Gero Becker

The mechanics of Norway spruce [Picea abies (L.) Karst]: mechanical properties of standing trees from different thinning regimes

Abstract In the first part, the authors discuss the mechanical stability of dominant and suppressed Norway spruce trees (Picea abies) grown under differing thinning regimes with a focus on the stem shape and the mechanical properties of the standing tree. In the second part, they concentrate on the variation of the modulus of elasticity of green wood (MOEfresh) and the density within the stem to analyse the effect of the underlying patterns in variation of these wood properties on the mechanics of the entire stem. At the standing-tree level, the investigations comprised a morphological description and static bending tests on the trees to measure flexural stiffness and structural Young’s modulus of the stem. Discs sampled from different stem heights were examined to distinguish between different tissues (cortex, wood, pith) and wood types (adult, adolescent, juvenile), and to measure quantitatively their contribution to the axial second moment of area of the stem. An analysis of the variation of density and MOEfresh within the stem was carried out on small wood samples cut out of stem sections taken from the same height as the stem discs. The flexural stiffness of the trees is mainly influenced by stem radius, resulting in a higher flexural stiffness for thicker trees. Independently from the stem dimensions, the structural Young’s modulus was slightly higher for the suppressed trees within each site. In an individual tree the structural Young’s modulus decreases with increasing stem height. The cross-sectional analyses of wood type proportions and their characterisation by density and MOEfresh showed that the distribution of adult, adolescent and juvenile wood within the stem affects the structural Young’s modulus and the flexural stiffness of the stem. Finally, a method is presented that allows a re-calculation of the mechanical bending properties of the entire standing trees using MOE and axial second moments of area of the different wood types. Our results suggest that further modelling of mechanical behaviour of trees might be possible taking into account the composite nature of conifer stems.

Land availability and potential biomass production with poplar and willow short rotation coppices in Germany

Several factors influence land availability for the growth of short rotation coppices (SRC) with fast‐growing tree species, including the nationwide availability of agricultural land, economic efficiency, ecological impacts, political boundaries and environmental protection regulations. In this study, we analysed the growing potential of poplar and willow SRC for bioenergy purposes in Germany without negative ecological impacts or land use conflicts. The potential biomass production using SRC on agricultural land in Germany was assessed taking into account ecological, ethical, political and technical restrictions. Using a geographic information system (GIS), digital site maps, climate data and a digital terrain model, the SRC biomass production potential on cropland and grassland was estimated using water supply and mean temperature during the growing season as parameters. From this analysis, a yield model for SRC was developed based on the analysed growth data and site information of 62 short rotation plantations in Germany and France. To assess the technical, ethical and ecological potential of SRC, restrictions in protected areas, technical constraints and competition with food and feed production were investigated. Our results revealed that approximately 18% (2.12 Mio. ha) of cropland and 54% (2.5 Mio. ha) of grassland in Germany were highly suitable for SRC plantations, providing favourable water supplies and mean temperatures during the growing season. These identified sites produced an average yield of more than 14 tons of dry matter per hectare per year. Due to local climate and soil conditions, the federal states in northern and eastern Germany had the highest theoretical SRC potential for agricultural land. After considering all ecological, ethical, political and technical restrictions, as well as future climate predictions, 5.7% (680 000 ha) of cropland and 33% (1.5 Mio. ha) of grassland in Germany were classified as suitable for biomass production with fast‐growing tree species in SRC.

Characteristics and needs of different user groups in the urban forest of Stuttgart.

Abstract In the urban forest of Stuttgart the forest roads are used by a growing number of people for recreational and leisure activities. To manage and channel the different user groups within an optimised forest road network needs a lot of information: Number and composition of visitors, demands of different user groups concerning standard of roads and trails they use for their activities, conflicts that may rise between different users using the same road at the same time, dedication of roads to special activities (e.g. fitness trail, hiking trail). A relatively new method of video monitoring was used to collect long-term information about number and composition of visitors, personal interviews with “experts” were made to obtain information about the specific demands of the different user groups, and analysis of road network was done with the help of GIS. The results show that these tools complement one another quite well and the combination of obtained data may help to channel visitor flows and to minimise conflicts between different user groups.

New Holland Forage Harvester's Productivity in Short Rotatation Coppice: Evaluation of Field Studies from a German Perspective

Abstract Modified forage harvesters are a common technology used to harvest short rotation coppice (SRC). This paper describes results of time studies from harvest trials with the New Holland forage harvester equipped with the cutting head 130 FB. Seven fields comprising a total of 13.6 ha SRC were harvested, and data from 22h 41 min were collected. In the studies, 0.77 hectares were harvested per productive machine hour (pmh−1). The share of productive times was 74% of the total work time. The average harvesting productivity was 20.5 odt pmh−1. Under good conditions, productivities up to 30 odt pmh−1 were reached. The harvesting costs were 19.70€ odt−1 on average, excluding the costs for the transport of the chips and of the harvesting machine to the fields.

Influence of wood properties and bonding parameters on bond durability of European beech (Fagus sylvatica L.) glulams.

Abstract• Considerable progress has been made recently to promote glue-laminated beams of European beech (Fagus sylvatica L.) for load-bearing structures in engineering. However, further investigations into the bond durability are required. The objective of the present study was to analyse material and manufacturing factors and their combination to improve the resistance in delamination tests as required for the use in building service class 1.• In the experimental work, the influence of selected wood properties, manufacturing conditions, and the effect of a hydroxy-methylated resorcinol primer on the delamination resistance of beech glulams bonded under laboratory and industrial conditions with a melamine-urea-formaldehyde adhesive were investigated.• The highest delamination resistance of the laboratory samples was achieved with the smallest lamellae thicknesses of 29 mm. A closed assembly time of more than 30 min and the use of the primer further enhanced the bond durability. Higher delamination rates observed in glulams manufactured industrially were related to the relatively thick (38 mm) and often twisted beech lamellae used.• The results suggested that bond durability required for service class 1 can be attained by restricting lamella thickness in beech glulam to a maximum of 30 mm and by using a minimum closed assembly time of 40 min.

