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  • Author or Editor: Michael Wimmer x
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This paper presents an analysis of 16 anatomical variables measured on 20 spruce trees [Picea abies (L.) Karst.] from sites in the managed forest district Seyde, Eastern Ore Mountains, south of Dresden, Germany. Ring width and latewood proportion did not show significant relationships with monthly climatic data, whereas maximum density, latewood cell-wall proportion and latewood density were highly correlated with temperature and precipitation. The climatic signals expressed in resin duct density, ray height, tracheid length and microfibril angles were less pronounced. Of 16 tree-ring parameters, densitometry – as an indirect measure of xylem anatomy – has again shown its great potential to record climatic conditions.

In: IAWA Journal

Pith to bark variation of vessel anatomy was studied in 17 clones of 7-year-old Eucalyptus globulus trees grown on two sites in Portugal. Vessels were measured by image analysis on transverse microsections cut from radial strips sampled at 25% tree height. The mean vessel area increased gradually from pith to bark, whereas the vessel frequency (number of vessels per unit area) decreased outwards from the innermost ring on and levelled off towards the bark. The proportion of vessels relative to other tissues remained constant across the radius. The vessel variables showed cyclic variations defined by minima (vessel area and proportion) or maxima (number of vessels). The effect of site and clone on vessel variability was significant. Clonal variation accounted for 30% and site explained 67% of the total variance of vessel proportion. At the least water stressed site, vessels appeared to be generally larger and occupied a greater proportion of total cross-sectional area.

In: IAWA Journal

The genus Larix is exceptional for its high content of extractives in the heartwood, with the dominant component arabinogalactan found abundantly in cell lumens of tracheids. On parallel samples prepared from 20 European, Japanese and hybrid larch trees (Larix decidua Mill., L. kaempferi Carr., and L. decidua × L. kaempferi, respectively) extractive contents and mechanical parameters were measured. The hot-water extractives in the heartwood had a significant effect on transversal compression strength and Young's Modulus. In heartwood, increasing extractive content went hand-in-hand with better mechanical properties in the transverse direction. The extraction procedure led to negligible changes in the sapwood. Anatomically the extractive-filled tracheids showed a tendency of being arranged radially, closely to wood rays. The extractive arabinogalactan in larch heartwood has multiple effects on different aspects of wood quality, among which is lateral mechanical enforcement.

In: IAWA Journal

Longitudinal shear strength and shear modulus of spruce and larch wood with a maximum of micro- and macro-structural variability was determined using a new testing method. Oven-dry density and slope of grain were measured after the shear tests. For the spruce wood samples, a data set of fiber and cell wall properties, i.e., lignin content, microfibril angle, fiber length, lumen diameter, cell wall thickness, latewood proportion, and ring width, was available. A multiple linear regression analysis of all fiber and cell wall properties showed a significant, but not very strong effect on the variability of shear strength (R2 = 0.21). It is thus demonstrated that micro-structural variability plays a minor role in the variability of shear properties. By contrast, a multiple linear regression involving shear modulus, density, and slope of grain as three independent variables revealed an excellent possibility to model the variability of shear strength (R2 = 0.72). This study demonstrates the potential for non-destructive evaluation of the shear strength of solid wood.

In: IAWA Journal