The basic wood properties of 45-year-old second-growth sitka spruce were examined to determine if rapid growth produces poor wood quality. Five dominant and codominant trees were sampled from each of four stands with stocking densities of 520, 640, 1080, and 1520 stems/ha. Stem size, extent of live crown, yearly wood relative density trends, and longitudinal shrinkage were measured.
This report describes some of the background and results of work done to date on second-growth western hemlock basic wood properties at Forintek Canada Corp. The B.C. Ministry of Forests (BCMOF) Research Branch, UBC Forestry Faculty and PAPRICAN were the other cooperating agencies on this project and they investigated live crown/tree growth relationships, strength properties of small clears, and pulping properties, respectively. Properties that were assessed by Forintek, both within and between trees include: relative density of wood, shrinkage, moisture content and relative proportion of heartwood-sapwood, bark thickness, content and distribution of compression wood, incidence and degree of spiral grain, incidence and severity of brown stain, and strength properties of small cleear bending samples. Naturally grown 90-year-old western hemlock stands represent much of the emerging timber supply in the B.C. coastal forest region. Information characterizing the commercial quality of this resource is needed now to support processing and marketing decisions and for product promotion. In addition, the BCMOF and industry members are making stand management decisions today which will determine the future quality of western hemlock. We can reduce the risk of making wrong investment decisions by providing information on how different growing conditions (e.g., biogeoclimatic zone, site, stand density, thinning) affect second-growth wood quality.
Les auteurs définissent la qualité du bois en fonction de ses emplois, puis décrivent l'anatomie et la croissance du bois en regard de ses caractéristiques microscopiques et macroscopiques telles qu'observées en coupe transversale. Les exigences liées aux emplois sont énoncées selon les différentes classes de bois. Diverses caractéristiques déterminant la qualité du bois sont présentées et leurs conséquences pratiques pour la transformation du bois et les produits sont expliquées. Ces caractéristiques sont: la densité du bois, les variations de la densité, la répartition des bois juvénile et adulte, la proportion de duramen et d'aubier, la longueur des fibres, l'orientation des microfibrilles, le bois de compression, les noeuds, le grain ou la texture, le fil et les substances extractibles. Enfin, les auteurs traitent de la possibilité de modifier les paramètres de croissance de l'arbre et la qualité du bois grâce à un contrôle de la densité du peuplement. Les forestiers sont invités à prendre en considération les répercussions des travaux sylvicoles propres à chaque station.
In a previously completed study, lumber obtained from a 95-year old lodgepole pine sample representing a final stand density of 700 live stems/hectare (s/ha) was found to have relatively low modulus- of-rupture (MOR) and modulus of elasticity (MOE). It was determined that this resulted from lower than average basic wood density, and larger than average knot size particularly in large diameter trees. It was also determined that average MOR and MOE could be predicted to some extent (R2 > .60) on the basis of tree diameter-at-breast height (d.b.h.) and breast-height average basic wood density. Before accepting the above results as typical of lodgepole pine of similar age and final stand density, it was considered important to compare the relationships between d.b.h. and breast-height wood density observed in this 700 s/ha sample with that of trees in open-stand-densities in other regions. Average branch size added only marginally to explained variation in the predictive equation, but knot size is known to effect lumber strength. Thus a measure of branch size was included in the current study plan. Biogeoclimatic zones were chosen as the basis for regional comparisons. A minimum of 30 trees were selected from open-stand sites in each of the following five biogeoclimatic zones: Montane Spruce (MS), Engelmann Spruce-Subalpine Fir (ESSF), Interior Douglas-Fir (IDF), Interior Cedar-Hemlock (ICH) and Sub-Boreal Spruce (SBS). Sampling was systematic by d.b.h. to ensure representation of small, medium and large diameter trees. Stem counts were made in 1/200 ha plots around each sample tree to ensure that samples were indicative of a relatively open stand density. Average basic wood density at breast height was determined from two pith-to-bark increment cores obtained from each sample tree. The size and height of the largest branch in the first 5 m of tree height was measured and recorded. Average basic wood density values and estimates of branch size obtained for the five samples in this study were compared to the values and estimates obtained from the original 700 s/ha sample site. Basic wood density obtained from three of the sites was not significantly different from that of the 700 s/ha sample. It was significantly higher in one site (ICH) and significantly lower in another (ESSF). The higher wood density was possibly the result of a slower growth rate to 30 years combined with older average tree age. The significantly lower wood density was attributed to a younger average stand age (80 years). Basic wood density showed a consistent relationship with d.b.h. in all of the tree samples, tending down as d.b.h. increased. There was a less consistent relationship between knot size and d.b.h. but what relationship there was would serve to reinforce the effect of differences in wood density on lumber strength and stiffness. Average size of the largest knots was smallest in the tree sample where wood density was highest, and largest in the sample where wood density was lowest. Important lumber strength determining tree characteristics (wood density and knot size) that resulted in the low MOE and MOR at the original 700 s/ha sample site were found to be unexceptional when compared to trees of similar age and final stand densities in other biogeoclimatic zones. Although a slower than average growth rate to 30 years offers a plausible explanation for the higher than expected wood density in the ICH sample, further investigation is recommended.
Commercial thinning at a relatively young age will result in changes not only to log size but to wood quality as well. One important change in the thinnings will be the increased proportion of juvenile wood relative to mature wood. In western hemlock (Tsuga heterophylla (Raf.) Sarg.), where the difference in wood density between juvenile wood and mature wood is relatively large, a higher proportion of juvenile wood can result in reduced lumber strength and lower pulp yields. Another change will be seen after thinning in the remaining standing trees; late-release growth pattern changes in terms of grain. The present report summarizes the results of X-ray densitometric analysis of 50-year-old western hemlock trees thinned from 1656 and 956 stems/ha plots, and amabilis fir (Abies amabilis (Dougl.) Forbes) from the 956 stems/ha plot. Results were compared to old-growth reference data, and to a recently completed basic wood properties study of 90-year-old western hemlock (Jozsa et. al., 1997).