毛竹纤维饱和点随竹龄的变化规律

竹材的纤维饱和点对于竹材的加工利用具有重要指导意义。以毛竹为研究对象,采用力学法和水分吸着等温线法对毛竹纤维饱和点及其随竹龄的变化规律进行了系统研究。结果表明,两种方法所得的纤维饱和点不同,顺纹抗压强度法0.5龄为36.12%;1.5～4.5龄为(24.49±0.78)%,水分吸着等温线法0.5龄为24.51%;1.5～4.5龄为(18.38±0.42)%;两种方法测得纤维饱和点的绝对数值虽然存在一定差异,但随竹龄的变化规律相同,即从0.5龄到1.5龄降幅明显,大于1.5龄后趋于稳定。     

The fiber saturation point of various morphological subdivisions of Douglas-fir and aspen wood

Summary In both Douglas-fir and aspen wood, the fiber saturation point of early wood is greater than that of late wood, solvent extraction lowers the fiber saturation point, and the fiber saturation point for reaction wood is less than that for whole wood.     

Modeling the process of absorption and desorption of water above and below the fiber saturation point

Summary The process of absorption of water along the tangential direction of the wood is studied by immersing the sample in water. The transport of water is then obtained below the fiber saturation point at the beginning of the absorption and above this fiber saturation point during the process. The potential which drives the transport of the bound-water and free-water through the wood has been considered by testing a diffusional transport model. The transient diffusion with a constant diffusivity has been found to describe not only the process of absorption but also the process of desorption with diffusion of water through the solid and evaporation from the surface. Analytical solutions have been successfully used to describe the stage of absorption during a time of four hours at the end of which an equilibrium of absorption is attained, as well as the following stage of desorption. A model based on a numerical method with finite differences has been found to describe the process of absorption and desorption in various cases, and especially when the equilibrium of absorption has not been attained.This work was carried out with the help and support of the M. R. T. and the French CTB (Wood Technical Center)     

Changes in physical properties of tropical and temperate hardwoods below and above the fiber saturation point

Changes in physical and mechanical properties of wood were analyzed using sorption tests combined with dimensional measurements and perpendicular-to-the-grain tangential compression tests. In order to determine the influence of wood structure on these changes, three hardwood species (Fagus grandifolia, Brosimum alicastrum and Cariniana domestica) presenting different anatomical structures were studied. Two experimental techniques were used to perform moisture sorption tests at 25°C. The first technique used saturated salt solutions (from 33 to 90% relative humidity) and the second used the pressure membrane method (above 96% relative humidity). Special attention was given to the “fiber saturation region”, where changes in wood properties started to take place. Results showed that at equilibrium moisture content (EMC), radial, tangential and volumetric shrinkage, as well as changes in transverse strength occurred above the fiber saturation point (FSP). This behavior can be explained by the effect of hysteresis at saturation on wood properties. This hysteresis indicates that loss of bound water takes place in the presence of liquid or capillary water, which contradicts the concept of FSP. The initial EMC at which bound water starts to be removed varied largely among the wood species.     

Distribution of the equilibrium moisture content in four hardwoods below fiber saturation point with magnetic resonance microimaging

Wood Science and Technology - The distribution of liquid and bound water in wood samples under equilibrium moisture contents (EMC) below fiber saturation point (FSP) was assessed by magnetic...     

Effects of extraneous substances, wood density and interlocked grain on fiber saturation point of hardwoods

Samples of nine tropical hardwoods from Peru and sugar maple wood from Quebec were selected for moisture sorption and swelling tests at 25°C. These tests evaluated the fiber saturation point (FSP) by two methods: following adsorption over distilled water, and from the volumetric swelling intersection point. Cold-water and hot-water extractives, sequential cyclohexane, acetone and methanol extracts, ash content, wood density and interlocked grain were also determined on matched samples. The results indicated that adsorption tests over distilled water were not applicable for determining FSP in all wood species. Condensation of water vapor apparently occurred, even though temperature during adsorption was controlled to the nearest 0.01°C. The volumetric swelling intersection point method was judged more appropriate. FSP ranged from 15 to 25% for tropical hardwoods and was 30% for sugar maple wood. FSP was negatively correlated with wood density, acetone extracted fraction, interlocked grain and ash content. These parameters each exerted similar effects on variability in FSP.     

