Deformation kinetics based rheological model for the time-dependent and moisture induced deformation of wood

Summary A new general rheological model for the calculation of the creep of wood is presented. The flow equation derived in the theory of molecular deformation kinetics is adjusted to account for creep flow, moisture content change induced swelling/shrinkage and their combined effect by making an assumption that both of these processes activate the same bond breaking and reforming process. The rheological model is built by making the dashpots in a generalised Maxwell material model to obey the adjusted flow equation and by placing an additional swelling/shrinkage component to each parallel Maxwell element. Two calculated examples of the performance of the model with comparisons to experiment results are given. It seems that an explanation for the mechano-sorptive effect can be found at the coupling of the creep deformation process and moisture swelling/shrinkage and the non-linearity of the phenomena.This work has been financed by the Academy of Finland and VTT (Technical Research Centre of Finland)     

Light sources with different spectra affect root and mycorrhiza formation in Scots pine in vitro

We studied the effects of broad-spectrum light quality on the interaction between the ectomycorrhizal fungus Pisolithus tinctorius (Pers.) Coker and Couch and Scots pine (Pinus sylvestris L.) seedlings and hypocotyl cuttings cultured in vitro. The light sources were cool white (CW), warm white (WW) and red-rich daylight (RD) fluorescent lamps. Inoculation with P. tinctorius enhanced adventitious root formation of the cuttings in all light treatments. Rooting of the inoculated cuttings was highest in WW light (89%), followed by CW (73%) and RD light (66%). During 6 weeks of in vitro culture, rooted cuttings formed only a few lateral roots. The fungus grew over lateral roots, but the Hartig net was absent in all light treatments. In non-inoculated cuttings, neither root formation nor subsequent root growth was affected by light quality. In the seedling experiment, inoculation in the WW treatment resulted in a significantly (P < 0.05) greater number of lateral roots than inoculation in the RD treatment. The percentage of lateral roots covered with fungal hyphae was also highest in WW light (62%), followed by CW (50%) and RD (27%) light. A similar pattern was observed in the intensity of Hartig net formation. We conclude that effects of broad-spectrum light quality on the ectomycorrhizal fungus-root interaction are dependent on the developmental stage of the root.     

The effect of compression and incision on wood veneer and plywood physical and mechanical properties

ABSTRACT

Drying takes the largest share of energy in plywood production, and varying moisture content of veneers necessitates re-drying that often leads to over-dry veneers with deactivated surfaces, which may promote imperfect bonding. In order to decrease the drying time, reduce the need for re-drying of veneers, and improve the quality of plywood, birch and spruce veneers were subjected to pre-treatment by cold compression, incision, or a combination of the two. The effects of pre-treatment on the veneer and plywood quality were assessed by standard tests. Compression had a beneficial effect on water removal of the wettest veneers (spruce sapwood (SW) and birch), but some thickness reduction was observed in the veneers as well as the finished birch plywood. Compression led to thickness reduction of spruce veneers, but had no effect on SW plywood thickness likely due to higher viscoelasticity. Both compression and the combination of incising and compression levelled the moisture variation within the compressed stacks. Incision improved the modulus of elasticity of birch plywood, shear strength of SW plywood, and both bending and shear strengths of heartwood plywood. Higher surface pressure decreased the drying time of spruce SW in both plain compression and combined incision and compression pre-treatment.     

Über einen Zusammenbruch der Gelbhalsmauspopulation im Nationalpark Bayerischer Wald

Zusammenfassung Der Energiesto? eines guten Samenjahres der Fichte im Nationalpark Bayerischer Wald bewirkte bei M?usen im Frühjahr 1972 zun?chst eine starke Zunahme der Gelbhalsmaus. Nach dem Zusammenbruch dieser Population unter Stresserscheinungen, hervorgerufen durch Nahrungsverknappung und überbev?lkerung, trat im Herbst die R?telmaus st?rker in Erscheinung, die insbesondere an Laubh?lzern im Winter 1972/73 deutliche Spuren hinterlie?. Im Frühjahr 1973 dominierte nach einem schneereichen Winter bei sehr geringer Dichte die Erdmaus. Untersuchungen über die Nahrungswahl, Energie- reserven, Reproduktionsrate und Stresserscheinungen zeigten, da? die Populationsentwicklung der Gelbhalsmaus vorwiegend durch das Nahrungsangebot gesteuert wurde. Die Bev?lkerungsentwicklung der R?telmaus erschien dagegen von der Gelbhalsmaus negativ beeinflu?t oder durch nicht aufgedeckte endogene Faktoren geregelt. Es ergaben sich hier keine Hinweise für das Vorhandensein von Stressoren in der entscheidenden Vermehrungspause bis zum August 1972. Eine starke Zunahme der Adrenal- gewichte wurde erst im November bei h?chster Dichte und dem Einsetzen des Winters beobachtet.

