Measurement of standard and off-axis elastic moduli and Poisson’s ratios of spruce and yew wood in the transverse plane

It is well known that in the radial–tangential plane of softwoods, the elastic modulus in the principal directions is clearly higher than the off-axis elastic moduli, which decrease to a minimum at a growth ring angle α of about 45°. However, this angular dependency was experimentally proven by only a few early publications. The aims of this study were (1) to analyze this relationship with up-to-date equipment in compression tests on miniature softwood specimens with varying growth ring angles and (2) to compare the experimental results with those calculated by a tensor transformation to assess whether it is admissible to treat the investigated wood species as orthotropic materials. Two softwoods with distinctly different anatomic structures (Norway spruce and common yew) were chosen, and further properties such as Poisson’s ratios were determined. The results confirm the above-mentioned angle-dependent tendency for spruce elasticity, but also show that it is not valid for softwoods in general since the behavior of yew was completely different. The tissue textures of both species, particularly density and density distribution, were discussed as possible reason for these observed differences. The determined Poisson’s ratios for principal and off-axis load directions may be useful for modeling of material behavior.     

Time dependence of Poisson’s effect in wood IV: influence of grain angle

Off-axis tensile creep tests were conducted on woods taken from Japanese cypress and Kalopanax by changing the angle of load to the grain direction in the longitudinal–tangential (LT) plane. The dependence of the Poisson’s ratio and trend of the viscoelastic Poisson’s ratio on grain angle were investigated. The Poisson’s ratios were found to reach their extrema when the grain angle was around 30°. Moreover, the Poisson’s ratio in the LT plane was observed to be negative when the grain angle was in the range of 15°–45°. Comparing the experimental results with theoretical values obtained from the theory of orthotropic elasticity, it was revealed that, although the Poisson’s ratio reached an extremum in both cases, the specific values did not match, especially when the angle was between 15° and 45°. Furthermore, the temporal variation of the viscoelastic Poisson’s ratio was found to depend on the grain angle and the measurement plane. It also appeared to be affected by the Poisson’s ratio, showing an increasing tendency above a specific Poisson’s ratio (Japanese cypress: 0.196, Kalopanax: 0.102) and a decreasing tendency below it, regardless of the grain angle and measurement plane. Additionally, the increment in the viscoelastic Poisson’s ratio after 24 h of creep was observed to reach its extremum when the grain angle was around 30°. Finally, by improving the six-element Frandsen–Muszynski viscoelastic model, which simultaneously considers the longitudinal and transverse strains, an eight-element model was presented, and the trend of the viscoelastic Poisson’s ratio was well reproduced by this model.     

Time dependence of Poisson’s effect in wood I: the lateral strain behavior

To understand the viscoelasticity of wood three dimensionally, a longitudinal tensile creep test for 12 species was conducted to examine the changes with time in the lateral strain and the viscoelastic, i.e., apparent Poisson’s ratio. The changes in the lateral strain (ɛ _T and ɛ _R) were similar to those in the longitudinal strain (ɛ _L). That is, during creep, the absolute value of lateral strain continued to increase with the gradual reduction in the increase rate; immediately after the removal of the load, it recovered abruptly; then, it recovered slowly and finally reached a certain value. The rate of increase in the longitudinal strain during creep was smaller than that in the absolute value of lateral strains. The apparent Poisson’s ratio became large during creep because the lateral strain increased more than the longitudinal strain. The analysis of lateral strain by decomposition into three components, that is, instantaneous strain, delayed elastic strain, and permanent strain, has revealed that the lateral permanent strain in the transverse direction contributes most to the increase in the apparent Poisson’s ratio during creep.     

Time dependence of Poisson’s effect in wood III: asymmetry of three-dimensional viscoelastic compliance matrix of Japanese cypress

To understand the viscoelasticity of wood three dimensionally, matched samples of Japanese cypress were loaded in uniaxial tensile creep in the longitudinal (L), radial (R), and tangential (T) directions at approximately 9.7 % equilibrium moisture content. Longitudinal and transverse strains were measured for the determination of viscoelastic Poisson’s ratios and three-dimensional viscoelastic compliance tensors concerning the normal strain. The changes in the transverse strains showed the same tendencies as those in the longitudinal strains, in all directions of loading. That is, during creep, the absolute value of transverse strain continued to increase with the gradual reduction in the increase rate; immediately after the removal of the load, it recovered rapidly, after which it continued to recover slowly. The transverse strain increased most easily in the T direction, followed by R and L, during creep. All the viscoelastic Poisson’s ratios and the absolute values of all elements of the viscoelastic compliance increased logarithmically with creep time. The three-dimensional viscoelastic compliance matrix for Japanese cypress is concluded to be asymmetric.     

