OAK HEARTWOOD - AN INDICATOR OF HISTORICAL TRENDS IN THE SOIL CHEMISTRY, RELATED TO ATMOSPHERIC DEPOSITION

When investigating historical alterations of the soil chemistry, it co uld be interesting to determine the mineral content of the successive annual tree rings. The study reported here aimed at verifying this ass umption. Oak heartwood was selected in order to minimize the disturban ce due to element translocations in the wood. This study was carried o ut in a forest included in a floristic and edaphic survey performed ea rlier throughout northeast France. Xylem cores were extracted from the boles of five over 60-year-old pedunculate oaks in each of 68 plots. The analysis showed on average an increase in nitrogen and aluminum, a decrease in phosphorus, potassium and magnesium, and no change for ca lcium, in the rings corresponding to the last 30 years of the heartwoo d (1938-1967). These results are consistent with those of the floristi c and edaphic survey, which had shown an increase in nitrogen and a tr end towards acidification in most of the soils between 1970 and 1990, mainly due to atmospheric deposition (Thimonier et al, 1992). Thus, th ese changes in the soil chemistry had probably already affected the fo rest studied between 1938 and 1967. Finally, tree-ring analysis of oak heartwood appeared to be an effective approach to reveal historical c hanges in forest soil chemistry.