Growth stresses and strains in cork

Summary A detailed study of the growth stresses and strains in the cork shell of the cork-oak was undertaken based on experimentally determined constitutive relations for cork in tension and compression. The stresses depend on the thicknesses of the cork shell and of the back layer around the cork shell, on the radius of the trunk and on its increase due to growth. The circumferential stresses in the cork shell and back layer are tensile and increase with increasing distance to the tree axis. The radial stresses are compressive and decrease with increasing distance to the tree axis. The strains due to growth are not recovered when the cork boards are removed, unless the boards are heated, for example, by immersion in boiling water. Other consequences of the growth stresses are analysed, such as the occurrence of corrugations in the lateral cell walls of cork, the variation of width of the successive growth rings and the occurrence of cracks in the back layer and outer cork layers.     

Identification of moisture-induced stresses in cross-laminated wood panels from beech wood (Fagus sylvatica L.)

The crosswise bonding of the layers in laminated solid wood panels results in internal stresses when the humidity varies. The layers hinder one another as a result of the anisotropy of wood. The purpose of this study was to determine the internal stress state in free and constrained swelling. The expansion properties in the three panel directions were measured. Furthermore, the swelling of samples was constrained while the resulting forces were recorded. Hygroscopic warping experiments were carried out inducing a climate gradient within the panels. Afterwards the stresses were calculated from released deformations and non-destructive measurements of the Young’s modulus. The materials used were untreated and heat-treated beech wood, the latter modified in two levels. In addition to homogenously structured panels, treated top layers were combined with an untreated middle layer. Swelling, swelling pressure, warping and internal stresses considerably decreased from untreated to treated wood. If layers from treated and untreated material were combined, stresses and deformations increased as compared to the variants produced only from treated wood. It was concluded that the lower equilibrium moisture content of heat-treated beech wood improves its dimensional stability, which results in smaller deformation differences between the layers. Hence, the stresses were less distinctive.     

Cutting-forces when up-milling in beech

By use of a load cell, a computer and a fast scanning device we have examined the cutting-forces on the tool in a milling machine. Several experiments have been elaborated with different rotation and feeding speeds. The aim is to study, in detail, how wood chips are produced. By a better understanding of this process it must be possible to manufacture wooden details for furniture and other products with minimal errors and, hence, there will be reduced need for sanding and other expensive extra treatment in order to achieve an acceptable result of the finished surface. The load cell was used to register the forces in three directions. These registrations, however, were not easy to interpret because of the vibrations which were introduced in the experimental setup when milling started. A computerized filter therefore had to be used in order to extract only those registrations which were of interest. We found that the cutting forces in beech varied from approximately 40 up to 86 N/cm in the work-piece feed direction, i.e. in the Y-direction, and from about 14 to 51 N/cm in the X-direction, i.e. in the normal to the cut surface. A larger average chip thickness resulted in larger forces but we could not find a clear relationship which, in full, explained our result.     

Adhesive penetration in beech wood: experiments

A study with synchrotron radiation X-ray tomographic microscopy (SRXTM) of PUR, PVAc, and UF adhesive bond lines in beech wood, bonded under various growth ring angles, is presented. The bond line morphologies and the adhesive penetration into the wood structure were evaluated after determining the hardening characteristics of the adhesives. Distinct bond line imperfections were found for the different adhesive systems. To describe the adhesive distribution inside the bond line, the saturation of the pore space instead of the commonly used maximum penetration depth seems to be adequate.     

Growth response of advanced planted European beech (Fagus sylvatica L.) after storm-caused loss of shelterwood

European Journal of Forest Research - Outcomes after an abrupt, storm-caused loss of spruce shelterwood (Picea abies L. Karst.) overstories on advanced planted beech (Fagus sylvatica L.) were...     

Bark phenolics of American beech (Fagus grandifolia) in relation to the beech bark disease1

The amount of total extractable phenols was determined for bark sections obtained from behind cankers naturally induced by Nectria coccinea var. faginata and from behind mechanically inflicted wounds on stems of American beech. Healthy bark from susceptible trees was found to contain a similar level of phenolics as bark from trees determined to be resistant to the beech bark disease. Six months after wounding, wound-altered bark from susceptible trees was found to be lower in phenols than woundaltered bark from resistant trees. Inoculation of wounds with N. coccinea var. faginata resulted in decreased phenolic levels in bark sections nearest the wound surface, and increased phenolic levels in sections nearest the vascular cambium, several mm distant. Phenolic levels in injured or infected bark appear to follow similar patterns as those resulting from injury or infection of xylem tissues.     

