In-forest assessment of timber stiffness in Norway spruce (Picea abies (L.) Karst.)

The objective of this study is to identify easily obtainable predictors for the mean timber stiffness of a forest stand. The most robust predictor is found to be the average taper of the trees in a stand, expressed as the tree height divided by the diameter at breast height (H/D-ratio). In a simple linear regression, the mean H/D-ratio of a stand yielded a R ²-value of 82 % in explaining the mean modulus of elasticity of boards from the corresponding stand. As a practical approach, exclusion of timber from stands with an H\D-ratio under a certain threshold is implemented. This shows an increase of six to ten percentage points in the C30-portion depending on the combinations of strength classes produced with a Dynagrade strength-grading machine. This must be considered a substantial improvement in grade yield and makes such pre-sorting in the forest very attractive since the H/D-ratio can easily be measured in forest inventories or by harvesters.     

The appearance of resin pockets in CT-images of Norway spruce (Picea abies (L.) Karst.)

Picea abies (L.) Karst.) was studied. The study also includes a comparison between measured and calculated CT-numbers of Norway spruce resin and wood. It was found that it should be possible to create algorithms that automatically detect large resin pockets in CT-images of Norway spruce. Compared to resin pockets in heartwood, resin pockets in green sapwood are more difficult to detect due to the high density of the surrounding wood. The study also showed that the correlation between measured and calculated CT-numbers was high and that it is possible to use the same function for conversion between CT-number and density for both green wood and resin.

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Modeling the longitudinal variation of sawn timber grades in Norway spruce (Picea abies (L.) Karst.)

Grades derived from visual assessments of sawn timber are determined by the worst part of each piece. Since grade varies longitudinally in timber, grade yield will decrease if the average length of timber increases. The variation in grade is caused by longitudinal variation in knot properties and other features as they appear on the sawn surface taken into account during grading. The objective of this study is to describe and analyze this variation in Picea abies. The study consisting of 768 boards for which all features that could lead to downgrading were recorded noting position, type and size. Based on this information, all boards were graded according to appearance by Nordic Timber, and strength by INSTA 142. Logistic regression models of grade as a function of position in the stem were developed, and the dependence between responses was taken into consideration by using General Estimating Equations (GEE). The models showed a decreasing trend in grade from the butt end toward the top end of the trees, and the effect was more pronounced in strength grading than in appearance grading. Models with binomial response and different correlation structures were tested, and it was shown that both independent and autoregressive correlation structures could be used. This suggests that a multinomial ordinal logistic regression with a GEE-approach with an independent correlation structure is appropriate for modeling grade in this study.     

Modeling the effect of length on yield of sawn timber grades in Norway spruce (Picea abies (L.) Karst.)

The aim of the study was to model and analyse the effect of length on grade yield of timber from different stem parts in Picea abies, and to use the models to simulate the cost of reduced grade yield due to increased length. The boards were simulated having lengths ranging from 20 to 60 dm starting at stump level, 4 m above stump level and 8 m above stump level, respectively. Logistic regression models showed that length had a significant effect on grade yield, and this length effect was stronger in strength grading according to INSTA 142 (IN) compared to appearance grading according to Nordic Timber (NT). The length effect was most pronounced in butt logs, and somewhat greater in middle logs compared to top logs. Also a smaller length effect in inner boards compared to boards farther from the pith was found for IN-grading. The cost of the decrease in grade yield with increasing length will depend on the assumptions about the price gap between the grades. Current market prices in both grading rules gave a decrease in value of the sawn timber in stock by about 6% with an increase in the log length from 45 to 60 dm. In addition, a decrease in yield of timber in longer logs will amplify this effect, while a higher efficiency in the production process will diminish it.     

Prediction of knot diameter in Picea abies (L.) Karst

Picea abies (L.) Karst. from three different site indexes in south-eastern Norway. Ten branch whorls were sampled from each tree, and diameters of all the knots were measured at the radial stem plane. Knot diameter was evaluated as mean diameter of the two thickest knots in each sample whorl. The whorl with the maximum value in each tree was on average located at 30% of tree height at G11, 40% at G17 and 60% at G23. The vertical location was related to the position of the crown base, and single tree models for predicting the position and the value were constructed. Knot diameter in the butt log, i.e. in the lower 30% of tree height, was related to annual ring width and site index, and to diameter at breast height and site index.

