Model analysis of temperature impact on the Norway spruce provenance specific bud burst and associated risk of frost damage

The annual growth cycle of boreal trees is synchronized with seasonal changes in photoperiod and temperature. A warmer climate can lead to an earlier bud burst and increased risk of frost damage caused by temperature backlashes. In this study we analysed site- and provenance specific responses to interannual variation in temperature, using data from 18 Swedish and East-European provenances of Norway spruce (Picea abies), grown in three different sites in southern Sweden. The temperature sum requirements for bud burst, estimated from the provenance trials, were correlated with the provenance specific place of origin, in terms of latitudinal and longitudinal gradients. Frost damage had a significant effect on tree height development. Earlier timing of bud burst was linked to a higher risk of frost damage, with one of the sites being more prone to spring frost than the other two. The estimated provenance specific temperature sum requirements for bud burst were used to parametrize a temperature sum model of bud burst timing, which was then used together with the ensemble of gridded climate model data (RCP8.5) to assess the climate change impact on bud burst and associated risk of frost damage. In this respect, the simulated timing of bud burst and occurrence of frost events for the periods 2021-2050 and 2071-2100 were compared with 1989-2018. In response to a warmer climate, the total number of frost events in southern Sweden will decrease, while the number of frost events after bud burst will increase due to earlier bud burst timing. The provenance specific assessments of frost risk under climate change can be used for a selection of seed sources in Swedish forestry. In terms of selecting suitable provenances, knowledge on local climate conditions is of importance, as the gridded climate data may differ from local temperature conditions. A comparison with temperature logger data from ten different sites indicated that the gridded temperature data were a good proxy for the daily mean temperatures, but the gridded daily minimum temperatures tended to underestimate the local risk of frost events, in particular at the measurements 0.5 m above ground representing the height of newly established seedlings

Teasing apart the joint effect of demography and natural selection in the birth of a contact zone

Vast population movements induced by recurrent climatic cycles have shaped the genetic structure of plant species. During glacial periods species were confined to low-latitude refugia from which they recolonized higher latitudes as the climate improved. This multipronged recolonization led to many lineages that later met and formed large contact zones. We utilize genomic data from 5000 Picea abies trees to test for the presence of natural selection during recolonization and establishment of a contact zone in Scandinavia. Scandinavian P. abies is today made up of a southern genetic cluster originating from the Baltics, and a northern one originating from Northern Russia. The contact zone delineating them closely matches the limit between two major climatic regions. We show that natural selection contributed to its establishment and maintenance. First, an isolation-with-migration model with genome-wide linked selection fits the data better than a purely neutral one. Second, many loci show signatures of selection or are associated with environmental variables. These loci, regrouped in clusters on chromosomes, are often related to phenology. Altogether, our results illustrate how climatic cycles, recolonization and selection can establish strong local adaptation along contact zones and affect the genetic architecture of adaptive traits

High-cycle thermal fatigue in mixing tees. Large-eddy simulations compared to a new validation experiment

ABSTRACT The present paper describes new experimental data of thermal mixing in a T-junction compared with results from Large-Eddy Simulations (LES) and Detached Eddy Simulations (DES). The experimental setup was designed in order to provide data suitable for validation of CFD-calculations. The data is obtained from temperature measurements with thermocouples located near the pipe wall, velocity measurements with Laser Doppler Velocimetry (LDV) as well as single-point concentration measurements with Laser Induced Fluorescence (LIF). The LES showed good agreement with the experimental data also when fairly coarse computational meshes were used. However, grid refinement studies revealed a fairly strong sensitivity to the grid resolution, and a simulation using a fine mesh with nearly 10 million cells significantly improved the results in the entire flow domain. The sensitivity to different unsteady inlet boundary conditions was however small, which shows that the strong large-scale instabilities that are present in the mixing region are triggered independent of the applied inlet perturbations. A shortcoming in the performed simulations is insufficient near-wall resolution, which resulted in poor predictions of the near-wall mean velocity profiles and the wall-shear stress. Simulations using DES improved the near-wall velocity predictions, but failed to predict the temperature fluctuations due to high levels of modeled turbulent viscosity that restrained the formation of small scale turbulence

