Effects of ecological factors on radial growth and wood density components of sessile oak (Quercus petraea Liebl.) in Northern France

摘要

Many studies have demonstrated that sessile oak (Quercus petraea Liebl.) wood density is related to ring width, but most have focused on within-tree variability and have never explored large ecological gradients. Other studies indicate that ring width is largely controlled by ecological factors. Hence it has been concluded that ecological factors have an effect on wood density, yet few studies have directly analysed the link between these two variables. The respective effects of climate, soil water capacity and nutrient richness on wood density are also debated. Lastly, sessile oak is a ring-porous species, so that earlywood and latewood are likely to be differently influenced by ecological factors. Our objectives were (1) to test whether wood density remains under the influence of ecological factors after statistically controlling for ring width, (2) to compare the direction and magnitude of site factors on ring width and mean ring density and (3) to compare the response of earlywood and latewood. A total of 18,287 rings were analysed from 297 dominant sessile oaks in 99 plots distributed over north-eastern and north-western France in mature, even-aged high-forest stands. Wood density and width were measured using X-ray microdensitometry. Multiple regressions were performed on plot means using ecological factors as predictors, and then using ring width or latewood proportion as covariable. Regressions were followed by variance partitioning. The ecological factors had an effect on mean ring density that was independent of ring width, but their effect was slight. The percentage of variance explained by ecological factors was twice as high for radial growth components (earlywood, latewood and total ring width) as for wood density components (earlywood, latewood and mean ring density). Climatic, water-related and nutrient-related factors did not always have a consistent effect on radial growth and wood density. Earlywood and latewood responded slightly differently to the ecological factors, with a higher sensitivity of latewood to climate/water-related factors. Unexpectedly, mean ring density did not correlate with ring width at plot scale, although mean ring density and ring width were nearly always positively correlated within a tree. No correlation between ring width and ring mean density at plot scale may be due to the opposite effects of water-related factors on latewood proportion and latewood density. Our results help identify best site conditions for high-quality sessile oak production and argue for a revision of the French management policy.