Birch Stem and Wood Traits in Genetic and Silviculture Trials in Southern Sweden

Sammanfattning: Swedish tree species of birch (silver: Betula pendula and downy: B. pubescens) are often neglected during forest management activities, resulting in low value logs. This thesis investigated birch stem characteristics and wood properties important for solid wood products, in genetics and management trials in southern Sweden. As well as visual stem size and form measurements, non-destructive testing and evaluation (NDT) tools were used to indirectly estimate wood density (hardness), wood stiffness, and grain angle.The results of this work suggest that for the 19-year-old silver birch and 15-year-old downy birch sites, important solid wood traits were under a reasonable degree of genetic control. It seems possible to breed birch to improve grain angle since heritability and genetic variation was high for this trait. Silver birch genotypes are expected to perform similarly across sites. At a site with both birch species, silver birch was larger with denser wood than downy birch. Few genetic correlations between measurements means selection for one trait will not inadvertently affect another trait. The radial density profiles showed density was continuing to increase. Acoustic velocity (AV) and fibre length were highly correlated, hardness and density were related, and ring width was related to ring density. In a 35-year-old planted Norway spruce stand, naturally regenerated birch AV was not different between treatments (20% or 50% of plot trees were birch by number). However, a correlation was observed between DBH and AV. This older site may reflect common Swedish conditions since planting birch is rare, and likely had more mature birch wood than the genetics trials. Although meeting an immediate need for studies of birch wood properties from managed stands, this work covered few sites. To meet this limitation the tools and techniques applied in this thesis could be used in further studies. The results of this thesis work will be of interest to forest managers who want to breed birch, or select birch stands, for solid wood products.