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Prediction of knot diameter in Picea abies (L.) Karst

(L.) Karst. from three different site indexes in south-eastern Norway. Ten branch whorls were sampled from each tree, and diameters of all the knots were measured at the radial stem plane. Knot diameter was evaluated as mean diameter of the two thickest knots in each sample whorl. The whorl with the maximum value in each tree was on average located at 30% of tree height at G11, 40% at G17 and 60% at G23. The vertical location was related to the position of the crown base, and single tree models for predicting the position and the value were constructed. Knot diameter in the butt log, i.e. in the lower 30% of tree height, was related to annual ring width and site index, and to diameter at breast height and site index.     

Internal distribution of sound and dead knots in Picea abies (L.) Karst.

(L.) Karst. in the south-eastern part of Norway. Distribution of sound and dead knots was evaluated as the mean and the range of the radial extension of sound knots within each whorl. The mean value was found to increase with increasing height in the lower 40% of the tree height followed by an upwards decreasing trend. It was related to diameter at breast height and annual ring width together with site index. The range of sound knot length within a whorl was calculated to 22 mm on average. It was found to be increasing up to 30% of tree height followed by a decrease upwards. The range was related to site index, diameter at breast height, eccentricity and to difference in height to the lowest living branch and the lowest living whorl.     

Internal distribution of sound and dead knots in Picea abies (L.) Karst.

Picea abies (L.) Karst. in the south-eastern part of Norway. Distribution of sound and dead knots was evaluated as the mean and the range of the radial extension of sound knots within each whorl. The mean value was found to increase with increasing height in the lower 40% of the tree height followed by an upwards decreasing trend. It was related to diameter at breast height and annual ring width together with site index. The range of sound knot length within a whorl was calculated to 22 mm on average. It was found to be increasing up to 30% of tree height followed by a decrease upwards. The range was related to site index, diameter at breast height, eccentricity and to difference in height to the lowest living branch and the lowest living whorl.

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Picea abies (L.) Karst.) in Südosten Norwegens gemessen. Die Verteilung wurde bestimmt als Mittelwert und Ausma? der radialen Tiefe der gesunden ?ste innerhalb der einzelnen Quirle. Der Mittelwert stieg zun?chst mit zunehmender H?he bis etwa 40% der Baumh?he. Danach kehrte sich die Tendenz um. Der Mittelwert ist auch korreliert mit dem Brusth?hen- durchmesser, der Jahrringbreite und der H?henbonit?t. Die L?nge der gesunden ?ste betrug im Mittel 22 mm. Bis etwa 30% der Baumh?he stieg der Wert an, danach fiel er wieder ab. Der Mittelwert ist korreliert mit H?henbonit?t, Brusth?hendurchmesser Exzentrizit?t sowie zur H?hendifferenz zum niedrigsten grünen Ast bzw. Quirl.

     

Effects of thermal modification on the adhesion between spruce wood (Picea abies Karst.) and a thermoplastic polymer

In order to study the effect of thermal treatment on the adhesion between wood and a nonpolar thermoplastic polymer, spruce wood boards (Picea abies Karst.) were heat-treated and bonded with polyethylene. As a result the contact angle of an applied water droplet increased significantly. A strong improvement of the adhesion between the modified wood surface and polyethylene was found by mechanical tests on unmodified and thermally modified samples.     

Automatic sorting of spruce (Picea abies (l.) karst.) sawlogs by grade

Grade sorting of logs in addition to diamoter sorting is a mean of customising production schedules and treatments, eg. sawing patterns and drying schedules. This paper analyses the feasibility of automatic grade sorting of spruce (Picea abies (l.) karst) saw logs by using optical log scanners, eg. shadow scanners. Differences in log geometry between grades, stands, diameter classes and log types were analysed. The material consisted of 699 logs from four different stands. It was tested if the differences in log geometry between high and low grade logs could be used for grade sorting in a logistic model. About two thirds of the logs were correctly classified into high or low grades. The methods and results are considered promising and further studies are recommended.     

Verteilung und Häufigkeit von Harzgallen im Holz der Fichte (Picea abies (L.) Karst.)

This study deals with the occurrence and the distribution of resin pockets in the wood of Norway spruce on the stand level as well as on the single tree level. The distribution of resin pockets in the stem in the longitudinal and radial direction and to a preferred cardinal point is analysed. It can clearly be seen that the resin pocket frequency between different stands as well as between trees of the same stand can vary considerably. Correlations between the resin pocket frequency and different tree parameters suggest that growth conditions combined with mechanical stress due to wind can contribute essentially to the explanation of the frequency of resin pockets. Especially the parameters “relative crown length”, “mean annual increment” and the “slope” may play an important role in this context.     

