This study investigates wood density and anatomy of juvenile silver birch stems in Sweden,grown in mixed conifer stands. Our aim is to investigate if fertilization provides increased growth, aswell as an eventual reduction in stem wood density. Measurements of basic density, ring width, cellwall thickness, and vessels are analyzed for 20 birch trees. Bark to pith radial sections are analyzedusing a light microscope and the freeware ImageJ to compare treatments and ages. The results showthat trees with fertilizer treatment have wider growth rings and thinner cell wall thickness comparedto unfertilized trees. The fertilized trees also have a lower cambium age at the same height and thesame diameter, and a slightly lower stem mean density (420 kg m³) than the unfertilized stems(460 kg m³). Fertilizer is a significant determinant of density and cell wall thickness in nonlinearmodels. The fertilized trees have increased growth and reached a fixed diameter earlier. The agedifference between the trees likely explains some of the differences in cell wall thickness. This studysupports the use of fertilizer as a silvicultural option for increasing the growth rate of silver birch fora relatively small reduction of wood density.

In response to the furniture industry’s growing demand for raw material, large volumes of juvenile silver birch and downy birch stems available from pre-commercial thinning operations in Sweden’s forests could offer solutions. However, such stems are not currently used on an industrial scale, and most research conducted on birch stems in general has neither focussed on young trees nor the potential use of the central stem part around the tree pith. The resulting lack of knowledge about the juvenile part of birch wood thus requires additional information about the material properties of birch, which could encourage its use for various purposes in the furniture and other industries.

The initial literature review performed for this thesis has highlighted some properties of juvenile birch required for its use as a furniture material, as well as identified topics concerning the physical characteristics of juvenile birch about which knowledge is currently limited. Consequently, the objectives of this thesis were to explore some characteristics of juvenile birch—bark thickness, wood-to-bark bonding ratio after drying, variations in the density and width of growth rings, and anatomical growth response to fertilisation—in order to increase the knowledge.

The material studied came from mixed birch and Norway spruce stands at two sites in southern Sweden, namely Asa and Toftaholm. The birch stems were naturally regenerated silver birch and downy birch, with breast height diameters between 30 and 83 mm. Fertilised and unfertilised silver birch trees were sampled at Toftaholm, whereas unfertilised stems of silver birch and downy birch were sampled at Asa. The characteristics of stems from the pith to bark (radial direction) and along the stem (longitudinal direction) were measured. The wood-to-bark bonding ratio on downy birch after drying was calculated as the percentage of the stem circumference with full contact between the wood and bark, while oven-dry density and basic wood density for silver birch were determined by using the water displacement method. The impact of ring width on wood density was statistically analysed, and an image analysis of the wood anatomy was conducted to elucidate their relationship.

Amongst the results, bark thickness along the stem had the highest deviation in the section closest to the stump. Moreover, the wood-to-bark bonding ratio after drying measured for juvenile downy birch seemed to depend more on the stem’s diameter than the sampling height along the stem. Such results are relevant for processors seeking to estimate the volume of wood under the bark. The wood-to-bark bonding ratio was highest for diameters between 30 and 39 mm, and neither did that relationship correlate with the sampling height along the stem.

Variation in wood density in the radial and longitudinal directions in juvenile silver birch suggested that such density negatively correlated with growth rate (ring width). That relationship held true for stems at each site and between the sites, irrespective of management or growing conditions. As expected, mean wood density was lower in fertilised trees than in unfertilised ones, and towards the bark, radial density increased more in trees that grew more slowly. At the same time, variation in longitudinal density in young silver birch trees was low. Quantitative wood anatomy studies confirmed that the fertilised juvenile birch had younger cambia, thinner cell walls, and fewer vessels per mm² than unfertilised trees in the same diameter class.

Overall, the knowledge generated in the study may facilitate the industrial use of juvenile birch stems and wood in interior and furniture applications. The role of wood anatomy in determining the mechanical performance of juvenile birch stems should be further examined, however, to possibly reveal new opportunities for the use of juvenile birch.

Det finns ett växande behov av råvaror till möbelindustrin. Stammar av juvenil vårtbjörk och glasbjörk finns tillgängliga i stora volymer från röjning i svenska skogar. För närvarande finns det inget storskaligt industriellt nyttjande av det virket. Bättre kunskap om dess virkesegenskaper kan öppna upp möjligheterna till olika användningsområden. Dock har en majoritet av den befintliga björkforskningen ofta exkluderat studier av innersta veden närmast kärnan, vilket resulterat i en låg kunskapsnivå om det juvenila virket.

I den inledande litteraturstudien i denna uppsats belyses vilka krav som ställs på materialegenskaperna i möbelvirke. Vidare identifieras befintliga kunskapsluckor i fysiska och mekaniska egenskaper för juvenil björk. Målet med denna uppsats är därför att utforska några egenskaper, såsom barktjocklek, barkvidhäftning efter torkning, densitet och årsringsbreddsvariation samt hur gödsling kan påverka vedanatomin.

Materialet kom från blandskogsbestånd med gran och björk i Asa och Toftaholm i Götaland. Björkarna var självföryngrad vårtbjörk och glasbjörk och stammarna hade en brösthöjdsdiameter mellan 30 och 83 mm. I Toftaholm var en del av beståndet gödslad respektive ogödslad vårtbjörk. Från Asa togs stammar av både vårtbjörk och glasbjörk. Virkesegenskaper och dess variationer i stammens radiella och longitudinella riktning studerades. Vidhäftningen av barken till veden efter torkning bedömdes procentuellt på omkretsen av ändträet. Relativ torrdensitet och rådensitet mättes. Påverkan av årsringsbredd på veddensitet analyserades statistiskt och vedanatomin studerades med mikroskop och bildanalys för en vidare förståelse av dess samband med gödsling.