Modelling the Material Resistance of Wood—Part 3: Relative Resistance in above- and in-Ground Situations—Results of a Global Survey

Durability-based designs with timber require reliable information about the wood properties and how they affect its performance under variable exposure conditions. This study aimed at utilizing a material resistance model (Part 2 of this publication) based on a dose–response approach for predicting the relative decay rates in above-ground situations. Laboratory and field test data were, for the first time, surveyed globally and used to determine material-specific resistance dose values, which were correlated to decay rates. In addition, laboratory indicators were used to adapt the material resistance model to in-ground exposure. The relationship between decay rates in- and above-ground, the predictive power of laboratory indicators to predict such decay rates, and a method for implementing both in a service life prediction tool, were established based on 195 hardwoods, 29 softwoods, 19 modified timbers, and 41 preservative-treated timbers

Modeling the material resistance of wood—part 2:Validation and optimization of the meyer-veltrup model

Service life planning with timber requires reliable models for quantifying the effects of exposure-related parameters and the material-inherent resistance of wood against biotic agents. The Meyer-Veltrup model was the first attempt to account for inherent protective properties and the wetting ability of wood to quantify resistance of wood in a quantitative manner. Based on test data on brown, white, and soft rot as well as moisture dynamics, the decay rates of different untreated wood species were predicted relative to the reference species of Norway spruce (Picea abies). The present study aimed to validate and optimize the resistance model for a wider range of wood species including very durable species, thermally and chemically modified wood, and preservative treated wood. The general model structure was shown to also be suitable for highly durable materials, but previously defined maximum thresholds had to be adjusted (i.e., maximum values of factors accounting for wetting ability and inherent protective properties) to 18 instead of 5 compared to Norway spruce. As expected, both the enlarged span in durability and the use of numerous and partly very divergent data sources (i.e., test methods, test locations, and types of data presentation) led to a decrease in the predictive power of the model compared to the original. In addition to the need to enlarge the database quantity and improve its quality, in particular for treated wood, it might be advantageous to use separate models for untreated and treated wood as long as the effect of additional impact variables (e.g., treatment quality) can be accounted for. Nevertheless, the adapted Meyer-Veltrup model will serve as an instrument to quantify material resistance for a wide range of wood-based materials as an input for comprehensive service life prediction software

High-Performance Composites from Modified Wood Fiber

The objective of this work was to produce and evaluate high-performance wood fiber composites. High-performance was defined as: high dimensional stability and a high durability, including resistance to wood-decaying organisms (fungi, bacteria, and insects). The main method, used to accomplish these properties, was acetylation of the wood fibers prior to the composite production. Acetylation involves a chemical modification of wood components, which was carried out by reaction with acetic anhydride. Another method applied was impregnation with kraft lignin followed by fixation of the lignin with an aluminum salt solution. Thus, lignin metal complexes are formed in situ - complexes that are insoluble under normal conditions in the environment. Test results show that both methods lead to more dimensionally stable composites, i.e. reduced swelling and shrinkage due to a varying moisture load. Kraft lignin treatment of wood fiber was estimated to be an economical method for obtaining a certain degree of stabilization of composites (fiberboards), although the composites cannot be labeled "high-performance" since they do not meet all requirements, as defined above. However, the use of acetylated fibers leads to a very high degree of dimensional stability as well as biological decay resistance and, furthermore, the mechanical properties are maintained during and after cyclic climate aging. Regardless of the lignocellulosic fiber source used, the thickness swelling of acetylated fiberboards in water is reduced by approximately 90% and results from cyclic testing according to EN 321 (three cycles, each comprising 72h water immersion, 24h freezing at -18\ub0C and 72h drying at 70\ub0C) show that more than 85% of the original internal bond strength, IBS, remains after testing. The latter figure should be compared with the corresponding value of 20-40% obtained for fiberboards made from unmodified fibers. Acetylated wood fiber composites have also been tested for resistance to biological decay in a worldwide field test where 30 cm long fiberboard stakes were half-buried in soil. After three years of testing, most of the control stakes (made from unmodified fiber) had failed due to heavy decay while most of the acetylated composite stakes were perfectly sound, showing no sign of decay. To determine whether the acetylation, and other methods of chemical modification, cause any degradation of the cellulose, .alfa.-cellulose was isolated from unmodified and chemically modified fibers after which the intrinsic viscosity and molecular mass distribution (determined by size exclusion chromatography) of the cellulose samples were analyzed. The main part of the cellulose from acetylated wood fiber seems to be unaffected by the modification method, whereas the other modification methods appear to yield more or less degraded cellulose. In order to manufacture products with complex shapes, moldable flexible fibermats were produced on both a small pilot scale (kilograms) and on a large scale (over one metric ton). A variety of industrial products were manufactured from the acetylated fibermats: exterior doors, automotive panels, fa\ue7ade claddings, flooring boards, wet-room wall panels, toilet lids and roof tiles. Generally, it was found that the dimensional stability of the products was high and that other important properties, such as mechanical and weathering properties, were also very satisfactory. The conclusion is that composites based on acetylated wood fiber are truly high-performance, as defined above