Suitability of Bamboo as an Energy Resource: Analysis of Bamboo Combustion Values Dependent on the Culm’s Age

Abstract Bamboo has gained increasing attention, especially due to its fast growth and its versatile utilization. It is used by millions of people in their daily lives and is a resource for timber, pulp and paper, and for food industries—not only in Asia. So far, the bio-energy sector has shown only marginal interest in bamboo, whose energetic properties are less intensively studied than its physical properties. This paper presents physical and chemical properties of two bamboo species—Phyllostachys pubescens and Bambusa emeiensis—for energy recovery. Both species were tested on calorific value, moisture, ash and chloride content in dependence on the culm’s age, and the sample’s position along the culm. Furthermore, the sustainable biomass potential from bamboo stands for energetic utilization of Phyllostachys pubescens was assessed. The obtained results show that both bamboo species have a potential for energy recovery and are essentially suitable to be used as an energy source for combustion. Compared to woody biomass, both species show similar calorific values and only slightly higher chloride and ash contents.

Fully Mechanized Harvesting in Aged Oak Coppice Stands

Coppice is a traditional forest management system used all over the world. It takes advantage of fast early growth and the vegetative reproduction of the respective trees. Coppice forests provide firewood and many other products and services, especially to rural communities. In Central Europe, regular periodic cutting and management of coppice forests was abandoned due to socioeconomic changes in recent decades, resulting in aged stands that have gradually lost their coppice characteristics. Today, coppice forests are recognized again not only for their growth potential but also for their benefits for biodiversity and nature conservation. Together with the rising demand for energy wood, this recognition could result in a renaissance of the traditional coppice management system. Several stands grow on relatively easily accessible terrain where fully mechanized systems (harvester, forwarder) could be used. However, there is no current information regarding the technical feasibility and productivity of moder...

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

ZusammenfassungIn dieser Arbeit werden das Auftreten und die Verteilung von Harzgallen im Holz der Fichte auf Bestandes- und auf Einzelbaumebene analysiert. Die Verteilung der Harzgallen im Stamm wird in stammaxialer und radialer Richtung, sowie hinsichtlich eines bevorzugten Auftretens in einer Himmelsrichtung untersucht. Es wird deutlich, dass die Harzgallenhäufigkeit sowohl zwischen verschiedenen Beständen, als auch zwischen den Bäumen eines Bestandes sehr stark variieren kann. Korrelationen zwischen der Harzgallenhäufigkeit und verschiedenen Einzelbaumparametern lassen vermuten, dass die Wachstumssituation in Verbindung mit der mechanischen Belastung des Stammes durch Wind wesentlich zur Erklärung der Harzgallenhäufigkeit beitragen kann. Dabei spielen vor allem die Parameter ,,relative Kronenlänge“, ,,mittlerer Radialzuwachs“ und die ,,Hangneigung“ eine Rolle. AbstractThis 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.

Performance of organic nanoparticle coatings for hydrophobization of hardwood surfaces

The protection of wood surfaces against water is a primary requirement to enhance their life-time and durability. In this article, a hydrophobic surface modification of selected hardwood surfaces (including high-density (HD) and low-density (LD) samples) is presented, by coating them with waterborne imidized nanoparticles under pure conditions or with vegetable oil. The performance of both nanoparticle coatings relative to noncoated and oil-coated samples was evaluated by water contact angles, microscopy, and optical profilometry. The pure nanoparticle coatings often increase the hydrophobicity, but they do not yet form a fully protective layer due to their porous structure after drying. The nanoparticle coatings with vegetable oil form a continuous layer with a maximum contact angle of 118°. The coating formation highly depends on the wood density (and resulting surface porosity), resulting in spreading of the aqueous dispersion on HD wood and penetration on LD wood. A thin continuous nanoparticle coating with incorporated vegetable oil provides highest contact angles, as the roughness of the original wood fibers remains visible in the surface profile.

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

ZusammenfassungSowohl für wissenschaftliche Untersuchungen als auch für praktische Anwendungen sind methodische Entwicklungen zur Erfassung und Messung des Reaktionsholzes der Fichte wünschenswert. Mit der vorliegenden Untersuchung wurde das Ziel verfolgt, ein innovatives Verfahren zur Erfassung und Messung von Reaktionsholz zu entwickeln und zu testen. Das vorgestellte Verfahren der digitalen Bildanalyse erlaubt es, anhand digitaler Fotografien von Stammscheiben der Fichte (Picea abies (L.) Karst.) Reaktionsholzbereiche zu erkennen, jahrringweise zu erfassen sowie deren Flächeninhalt, die Lage als Abweichungswinkel von der Nordrichtung und den Abstand von der Markröhre zu berechnen. Des Weiteren kann der Flächeninhalt der gesamten Stammscheiben anhand der Bilder ermittelt werden, so dass die Reaktionsholzflächen auch in Flächenanteile umgerechnet werden können. Die Größe der beim Fotografieren auftretenden Abbildungsfehler, die sogenannte Verzeichnung, wurde im Rahmen der vorgestellten Untersuchung geprüft, die als Prozentwert angegebene Abweichung liegt jedoch unter 1% und kann daher vernachlässigt werden. Mit dem Verfahren ist es möglich, rasch, objektiv und detailliert das Reaktionsholz bei Fichte zu erfassen, so dass die Kenntnisse über die Reaktionsholzverteilung in Stämmen, aber auch in Schnittholz vertieft werden können.AbstractBoth 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.