Differences in bark anatomy between stem and branches of Olea europaea L.

Summary In addition to morphological characteristics, bark anatomy can provide a more detailed picture of the function of different bark tissues. In the current study, we examined and compared the bark anatomy of the stem and branches of 20-year-old Olea europaea L. We hypothesised that there are differences in bark anatomical traits between stem and branches, which reflect their functional differences in a tree. We found that the widths of bark, phloem + cortex, and periderm significantly differed in the stem and branches; all tissues were wider in the stem. The size and area of the sieve tubes and the proportion of sclerenchyma in the oldest part of the phloem + cortex differed in the stem and the branches. At the same time, numerous similarities in the stem and branch bark anatomy were observed: (1) annual phloem increments could not be determined in the youngest phloem adjacent to the cambium; (2) a distinction between non-conducting and conducting phloem was not possible because the collapse of sieve tubes in non-conducting phloem was not prominent enough to be determined visually; (3) dilatation of rays and axial parenchyma was locally clearly visible; (4) the proportion of phloem and cortex changed with distance from the cambium; secondary phloem constituted the entire bark tissue adjacent to the cambium, while cortex prevailed next to the periderm and (5) phelloderm width did not change with bark age. Differences in the bark structure of the stem and branches of olive trees imply functional differences between these two tree parts and point to different ecological contexts. Moreover, branch bark trait values cannot be used to extrapolate to the main stem bark (or vice versa). Differences support previous studies that have reported that different tree parts are exposed to different microenvironments.