Observation of Quercus petraea epicormics with X-ray CT reveals strong pith-to-bark correlations: Silvicultural and ecological implications

Our knowledge about oak epicormics has considerably increased in recent years, particularly thanks to the external recording of all epicormic types (suppressed buds, bud clusters, sprouts, picots and burls) and to internal observations made using X-ray computed tomography (CT). Several stages of epicormic ontogeny have been identified. The aims of this study were to provide the quantification of oak epicormic ontogeny and to identify the relationships between epicormics present near the trunk pith and epicormics present at the surface of the bark, based on data recovered from X-ray CT scanning. One to three 1-m-long logs per tree were recovered from crop trees felled in five experimental stands located in four forests in northern France. The manual interpretation of the images provided by X-ray CT makes it possible to identify the origin and fate of every rameal trace, i.e., branch knot, epicormic shoot or trace of suppressed buds. The fate of branches and the origin and the fate of suppressed buds and sprouts were quantified. A strong relationship between the number of epicormics at the surface of the bark and the number of epicormics near the pith was highlighted. This could result in important silvicultural recommendations in terms of the necessary early selection of crop trees with the lowest number of epicormics possible, especially suppressed buds. From a broader ecological point of view, this paves the way to a better understanding of the variability of the sprouting response induced by disturbances, which is assumed to develop at an early stage in the tree life.

► Provides a quantitative assessment of the rameal ontogenesis based on internal X ray CT observations.
► Reveals for the first time a strong correlation between pith and bark epicormics.
► Highlights a quite low variability of the number of sequential branches per meter.
► Proposes an early selection of crop trees of future high quality by a thoroughly inspection of the trunk epicormics.
► Deduces ontogenic implications for studies concerning sprouting ecology in disturbed environments.