Isotopic evidence in tree rings for historical changes in atmospheric sulfur sources

Little is understood about the usefulness of sulfur isotopic ratios (sigma 34S) in tree rings because the sulfur content in rings is generally insufficient for analysis using conventional methods. We present sigma 34S values of the water-soluble and the organically bound sulfur fractions in rings of coniferous trees grown in Japan, analyzed using a large-volume oxygen bomb. Comparing the sigma 34S values of the organically bound fraction in tree rings with past atmospheric sulfur concentrations and with those of their sources, we find clear evidence that the sigma 34S values of the organically bound fraction in the rings are dependent upon the values of the atmospheric sulfur sources. The evidence suggests that the sigma 34S values in tree rings are a useful chronological proxy for evaluating possible causes of past atmospheric sulfur pollution.     

Reliability of proof-loaded Norway spruce

Strength grading of structural timber is a prerequisite for the use of timber in load-bearing constructions. The grading methods used in production today are mainly based on estimation of the modulus of elasticity (MOE) determined from measurements of either flatwise bending stiffness or resonant vibrations. By using proof-loading techniques, the yield can be increased and the reliability of the graded material can be improved. Unfortunately, this technique can cause damage to some of the graded material. This paper deals with the quantification and severity of damage caused by proof-loading of Norway spruce (Picea abies) timber. A total of 410 specimens were loaded in cyclic bending with increasing load level in each cycle until failure. The maximum loads during the tests were compared to the failure loads of a reference sample. If the failure load was lower than the maximum load, the specimen was assumed to have been damaged in the previous load-cycle and was defined as a rogue. The technique used is similar to the technique used for example in Australia. The results obtained fit well with the results obtained from Australian species. Examination of the MOE indicates no damage in the specimens at stress levels below 75% of the strength. Damage is in this case defined as a decrease in the MOE. Regarding Norway spruce grown in Sweden it can be concluded that the problem of damage due to proof-loading is small for timber graded to strength classes C24 or C30. For both classes the number of rogues can be expected to be less than 5%. For timber graded to higher strength classes the problem of damage due to proof-loading will increase.     

Studies on hygroscopic moisture transport in Norway spruce (Picea abies) Part 1: Sorption measurements of spruce exposed to cyclic step changes in relative humidity

Picea abies ) have been exposed to repetitive daily and weekly step changes in relative humidity with the surrounding temperature at an approximate constant level. The results show that the moisture sorption is a two-step sorption process with the major change in moisture content in the first fast initial part. The major part of the moisture change happens within a relatively short period of time. No significant phase lag has been observed for neither transverse nor longitudinal specimens up to 10 mm thickness. The moisture change in absorption is slightly different from the moisture change in desorption. Curves in absorption and desorption for specimens with both transverse and longitudinal direction are rather similar in shape.

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Picea abies) wurden im Wechselklima mit t?glichen und w?chentlichen Feuchtezyklen bei konstanter Umgebungstemperatur ausgesetzt. Der Sorptionsvorgang erwies sich als zweistufiger Proze?, wobei die haupts?chliche Feuchte?nderung in einer anf?nglichen raschen Stufe erfolgt. Eine signifikante Phasenverz?gerung konnte nicht beobachtet werden, weder für quergeschnitte noch für longitudinale Proben bis 10 mm Dicke. Die Feuchte?nderung bei der Adsorption unterscheidet sich geringfügig von der bei der Desorption. Die Sorptionskurven für Quer- und L?ngsproben haben einen sehr ?hnlichen Verlauf.

     

Alternative normalization method of atmospheric polycyclic aromatic hydrocarbons pollution level recorded by tree bark

An alternative normalization method was developed for evaluating atmospheric polycyclic aromatic hydrocarbons (PAHs) pollution level when using tree bark as a passive sampling medium. Perylene (PER), which mainly stems from natural biogenic processes, was proposed as a "natural internal compound" (NIC) of atmospheric PAHs accumulation processes from air into the bark, and a concentration ratio of target PAH to PER (RPAH/PER) was used to minimize the uncertainty in the evaluation of atmospheric PAHs pollution level. Systematic investigation of the effects of intrinsic bark characteristics and extrinsic seasonal meteorological conditions on the partition processes of atmospheric PAHs indicated that RPAH/PER is as an alternative index as compared to bark mass concentration (BMCPAH, ng/g dry bark), lipid mass concentration (LMCPAH, ng/g lipid of bark), and area mass concentration (AMCPAH, ng/m2 surface area of bark) for the evaluation of atmospheric PAHs pollution and that it allows more flexible sampling of tree barks. Clearly, the methodology should be expected to be useful for the objective evaluation of atmospheric pollution levels of other persistent organic pollutants when using tree bark and other passive sampling media if corresponding NICs are found in the future.     