Erkennung und Messung des Reaktionsholzes bei Fichte (Picea abies (L.) Karst.) mittels Verfahren der digitalen Bildanalyse

Both for scientific analyses and for practical applications methodical developments are desirable for identifying and measuring compression wood of Norway Spruce. The objective of the present study was to develop and to test an innovative method for identifying and measuring compression wood. Methods of digital image analysis using digital photographs of discs of Norway Spruce (Picea abies (L.) Karst.) permit, to detect and to identify independently compression wood areas within single annual rings, and to calculate their area, the position given as an angle of the deviation to the direction of North and the distance from the pith. Furthermore the total area of the discs can be determined, so that the compression wood areas can be converted to proportions of the total disc area. The quantity of the images’ inaccuracy, the so-called lens distortion, was tested within the frame of the study presented, however the inaccuracy given as a percentage amounts to less than 1% and can therefore be neglected. Using this method it is possible to identify quickly, objectively and detailed compression wood of Norway Spruce, so that the knowledge about the distribution of compression wood in stems and in sawn timber as well can be extended.     

Variation of wood density and shrinkage in European aspen (Populus tremula)

Populus tremula L.) stems. The stems were randomly selected from three pure aspen stands with similar diameters at breast height and with similar tree heights. The samples for measuring the wood density and shrinkage were taken at stump height and from the heights of 3, 6, 9, 12 and 15 meters. The results showed that wood density of European aspen is highest in the living crown. At lower heights (up to 12 meters) wood density is also higher just beneath the bark rather than in the pith. The volume shrinkage in aspen wood is largest in the middle of the cross-section pith-surface and smallest close to the pith. Longitudinal shrinkage grew slightly upwards from a height of 3 meters, radial wood shrinkage was the smallest at stump height and at a height of 15 meters and tangential shrinkage was the smallest at a height of 15 meters and it remained quite steady within tree.

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Holzeigenschaften stark immissionsgeschädigter Fichten (Picea abies [L.] Karst.) in den Hochlagen des Osterzgebirges

The question for the wood properties of the tree species in regard to its further worthiness of cultivation and silvicultural treatment has been raised within the framework of the joint project “Investigations of Forest-Ecosystems in Erz Gebirge as a basis of a Forest Reconstruction by Ecological Criteria” undertaken within the framework of the Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF) (Federal Ministry of Education, Research, and Technology). A decrease of tracheid lengths as well as of the lumina of early wood has been ascertained in sapwood annual rings smaller than 0.5 mm in width of mature spruce, the wood of which having been subject to heavy damage due to SO₂ pollution. The late wood was characterized by decreasing cell wall thickness and larger microfibril angles within the cell wall layer S₂. The anatomical and structural features of wood distinguished by narrow annual rings have been found both in heavily pollution-damaged trees as well as in trees with comparably narrow annual rings of non-polluted sites. Strength investigations in terms of materials testing according to DIN yielded normal strength values of wood that was not affected by secondary agents. Investigations on particularly small test specimens (Dynstat examinations) up to a minimal annual ring width confirm the known relationships between wood density and impact bending strength. Thus, the wood of spruces growing in the high-altitude belts of the eastern parts of Erz Gebirge may be used without reservations.     

Sekundäre Veränderungen im Holz akut belasteter Fichten (Picea abies [L.] Karst.) in Hochlagen des Osterzgebirges

Within the framework of an interdisciplinary research project “investigation of forest ecosystems in the ore-mountains as basis for an ecologically oriented silviculture” supported by the Federal-ministry for education, science, research and technology (BMBF), Bonn, a study of the wood quality of heavily SO₂-polluted and wind-exposed spruce trees from high altitude stands was conducted. For this study wood from 6 standing, wind-exposed and 6 storm-tossed trees with brash fractures was considered. By means of light microscopy (polarization, phase contrast) and electron microscopy the formation, distribution and extension of slip planes within the cell walls were examined and their significance for fracture initialization quantified. Wood discolouring and wood destroying fungi were isolated from the fracture zones and taxonomically determined. The extent of wood decay was characterized on a cellular and subcellular scale by means of fluorescence microscopy and UV spectroscopy. In the heavily SO₂-polluted and thinned-out spruce stands at the high altitudes of the ore-mountains extreme wind stresses initiate in some tress slip planes which accumulate in the vicinity of rays and branch tracers. The slip plane zones are subsequently infected by wood degrading fungi, in particular by Stereum sanguinolentum (Alb. et Schw.: Fr.) Fr. resulting in a simultaneous decay of carbohydrates and lignin in the cell walls. The combined effect of wind stress and cell-wall degradation apparently induces brash, staircase-like fractures in some stems, which limitates the utilization of the timber. Eventually reduced SO₂ immissions and an improved stand structure will help avert this kind of damage and spruce grown at this site will again satisfy standard wood quality requirements.