Brief report on theoretical research upon wood thermal property

lntroductionThermaIpropertiesofwoodsuchasspecificheat,thermalconductivityandsoonareparameterswhichisrequiredinscientificresearchandheattreatmentofwood.BecausewoodisakindofnaturaIpolymerorganismwhosechemicaleIementandmicrostruc-tureareverycomplicated,it'sverydif=ficulttostudyitsthermaIpropeFtytheoreticalIy,therefOre,foraImostonecentury,itwasbymeansofexperimentthatthescientistsathomeandabroadstudiedthethermalpropertyofwooddirectIy(Dunlap19121KotImann1968,Cheng1985,Gao1985,Zhang1986)Buttheq…     

木材横纹导热系数的类比法研究

分析导热与导电间某些属性的相似性 ,应用类比法推出导热系数具有导电系数的某些属性 ,可用导电系数类似的定义式定义导热系数 ,即木材导热系数等于木材单位长度单位截面的热阻的倒数。根据木材微观细胞形态 ,选用圆柱形模型推导木材横纹导热系数的理论计算式。应用该公式计算 2 0种木材的横纹导热系数 ,理论值的最大误差 14 1% ,平均误差 7% ,理论值与试验值较为吻合 ,为理论研究木材热学性质提供一种可适用的方法。     

木材导温系数的理论表达式(英文)

本文从木材的化学组成和微观结构出发,从理论上推导出木材导温系数的理论表达式,应用该表达式计算20种左右木材弦向和径向导温系数,并与实验值对照,得出木材弦向导温系数与理论值的平均误差在7.2%,木材径向导温系数与理论值得误差为6.2%。     

木材弦向导热系数的理论表达式

分析木材细胞结构形态,以长匣子形作为木材细胞模型,根据材料导热与导电规律的相似性,应用类比推理方法,从欧姆电阻定律推出材料导热的热阻公式;依据该细胞模型和热阻公式推导木材弦向导热系数的理论表达式,从而揭示木材弦向导热系数是木材孔隙率的函数。孔隙率越大的木材,导热系数越小,并实际计算了24种木材的弦向导热系数,与试验值比较,理论值的最大误差12.6%,平均误差小于6.4%。     

Geographic variation and genetic performance of Picea koraiensis in growth and wood characteristics

Eight provenances of 19-year-oldPicea koraiensis Nakai from the provenance trials of Maoershan (45°20′N, 127°30′E), Liangshui (47°10′N, 128°53′E) and Jiagedaqi (50°24′N, 124°07′E) in Northeast China were investigated to analyze the genetic variation in growth characteristics (tree height and diameter) and wood characteristics (tracheid length, tracheid diameter, tracheid wall thickness, annual ring width as well as wood density). Great variation in height growth and breast height diameter growth was observed among the provenances, and along with the increase of tree age, these provenances presented different geographic adaptability. The growth characteristics ofPicea koraiensis stand at age of 10 in Maoershan and Liangshui provenance trials had a positive correlation with longitude, and with increase of tree age to 15 and 19, the tree growth of the provenances displayed a significant positive correlation with latitude as well as altitude. For wood characteristics, great variation was also found among the provenances. There exists a close relation between growth characteristics and wood properties of the provenance. The height and breast height diameter growth of the provenance had a positive correlation with tracheid diameter and annual ring width, and a negative correlation with tracheid wall thickness and wood density. Genetic performance of the provenance in all above characteristics was also investigated in order to provide more useful information for comprehensive selection of this species for pulpwood and plywood production. Foundation item: The paper was supported by National Key Project of The State Forestry Administration. (96-011-01-06) Biography: WANG Qiu-yu (1957-), female, professor in College of Life Sciences, Northeast Forestry University, Harbin 150040, P. R. China. Responsible editor: Song Funan     

Monitoring of changes in tree and shrub layers in Wytham Woods (Oxfordshire), 1974-1991

