Comparison of radial increment and volume growth in stems and roots of Quercus petraea

Dendrochronological studies dealing with roots, stems and branches are very rare or often take the form of short notes. The difficulties of detecting rings and of quantifying the radial growth in roots have already been described for various species. In oak the anatomical root structure differs from stemwood. The roots are radial-porous or diffuse-porous, and there is often no clear distinction between individual rings. In our study visual and radiographic techniques were used to examine radial increment in roots of sessile oak (Quercus petraea L.) which was compared with radial growth in branches and along the stem. Coarse roots were cut from four 30- to 34-year-old trees that had been uprooted mechanically and disks were taken at different distances from the stem-root base. Ring widths were measured in the stem at height of 0.3 m, at breast height (1.3 m), beneath the crown, in branches of the crown, and in roots every 20 cm. The ring widths were cross-dated, and the heterogeneity of growth within a root and within the root system were analysed. Asymmetric growth frequently occurred in roots so that ovals, I-beam and T-beam shapes were developed. With the method used in our study the annual growth layers close to the central cylinder could be distinguished as well as beneath the bark. Pointer years were detected in all sections of the tree and permitted correction of ring widths in roots. Root system, stem and branch showed a basic similarity in their radial sequence of ring width. The annual biomass increment was weaker and more variable with several consecutive changes in the roots than in the stems. The root/shoot ratio reached a minimum rather early, beginning at the cambial age of 20 years.