The variation in density, longitudinal and radial permeability was investigated in eight seed origins of Sitka spruce (Alaska -AL, British Colombia -BC, Queen Charlotte Islands -QCI, North Washington -NW, South Washington -SW, North Oregon -NO, South Oregon -SO, California -CA) grown at two sites in the UK (Dalby, Eastern England and Rhondda, South Wales).
Five trees of each seed origin at each site were sampled at three heights (1.3, 2.3 and 3.3 m above ground level). For the investigation of permeability, cylindirical plug samples (30 x 15 mm diameter) were used because this overcome problems of block orientation and allowed large numbers of samples to be tested. Outer sapwood plug samples were prepared with their long axis either in the longitudinal or the radial direction.
The density of the samples decreased withincreasing height within the stem. This corresponded to a trend of increasing ring width. The trees of seed origins NW, SW and NO at both sites, and QCI and SO at Rhondda had the highest wood density partly due to their slow rates of incremental growth. The seed origin CA had the lowest density on account of its rapid incremental growth. Therefore, it is suggested that to optimise density QCI, NW, SW and NO should be selected for plantation use. The seed origins AL and BC should be avoided in the future plantations as they grew poorly at both sites.
The wood permeability of the different sites showed an inverse relationship between longitudinal and radial permeability. The general trend showed that although they were less treated longitudinally, the trees on the Rhondda site were more treated radially as compared to those at Dalby. Results obtained in this study generally show that of the seed origins QCI and NW had the greatest permeability both longitudinally and radially. This is in contrast to NO and SO which had the lowest permeability longitudinally (NO) and radially (SO).
It appears that there are reasonable explanations for differences in longitudinal permeability and that the differences are linked to density which is in current breeding programs. Furthermore, the major influences on longitudinal permeability are associated with post-harvest processing, e.g. drying. Little is known however about radial permeability and differences seen in this study between QCI and SO (the most and least radially permeable) are investigated further in this thesis at an anatomical level.
The ray structure of these two seed origins was examined microscopically and different patterns of ray composition were observed. The most important anatomical features influencing radial permeability were the nature of both the ray tracheids and the ray parenchyma cells, and the condition of the cross-field pits in particular.