In 1974–76 164 permanent 10x10 m plots were recorded atalternate intersections of a 100x100 m grid in Wytham Woods,Oxfordshire. Tree and shrub data were collected from all theplots in 1974–76, from 27 in 1984–85 and from allbut one in 1991–92. Changes in the structure and composition of the wood were assessedin terms of canopy cover, mean tree diameter, basal area andspecies occurrence. The wood has become more open (reduced canopycover) partly through management, partly through natural processessuch as windthrow and disease. The shrub cover has also declinedgreatly, probably because of increased deer browsing. Most standsare predominantly young growth and for the wood as a whole meantree diameter, basal area and tree height have increased. Theoverall composition of the wood has changed little, but therehas been a significant decline in mean woody species numberper plot from 5.8 to 4.1, mainly through declines in understoreyspecies and young oak (Quercus spp.). Elm (Ulmus spp.) coverhas been reduced by disease and birch (Betula spp.) sufferedpreferentially from windthrow. The results are used to indicate gains and losses in natureconservation terms for the wood as a whole. The strengths andweaknesses of this system may hold lessons for future woodlandmonitoring exercises.     

Allometric model of the height–diameter curve for even-aged pure stands of Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis>)

We derived an allometric model of the height–diameter curve for even-aged pure stands, which was a modification of the earlier model proposed by Inoue (2000a). An individual-dependent allometric equation was used as the height–diameter curve. Using the discriminant analysis method, all trees composed of a stand were stratified into upper and lower trees. It was assumed that both relationships between mean tree height H _m and upper tree height H _u and between mean DBH D _m and mean DBH of upper trees D _u could be described by the time-dependent allometric power equations. The height–diameter curve showed an average relationship between tree height and DBH of a given stand at a given time, and hence it could be assumed that the height–diameter curve contained two points (D _m , H _m ) and (D _u , H _u ). With these assumptions, we derived an allometirc model of height–diameter curve, which allowed the coefficients of the curve to be estimated from mean tree height and mean DBH. The proposed model was fitted to Japanese cedar (Cryptomeria japonica D. Don) data. The error ratio of the allometric model ranged from 2.254% to 13.412% (mean = 6.785%), which was significantly smaller than that of the earlier model. When the error of mean tree height was ±1.0 m or less, the effect of the error of mean tree height on the error ratio was comparatively small. This suggested that the error of ±1.0 m in mean tree height could be accepted in the estimation of height–diameter curve using the allometric model. These features enable us to combine the allometric model with Hirata’s vertical angle-count sampling or growth models. In conclusion, the allometric model would be one of the most practical and convenient approaches for estimating the height–diameter relationship of even-aged pure stands.     

Variations in compression strength and surface roughness of heat-treated Turkish river red gum (Eucalyptus camaldulensis) wood

This article reports the effects of heat treatment on compression strength parallel to the grain, the surface roughness [average roughness (R_a)], and the air-dry den-sity of wood from the river red gum tree (Eucalyptus camaldulensis Dehn.) planted in Turkey. Eucalyptus wood was heat-treated at temperatures varying from 120° to 180°C for durations of 2–10 h. Samples cut from the heat-treated wood were tested for air-dry density, compression strength parallel to grain, and surface roughness properties. Roughness measurements by the stylus method were made in the direction perpendicular to the fiber. Based on the findings in this study, the results showed that density, compression strength, and surface roughness values decreased with increasing treatment temperature and treatment times. Eucalyptus wood could be utilized by using proper heat treatment techniques without any losses in strength values in areas where working, stability, and surface smoothness, such as in window frames, are important factors.     

Relation between combustion heat and chemical wood composition during white and brown rot

Summary The results of respective investigations indicate that during white rot the combustion heat of wood (Q_exp (J/g)) remained virtually unchanged and at the greatest extent of decomposition it was in the range also found in non-rotten wood. During brown rot the combustion heat of wood samples increased, beginning at a weight loss of 20–30%. The difference between Q_exp and the weighted mean of combustion heat values of isolated chemical wood components (Q_cal) were neglectable. If Q_exp values measured for each sample were taken as 100%, then Q_cal averaged from 101.1–105.6% and from 97.4–108.2% during white and brown rot, respectively. The Q_cal calculation error is expressed as coefficient k; it varies depending on the accuracy and selectivity of the separation methods used.     