Silylation of solid beech wood

This report presents a new derivative from the chemical conversion of hardwood. Silylation of hardwood was successfully achieved using trimethylsilyl chloride with pyridine as base. The new wood compounds were analyzed by FTIR spectroscopy. The FTIR spectra of the silylated wood compounds show new absorption bands derived from trimethylsilyl ether groups. Furthermore, the products were investigated by means of EDX analysis. The presence of silicon confirmed the conversion of wood into the corresponding silyl ether derivative. Electron microscopy, i. e. SEM, shows that the location of the silicon was not restricted to the surface of the wood fibres. Penetration of the reactants into the wood body occurred, when a solid wood sample (beads) was used.     

Multispecies Phytophthora disease patterns in declining beech stands

Decline diseases are typically caused by complex abiotic and biotic interactions and characterized by a suite of symptoms indicative of low plant vigour. Diseased trees are frequently infected by Phytophthora, but the complex interactions between pathogen, host and the heterogeneous forest environment mask a comprehensive understanding of the aetiology. In the present study, we surveyed European beech (Fagus sylvatica) stands in Swiss forests with recent increases in bleeding lesions for the presence of Phytophthora. We used a combined approach of analysing soil and bark samples from trees displaying bleeding lesions and trees free from bleeding lesions. Soil baiting revealed a higher prevalence of Phytophthora spp. around trees with bleeding lesions than around trees without bleeding lesions. For the bark samples from bleeding lesions, we used several detection methods. Phytophthora spp. were detected in 74% of the trees by an immunological on‐site diagnostic kit, in 64% by a specific PCR assay, and 38% by isolation on selective media. All samples tested were negative for P. ramorum using qPCR. Overall, nine Phytophthora species were identified by ITS sequencing, the most common of which were P. plurivora, P. gonapodyides, P. × cambivora and P. syringae. We identified distinct species in bleeding lesions and the rhizosphere of the same host tree which suggests a multispecies Phytophthora disease patterns in these declining beech. Among the recovered species, P. × cambivora and P. × serendipita were identified as hybrid genotypes with the former abundant in bleeding lesions.     

Liquefaction of beech wood in various supercritical alcohols

The liquefaction of Japanese beech (Fagus crenata Blume) was studied with various straight-chain alcohols in subcritical and supercritical states using a batch-type reaction vessel to obtain liquid fuel from lignocellulosics. Under the reaction condition of 270°C, beech wood was liquefied to some extent in all alcohols with about 50%–65% insoluble residue left after treatment for 30min. Under the condition of 350°C, however, more than 90% of wood was decomposed and liquefied in all alcohols. Alcohols with longer alkyl chains liquefied lignocellulosics in shorter reaction times. Because many kinds of alcohols, such as methanol and ethanol, can be produced from biomass, 100% biomass-based liquid fuel can be prepared by supercritical alcohol technology when using such bioalcohols. This study was presented in part at the 55th Annual Meeting of the Japan Wood Research Society, Kyoto, Japan, March 16–18, 2005     

Effect of canopy gap size and ecological factors on species diversity and beech seedlings in managed beech stands in Hyrcanian forests

We studied the species diversity of the herb layer and ecological factors in harvest-created gaps in beech stands under a single-tree selection system in Northern Iran. To determine diversity, the number of beech seedlings, and other ecological factors, 16 gaps were selected and subplots of 5 m2 were positioned at the centre and at the cardinal points of each gap. Species richness and Simpson diversity index increased with increasing gap area as did numbers of seedlings. With increasing humus layer thickness, species richness declined but the Hill evenness index increased. Species richness increased with increasing light availability. There was no relationship between crown radii of beech trees and diversity indices. Correlations between environmental factors and numbers ofindividuals of some species in the herb layer were not significant except in a few cases. The results help explain the effects of man-made gaps on the dynamics of managed beech stands and this benefits evaluation of silvicultural operating plans.     

