Tree-ring response of<i>Populus tremula</i>L. and<i>Quercus robur</i>L. to recent spring floods of the Saône River, France

Abstract

:The effects of floods on the radial growth of Populus tremula L. and Quercus robur L. in past decades were studied on a forested island in the Saône River (France). The study considered two stands including both tree species, located above and below the altitude of 169 m, which corresponds to the altitude reached by major river floods. Only the Populus trees closest to water showed a significant growth reduction (narrow rings) in response to recent floods. The reaction of Quercus to prolonged flooding was reflected in the size and distribution of vessels in annual rings. Rings formed in years when trees were flooded have a larger porous zone, including homogeneous small vessels forming a wide earlywood zone. Since 1980, the Saône River floods have shifted from late-winter - early-spring to late-spring flood events (March-April and even early June). Late floods of large magnitude and duration, as in 1983, 1986 and 1989, had precedents only in the 19th century (1856). We hypothesize that such major floods were produced by minor changes in regional atmospheric circulation which favor a higher frequency of rain events of Atlantic influence. Tree-ring signatures of flooded trees are therefore narrow rings in Populus and anomalous structure of porous earlywood in Quercus.