Rupert Wimmer

Longitudinal hardness and Young's modulus of spruce tracheid secondary walls using nanoindentation technique

SummaryUsing a mechanical properties microprobe, measurements of hardness and elastic modulus of tracheid walls in the longitudinal direction of spruce wood were obtained by continuously measuring force and displacement as a diamond indenter impressed a cell wall. Maximum mechanical properties were found at the edges of the walls of angular shaped tracheids. Both the hardness and elastic modulus of latewood cell walls were higher than cell walls in the earlywood. The high spatial resolution of this new concept of mechanical testing allows a direct comparison with ultrastructural and microchemical parameters of lignified cells which opens a wider area of applications for the understanding of intrinsic wood properties.

Genetic parameters of growth and wood quality traits in Picea abies

Genetic parameters were estimated for wood and growth traits in two 19-yr-old clonal trials and a 40-yr-old full-sib progeny trial of Norway spruce [Picea abies (L.) Karst.]. In the clonal trials high (>0.4) broad-sense heritabilities were found for wood density traits, lignin content, number of internal cracks, growth traits, spiral grain and number of resin canals. Moderate (0.2–0.4) heritabilities were found for tracheid lumen diameter and cell wall thickness, microfibril angle and tracheid length, while low heritabilities (<0.2) were found for pulp yield, fibre strength, wood stiffness and wood colour. Lignin content and pulp yield showed low genetic variation, whereas the genotypic coefficient of variation for most other traits ranged between 5 and 15%. Most traits showed low levels of genotype by environment interaction. Among the wood properties, latewood proportion, earlywood density and ring density showed significant, adverse correlations with volume in both clonal trials.

The influence of temperature on latewood lignin content in treeline Norway spruce compared with maximum density and ring width

Abstract. The latewood lignin content, maximum density and total ring width of ten consecutive annual increments were determined in treeline Norway spruce (Picea abies [L.] Karst.) using ultraviolet (UV) microscopy and radiodensitometry, respectively. A positive correlation between the total ring width and the mean temperature of mid-July to August was identified, as was one between the maximum density and the temperature of August–September. Lignin content in the secondary cell wall layer of the terminal latewood tracheids was positively correlated with the temperature for the period running from the beginning of September until the third week of October. It can, therefore, be concluded that lignification of the cell wall is susceptible to the influence of climatic variability, as is the case with ring width and maximum density.

Wood anatomical features in tree-rings as indicators of environmental change

Summary Wood anatomical and structural features observed and measured in tree- rings have proved to be useful in dendrochronology. They have added understanding and new insights to processes going on in trees with structural features that have shown linkages to environmental parameters, not given by other parameters. This review emphasizes work done primarily on continuous and non-continuous wood anatomical features measured in dated tree-rings, reflecting internal and external conditions and processes. This review also includes new results from a study conducted in the East-Ore Mountains, Germany, where several anatomical features in rings of trees grown under severe stresses were measured. It is shown how environmental changes have caused modifications or adaptations of structural features in dated tree-rings. The measurement of many structural features in tree-rings remains tedious, although for some features such as cell sizes or microfibril angle fast scanning devices have now been made available. Overall, wood anatomy indicates that growth and development of trees are dynamic processes. All these aspects, which are commonly illustrated in two and three dimensions, have in reality a fourth dimension – time.

Colour of larch heartwood and relationships to extractives and brown-rot decay resistance

Larch heartwood is appreciated for its good mechanical properties, its colour and its texture, and it is often used outdoors because of its natural durability (decay resistance). In this study the colour of larch heartwood was studied in relation to extractives and decay resistance, with the aim to estimate durability of larch heartwood from its colour. On a total of 293 trees colour in the CIE L*a*b* space (L* lightness, a* red/green axis, b* yellow/blue axis), extractives content (acetone and hot-water extractives, amount of phenolics) and the brown-rot decay resistance were determined. For calculating the relative decay resistance ( x), mass loss after inoculation for 16 weeks with two fungi [ Coniophora puteana (Schum.ex.Fr.) Karst., Poria placenta (Fr.) Cke, European standard EN 113] of larch heartwood samples was compared to Scots pine ( Pinus sylvestris L) sapwood reference samples (EN 350-1). Different species [Japanese larch ( Larix kaempferi Lamb.), Hybrid larch (Larix deciduax L. kaempferi) and European larch ( L. decidua Mill.)], provenances and age classes (38-year, >150-year) were included. Japanese larch heartwood turned out to be significantly more reddish (higher a*-values) compared to the European larch provenances. Reddishness of the hybrids was intermediate. The red hue (+a*) was strongly correlated with the amount of phenols ( r =0.84) and decay resistance ( r =0.63) and therefore suitable for prediction of both parameters. The results suggest that colour measurements of larch heartwood could be of benefit in tree breeding programs and for an optimised utilization of larch timber.

