Anatomy of bark and xylem of Egonoki (Styrax japonicus) suffering from bark-stripping by sika deer

Abstract

Bark-stripping by sika deer has often been reported to lead to high tree mortality. Only few species were reported to survive heavy bark-stripping. Here I report on bark recovery in Egonoki (Styrax japonicus), and discuss anatomical features related to successful bark recovery. The regenerated outer layer of a stem after bark-stripping in the previous year was investigated. The regenerated bark consisted of an inner bark and an outer bark segmented by a periderm. The innermost surface on the separated bark-side sample was a rather wider layer of thin-walled cells, presumably composed of cambial zone and developing phloem. The outermost layer on the separated xylem side was a developing-xylem-tissue with a wider primary-wall-zone but no apparent cambium remaining. Traumatic tissue was observed only as small traces in the previous-year’s growth ring. In contrast, primary-wall-developing xylem elements were only in 1 to 2-cell-layers remaining on the outermost surface of the stem soon after bark stripping, and was covered with a translucent substance. Interestingly, wood anatomical features common to tree species that can survive heavy bark-stripping by deer are “apotracheal axial parenchyma in tangential to oblique lines or in narrow bands” and “diffuse-porosity with narrow-diameter vessels”. Cambium can be regenerated within a surface callus formed over the entire wound area for some species. Although traumatic parenchyma zone was not formed in Egonoki, wound cambium may regenerate similarly. The fact that axial parenchyma cells can form a more-or-less continuous tangential plane just like a cambium leads to the speculation that cells differentiating into axial parenchyma cells under the covering substance can be reprogrammed (dedifferentiated) into meristematic cells, comparable to cambial initials, by the stimulation of bark-stripping.