Experimental determination of the convective heat and mass transfer coefficients for wood drying

The knowledge of the convective heat and mass transfer coefficients is required for the characterization of the boundary conditions of the heat and mass transfer equations of a wood drying model based on water potential. A new experimental method for the determination of the convective mass transfer coefficient is presented. This method is based on the measurement of the moisture content, and indirectly the water potential, at the surface of a wood specimen at different drying times. Drying experiments were performed on red pine (Pinus resinosa Ait.) sapwood from nearly saturated to dry conditions at 56 °C, 52% relative humidity and air velocities of 1.0, 2.5 and 5.0 m s⁻¹. The results show that the convective mass transfer coefficient is constant until the wood surface moisture content reaches about 80% and then decreases more or less gradually as the moisture content decreases further. The convective mass transfer coefficient increases with air velocity. A regression analysis shows that there is no significant improvement in considering the water potential gradient near the wood surface when the difference in water potential between the surface and the surrounding air (ψ_s − ψ_∞) is used to determine the convective mass flux at the surface. Also, ψ_s − ψ_∞ is more appropriate than the water vapour pressure difference (pv_s − pv_∞) as the responsible driving force of the moisture flux leaving the wood surface. The convective heat transfer coefficient was determined during the same experiments. A plateau is observed at high values of moisture content corresponding to the constant drying rate period. Received 27 February 1998     

Surface characteristics of electroless nickel plated electromagnetic shielding wood veneer

Wood is a kind of porous natural material with very poor electro-conductivity, and it has almost no function of electromagnetic shielding. The method of electroless nickel plating was used to produce wooden material with electrical and effective electromagnetic shielding properties. Ni-P alloy layer was obtained on wood surface. The surface feature of plated wood veneer was observed by SEM and the surface composition and microstructure of the layer under different conditions were investigated by EDS and XRD respectively. Meanwhile, the relevant surface resistivity and electromagnetic shielding effectiveness were measured. Correlations of the phosphorous content in the layer to the structure of Ni-P alloy, electro-conductivity and electromagnetic shielding of plated veneers were discussed. SEM photos showed that the surface of electroless nickel plated veneers were covered with Ni-P alloy layer entirely, which made wood veneers more like metal. At the same time, the results showed that with the decreasing of the phosphorous content in the layer, the microstructure of Ni-P alloy layer transformed to be microcrystalline and electro-conductivity and electromagnetic shielding effectiveness were improved. When the phosphorous content was less than 2.37wt pct in the layer, the microstructure of Ni-P alloy layer was microcrystalline structure and its sur- face resistivity and electromagnetic shielding effectiveness were nearly 0.5Ω/□ and 55-60dB respectively.     

Vessel size and number are contributors to define wood density in cork oak

Cork oak (Quercus suber L.) has a dense wood that allows high-quality uses. In the present work, we study the influence of vessel characteristics, measured through image analysis and optical microscopy, on wood density, measured using X-ray microdensitometry, on 40-year-old trees. Vessel area increases with cambial age (5403–33064 μm²), while wood density decreases (1.229–0.836 g/cm³). The number of vessels is relatively constant at 6 vessels/mm², while vessel proportion in cross-section increases from 3.3% near the pith to 20.5% near the bark. In growth rings closest to the pith, with high wood density and low vessel area, the relationship between the two variables is linear (R ² = −32.1%, P < 0.01) but with increasing tree age and vessel size, the wood density remains rather constant, suggesting that decreases in density might compromise mechanical support of the tree at a stage when the increase in cross-sectional area alone might not provide mechanical stability. Other anatomical characteristics not considered in this study, like large xylem rays that increase with cambial age, may be responsible for the constant density.     