Effects of extraneous substances,wood density and interlocked grain on fiber saturation point of hardwoods

Abstract

Samples of nine tropical hardwoods from Peru and sugar maple wood from Quebec were selected for moisture sorption and swelling tests at 25°C. These tests evaluated the fiber saturation point (FSP) by two methods: following adsorption over distilled water, and from the volumetric swelling intersection point. Cold-water and hot-water extractives, sequential cyclohexane, acetone and methanol extracts, ash content, wood density and interlocked grain were also determined on matched samples. The results indicated that adsorption tests over distilled water were not applicable for determining FSP in all wood species. Condensation of water vapor apparently occurred, even though temperature during adsorption was controlled to the nearest 0.01°C. The volumetric swelling intersection point method was judged more appropriate. FSP ranged from 15 to 25% for tropical hardwoods and was 30% for sugar maple wood. FSP was negatively correlated with wood density, acetone extracted fraction, interlocked grain and ash content. These parameters each exerted similar effects on variability in FSP.     

Analysis of the pore-size distribution and fiber saturation point of native and thermally modified wood using differential scanning calorimetry

The aim of this paper was to investigate pore-size distributions in the nano-diameter range of wood and their alteration due to thermal modification of wood using thermoporosimetry, and to find out what consequences can be derived regarding the biological durability. Thermoporosimetry is a technique that is based on the measurement using differential scanning calorimetry (DSC). The method is based on the fact that frozen water contained within small pores is at elevated pressure and therefore has a depressed melting temperature as a function of the appropriate pore diameter. In addition, the fiber saturation points (FSP) were determined by DSC. The former were performed in an isothermal-step method and the latter using the continuous heating-up method. Native and thermally modified twin samples of Norway spruce (Picea abies (L.) Karst.), Sycamore maple (Acer pseudoplatanus L.) and European ash (Fraxinus excelsior L.) were analyzed. The results clearly show that the pore shares of wood for the measurable diameter range between 4 and 400 nm decrease considerably in all studied wood species due to thermal modification of the wood. Furthermore, thermal modification of wood leads to a decreased FSP for all studied wood species. For evaluation as well as reproducibility of the results of pore-size distribution and FSP, the consideration of sensible heat and specific heat of fusion plays an important role. If this is not done, it can lead to misinterpretations.     

Moisture content-water potential relationship of red pine sapwood above the fiber saturation point and determination of the effective pore size distribution

Summary The pressure membrane and pressure plate techniques were used to establish the moisture content-water potential (M-) relationship of red pine (Pinus resinosa Ait.) sapwood in desorption above the fiber saturation point. The moisture content-water potential relationship is required for the development of a model of drying considering the gradient of water potential as the driving force of moisture in wood. This relationship was established at 18, 56 and 85 °C for radial desorption. The results obtained demonstrate that water potential increases with temperature T at a given moisture content M. There is no significant variation of /T with temperature. Also, there is no plateau at intermediate moisture contents as was the case for the M- relationship of aspen sapwood established in a previous work. The effective integral and differential pore size distributions inferred from the M- relationship are also presented. The largest proportion of effective pore openings was found for a radius of 0.2 m. This value can be related to the pit membrane openings of red pine.This research project is currently supported by the Natural Sciences and Engineering Research Council of Canada under grant no. OGP0121954     

Probing red maple pit membrane pore size at fiber saturation point and oven dry using polystyrene macromolecules

Summary A modified solute exclusion technique was used to pressure impregnate a polystyrene molecular weight (MW) series dissolved in styrene into red maple samples at approximately the fiber saturation point (FSP) and oven dry (OD). Radial penetration was less than tangential and FSP less than OD. There was a marked change in radial OD penetration at 900,000 MW. There was no marked penetration change with MW in the tangential direction, although there appeared to be a slight decrease in FSP penetration at the higher MW tested.     