Mechanical properties of sawn timber from Norway spruce

Picea abies ) of three different cross sectional sizes: 38×89 mm², 38×140 mm², and 38×184 mm². Specific material characteristics for the lumber are presented. The tests also enabled comparison between results from two testing methodologies. The mean value for the modulus of elasticity established from the dynamic tests was found to be approximately 10% higher than the corresponding value established from static tests. The statistical correlation between statically and dynamically established moduli is very strong. The dynamic E modulus was found to be as good a strength predictor as the static E modulus. Cross sectional size and the existence of the pith in the sawn lumber were found to significantly influence the material properties. In general terms, it was found that deeper beams correspond to lower values for the E modulus and for the bending strength. The reason for this tendency is believed to be a combination of a volumetric effect (in the case of strength) and a phenomenon related to the log selection and sawing process in the mills. Lumber that comprises the pith has been found to have generally lower values of the E modulus and bending strength while the shear modulus is higher, compared to lumber without pith sawn further out in the log.

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Picea abies ) wurden dynamische und statische Prüfungen vorgenommen. Die Proben hatten drei verschiedene Querschnitte: 38×89 mm², 38×140 mm² und 38×184 mm². Anhand der vorgelegten Ergebnisse wurden auch zwei Prüfmethoden verglichen. Die Mittelwerte der dynamischen MOE-Prüfung lagen etwa 10% h?her als die statisch ermittelten Werte. Die Korrelation beider MOE-Werte ist sehr streng. Beide Werte k?nnen zur Vorhersage der Festigkeit verwendet werden. Der Querschnitt und die Anwesenheit von Markanteilen beeinflussen das Ergebnis wesentlich. Je tiefer die Balken waren d.h. je n?her sie der Markr?hre lagen, desto geringer waren E-Modul und Biegefestigkeit. Die Gründe dafür werden teils einem Volumeneffekt zugeschrieben (im Falle der Festigkeit), teils auf das Auswahlverfahren der St?mme im S?gebetrieb zurückgeführt. Schnittholz mit Markanteil hatte allgemein. einen geringeren E-Modul und niedrigere Biegefestigkeit als Proben aus ?u?eren Stammbereichen; die Scherfestigkeit lag dagegen h?her.

     

Colour changes of Scots pine and Norway spruce

Surface of boards, dried with wet bulb temperature above 60 °C are often called discoloured caused by severe resinflow. Discolourisation was evaluated using a tristimulus colour analyser, for measuring the colour changes during drying at three different drying schedules; 50 °C, 60 °C and 70 °C wet bulb temperature. The colour properties were pictured by lightness (L^*), chroma (C^*) and hue (h°). Results showed that lightness decreased and chroma increased during drying. When comparing the three differnt drying schedules the lightness decreased and chroma increased with higher drying temperature. No significant change of hue during drying was noticed, but when comparing the three schedules, hue decreased with higher drying temperature. Drying time and drying temperature level effect the value of lightness more than any other colour properties Values of lightness and chroma returned to its original value after 3 mm planing, while the value of hue for sapwood of Scots pine decreased after 1 mm planing, but increased again after 3 mm, even more for series C (70 °C) than for series A (50 °C). For sapwood of Scots pine, lightness decresed and chroma increased more than for sapwood of Norway spruce, both during drying and with higher drying temperature. A hypothesis is that red-making (or blue) substance such as nutrients and extractives are transported toward the surface during drying and making the surface look more red. That leaves the yellow-making substance in the inner parts of the board and when planing the board, the surface will be more yellow than before.     

Planing of Norway spruce with very varied ring width

A way of defining a “machining ability” is proposed. Cutting forces: The samples from the slow grown spruce give well known results. In this case the cutting forces are linked with specific gravity by a linear relation. For the samples coming from the fast grown spruces (A), there is no significant relationship between the cutting forces and the specific gravity. These different behaviours are illustrated by the aspect of the chips produced by both batches of spruce. Dimensions scattering. Analysis shows clearly that distributions of dimension quality are similar for spruces A and B. That means there is no compression in the thickness of the samples (z axis). Surface, roughness: More than one roughness criterion is needed to describe surface quality. The 8 criteria used in this work describe the vertical distribution of the roughness measurements. For all the samples, best results are measured on A sample.     

