Links between tree phenology and wood traits in sessile oak (Quercus petraea (Matt.) Liebl.)

Tree phenology and wood traits are considered of foremost importance in understanding species' responses to the influence of climate change, thus the existence of a link between tree phenology and wood traits has become increasingly appealing in forestry research. The aim of this study was to explore the relationship between leaf flushing and wood traits (basic wood density, tree ring width, tree ring phenology, sapwood width and number of sapwood rings) in sessile oak (Quercus petraea (Matt.) Liebl.). We investigated trees with distinctive phenological behaviour (early flushing and late flushing) from three peripheral populations, one non-peripheral population and one sessile oak comparative trial close to the species eastern distribution range in the Eastern Carpathians. Covariance analysis, partial correlations, nonparametric statistics, and Principal Component Analysis were used to investigate the link between tree phenology, wood density, and some structural metrics. It was statistically confirmed that, at comparable ages and radial growth, the sessile oak trees exhibiting late leaf flushing had lighter basic wood density and greater density differences between sapwood and heartwood than early flushing trees. Independent of age, trees with intermediate flushing have wider rings, the formation of which is much earlier than in early flushing trees. At the same age, late trees from geographically peripheral populations have a higher number of sapwood rings. Also, the results revealed that peripheral populations had lower basic wood density, while this was not the case for peripheral provenances tested in the comparative trail established in an ecologically optimal area. These findings help us enlarge our understanding of the relationship between leaf flushing and wood traits, which could be useful for improving sessile oak management strategies near the eastern limit of the sessile oak natural range, which is becoming more and more critical in the context of the current climate changes.