Determination of the fibre saturation point in whole wood using differential scanning calorimetry

Summary A new method for determining the fibre saturation point (FSP) of whole never-dried wood is described. Enthalpy of melting values from differential scanning calorimetry (DSC) experiments are used to calculate the proportion of non-freezing water. Two methods for calculating the FSP from the enthalpy data are described. FSP determinations were carried out on the commercially important West Australian eucalypt species, Eucalyptus marginata and Eucalyptus diversicolor and a plantation softwood, Pinus radiata. Results are reproducible and are corroborated by the traditional volumetric shrinkage method for determining the FSP. On all samples below 10 mg a low temperature endothermic peak is observed as a shoulder on the main peak. It is postulated that this is due to an intermediate layer of water between the freezing and non-freezing water.Use of the DSC at Curtin University of Technology, and the help of Mr. I. Sills is greatly appreciated. This and related work is supported by the Australian Govt. Department of Primary Industry and Energy (Forestry)     

A contribution to the ultrastructure of tension wood fibers

Summary Pronounced tension wood from four North-American hardwood species has been examined by light and electron microscopy. Delignified fibers were also studied. The gelatinous layer was in all cases loosely attached to S₂ but varied considerably in thickness within each species and was in one case terminated towards the lumen by a layer resembling S₃. A terminal lamella was not observed. After considering both earlier evidence and the present results, it was concluded that the gelatinous layer has neither a honeycomb nor a homogeneous texture, as has been suggested, but that it consists of concentric lamellae of cellulose microfibrils. In the absence of hemicelluloses and lignin, the microfibrils are probably bound together less firmly than they are in other cell wall layers. The gelatinous layer is more readily separated from the remainder of the cell wall by mechanical forces than by chemical reagents.

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Zusammenfassung Zugholz von vier nordamerikanischen Laubbäumen wurde im Licht-und im Elektronenmikroskop ebenso wie entlignifizierte Fasern untersucht. Die gelatinöse Schicht war überall locker an die S₂ gebunden, zeigte aber sehr verschiedene Dicken und war in einem Fall gegen das Lumen von einer Schicht, die der S₃ ähnlich sah, begrenzt. Eine Abschlußlamelle konnte nicht beobachtet werden. Frühere und die eigenen Resultate zeigten, daß die gelatinöse Schicht weder eine Wabenstruktur noch eine homogene Struktur besitzt, sondern daß sie aus konzentrischen Lamellen von Cellulosemikrofibrillen besteht. Da Hemicellulosen und Lignin nicht vorhanden sind, sind die Mikrofibrillen wahrscheinlich nicht so fest aneinander gebunden wie in den anderen Zellwandschichten. Die gelatinöse Schicht läßt sich von der übrigen Zellwand durch mechanische Kräfte leichter als durch chemische Reagenzien trennen.

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This investigation was supported by the United States Department of Agriculture, Forest Service, through Forest Service Research Grant No. 1, which is hereby gratefully acknowledged.     

刍议塞罕坝森林对气候和大气之贡献

用各种生态效能计算方法,量化显示塞罕坝地区百万亩林海在固碳制氧、涵养水源、调节小气候、减少空气有害物质、改善空气质量等方面的生态效益,彰显该区域在应对全球气候变化和提高空气环境质量的积极作用。鉴于其森林生态重要贡献,笔者进行了有关思考并提出了相关建议。     

A contribution to the pollen morphology for arboreal type of caesalpinioideae in Korea

The pollen morphology of 7 taxa of three genera of the subfamily Caesalpinioideae in Korea was investigated by light microscope (LM) and scanning electron microscope (SEM). The pollen grains of this subfamily are monads, prolate spheroidal or subprolate, and trizonocolporate. Sculpture pattern is reticulate or perforate. Based on sculpture pattern, colpus width and grain shape at equatorial view, 4 major pollen types of the subfamily are discernible;Caesalpinia, Cercis, Gleditsia I, andGleditsia II. This study was supported by Korean Academic Promotion Foundation. During this study, Botanic Garden of Kyoto University, Japan, Anmyondo Arboretum and Dr. Byongsoo Kang at Dongkuk Univ., Korea provided materials and informations which are greatly appreciated.     

