Long-term changes in wood density and radial growth of Quercus petraea Liebl. in northern France since the middle of the nineteenth century

Long-term changes in sessile oak (Quercus petraea Liebl.) growth and wood d ensity were studied using cores collected from 99 even-aged high forest sta nds between 56 and 187 years old, located in north-eastern and north-centra l France. Growth and density trends were tested by analysis of variance and covariance. Two models were applied to two samples, sample A and sample B (sample B being a sub-sample with limited cambial age and calendar date ran ges). Model 1 showed a significant increase in radial growth: +35%, +87% an d +66% in earlywood width, latewood width and ring width, respectively, fro m 1811 to 1993 for sample A. Consequently, there was a positive trend in la te wood ratio (+14%). A slight decrease in wood density was found: -3.3% an d -5.4% for earlywood and late-wood density, respectively. Despite an incre ase in late wood percentage, mean ring density showed a -2.0% decrease. Mod el 1 applied to a biomass indicator (densityxring width) showed a 62% incre ase from 10.4 to 16.8 kg m(-3) between 1811 and 1993 for sample A. Results for sample B were slightly different: the increase in latewood ratio was no t detected. Model 2 showed a change with time in the positive hyperbolic re lationship between mean density and ring width. The results are discussed. The decrease in wood density cannot be explained by N atmospheric depositio n or by long-term changes in average temperature. Increasing atmospheric CO 2 levels cannot be invoked owing to the present lack of studies. Finally, h ypotheses concerning long-term changes in wood anatomical characteristics a re proposed.