Time dependence of Poisson’s effect in wood II: volume change during uniaxial tensile creep

To determine the viscoelasticity of wood three-dimensionally, a longitudinal tensile creep test was conducted on 12 species of wood to examine the change in the rate of volume increase (ΔV/V) with time. Immediately after the beginning of creep, ΔV/V was positive, and during creep, ΔV/V decreased rapidly, then more gradually. The decrease in tangential strain was considered to mainly contribute to the decrease in ΔV/V during creep. Immediately after the removal of the load, ΔV/V decreased to a negative value; thereafter, it decreased slowly and finally reached a certain value. The value of ΔV/V during creep tended to decrease with increasing density of wood. Also, there was a negative correlation between wood density and the rate of increase in ΔV/V.     

Discussion of Xixia’s Forestry A Model for the Development of China’s Township Forestry

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Rural household and forest: an evaluation of household’s dependency on community forest in Nepal

The aim of this paper is to analyze the level of dependency of rural households on forests, based on the economic status of the households and the property regimes of forests. The analysis of household-level dependency suggests that large numbers of rural households are benefiting regularly from their community forests. Out of three forest property regimes examined, community forests were found to be the most prominent sources for supplying forest products to local households. Analysis of the degree of forest-products dependency and the economic status of households shows that the low economic status households rely more on the community forest than the economically better-off households. In addition, a ² analysis indicates that the economic status of households affects the degree of forest-product collection activities. The results show three types of property regime with respect to forest management in Chitwan. Each regime holds its own ownership rights, which control the harvesting of forest products and provides incentives to the local households.     

Pattern of resting site of sables in Daxing’an Mountains

The use of resting sites of sables (Martes zibellina) was studied by radio-tracking techniques in Daxing’an Mountains in 1994-1996. The results showed that the males used 191 different resting sites, while females used 159 sites averagely in a year. The number of used resting sites varied among seasons, and the reuse index calculated for each individual in each season varied from 0.07 to 0.94. The reuse index was highest for males in autumn-winter. In spring the number of resting sites of females was significantly less than that of males. In summer, both sexes used more resting sites. In winter, the reuse index was negative related to snow depth. The average distance between consecutively used resting sites differed significantly between males (716 m, SD=479, n=1 081) and females (455 m, SD=298, t=-8.59, P<0.001). For males the average distance was the shortest in February-March and the longest in August-September, whereas the shortest distance was recorded in April-May for females. In spring and autumn-winter, most individuals used resting sites that randomly distribute in their home ranges. The standardized Morisita coefficient of resting site dispersion in the home range varied from 0.06 to 0.50. In summer, the standardized Morisita coefficient of resting site dispersion in the home range varied from 0.38 to 0.51. Furthermore, in summer, 72% of all resting sites used by sables were located near the edges of their home ranges.     

Determining Young’s modulus of timber on the basis of a strength database and stress wave propagation velocity I: an estimation method for Young’s modulus employing Monte Carlo simulation

In this article, we report on an estimation method for Young’s modulus that entails measuring only the stress wave propagation velocity of timber built into structures such as wooden buildings. Methods of estimating Young’s modulus that use the stress wave propagation velocity and characteristic frequency of timber in conjunction with timber density have long been used. In this article, we propose a method of easily and accurately estimating Young’s modulus from the stress wave propagation velocity without knowing the timber density. This method is based on a database of wood strength performance and density accumulated from a variety of research data and the method estimates Young’s modulus by a simulation method. We compared the Young’s moduli estimated by this method with those obtained by the bending test and by the measurement of the stress wave propagation velocity and density, and found similar results. This coincidence suggests that the method of estimating Young’s modulus presented in this article is valid. For example, the method is effective for convenient evaluation on site when determining whether a wooden building’s structural components should be reused or replaced when repairing or remodeling a building.     

Discussion on Status and Functions of China’s Forestry

In recent years, the quantity and quality of global forest resources are declining continually. Contrarily, the both in China are increasing, which is deeply related to the sustainable forest management and eco-system management in China. With the trend that world community knows more about the important role of forest, more and more functions of forest are recognized. The impact and functions of China’s forestry deserve more concern. Based on some experiences in the field of forestry research, the authors introduced and analyzed the key role of China’s forestry for the sustainable development, and explained the functions of China’s forestry, such as ensuring ecological safety, addressing climate change, improving economic development, promoting social harmony and prospering ecological culture.     

