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991.
Thomas?HolstEmail author Helmut?Mayer Dirk?Schindler 《European Journal of Forest Research》2004,123(1):13-28
Within the framework of an interdisciplinary project on the effects of climate and forest management on beech-dominated deciduous forests (Swabian Jura, south-western Germany), forest meteorological investigations are carried out to analyse the influences of exposure and canopy density on the microclimate within various beech stands (Fagus sylvatica L.). This second paper of the series Microclimate within beech stands focuses on the thermal conditions that exist mainly in the near-surface layer at different test plots. They were analysed by air temperature, Ta, (at 1.5 m a.g.l) and soil temperature, Ts, at six depths measured continuously in the period 1999–2003. The main results can be summarized as follows. (1) The thermal situation within the beech stands described by Ta depended primarily on the turbulent air-mass exchange conditions which were based on the slope-specific energy balance of the forest floor and advective heat fluxes. (2) The thermal situation within the soil described by Ts at 3 and 20 cm depth was governed by the molecular heat transport. Therefore, the heating and cooling rates of Ts were always lower than for Ta. Higher Ta and Ts values for the test plots on the SW slope showed that the thermal conditions within the beech stands depended primarily on the exposure. (3) Based on slope-specific differences of daily extremes of Ta and Ts at 3 cm depth between the silviculturally treated and control plots, the influence of the more pronounced height growth of the understorey vegetation under the near-surface thermal conditions could be clearly verified for the NE slope.Abbreviations PAR Photosynthetically active radiation - PAI Plant area index - LAI Leaf area index 相似文献
992.
Dietmar?Zirlewagen Klaus?von?WilpertEmail author 《European Journal of Forest Research》2004,123(4):269-282
Silviculture, forest conversion and technical tools of ecosystem management, such as forest liming, display their effects at the landscape level. Therefore their planning and control should take place at the same scale. The primary objective of this work was to assess soil chemical properties and their changes in relationship to ecosystem management, especially forest conversion and forest liming. We calculated scenario models, based on regression analysis, which allow such an examination in the context of understanding landscape processes which can be expected to operate in the sampling region. Stepwise multiple linear regression analysis was used to predict soil chemical attributes (base saturation, pH, C/N content and stock, exchangeable stocks of Ca and Mg) as indicators of site stability or off-site effects of forest ecosystems such as effects on clean drinking water from forested watersheds. Because of space limitations, in this paper only the modelling results of base saturation are presented. Base saturation was used as an integrative example for other soil chemical properties. The transformation of measurements to the regional scale, i.e., the regionalization, was calculated for the forested parts of two test regions in the Black Forest on the basis of measured chemical properties of 90–150 soil profiles per test region. The models have a spatial resolution of 50×50 m, which is a spatial scale relevant for forestry practice and forest management. Topographic variables (e.g., elevation, aspect, slope gradient, and slope length), the stratigraphic classification of the geologic substrate, stand characteristics from forest inventory data, and finally technical information about forest liming were the auxiliary variables (secondary site properties) that provided indirect information about base saturation and were available for the whole forested area of the test regions. Base saturation could be predicted with an accuracy of ~50–70% (in terms of the multiple R2) by using these properties as predictor variables in multiple linear regression analyses. The explained proportion of variance was unexpectedly high considering the high geomorphological heterogeneity of the two test regions. Based upon the regionalization models, it was possible to establish scenarios showing the landscape-related effects on base saturation that may be achieved by forest conversion towards a higher proportion of forests with broad-leaved mixed stands and by forest liming. These scenarios allow the interactions between several influencing factors and management strategies and the impacts on the target variable to be synoptically judged. Thus the presented regionalization models achieve the role of decision support tools for the planning of forest management at the landscape level. They allow an assessment of the environmental effects of forest management strategies in terms of site sustainability or preservation of water resources in forested catchments. 相似文献
993.
Species composition of galls on the leaves of Acer pseudoplatanus L. was analysed in 2002 in three localities: the Wolski Forest, near an urban agglomeration of Kraków, the Ojców National Park and the Andrychów Forest District. A total of 12,013 galls were found. The galls were caused by six insect or mite species. The species composition of the galls was identical in the three localities. Artacris cephaloneus (Nalepa) was the most abundant species. The index of occurrence frequency and Agrells index of species co-occurrence were calculated. The index of occurrence frequency (F) value was highest in the case of A. cephaloneus (1.277) and the lowest value, i.e. 0.00005—both from the Wolski Forest. The highest value for Agrells index of species co-occurrence, i.e. 0.900, was found in the case of Eriophyes pseudoplatani Corti and Drisina glutinosa Giard (Ojców National Park), and the lowest,0.050, for D. glutinosa and Coptophylla gymnaspis (Nalepa) (Wolski Forest; Andrychów FD) and for D. glutinosa and Dasineura irregularis (Bremi) (Andrychów FD). 相似文献
994.