Distortion of Norway spruce timber Part 2. Modelling twist

Picea abies ). Several material parameters were also measured, such as spiral grain angle, shrinkage in all three directions, annual ring width and density. Twist in the studs was measured at four different times at different moisture contents. The amount of twist correlated well with the moisture content and was reversible throughout several moisture changes. When the moisture content decreased, the twist increased and vice versa. About 50% of the variation in twist could be explained by a single parameter, i.e. the average growth ring curvature. All studs with severe twist were cut with its centroid within a radius of 75 mm from the pith. A statistical analysis of the data shows that growth ring curvature and spiral grain angle together explained about 70% of the variation in twist. Other parameters, such as shrinkage strains, density and ring width, did not increase predictability. When using a model developed by Stevens and Johnston (1960), about 66% of the variation in twist could be explained. The model also explained twist quantitatively well. The model included curvature of the growth ring, spiral grain angle and the tangential shrinkage strain.

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Picea abies ). Mehrere Materialeigenschaften wurden ebenfalls gemessen, und zwar: Faserwinkel, Schwinden in drei Richtungen, Jahrringbreite und Dichte. Die Verdrehung der Kanth?lzer wurde zu vier verschiedenen Zeitpunkten bei unterschiedlichen Feuchtegraden gemessen. Das Ausma? der Verdrehung war gut korreliert mit der Feuchte. Mit abnehmender Feuchte stieg die Verdrehung und umgekehrt. Rund 50% der Verdrehungswerte sind durch einen einzigen Parameter erkl?rt, n?mlich die Jahrringkrümmung. Bei allen Kanth?lzern mit starker Verdrehung lag die Mittelachse innerhalb eines Abstandes von 75 mm von der Markr?hre. Die statistische Analyse ergab, da? Jahrringkrümmung und Faserwinkel zusammen ca. 70% der Variation der Verdrehung erkl?ren. Andere Parameter wie Schwindspannungen, Dichte und Jahrringbreite erh?hten die Vorhersagbarkeit nicht. Mit Hilfe des Modells von Stevens und Johnson (1960) konnten rund 66% der Verdrehung erkl?rt werden. Dieses Modell lieferte auch zufriedenstellende quantitative Ergebnisse. Berücksichtigt werden dabei Jahrringkrümmung, Faserwinkel und tangentiale Schwindspannung.

     

Seasonal effects on the atmospheric corrosion of spruce micro-sections

The results of recent investigations revealed that the atmospheric corrosion (weathering) of micro-sections from spruce was dependent on the season. This was substantiated by the reduction in tensile strength parallel to the grain amounting from 30% in the micro-sections subjected to atmospheric corrosion in April to about 70% in those exposed in July. The decisive factor for the atmospheric corrosion in summer is the intensity of solar radiation, while in winter the increased amount of sulphur dioxide in the surrounding air is the main factor.     

Unexplained site variance in machine strength grading of Norway spruce structural timber

The aim of the study was to assess site effects in terms of unexplained site variance in machine strength grading of Norway spruce structural timber. The site effects were estimated for grading based on axial resonance frequency and timber length, and for grading based on dynamic modulus of elasticity. Timber was collected from 14 sites in Norway, and linear mixed models were developed based on 1188 boards. The study showed that strength grading based on axial resonance frequency and timber length leaves out effects of site that are related to altitude, latitude and site index. The variance could be reduced when the grading was based on dynamic modulus of elasticity. For both grading methods, the site effects were smaller for bending strength than for modulus of elasticity and density. Major parts of the site effects were explained by mass density, and simulations showed that it is possible to fulfil the requirements of the strength classes with a higher yield when the sorting is based on a combination of exclusion by mass density and exclusion by the frequency-based indicating property.     

