Abstract
Wood use for structural purposes has increased in the last decade in Spain. However, as a raw material, wood needs to comply with requirements that are not always present. Knowledge about the wood quality from the trees on the stand is essential for providing feedback to forest managers and for taking the required actions to obtain suitable silviculture treatments. Two of the main wood species used in construction in Spain, Pinus nigra and Pinus sylvestris, have been studied in order to determine the amount of juvenile wood, which has been identified as a harmful characteristic for its decrease in quality of the physical-mechanical properties of these species. Being relevant for the best quality of timber in the part along the bole where the logs are obtained, the distribution of juvenile wood at different heights and the effect of several silvicultural treatments have had on juvenile wood formation has been considered. The juvenile-mature wood boundary (transition year) was calculated through segmented linear mixed models employing as variables annual latewood density, obtained through micro X-ray densitometry, silvicultural practices, and a drought index. The results show how juvenile and mature wood is distributed along the bole and the proportion of juvenile wood. Its reduction according to the different thinning and pruning silvicultural practices is presented
Highlights
On wood used for structural purposes, the properties from round wood lumber are decisive in terms of complying with construction standards
At the basal height the transition year (TY) varied a lot among trees, being achieved sometimes even later than further up the bole, this could be due to the mechanical demands and the proximity to the root system (Lachenbruch et al 2011), if only one measurement can be done per tree, basal height should not be the height chosen
The Juvenile wood volume of P. nigra and P. sylvestris is not significantly decreased at most heights of the bole when thinning and pruning treatments are performed after the TY occurrence
Summary
On wood used for structural purposes, the properties from round wood lumber are decisive in terms of complying with construction standards. As a result of this, the trees have a different proportions of anatomical and wood structures deriving into a significant reduction in their mechanical properties (Dowse and Wessels 2013, Wessels et al 2014, Hermoso et al 2016) As these problems arose, there have been several researches carried out on wood quality, related to wood density and MFA (micro fibril angle) being the two most influential properties for predicting mechanical properties (Tsoumis 2009, Burdon et al 2001, Auty et al 2014, Moore et al 2015, Mäkinen and Hynynen 2012). The impact of silvicultural interventions and planting density affects growth and wood volume; and, how straight the bole is, the type and amount
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