Structure and subsequent seasonal changes in the bark of sessile oak (Quercus petraea)

Key message The collapse of some cell types and the simultaneous growth or expansion of others hinder the estimation of the contribution of individual tissues to the variation of bark dimension over time. Information on the spatio-temporal pattern of secondary changes occurring in older bark, as well as the activity of phellogen and the development of periderm is still relatively scarce. Anatomical and histometrical investigations were carried out on the bark of mature Quercus petraea growing in Ljubljana, Slovenia. The bark of the oaks was on average 19 mm thick, with the inner bark and the rhytidome accounting for 39 and 61 %, respectively. A high correlation was found between the widths of the rhytidome and of the entire bark, but a fairly weak one between inner bark and entire bark. The youngest phloem increment on average represented around 5 % of the inner bark and around 2.1 % of the entire bark. Growthring boundaries were not distinguishable in the collapsed phloem; however, counting the phloem increments was possible due to the presence of phloem fibres at the transition from early to late phloem. We also followed the spatial-temporal secondary changes in collapsed phloem tissue. Phloem increment development in Q. petraea showed that patterns of phloem formation at one location remained practically unchanged in different years. The relationship between processes occurring in different bark tissues is not linear. In addition to the high variability in bark, the collapse of some cell types and the simultaneous growth or expansion of others hinder the estimation of the contribution of individual tissues to the variation of bark dimension over time.