Abstract
The growth response of sessile oak to extreme climatic years has been investigated from 1914 to 1993 using extreme years growth, i.e. pointer years. 31 mature and pure stands were cored in northern France (720 trees), under varied climates, from oceanic to semi-continental conditions. The analysis has highlighted similarities in growth characteristics throughout the study area : abrupt growth changes depend mainly on summer temperatures and precipitations (from May to July), narrow rings generally correlate with warm and dry climate (1921, 1976, 1989). Narrow rings also occur with strong winter frosts (1956). Pointer years analysis has allowed to define 2 main regions in northern France, with specific responses to extreme climatic events : plots in north-western France (from Brittany to Champagne) under oceanic climate, with a decennial pointer years frequency around 0,2 strongly correlated with summer De Martonne Index, and plots in north-east France (Lorraine, Alsace, Franche-Comté) under semi-continental climate, with higher frequency (around 0,3), depending on both summer and winter conditions.
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