Wood modification with alkoxysilanes 总被引:4,自引:0,他引:4
Steffen?Donath Holger?Militz Carsten?MaiEmail author 《Wood Science and Technology》2004,38(7):555-566
Wood was treated with three different alkoxysilanes which are able to undergo a sol–gel process: tetraethoxysilane (TEOS), methyl triethoxysilane (MTES) and propyl triethoxysilane (PTEO). Two types of treatments were compared: impregnation of fibre saturated wood with monomeric silane solutions, and impregnation with pre-hydrolysed partly oligomeric silanes. Wood properties such as cell wall bulking, anti-swelling efficiency (ASE), moisture uptake and durability were more significantly improved in samples treated with monomeric silanes than in samples treated with oligomeric silanes. SEM-EDX mapping showed that this treatment resulted in a higher degree of silicon incorporation into the cell wall, although the weight percent gain (WPG) was lower compared to the treatment with pre-hydrolysed partly oligomeric silanes. The resistance against soil micro-organisms was enhanced in the initial phase of incubation especially in those samples treated with organo-functional-alkoxysilanes. In miniaturised block tests with the white-rot basidiomycete Trametes versicolor, an improved durability was observed within the test period. During an air conditioning step, a weight loss of the treated samples occurred which was accompanied by a reduction in bulking and ASE. The initial reduction of moisture uptake observed after treatment diminished almost completely. This effect was explained by an ageing of the gels in the wood cell wall which is a consequence of uncompleted hydrolysis and condensation of the silanes during the treatment. 相似文献
995.
Knowledge of the occurrence of sound and dead knots on the surface of sugi is important for the classification and application of the material. This study examined a color vision system for detecting sound and dead knots on sugi. The system can be conceptually divided into three components: a CCD-camera scanning system, an image-segmenting module, and a rule-based defect identifying module. The results showed that the potential defect regions could be located by Otsus threshold algorithm in conjunction with t-test analysis. The accuracies of locating sound knots and dead knots were 92.6% and 97.1%, respectively. The rule-based approach was used to identify sound and dead knots and the identifying accuracies for sound knots and dead knots were 92.0% and 94.1%, respectively. The overall detection accuracy of the system was 87.6%. The results indicated that the rule-based color vision system is an efficient means of detecting sound knots and dead knots on sugi. 相似文献
996.
Different methodological approaches from the field of spatial statistics, the index of cluster size (ICS) and quadrat methods such as the two-term and three-term local quadrat variance (TTLQV and 3TLQV) and the new local variance (NLV) were tested to find a simple spatial measure to classify mixed coniferous uneven-aged, even-aged and conversion stands in the central Black Forest area of Germany. Altogether six stands were analysed with regularly distributed sample plots of 0.25 ha (50×50 m), each subdivided into 25 quadrats of 10×10 m. In each of the quadrats, diameter at breast height (dbh) for trees of the overstory (dbh>7 cm) was assessed and classified into three diameter classes. Height measurements were used to develop specific stand height curves for each stand and to calculate the standing volume per tree and per quadrat. The even-aged stands showed a regular distribution of the standing volume, while the conversion and uneven-aged stands were more clustered. This was detected using ICS, which proved to be a simple but very efficient measure for stand structure. The ICS also showed a highly random distribution of small and medium trees and a regular distribution of large trees of the overstory in the uneven-aged stand. Large and medium trees of one even-aged stand were also regularly distributed while conversion stands showed a regular, random or slightly clustered distribution of these trees. The more uneven the ages in the stands were, the larger were the phases detected by the NLV. The findings of the ICS were generally supported by the TTLQV and 3TLQV. The more uneven the ages in a stand were, the less clustered were the trees of different sizes of the understory. Clustering also decreased with increasing height of understory trees. The patterns detected in the investigated stands were related to the effect of different management regimes. Implications for the management of conversions stands based on the findings of the study are given. 相似文献
997.
