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.
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.
A total of 110 white spruce (Picea glauca (Moench.) Voss) trees were systematically sampled by 30, 40 and 50 cm diameter-at-breast height (DBH) classes from three natural stands in Saskatchewan located near Big River, Candle Lake and Hudson Bay. Mean ages of the tree samples were 120, 110 and 107 years respectively. Based on sample trees, site indices at breast-height age 50 were 18.5, 18.1 and 18.3 respectively. Wood basic relative density at breast height was determined for each sample tree by X-ray densitometry. Mean values for each tree sample were 0.372, 0.369 and 0.361 respectively. ANOVA of basic relative density on DBH class and stand (R2 = 0.32) revealed that differences in mean density between stands were not significant. The effect of DBH class (rate-of-growth) was significant (p < 0.0001). Consequently, mean relative density values were determined for the 30, 40 and 50 cm DBH classes for the three tree samples combined. These were 0.384, 0.368 and 0.349 respectively compared to the species average of 0.354. Pith-to-bark density trends were inversely related to ring-width trends, consistent with expectations for white spruce.
Density trends observed in Saskatchewan coincided with those obtained from white spruce trees sampled similarly from three stands in northeastern British Columbia and three stands in north central Alberta. In the BC study trends in breast-height wood density were reflected in similar and more significant trends in bending modulus of rupture (MOR) and modulus of elasticity (MOE), MOE in compression, and ultimate compression strength (UCS) of small clear specimens. The combined results of the two previous studies demonstrated robustly that for stands of similar age and site index, wood density and related structural wood properties of white spruce are influenced primarily by rate-of-growth. Pooled results for the three Saskatchewan stands confirmed this wood density/growth-rate relationship.
Considered within each stand, wood density generally declined significantly (a = 0.05) as diameter class increased. A notable exception occurred at Candle Lake. In that stand, although not significantly different, the mean wood density in the 30 cm DBH class was slightly lower than that of the 40 cm class. On review, a similar lack of significant difference in mean density occurred between the 30 and 40 cm DBH classes in two previous samples, one in BC and one in Alberta, but in those stands the density hierarchy remained as expected. One plausible explanation is a deleterious effect of greater competition combined with low site index. The lower than expected density values for small diameter trees coincided with the three lowest site indices of the nine samples.
Wood density of Saskatchewan white spruce was higher than that observed in BC and Alberta with even the 50 cm DBH class showing no significant difference from the species average. This suggests that faster growth can be pursued in Saskatchewan before encountering a detrimental reduction in average wood density. Pronounced increases in annual growth rate that occurred after cambial age twenty in the 40 cm and 50 cm trees at the Big River stand coincided with pronounced declines in breast-height wood density. This was consistent with results observed in two of the previous six samples studied, and strengthens evidence that natural events that result in release will reduce white spruce wood density. Silvicultural interventions that result in similar release can be expected to have a similar effect.
The study objective was to determine if differences in the quality of Douglas-fir in the B.C. Interior could be assessed on the basis of characteristics visible in standing trees so as to provide site-specific measures of stand value. Six sawmill studies, with a final sample of 1,862 trees are described. Sample trees were selected and their quality characteristics recorded. These trees were felled and their logs processed into finished lumber from which individual tree values were calculated. An index shows the effect of tree quality and tree size on average lumber value per unit volume. A description of each mill study allows comparison of average sound lumber recovery factors.