Public defence in forestry industry production systems: Grace Jones

Link to the thesis in DiVA Birch Stem and Wood Traits in Genetic and Silviculture Trials in Southern Sweden

Public can also participate at the Public defence May 13 via Zoom. 

Link too zoom Public defence Grace Jones 
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Abstract 

Swedish tree species of birch (silver: Betula pendula and downy: B. pubescens) are often neglected during forest management activities. Modern policy and preferences may favour the retention of broadleaved tree species, yet Swedish birch is mostly used for pulp, fuel and firewood as there are few local birch sawn wood producers. This thesis investigated birch 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. Stiffness relates to both wood density and acoustic velocity (AV), and here the two were usually considered separately. Wood properties were also measured in the laboratory with both light microscopy for wood cell dimensions, and X-ray densitometry or volumetric displacement for wood density. Radial density profiles of ring width and density by year and age were then made from the X-ray images, and used to investigate internal radial variation.

These measurements represent some of the first NDT measurements on birch genetics trials, however silver birch density and cell properties had been previously assessed in Sweden for a study of pulping properties. The genetics trials had reasonable heritability estimates for both birch species with regards to hardness and grain angle, but the NDT trait AV had low heritability. It seems possible to breed birch to improve grain angle since there was also high genetic variation for this trait. Silver birch was planted at two sites and there was a high genetic correlation between sites, suggesting genotypes could have similar performance across a range of sites. Few genetic correlations between measurements means selection for one trait will not inadvertently affect another trait. The results of this work suggest that for the birch material studied, solid wood traits are under a reasonable degree of genetic control.

Few managed birch sites exist in Sweden, so this is also one of the largest Swedish studies of birch wood properties from stands with known management history. This opportunity allowed for the comparison of silver and downy birch grown at a single site, where generally silver birch had better trait performance (stem size, wood density, and AV), except downy birch had slightly better average grain angle. As for phenotypic relationships, AV and fibre length were highly correlated, hardness and density were related, and ring width was related to ring density. This could help forest managers to indirectly assess wood properties of managed birch, using related traits like growth rate or NDT tools.

In a 35-year-old planted Norway spruce (Picea abies (L.) Karst.) stand, there were three treatments of basal area proportion of birch in each plot (0%, 20% and 50% birch). There was an insignificant difference in AV between treatment groups. The correlation between DBH and AV (0.4) was much higher than in the young planted birch genetic trials (0.2-0.3). This site also differs to the genetics trials as it was naturally regenerated birch in a planted spruce stand, however this may better reflect common Swedish conditions since planting birch is rare. The radial density profiles from young genetics trials showed density was continuing to increase, and based on other studies it is likely the species mixture trial had more mature birch wood. Despite differences in age and size, wood moisture content generally increased towards the pith for all sites and samples.

Although meeting an immediate need for studies of birch wood properties from managed stands, a key limitation with this work is the lack of sites. The tools and techniques applied in this thesis work could be used in future studies, since here the effect of climate and growing conditions were difficult to account for. A greater number and scope of studies on birch properties should occur as the interest in birch management continues to increase in Sweden. This will help with site selection and wood resource allocation, to hopefully increase the volume of Swedish birch suitable for use by sawmills, instead of low values uses like pulp, fuel, and firewood. 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.

Keywords acoustic velocity, Betula spp., dynamic MOE, genetic parameters, grain angle, hardwood, Itrax densitometry, mixed forests, non-destructive testing, stem form