Development of an Ideotype-Based Selection Tool for Native Tropical Tree Breeding by Smallholder Planters in Mexico’s Maya Forest

Tree planters of the Yucatan peninsula in México are mostly first-generation small-scale forest owners. As a consequence of the lack of a management plan, trees employed for plantations are currently produced without any traceability or genetic improvement protocol, resulting in the reduced quality and heterogeneity of established materials. Recently, the Mexican government published a law to force planters to reverse this situation through the initiation and operation of germplasm management and traceability programs within each physiographic sub-province. Thus, planters located in the “Campeche Karts sub-provenance” now need to select superior trees for plant production, provenance assays, and orchard establishment. As a reference for the improvement goals in this work, we developed a model ideotype tree and qualification tool based on a weight-free selection index to compare trees in established plantations to enable the effective selection of superior trees to be used as seed sources and as a starting population for genetic improvement programs. The tool presented here is easy to use by planters, requiring a very basic computer or smartphone to run a spreadsheet where simple morphometric evaluation are captured, trees are qualified in comparison to the ideotypic values of each parameter with the aid of common field equipment. When this tool was applied to individuals from two different plantations, the qualification methodology ranked the individuals, allowing for the selection of superior trees in a more robust way, in contrast to the use of parameters mostly based on price and driven by wood volume.     

Supercritical extracts of forest fuels in Great Xing’an Mountains

Extracts are important components of fuels.Fatty-extracts with high heating value(HV) are hypothesized by researchers as positively related to the HV of fuels.The Soxhlet extractor is typically used to extract fatty-extracts but it has shortcomings,including long processing time(8–10 h) and the requirement for large amounts of organic solvent.Supercritical extraction is an alternate and useful technique for extraction of natural products.However,published studies rarely discuss the relationship between extracts and HV.In this study,we assessed the supercritical extracts(Su E) of forest fuels in the Great Xing'an Mountains.Our results indicated that the optimum conditions for extraction of Su Es were40–60 mesh,40–50 MPa,45 °C,80 min and a CO_2 flow rate of 1.5–2.0 dm~3/min.The Soxhlet extracts contents and the Su E contents were all related to HV.However,R~2 of the coniferous samples(0.8499) and needle samples(0.9722) demonstrated that the correlation between HV and the Su E content was closer.We conclude that supercritical fatty-extracts provide a useful index of the HV of fuels,especially coniferous fuels.Su E data can be used in fire management,for example to estimate the rate of fire spread or fire intensity.     

Erratum to: Pattern of resting site of sables in Daxing’an Mountains

Northeast Forestry University and Springer-Verlag Berlin Heidelberg 2011 Retraction: XU Cheng-shui, ZOU Hong-fei, ZHANG Hong-hai. Pattern of resting site of sables in Daxing’an Mountains.     

Forecast of China’s Forestation Area Based on ARIMA Model

Man-made forest, which is the forest ecosystem of rehabilitation and reconstruction, plays a significant role in the provision of forest products and improvement the ecological environment. In this paper, we established the AR (5) model to predict China's forest area from 2009 to 2015. This study shows the slow growth of the national plantation area trend with some fluctuations, but the overall growth rate is not large. We proposed that on one hand China should continue to increase the plantation area, on t...     

Regional differences of water conservation in Beijing’s forest ecosystem

The water conservation capacities of main forests in Beijing,China were estimated through the quantitative analysis.Various methods developed in published papers on forest hydrology were employed.The forests in Huairou,Yanqing,Miyun,Mentougou and Fangshan districts are the main contributors to water conservation(the cumulative ratio reaches 65%),and the forests in Tongzhou,Chaoyang,Shunyi and Daxing districts have the highest water conservation capacity(3000 m3/ha).Altitude and slope are the key factors to affect the water conservation capacity.The forests located in Plain Area,Hilly Area,Low Mountain,and Middle Mountain contributes 27%,28%,24% and 21% of the conserved water,respectively.The water conservation capacity of forests in Plain Area(2 948 m3/ha),is superior to the forests in other regions.And the forests situated on Flat Slope,Moderate Slope and Gentle Slope constitute the largest proportion(nearly 93%) of water conservation,while the forests on Flat Slope has the highest water conservation capacity(2 797 m3/ha),and the forest on Steep slope has the lowest water conservation capacity(948 m3/ha).