J?rgen Lauritzen?JensenEmail author Per-Johan?Gustafsson 《Journal of Wood Science》2004,50(2):123-129
Splitting failure in beam splice joints with glued-in rods parallel to grain in endwood subjected to pure shear is considered. A simple theoretical expression based on beam-on-elastic-foundation theory and quasi-non-linear fracture mechanics is presented for calculation of the joint strength. Tests were conducted on jointed beams in a four-point bending test setup in which the joints were located at the point of pure shear force. Hardwood dowels with a diameter of 12mm and a glued-in length of 120mm were used as rods, and various beam cross sections and dowel configurations were tested. The theory presented is found to agree well with test results in all cases in which the edge distance of the glued-in rods is relatively small. Some test results indicate that the theory may be conservative in case of large edge distances. 相似文献
998.
Joanne M.?Thwaites Roberta L.?FarrellEmail author Kunio?Hata Peter?Carter Marco?Lausberg 《Journal of Wood Science》2004,50(5):459-465
Supply of clear, unstained logs from an export country is important economically as well as in reducing the biosecurity risk to an importing country such as Japan. Although conditions found within the holds of ships containing logs are thought to be ideal for rapid colonization of sapstain fungi, no research has been conducted. Research-focussed log export trials were designed to determine the extent of sapstain colonisation at specific points in the processing of logs from harvesting to arrival at the export destination. Two trials were established, in the austral summer and winter, in which mature Pinus radiata logs were harvested in New Zealand and shipped to export ports in Japan. Data loggers placed above and below deck of the ships recorded microclimatic conditions. Nine species of sapstain fungi were isolated from logs during the summer trial; the most common species isolated were Ophiostoma floccosum, Ophiostoma querci, and Ophiostoma setosum. In contrast, ten sapstain species were detected during the winter trial, with Sphaeropsis sapinea, O. querci, O. floccosum, and O. setosum most commonly isolated. This research was the first successful attempt at measuring visual sapstain development and isolating sapstain fungi from the time of harvesting to arrival at an export destination. 相似文献
999.
Optimization of the manufacturing conditions of the veneer strand flanged I-beam invented in the previous study was investigated using different combinations of strand dimensions, resin types between web and flange, different pressing times, and different wood–resin moisture contents under conventional hot pressing conditions. The main results revealed that the strand dimensions have no effect on the bending properties of the flange part and the dimensional stability of the I-beam. Increasing the resin application rate between strands was found to improve the dimensional stability of the I-beams. The use of isocyanate (MDI) resin between web and flange significantly improved the bond strength between web and flange, the modulus of rupture of the I-beam, and the modulus of rupture of the flange part. Dimensional stability was also improved. Shortening the pressing time from 20 to 12min was found to be feasible. Using low wood-resin moisture content was found to interfere with the curing of the phenol–formaldehyde (PF) resin at the flange part resulting in poor quality beams. Of the three moisture content levels tested, 12% was found to be the optimal level for producing I-beams with balanced mechanical properties and dimensional stability.Part of this work was presented at the 53rd Annual Meeting of the Japan Wood Research Society, Fukuoka, March 2003 相似文献
1000.
Compressive deformation of wood impregnated with low molecular weight phenol formaldehyde (PF) resin II: effects of processing parameters 总被引:1,自引:0,他引:1
To obtain high-strength phenol formaldehyde (PF) resin-impregnated compressed wood at low pressing pressure, the effects of resin content, preheating temperature, pressing temperature, and pressing speed on the compressive deformation of oven-dried low molecular weight PF resin-impregnated wood was investigated. With an increase of PF resin content, the Youngs modulus of the cell wall perpendicular to the fiber direction decreases, and collapse-initiating pressure decreases linearly with the Youngs modulus. This indicates that the occurrence of cell wall collapse is strain-dependent. By increasing preheating temperatures, the collapse-initiating pressure increases due to the increment of the Youngs modulus of the cell wall. An increase in pressing temperature results in the thermal softening of the cell wall and causes collapse at a lower pressure. The wood is compressed effectively despite accelerated resin curing. The pressing speed significantly affects the viscoelastic deformation of the cell wall and the wood is well deformed with decreasing pressing speed, although the differences in density and mechanical properties are relatively small after a pressure-holding period of 30min. In all the parameters examined in this study, the Youngs modulus and bending strength increase with increasing density. 相似文献