Ultrastructural evaluation of compression wood-like properties of common juniper (Juniperus communis L.)

To date, very little is known about the ultrastructure of common juniper, Juniperus communis L (juniper). In this study, the mechanical properties of juniper, its chemistry and ultrastructure has been analyzed. The data are presented in comparison to the normal wood (NW) and compression wood (CW) of spruce. Helical grooves, which are a characteristic of CW, were clearly visible in micrographs of juniper. The angle of the grooves with respect to the fiber axis was ca. 40 degrees, which correlates with the microfibril angle determined by X-ray diffraction. Data from 4-point bending tests show that juniper and spruce CW exhibited similar behavior. The elastic moduli of both species were only ca. half from that of NW spruce. The composition of juniper fibers resembled that of CW fiber with respect to high lignin and hemicelluloses contents. However, the galactose content in CW of juniper was low and in CW of spruce was high. Raman imaging clearly revealed that the lignin/cellulose ratio in the fiber cell wall of juniper was similar to that of NW spruce.