Beech (Fagus sylvatica L.) branches show acclimation of xylem anatomy and hydraulic properties to increased light after thinning

Hydraulic acclimation of Fagus sylvatica L. was analysed in response to forest thinning. Several months after thinning, leaf and xylem water potential and stomatal conductance of thinned branches were compared to sun-exposed and shade branches. We characterised vulnerability to cavitation for branches taken from these three treatments. We compared effect of thinning on xylem anatomy (mean vessel diameter, vessel density). Thinned branches exhibited higher stomatal conductance and lower leaf water potential. These results were well correlated with vulnerability to cavitation. Thinned branches were less vulnerable than shade branches and mean vessel diameter and vessel density increased in thinned branches. These differences showed a partial hydraulic acclimation to climate changes. We confirmed that vulnerability to cavitation and xylem anatomy in Fagus sylvatica acclimate to changing light conditions, and we concluded that hydraulic architecture acclimates sufficiently fast after environmental changes to protect xylem from dysfunction while maintaining open stomata.