Moisture-dependent orthotropic elasticity of beech wood

Elastic material properties are one of the most important material characteristics in mechanical modelling. Wood with distinctively different properties in the longitudinal, radial and tangential directions exhibits a strong moisture-dependent material characteristic in the elastic range. In order to characterise beech wood as an orthotropic material, all of the independent elastic properties were determined at different moisture conditions. These characteristic properties have never been determined before as a function of moisture content yet are vital to the field of wood modelling. All elastic parameters, except for some Poisson’s ratios, show a decrease in stiffness with increasing moisture content. In comparison to available literature references at a moisture content of ω?≈?12%, the identified values were of the same order of magnitude. The determined material properties can be used to investigate the mechanical behaviour of beech wood structures including different moisture conditions.     

Bud dormancy in beech (Fagus sylvatica L.). Effect of chilling and photoperiod on dormancy release of beech seedlings

Two-year-old Fagus sylvatica L. seedlings were subjected to natural winter chilling or were overwintered in a heated greenhouse. Plants were then grown in controlled environment chambers with photoperiods of 9 or 13 h. Renewal of bud growth was found to be mainly determined by winter chilling. There was a slight interaction between chilling and photoperiod. Sprouting of apical buds took two to three times as long in unchilled plants as in chilled plants. Shoot elongation was influenced by chilling and was also greater in the 13-h photoperiod than in the 9-h photoperiod, but this may have been due at least in part to the higher irradiance. Chilling resulted in rapid dormancy loss and changed the growth pattern from basitonal to acrotonal.     

Growth of European beech (Fagus sylvatica L.) saplings is limited by elevated atmospheric vapour pressure deficits

There is an ongoing debate about how European beech might be affected by a future drier climate. While numerous studies have examined the effects of soil drought on beech growth and development, studies investigating the effects of elevated atmospheric water vapour pressure deficit (VPD) are lacking. By increasing VPD in climate and open-top chamber experiments, with moisture in the rooting medium near optimum, we tested the hypothesis that increased VPD negatively affects the growth and development of European beech saplings. In the climate chambers, a reduction in relative air humidity by 40% resulted in a 68% reduction in productivity. Similarly, in the open-top chamber experiment conducted on the forest floor, biomass declined by 30% when relative air humidity was 15% lower. The reduction in biomass was mainly a consequence of a dramatically reduced leaf growth of beech in the elevated VPD treatments. Our results show that growth and development of beech saplings strongly depend not only on soil moisture but also on the prevailing VPD level. We conclude that the vapour pressure deficit is a widely ignored factor which influences the growth and vitality, and possibly also the distribution of European beech. Future forest management schemes under an altered climate should take this factor into account.     

Relationships among beech bark disease,climate, radial growth response and mortality of American beech in northern Maine,USA

A majority of beech forests across Maine first experienced beech bark disease (BBD) from 1935 to 1960 when sap feeding by an introduced beech scale insect, Cryptococcus fagisuga, allowed lethal fungal infections primarily by Neonectria ditissima and/or Neonectria faginata. Beech stands along the Maine–Quebec border in northern Maine were excluded from this initial killing phase presumably due to cold winter temperatures that inhibited scale survival. However, a sharp increase in beech mortality after 2002 occurred in previously uninfected border stands and stands long affected by BBD. Beech mortality averaged 50% across northern Maine during 2003–2006. To identify plausible stresses that could explain the mortality, a dendropathological study was conducted from 2005 to 2006 in northern Maine that quantified temporal and spatial relationships between possible stressors with beech mortality and growth decline. Nineteen sets of high‐ and low‐mortality plots were located randomly across four bioregions. Increment cores were taken from both beech trees (n = 565) and associated tree species (n = 450). A growth change index of increments was used to evaluate beech responses to biotic and climatic stresses. A prolonged period of relatively mild winters without temperatures lethal to scale insect (Neonectria was found infecting weakened trees across the region. Drought, beech scale and Neonectria are plausible explanations for the episode of high beech mortality in northern Maine. This is the first report of a major killing phase of beech within the BBD ‘aftermath’ forests.     