High-Performance Composites from Modified Wood Fiber

The objective of this work was to produce and evaluate high-performance wood fiber composites. High-performance was defined as: high dimensional stability and a high durability, including resistance to wood-decaying organisms (fungi, bacteria, and insects). The main method, used to accomplish these properties, was acetylation of the wood fibers prior to the composite production. Acetylation involves a chemical modification of wood components, which was carried out by reaction with acetic anhydride. Another method applied was impregnation with kraft lignin followed by fixation of the lignin with an aluminum salt solution. Thus, lignin metal complexes are formed in situ - complexes that are insoluble under normal conditions in the environment. Test results show that both methods lead to more dimensionally stable composites, i.e. reduced swelling and shrinkage due to a varying moisture load. Kraft lignin treatment of wood fiber was estimated to be an economical method for obtaining a certain degree of stabilization of composites (fiberboards), although the composites cannot be labeled "high-performance" since they do not meet all requirements, as defined above. However, the use of acetylated fibers leads to a very high degree of dimensional stability as well as biological decay resistance and, furthermore, the mechanical properties are maintained during and after cyclic climate aging. Regardless of the lignocellulosic fiber source used, the thickness swelling of acetylated fiberboards in water is reduced by approximately 90% and results from cyclic testing according to EN 321 (three cycles, each comprising 72h water immersion, 24h freezing at -18\ub0C and 72h drying at 70\ub0C) show that more than 85% of the original internal bond strength, IBS, remains after testing. The latter figure should be compared with the corresponding value of 20-40% obtained for fiberboards made from unmodified fibers. Acetylated wood fiber composites have also been tested for resistance to biological decay in a worldwide field test where 30 cm long fiberboard stakes were half-buried in soil. After three years of testing, most of the control stakes (made from unmodified fiber) had failed due to heavy decay while most of the acetylated composite stakes were perfectly sound, showing no sign of decay. To determine whether the acetylation, and other methods of chemical modification, cause any degradation of the cellulose, .alfa.-cellulose was isolated from unmodified and chemically modified fibers after which the intrinsic viscosity and molecular mass distribution (determined by size exclusion chromatography) of the cellulose samples were analyzed. The main part of the cellulose from acetylated wood fiber seems to be unaffected by the modification method, whereas the other modification methods appear to yield more or less degraded cellulose. In order to manufacture products with complex shapes, moldable flexible fibermats were produced on both a small pilot scale (kilograms) and on a large scale (over one metric ton). A variety of industrial products were manufactured from the acetylated fibermats: exterior doors, automotive panels, fa\ue7ade claddings, flooring boards, wet-room wall panels, toilet lids and roof tiles. Generally, it was found that the dimensional stability of the products was high and that other important properties, such as mechanical and weathering properties, were also very satisfactory. The conclusion is that composites based on acetylated wood fiber are truly high-performance, as defined above

Regionerna och finansieringen av infrastrukturen : Exemplet Botniabanan

Uppsaten presenterades vid CTS konferens i Borlänge i november 1997 om finansiering av infrastruktur. Arbetet har erhållit finansiering av KFB