Tension wood occurrence in three cultivars of Populus x euramericana. Part I: Inter-clonal and intra-tree variability of tension wood

The main wood quality problem affecting poplar trees is tension wood occurrence associated to end-splits after felling, distortions of products, woolly wood, etc. The objective of this study was to estimate the occurrence of tension wood by using the external shape of the stem and the 3D distribution of annual growth rings. This paper is the first of two papers and presents the inter-clonal and intra-tree tension wood variability. A clear clonal-effect was observed on tension wood area percentage (I-MC > I214 > Luisa Avanzo). The clone with the best tree morphology (I-MC) showed the highest percentage of tension wood (15.3%). Concerning the intra-tree variability, tension wood extent increased significantly at the tree base (< 30-50 cm). In the radial direction of the stem, the percentage of tension wood showed an U-shape distribution. The first peak, close to the pith, corresponds to the establishment growth period during the open growth and the second peak, close to the bark corresponds to the competition growth period.