A novel application of the ecological field theory to the definition of physiographic and climatic potential areas of forest species

A new approach to the definition of physiographic and climatic potential areas for forest species, based on the ecological field theory, is outlined in this paper. The proposed formulation is tested on the Spanish juniper (Juniperus thurifera L.), using data from 883 permanent and temporary plots throughout its distribution area in the Spanish autonomous region of Castilla y León. The suitability of the territory for the species is assessed by previously studying its habitat, which in turn is analyzed through physiographic and climatic parameters. This new method is rooted in an additive index that depends on the Mahalanobis distance in the parametric space that evaluates the ecological resemblance between the studied site and each of the points defining the parametric habitat. Thereby the ecological potential of any site within the territory can be established, integrated in a geographical information systems and accordingly charted. The results are compared with those obtained with the methodology traditionally used by Spanish foresters (factorial index), showing that the overall potential area is similar in size but quite different in its distribution.     

Rapid prediction of shrinkage and fibre saturation point on teak (Tectona grandis) wood based on near-infrared spectroscopy

? Dimensional stability, along with the natural durability and colour of the wood, is one of the most important characteristics of teak used as timber. However, it is very time-consuming to take measurements of this kind. For the purposes of selection for the production of improved varieties, the number of samples to be measured rapidly exceeds the capacity of a traditional laboratory.

? Near-infrared spectroscopy, based on a set of reference data, is a tool enabling many of the chemical properties of wood to be predicted and the number of laboratory measurements to be reduced exponentially. The issue here is a question of checking the effectiveness of NIRS tool to build models and predict the shrinkage and fibre saturation point of teak wood from Togo.

? The results show the possible use of NIRS to measure the dimensional stability of teak wood and that it is appropriate to choose the type of wood and type of surface to be measured by NIRS. The best prediction models for radial and tangential shrinkage and fibre saturation point give R ² values of 0.72, 0.83 and 0.87 respectively with ratios of performance deviation of 1.8, 2.4 and 2.8.

? Consequently, after verification on other sets of teak samples, which may or may not be included in the prediction model, NIRS can be used to predict shrinkage and fibre saturation point values accurately for a large number of samples, making it possible to include these characteristics in the selection criteria for classifying wood and high throughput phenotyping.

     

Olevi Kull's lifetime contribution to ecology

In this article dedicated to Olevi Kull (June 22, 1955-January 31, 2007), we draw on his writings (in English and translated) to outline his thoughts on the relationship between scientists and science. We provide a brief synthesis of his most important work, give a short account of his career and, to bring the man into focus, share some personal stories of interactions with him. Kull considered that for a personal understanding to become scientific knowledge it must be explained convincingly based on theory and empirical support, and then taught to others in both spoken and written words. He saw the last step as the main distinction between learning and science. Olevi Kull's approach to science relied on two principles: first, linking theory and experiments in challenging settings, e.g., to test the generality of his ideas he often challenged them in multi-layered, mixed-species canopies. Second, he insisted on setting experiments to test assumptions used in quantitative analyses or in explaining an observed outcome; this, at times, led to falsification of commonly held ideas, thus enhancing ecophysiological understanding. After describing Kull's application of these principles, we give a brief synthesis of his most important work, in which he demonstrated through experimentation and modeling how the vertical distribution of leaves in canopies is consistent with the acclimation of the photosynthetic apparatus. We also review some of his findings on the interactive effects of carbon dioxide and ozone on canopy photosynthesis.     

The contribution of agroforestry to world forestry development

Agroforestry with its outstanding variety of systems and technologies has been practiced in all parts of the world since times immemorial. Its worldwide recognition, scientific promotion and application in rural development strategies in the tropics, however, ‘exploded’ with two events: the foundation of the International Council for Research in Agroforestry (ICRAF), 1977 and the Eighth World Forestry Conference in Jakarta, 1978. This is important to be recalled at the occasion of the Ninth World Forestry Congress to be held in Mexico this year. Agroforestry's holistic approach to solving land use problems under prevailing conditions and constraints of different humid, semiarid and mountainous regions has gained importance and produced first remarkable results with regard to increasing the human-ecological carrying capacity. Forestry is gaining from the newly promoted strategies of integrated land use in various ways: less pressure on forest resources and thus less destruction of forest vegetation, additional lands for wood production outside the forest estate, cooperation instead of confrontation with other target groups, and an expanded multiple-use concept increasing the value of marginal forest lands. Agriculture and livestock management are improved by various environmental benefits of the forest component and by the availability of forest products within agroforestry systems. First achievements over the past seven years have been encouraging in many instances. Much more, however, remains to be done in future.