Tartaric acid catalyzed furfurylation of beech wood

European beech (Fagus sylvatica L.) is a major tree species of European forest which is underexploited because of its low dimensional stability and durability. Similarly to what has been developed with radiata pine, furfurylation might be the answer to optimize the utilization of local beech wood. Beech wood furfurylation process was studied using five different catalysts: maleic anhydride, maleic acid, citric acid, itaconic acid, and tartaric acid. Optimization of the furfurylation process was investigated for different catalyst and furfuryl alcohol (FA) contents, and different duration of polymerization. The following properties were studied: weight percent gain (WPG), leachability, anti-swelling efficiency (ASE), wettability, modulus of elasticity, modulus of rupture, Brinell hardness, and decay durability. Tartaric acid, never investigated up to now, was retained as catalyst to perform furfurylation due to its efficacy compared to other catalysts and its novelty. Wood modification with FA and tartaric acid as catalyst led to samples with high WPG even after leaching, improved ASE, and lower wettability with water. Increasing the polymerization duration increased the fixation of FA in treated wood. Most of all, treatment gave a significant improvement in mechanical properties and resistance to wood decaying fungi.     

Alkaline degradation of spruce and beech wood

Summary The alkaline delignification of spruce and beech wood is accomplished in three phases. The first phase results in a decrease of yield down to 83...80%, the second one in a decrease from 83...80% to 64...61% and the third one in a yeld drop from 64...61% to 50...46%. The amount of polysaccharides removed in the first phase was 22%, in the second phase 5...6% and in the third phase 10% of the total polysaccharides in the original wood. The amount of lignin removed in the first phase of delignification was 9...11% in the second phase 53...54% and in the third phase 28% of the total lignin in the original wood. The polysaccharides extracted in the second and third phase amounted to 70...78% of the polysaccharides removed in the first delignification phase. For an entire characterization of the delignification reaction not only the course of lignin removal is of importance but also the course of the polysaccharide extraction. The results show that for a two-stage alkali-oxygen-cooking technology the optimum yield after initial partial alkaline delignification lies in the range of 64...61%.     

Growth recovery of mature Norway spruce and European beech from chronic O<Subscript>3</Subscript> stress

Elevated O₃ levels can strongly impair the health and vitality of forest ecosystems. Free-air exposure systems reveal that forest tree and stand growth can be reduced strongly under chronic O₃ stress. Detailed knowledge of the effect of O₃ exposure on photosynthesis, carbon sequestration, allometry and growth during chronic stress is available. However, knowledge of growth response after O₃ reduction is scarce. Here, we analyse the growth of mature Norway spruce (Picea abies (L.) Karst.) and European beech (Fagus sylvatica L.) in the free-air O₃ fumigation experiment at Kranzberg Forest. We compare tree growth over a 9-year period (2008–2016) after exposure to O₃ (2000–2007). During 2?×?O₃ exposure, the annual basal area growth of Norway spruce and European beech decreased by 24 and 32%, respectively. After cessation of 2?×?O₃ exposure, the annual basal area growth of Norway spruce and European beech not only recovered but exceeded the growth of the trees in the control condition by 14 and 24%, respectively. The growth resilience and resistance of trees previously exposed to 2?×?O₃ towards drought stress and late frost was hardly lower than that of the trees in the control condition. The capacity for growth recovery even after long-term chronic O₃ stress emphasizes the strong beneficial effect of air pollution control on the health of forest ecosystems and on the global land carbon sink.     

Disturbances in European beech water relation during an extreme drought

Context

In the context of a probable increase in intensity and frequency of extreme summer drought events, a better understanding of the key processes involved in water relations is needed to improve the theoretical foundations of predictive process-based models.

Aims

This paper aims to analyse how temperate deciduous trees cope with water shortage.

Methods

The exceptional summer drought of 2003 in Europe provided an opportunity to monitor stomatal conductance and twig water potential in European beech (Fagus sylvatica L.) at predawn and midday and to analyse variations with respect to leaf height within the canopy. By comparing our field measurements of twig water potential to values found in the literature, we confirmed the strong impact of soil water shortage on crown water relations.

Results

This paper shows that (1) the vertical gradient of stomatal conductance within the crown disappeared under extreme soil water depletion; (2) at maximum drought intensity, predawn twig water potential (ψ _pd) reached ?2.3 MPa at a height of 14 m in the crown and ?2.0 MPa at a height of 10 m. The significant differences in ψ _pd between the two measurement heights in the canopy may be due to night transpiration; (3) there was a close relationship between predawn twig water potential and relative extractable soil water; (4) as drought conditions intensified, there was a close relationship between canopy radiation interception and predawn water potential, as estimated daily from relative extractable soil water.