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Summary Studies about a turnover of a Field-Mouse-population in the Bavarian National Park. In 1972 and 73 research work was carried out about population dynamics of the three most commonly species of rodents in the Bavarian National Park near the czech border: The Yellownecked Field Mouse (Apodemus flavicollis L.), the Bank Vole (Clethrionomys glareolus) and the Common Vole (Microtus agrestis L.). A great amount of spruce- seeds seemed to be most important for increased numbers of the Field Mouse trapped in the spring 1972 on all five localities (A, B, C, D and E) which were observed (Abb. 1). After the crash of this population in August 1972 by good weather conditions (Abb. 2) numbers of the Bank Vole were increased and this species was now most numerous in all localities (Abb. 1). In June 1973 the lowest density of all species was observed and the Common Vole dominated. This latter fact may be related to the high snow-cover until May 1973. Studies about ingested food-stuffs, body-fat content (Tab. 1) reproduction-rate (Abb. 3) and signs of stress (Abb. 4) showed, that the crash of the Field Mouse was caused primarly by detioration of food coupled with crowding effects. The population dynamics of the Bank Vole seemed interfered by the Field Mouse. No signs of stress were however detected during the recess of reproduction until August 1972 when the Field Mouse was dominating.

     

Photosynthetic responses to needle water potentials in Scots pine after a four-year exposure to elevated CO(2) and temperature

Effects of needle water potential (Psi(l)) on gas exchange of Scots pine (Pinus sylvestris L.) grown for 4 years in open-top chambers with elevated temperature (ET), elevated CO(2) (EC) or a combination of elevated temperature and CO(2) (EC + ET) were examined at a high photon flux density (PPFD), saturated leaf to air water vapor pressure deficit (VPD) and optimal temperature (T). We used the Farquhar model of photosynthesis to estimate the separate effects of Psi(l) and the treatments on maximum carboxylation efficiency (V(c,max)), ribulose-1,5-bisphosphate regeneration capacity (J), rate of respiration in the light (R(d)), intercellular partial pressure of CO(2) (C(i)) and stomatal conductance (G(s)). Depression of CO(2) assimilation rate at low Psi(l) was the result of both stomatal and non-stomatal limitations on photosynthetic processes; however, stomatal limitations dominated during short-term water stress (Psi(l) < -1.2 MPa), whereas non-stomatal limitations dominated during severe water stress. Among the nonstomatal components, the decrease in J contributed more to the decline in photosynthesis than the decrease in V(c,max). Long-term elevation of CO(2) and temperature led to differences in the maximum values of the parameters, the threshold values of Psi(l) and the sensitivity of the parameters to decreasing Psi(l). The CO(2) treatment decreased the maximum values of V(c,max), J and R(d) but significantly increased the sensitivity of V(c,max), J and R(d) to decreasing Psi(l) (P < 0.05). The effects of the ET and EC + ET treatments on V(c,max), J and R(d) were opposite to the effects of the EC treatment on these parameters. The values of G(s), which were measured simultaneously with maximum net rate of assimilation (A(max)), declined in a curvilinear fashion as Psi(l) decreased. Both the EC + ET and ET treatments significantly decreased the sensitivity of G(s) to decreasing Psi(l). We conclude that, in the future, acclimation to increased atmospheric CO(2) and temperature could increase the tolerance of Scots pine to water stress.     

Moisture content penetration in wood elements under varying boundary conditions

Knowledge of effects of moisture exposure on timber structures is important for serviceability and load bearing capacity of timber elements and systems. Varying climate affects the moisture content profiles in timber as the relative humidity changes in the ambient air. This paper presents methods for calculation of diffusion based moisture transport and corresponding results on how timber responds to varying moisture with regard to moisture penetration and distribution. The calculations are based on measured outdoor relative humidity and temperature at different climatic locations in Sweden. No remarkably large deviations between the different climatic locations were found in general, which is positive in a design code perspective.     

Beschädigungen in einer Wohnung durch Wespen

Ohne Zusammenfassung