Impregnation of softwood cell walls with melamine-formaldehyde resin

Melamine-formaldehyde (MF) resin impregnation has shown considerable potential to improve a number of wood properties, such as surface hardness and weathering resistance. In this study, selected factors influencing the uptake of MF resin into the cell wall of softwood were studied. Using UV-microspectroscopy, it could be shown that water soluble MF diffused well into the secondary cell wall and the middle lamella. Concentrations as high as 24% (v/v) were achieved after an impregnation of 20 h. High cell wall moisture content, high water content of the resin used for impregnation, and low extractive content are factors which are favourable for MF resin uptake into the cell wall. For dry cell walls, solvent exchange drying improved resin uptake to a similar extent, as was the case when cell walls were soaked in water.

Rapid determination of heartwood extractives in Larix sp. by means of Fourier transform near infrared spectroscopy

The feasibility of Fourier transform near infrared (FT-NIR) spectroscopy to rapidly determine extractive and phenolic content in heartwood of larch trees (Larix decidua MILL., L. leptolepis (LAMB.) CARR. and the hybrid L. x eurolepis) was investigated. FT-NIR spectra were collected from wood powder and solid wood using a fibre-optic probe. Partial Least Squares (PLS) regression analyses were carried out describing relationships between the data sets of wet laboratory chemical data and the FT-NIR spectra. Besides cross and test set validation the established models were subjected to a further evaluation step by means of additional wood samples with unknown extractive content. Extractive and phenol contents of these additional samples were predicted and outliers detected through Mahalanobis distance calculations. Models based on the whole spectral range and without data pre-processing performed well in cross-validation and test set validation, but failed in the evaluation test, which is based on spectral outlier detection. But selection of data pre-processing methods and manual as well as automatic restriction of wavenumber ranges considerably improved the model predictability. High coefficients of determination (R2) and low root mean square errors of cross-validation (RMSECV) were obtained for hot water extractives (R2 = 0.96, RMSECV = 0.86%, range = 4.9–20.4%), acetone extractives (R2 = 0.86, RMSECV = 0.32%, range = 0.8–3.6%) and phenolic substances (R2 = 0.98, RMSECV = 0.21%, range = 0.7–4.9%) from wood powder. The models derived from wood powder spectra were more precise than those obtained from solid wood strips. Overall, NIR spectroscopy has proven to be an easy to facilitate, reliable, accurate and fast method for non-destructive wood extractive determination.

A COMPARISON OF TREE-RING FEATURES IN PICEA ABIES AS CORRELATED WITH CLIMATE

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.

Investigation of element variability in tree rings of young Norway spruce by laser-ablation-ICPMS

Laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) has been used to investigate the elemental variation for tree rings of 20-year-old clonal Norway spruce trees that grew nearby an aluminum smelter. Four years prior to analysis this source of fluoride pollution was shut down and the subsequent variation of the concentration of elements in the tree ring according to their mobility in the tree stem was investigated by means of a LA-ICPMS. The elements Al, Fe, Ca, Ba and Sr showed a significant increase in values after the pollution shutdown. Elements with similar chemical behavior and mobility show similar patterns of distribution. Circular investigations of tree rings show a variation of up to 60% of the elemental concentration depending on the geographical direction following the changing properties (e.g density) of wood. The circular pattern correlate again for elements with similar properties and function. Furthermore, wood which develops in response to unbalanced mechanical pressure, such as wind for example (so called compression wood) shows significant differences in element concentration compared with unstressed wood.

Direct Effects of Wood Characteristics on Pulp and Handsheet Properties of Eucalyptus globulus

Summary Fibre length, microfibril angle and wood density were measured in eight-year-old Eucalyptus globulus clones planted on three different sites. Samples were chipped and pulped, and the pulps beaten prior to preparation of 60g/m2 handsheets. Eleven physical handsheet properties, together with pulp freeness, were measured using standard methods. Direct relationships between wood properties and pulp/paper properties were studied using path analysis. Fibre length had a strong, direct effect on tear index, bending stiffness, freeness, pulp yield and active alkali consumption. Wood density was a strong predictor of most handsheet properties: high density woods produced bulkier, more porous sheets with higher bending stiffness, while lower density woods produced smoother, denser sheets with higher tensile strength.The effect of microfibril angle was small and more evident in handsheets made from beaten pulp.