木材导热系数的理论表达式(英文)

本文从木材的微观结构出发，应用物理力学导出木材弦向和径向导热系数的理论表达式 ，计算20种左右木材导热系数并与相同条件下的实验值比较，平均误差在5%附近，两者吻合 程度令人满意。     

心材提取物和专用木材防腐剂作为木材保护剂的相对功效

本文调查了三种耐用木材(Afzelia africana J.E. Smith; Erythrophleum suaveolens (Guill & Perr.) Brenam. Syn. E guinensis G.Don. or Milicia excelsa (Welw) C.C. Berg. Syn. Chlorophora excelsa (Welw) Benth.)的心材提取物（在60%的甲醇中风干提取）和两种专用木材防腐剂（CCA和Penta）在暴露的土壤区组设计条件下，抑制三种木材腐朽菌(Coridopsis Polyzona Klotzch; Lenzites trabea; or Trametes cingulata Fr.)对见血封喉边材的侵袭的相对潜能，并测定其阈值。提取物和防腐剂的剂量分别是8.009、24.778、48.056、96.111、144.167 kg·m-3 ，样品的暴露处理时间与ASTM D1413-72规定的一致分别是14周和18周。结果显示：在阈值范围内，任何一种心材提取物或木材防腐剂在研究中对木材腐朽菌的抑制能力在0.01的显著水平下，差异显著。这些生物杀灭剂的相对功效是取决于真菌的种类。没有任何一种心材提取物或木材防腐剂（除在用最高的存留水平处理被侵袭的非洲毒箭木的条件下）对于被处理的木材能够授予"非常持久"等级。本土树种的心材提取物相对持久力的减少的可能原因是复杂的。在最高的存留量（144.167 kg·m-3）水平下，在0.05显著水平下每种心材提取物和任一种专用木材防腐剂（CCA和Penta）之间的功效差异不显著.     

Classification of Picea abies Pulpwood According to Wood and Stand Properties

Different classification systems for Norway spruce (Picea abies (L.) Karst.) pulpwood were compared. The classification systems were applied on truckloads or single logs in southern Sweden. Truckload classification according to mean annual growth ring width gave better separation of the wood properties basic density, juvenile wood and dry matter content, than classification according to harvest type (first thinning, later thinning or final felling). The assortments did not have significantly different wood brightness. Sorting at log level according to diameter, mean annual growth ring width or number of annual growth rings, which could be done at harvesting, did not drastically improve differentiation of the mean values of the wood properties or reduce variance compared to truckload classification. The variation in wood properties within assortments remained large owing to the large variation in wood properties between and within logs. Substantial reduction in dry matter variation could be achieved by truckload classification during the summer.     

Control of tracheid cross-sectional dimensions in Norway spruce and Scots pine wood raw material

Abstract

Wood properties, including tracheid cross-sectional dimensions, show a large degree of variation. To improve the properties of products made from wood, different methods to control variation have been developed. This study aims to determine the theoretical efficiency of three control strategies: the fractionation of pulped tracheids into earlywood and latewood, the separation of juvenile and mature wood, and sorting of logs according to tree size. The efficiency of each method was studied by first constructing virtual trees from measured tracheid cross-sectional dimensions, then simulating the efficiency of above-mentioned methods. The tracheid dimension data include Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.). The simulations show that separation into earlywood and latewood classes has the highest theoretical efficiency and yields the lowest variances in raw material. Classification into juvenile and mature wood groups is the second most efficient method, and the sorting of logs according to the size class of the tree is the least efficient method. It was also concluded that the variation in cell-wall thickness and radial diameter mainly originates from differences between earlywood and latewood, whereas the variation in tangential diameter mainly originates from differences between mature and juvenile wood.     

Climate change impacts on stand structure and competitive interactions in a southern Swedish spruce–beech forest