Effect of high-temperature drying on properties of Norway spruce and larch

In timber drying, mechanical properties may be changed due to treatment temperature and treatment duration. In general, when increasing the kiln temperature, drying time is decreased and some timber properties are negatively affected. In this study, the effect of different drying temperatures (80, 120 and 170 °C) on equilibrium moisture content and sorption rate, on bending strength and stiffness was investigated for Norway spruce and larch from four proveniences and the results were compared to those obtained for heat-treated wood (Thermowood ^®). The experiments confirm earlier research that both treatment temperature and treatment duration affect the properties. High-temperature drying or treatment can be optimized for several applications, yielding strong but not so durable timber or vice versa.     

Untreated Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) wood-panels exposed out of ground contact in Sweden for two years

In this study, the durability of 230 wood panels, consisting of both Scots pine (Pinus sylvestris) and Norway spruce (Picea abies), were examined in an above-ground durability field test, for two years, in southern Sweden. The samples consisted of three pieces of wood, 22×95×500 mm³. The pieces were screwed together with an overlap so as to obtain an efficient moisture trap. The results of the durability test showed large differences between Scots pine sapwood and heartwood. Sapwood displayed unacceptably high moisture contents and fungal discoloration, while heartwood had low and stable moisture contents, and lesser discoloring. Norway spruce had moisture dynamics similar to pine heartwood, although a some what higher moisture content was recorded. The differences in moisture dynamics among the spruce samples, which were divided into: juvenile wood, mature wood with horizontal annual rings, and mature wood with vertical annual rings, were small. Juvenile wood showed more discoloring caused by mould fungi. The samples with horizontal annual rings suffered massive cracks.     

Determination of fiber orientation in Norway spruce using X-ray diffraction and laser scattering

Spiral grain reduces the quality of timber since it causes twisting during drying and reduces the mechanical strength of wood products. The orientation of wood fibers in Norway spruce as a function of the distance from the pith was studied using both x-ray diffraction and light scattering. In radial-longitudinal plane upper tips of fibers were tilted towards the pith and the tilt angle increased gradually towards the bark in most of the samples. Periodic oscillations in the spiral grain angle were observed. Increased growth rate was found to increase the amplitude of this oscillation. There was no clear correlation between the angles determining the fiber orientation and other parameters like the lumen diameter, the cell wall thickness, the density of the sample, the fiber length, the circularity index of the cell lumen, or the mean microfibril angle. However, fiber orientation in tangential-longitudinal plane varied more in broad annual rings than in narrow annual rings.     

Full-field moisture induced deformation in Norway spruce: intra-ring variation of transverse swelling

The transverse hygro-expansion of Norway spruce wood is studied on the growth ring level using digital image correlation. This non-destructive technique offers the possibility for a contactless study of deformation fields of relatively large areas. The measured full-field strains are segmented into individual growth rings. Whereas radial strains closely follow the density progression with the maximum in the dense latewood (LW), tangential and shear strain remain constant except for positions around the edges of the sample. A simple FE three phase growth ring model is in good agreement with the experimental values. The selective activation of individual phases like earlywood (EW), transition wood and LW demonstrates that the radial hygro-expansion is dominated by the EW deformation, whereas tangential deformation is a complex interplay of expansion and compression that needs all tissues to fully develop.     

Three-dimensional model for size and location of resin pockets in stems of Norway spruce

Resin pockets, being an important natural characteristic for wood quality and tree physiology, were observed on the surfaces of boards sawn from four large Norway spruce (Picea abies (L.) Karst.) trees and analysed for size and distribution. Axial length varied between trees and increased from pith to surface and from butt to top; however, three quarters of the variation were random and normally distributed. Also resin pocket frequency varied between trees. Within the stem, the resin pockets remained independent and randomly distributed following the exponential distribution in all three directions: radial, angular and axial, corresponding to a constant probability during the lifespan of the tree. No association between size and frequency was identified. The initiation and the expansion of a resin pocket appear to be controlled by two different physiological processes. The findings should add to the understanding of resin pocket formation in spruce and should be applicable to wood quality     

Hygroscopicity of heat-treated Norway spruce (Picea abies) wood

Hygroscopicity of heat-treated spruce wood is investigated in relation to the mass loss that occurs during the thermal treatment. It is found that the reduction in hygroscopicity is not only due to mass loss, but another mechanism exists. It is hypothesized that this mechanism is related to irreversible hydrogen bonding in the course of water movements within the pore system of the cell walls. Regarding batch experiments with constant amount of water and wood, such hornification occurs during a wetting and drying cycle induced by heating to a predetermined steady-state temperature, provided an intermediate relative humidity prevails at the isothermal stage.