Shrinkage pattern assessment for black pine juvenile wood delimitation

Abstract

Juvenile wood is associated with shrinkage and a high probability of warping and checks in end products, reducing their value and even causing them to be rejected for structural purposes. This work studies the variations in yearly shrinkage caused when wood passes from green to dry state. The methodology proposed is based on the juvenile wood (JW) location using annual shrinkage variations. Pinus nigra Arn. grown using different silviculture techniques was chosen for study because its wood is characterized by severe shrinkage problems. This characteristic is analyzed in the radial and angular directions, of which the latter is a different methodology for evaluating warping problem rather than the commonly used ratio of anisotropy. It takes into account the annual measurements obtained from a disc cut from the tree trunk at various heights. The results were compared with the segregated JW and mature wood (MW) area obtained by radial densitometry pattern variation methodology. The results show that radial shrinkage is higher near the pith but stabilizes earlier (3–7 rings) than angular shrinkage (9–11 rings). Nevertheless, the opposite initial radial pattern occurs in angular shrinkage, which is low near the pith but increases annually towards the bark until it stabilizes. No clear effect of height in the tree when comparing the radial shrinkage patterns obtained along the bole can be defined. Silviculture practices have no significant influence on shrinkage percentage. Shrinkage and densitometry methodologies show differences in the quantification of JW volume percentage between JW and MW estimation. Results show that radial shrinkage pattern methodology, which is associated with warping problems, classifies a higher tree volume as good quality for end uses in comparison to the use of radial densitometry pattern methodology. On the other hand, if classified by radial densitometry pattern variation, warping problems associated with JW should not be a problem when sawn.