It is believed that European beech (Fagus sylvatica L.) will increase its competitive ability at its northern range margin in Scandinavia due to climate change. In mixed old-growth forests of beech and Norway spruce (Picea abies (L.) Karst.) at Siggaboda nature reserve (southern Sweden), stand structure characteristics were sequentially recorded in the years 2004, 2005 and 2007 as well as growth in stem diameter using tree-coring analyses. Using these measurements, we studied the effects on stand dynamics of an extreme storm event (2005 “Gudrun” hurricane), drought and heat (mid-summer 2006, spring 2007) and subsequent bark beetle attacks on spruce (growing season 2007), overlaid with warming tendencies. The storm, which caused disastrous damage in many stands nearby, had comparatively little impact on the structure of the spruce–beech stand. All together, only 32 trees (19 spruces, 10 beeches, 3 other species) per hectare were thrown or broken mainly in the leeward direction (NE) or impacted by secondary damage by uprooted neighbour trees; this represents 7% of the total tree number and 11% of the growing stock. Diameter and height structure did not change significantly. However, the 2006 drought and the 2007 attack of biotic agents changed the stand structure and composition strongly due to the death of about 19% of the dominating older spruce trees that accounted for 35% of total stand volume. This resulted in a considerable increase in beech’s contribution to stem number (4% increase) and wood volume of the living stand (7% increase). A comparison of diameter growth of beech and spruce during the periods 1894–1949 and 1950–2005 showed a distinct decrease in growth superiority of spruce during the last 50 years. These results support the idea of a northward migration of European beech as a nemoral tree species in Sweden, due to a higher tolerance to the abiotic and biotic threats accompanying climate change and an increased competitive ability compared to boreal tree species Norway spruce.     

Effect of sensor quantity on measurement accuracy of log inner defects by using stress wave

Wood nondestructive testing （NDT） is one of the high efficient methods in utilizing wood. This paper explained the principle of log defect testing by using stress wave, and analyzed the effects of sensor quantity on defect testing results by using stress wave in terms of image fitting degree and error rate. The results showed that for logs with diameter ranging from 20 to 40 cm, at least 12 sensors were needed to meet the requirement which ensure a high testing accuracy of roughly 90% of fitness with 0.1 of error rate. And 10 sensors were recommended to judge the possible locations of defects and 6 sensors were sufficient to decide whether there were defects or not.     

Effects of high temperature kiln drying on the practical performances of Japanese cedar wood (Cryptomeria japonica) II: Changes in mechanical properties due to heating

Japanese cedar wood specimens were steamed at 80°, 100°, and 120°C over 14 days, and their equilibrium moisture content (M) at 20°C and 60% relative humidity, longitudinal dynamic Young’s modulus (E), bending strength (σ _max), and breaking strain (ε _max) were compared with those of unheated specimens. Steaming for a longer duration at a higher temperature resulted in a greater reduction in M, σ _max, and ε _max. The E of wood was slightly enhanced by steaming at 100°C for 1–4 days and 120°C for 1–2 days, and thereafter it decreased. The slight increase in the E of sapwood was attributable to the reduction in hygroscopicity, while sufficient explanation was not given for a greater increase in the heartwood stiffness. Irrespective of the steaming temperature, the correlations between M and the mechanical properties of steamed wood were expressed in terms of simple curves. M values above 8% indicated a slight reduction in E and s max, whereas M values below 8% indicated a marked decrease in the mechanical performances. In addition, the e max decreased almost linearly with a decrease in the value of M. These results suggest that hygroscopicity measurement enables the evaluation of degradation in the mechanical performances of wood caused by steaming at high temperatures.     

Tree mortality after low-intensity prescribed fires in managed Pinus sylvestris stands in southern Finland

Abstract

Tree mortality, its causes, and the input of dead charred wood were studied in 11 managed 30–45-year-old Scots pine (Pinus sylvestris L.) stands 1 year after experimental low-intensity prescribed burnings in southern Finland. First, the relationship between fire-induced tree damage and several external variables, e.g. stand density, within-stand wind speed, open-air wind speed, the Finnish Forest Fire Index (FFI) and flame height, was studied. Secondly, the study examined which damage and morphological characteristics best predicted tree mortality. Tree mortality was very variable in the experimental plots, ranging from 0% to 48% on the basis of stem number and from 0% to 41% in terms of wood volume. The input of dead and charred wood decreased with stand age, being 19.4 m³ ha^?1 in 30–35-year-old stands, but only 1.7 m³ ha^?1 in 45-year-old stands. The input of dead wood was on average 10 m³ ha^?1, representing less than 5% of the mean volume before the prescribed fire. The external variables that best explained fire-induced damage were within-stand wind speed, flame height and FFI. Tree mortality was best predicted by charred stem ratio with bark thickness, and by charred stem ratio with tree diameter. The results indicate that prescribed burning that is conducted downwind increases tree mortality and changes subsequent stand structure with increasing within-stand wind speed.