Resultaten gällande barktjocklekens variation visade att den nedre delen av stammen hade störst medelavvikelse. Dessa resultat kan vara relevant information för vidareförädling efter avbarkning. Barkens vidhäftning till veden efter torkning mättes på juvenil glasbjörk. Det visade ett visst samband med stamdiameter där den högsta vidhäftningen fanns på stammarna med en diameter mellan 30 och 39 mm. Sambandet var däremot inte korrelerat till stamhöjden där provet togs.

Densitetsvariation i radiell och longitudinell riktning studerades för juvenil vårtbjörk. Densiteten hade en svag negativt korrelation till årsringsbredd. Detta samband sågs både inom bestånd och mellan bestånd med olika tillväxtförhållande samt skötsel. Medeldensiteten för virket var, som förväntat, lägre i de gödslade träden jämfört med de ogödslade.

I den radiella riktningen  hade det senvuxna virket en högre faktor på densitetsökningen. Den longitudinella densitetsvariationen i unga vårtbjörkar var låg.

Kvantitativa vedanatomistudier bekräftade att ungdomsveden i gödslad vårtbjörk hade en lägre kambiumålder, tunnare cellväggstjocklek och färre kärl jämfört med ogödslade träd med samma diameter, resultat som tidigare påvisats för mogen björk.

Sammanfattningsvis kan resultaten från den här uppsatsen förbättra kunskapen och därmed underlätta för en industriell användning av juvenila björkstammar inom inredning och möbler. Dock bör vedanatomins påverkan på de mekaniska egenskaperna för juvenila björkstammar studeras vidare. Det kan möjliggöra nya användningsområden för juvenil björk.

Today a majority of the pre-commercial thinning (PCT) cut birch stems in Sweden are retained on the site for biodegradation, since their market value is lower than the cost of harvesting. Some stems are removed as firewood. The uses of the PCT material can be difficult to find, and the costly PCT is carried out in expectation of greater returns later in the forest rotation. There is a growing body of literature that recognises the possibility of using low value wooden material for furniture and interior purposes. While some research has been carried out on character-marked wood, there have been few investigations on utilization of small-dimensioned roundwood. However, proper utilisation of this material requires appropriate matching of the material attributes with the end-user’s expectations on furniture or joinery products. The aim of this work is to understand challenges and possibilities for the utilization of small-dimensioned roundwood birch in furniture and joinery products. The study synthesizes literature on customers’ demands on hardwood and important material properties. A case-study approach was used to evaluate how a bench, made out of small-dimensioned roundwood birch, can meet the requirements from customers and manufacturing industries. The results demonstrate that opportunities exist within the customer segment appealed by naturalistic furniture design. Proposals are made for future research needed for successful use of small-dimensioned roundwood birch for furniture applications.

In Nordic countries, birch wood has gained interest in furniture and interior applications due to its very unique aesthetic qualities. A significant share (33%) of the small-dimensioned (diameter at breast-height smaller than 9 cm) standing tree volumes in the Swedish productive forest land consists of silver and downy birch (Betula pendula and Betula pubescens). In today’s forest industry, the small-dimensioned material from pre-commercial thinning operations of birch and Norway spruce mixed forests is normally left in the forest if not used as fire-wood. For the furniture industries these fractions may be a new source of raw materials’ supply. However, a proper utilization of this material requires a better knowledge of its properties. This paper presents a review on the utilization aspects of solid wood from small-dimensioned timber as well as some useful concepts for successful material selection in product design. Therefore, based on customer requirement concepts, it is analyzed which wood material properties are important for furniture or joinery applications from hardwoods and how small-dimensioned roundwood birch could meet the requirements. Proposals are made for future research needed to fully explore the potential of using small-dimensioned roundwood birch for furniture applications.

Many interior and furniture applications today use the natural aspects of wooden materials as a sales advantage. Defects such as knots, colour variations and rough surfaces are called rustic, natural or vintage and will be considered as an appreciated feature by the consumers. This approach changes the traditional view of wood quality for technical uses, and also the industrial processing of the material. As a consequence, more variables of the material than before must be handled in the production. A specific challenge in the furniture industry is to treat the raw materials under this view with as small volume losses as possible. One way of decreasing losses could be achieved by fewer processing steps. The present study aims at exploring the possibility to relate the dimensions of the trees already in the forest in relation to specific furniture components, and furthermore to leave the bark on for creating specific aesthetical characteristics to the end product. In Nordic countries, birch wood has gained interest in furniture and interior applications due to its unique aesthetic qualities. In today’s forestry industry, the small-dimensioned material from harvesting operations of birch forests is normally used by the pulp industry or as fire-wood. For the interior and furniture industries these fractions may be a new source of raw material supply. However, a proper utilization of the material requires a better knowledge of its properties. The potential of using un-barked material in round form also sets special requirements in the process. The present study presents results from initial testing concerning the behaviour of the bark in round wood pieces. For the experiments, round specimens of downy birch (Betula pubescens Ehrh.) measuring 450 mm in length and with varying diameters from 30 to 80 mm at the top were used. The green wood was dried with and without bark as to study the drying velocity in relation to dimensions. The bark was studied in respect of changes in bonding to the wood and its characteristics. The preliminary results are promising for using the material in interior and furniture applications. However, there are still some shortcomings to be addressed in the future, such as the impact of the bark in the drying process as well as the bark bonding.