Abstract
Scots pine has a large natural distribution, covering areas from Siberia to Spain. Within this area, the species needs to adapt to different growth conditions which results in a wide variation of material properties. In northern Europe, Scots pine is the second most important forest tree after spruce. Corresponding to its easy availability on the market and its good mechanical properties, it is widely used in construction and the building sector. For outdoor applications though, the sapwood has to be protected for adequate service life performance due to its low natural durability. Scots pine is usually considered easy to impregnate, however, large variations in Scots pine sapwood treatability are reported.
It was the aim of this study to investigate the variation in treatability of Scots pine sapwood, relative to growing conditions and material properties.
Scots pine trees were sampled from 25 stands with a wide range of growing conditions in northern Europe. A mild impregnation with an experimental furfuryl alcohol mix was applied to study the variation in treatability. Statistical models describing the effect of growing conditions and material properties on treatability were developed, and microscopical analyses were performed on anatomical properties of material with contrasting treatability. The genetic diversity and structure of the sampled material were studied and related to treatability.
Significant differences in treatability were found between some of the stands. The results showed that high latewood content and wide annual rings are a good combination for treatability. This factor combination is obtained from stands with sufficiently high annual mean temperatures. Growing conditions leading to smaller annual height and diameter increments decreased the treatability. In addition, competition in form of increasing stand density and decreasing sociological position within stand reduced treatability. Trees growing near the timberline of the species and under environmental conditions impairing wood growth developed refractory wood.
Easy to impregnate material contained a higher number of ray parenchyma cells leading to an increased area of window- like pits in the cross-field between ray parenchyma and longitudinal tracheids. These enlarged interconnections could greatly enhance transverse fluid passage in the wood structure. Refractory samples on the other hand had developed smaller bordered pit features with comparatively small pit apertures. A combination of smaller and fewer connections led to lower interconnectivity of the refractory wood structure as compared to the easily treatable samples.
An analysis of the genetic structure of the sampled Scots pine revealed a segmentation into two groups: an eastern and a western one. This might be a result of recolonizing Fennoscandia from at least two different directions after the last glaciation. The segmentation into different refugia can be a reason of variant adaptions to growth conditions, as the eastern group developed larger latewood proportions under similar conditions as compared to the western group.
The study has shown a systematic variation in treatability. This information can be used to improve the selection of raw materials for impregnation and for adaptation of industrial process control. This will allow exploiting the potential of this domestic European tree species for products of high added value through impregnation.
Katerine ZimmerNorsk institutt for skog og landskap, Ås, Norway
