木材密度力学性质及其换算关系

由于我国木材物理和力学强度试验标准与外国不同，很难互相比较和直接应用，国此本文提供了换算系数，同时重点提出美国木材密度试验方法 ＡＳＴＭ Ｄ５２与我国的换算值，旧国标ＧＢ１９３３－８０和新国标ＧＢ１９３３－９１的换算系数，木材密度是木材物理力学性质的标志，可以通过它推算出多种力学强度数据，本文根据以往的数据统计分析得出换算系数。     

黑杨源新无性系木材物理力学性质研究

代取浙江临海无性系试验林5年生10个速生黑杨新无性系30个样株，测定木材的物理力学性质。结果表明，其木材密度高于同地区速生杉木、柳杉10年生木材的测定值，力学性质与之相近；木材物理性质在速生无性系间无显著差异，而力学性质差异显著或极显著；木材密度与力学性质显著相关，而木材性质与胸径生长相独立；参试无性系中367、366、370、1388、121等无性系最适于营建短伐期工业用材林。     

杉木材性株内变异的研究Ⅰ.木材力学性质和木材密度

对１５株浙江产杉木株内不同高度和圆周不同方位上木材的抗弯强度、抗弯弹性模量、顺纹抗压强度和木材密度的差异，木材密度的径向变异模式和木材力学性质与木材密度的相关关系进行了测定和分析。主要结果是：抗弯强度和抗弯弹性模量在株内不同高度上差异特别显著；顺纹抗压强度和木材密度未表现出显著差异；在圆周不同方位上，三项力学性质和木材密度均为南北向高于东西向，差异不显著；木材密度径向变异模式在不同高度和不同方位上均为接近水平有一定波动的直线；三项力学性质与木材密度的相关关系在不同高度和不同方位上均特别显著，但不同力学性质与木材密度的相关系数有明显差异，不同高度上和圆周不同方位上，亦有差异。     

中外木材物理力学数据的换算(续)

２木材力学强度数据的换算我国木材力学强度数据与国际接轨的换算，包括单位制不同、试样含水率不同以及试验方法不同而需要进行的换算。２．１单位制不同的换算我国老标准的木材力学强度数据单位是公制，为了与国际标准及和我国新标准取得一致，须转换为国际单位制，即：力的单位由过去公制的ｋｇｆ（千克力），改为Ｎ（牛顿或牛）─—指１千克质量的物体产生１ｍ／ｓ２加速度的力；木材力学强度单位（大多数）由公制的ｋｇｆ／ｃｍ２改为Ｐａ（帕）。我国新老标准的木材力学强度数据，若与西方一些主要国家的数据比较，则应换算成英制。为…     

云南松木材显微力学的研究

于力学试验过程中,借显微镜连续观察木材构造由于外力作用所出现的变异,是研究木材显微力学的基础。作者试图通过云南松木材显微力学的研究,阐明木材力学性质与构造的关系中的某些问题,并就强度理论上的个别问题进行初步探讨。苏联Ю.М.Иванов教授开辟了木材显微力学的研究领域,这是苏联近年来木材学上一大进展。研究木材显微力学,一方面可以深入地了解木材力学性质与构造的关系,为阐明木材力学性质中一些基本问题与建立木材学综合理论的基础提供了可能;同时亦可以揭示木材在加工利用过程中所发生的一系列现象的本质,这就关系着加工部门控制加工工艺过程、建立新的加工方法以及发现新的木材利用范围;其次也为木材强度理论的     

热工学在木材科学与技术学科中的地位与改革设想

热工学在木材科学与技术学科中的地位与改革设想北京林业大学张璧光热工学在本学科中的地位和作用木材科学与技术学科（以下简称木材学科）包括木材学与木材加工技术两大部分，前者属于理科，后者属于工科种。木材学又包括木材构造、木材物理、木材力学、木材解剖与木材化...     

五种白桦木材的抗弯强度和抗弯弹性模量的研究

本研究主要对五种新培养的速生白桦木材的物理力学性质进行了测试，并根据测试结 果进行了变异分析及方差分析，分析结果表明，白桦木材的力学性质较好，物理力学性质差 异不显著，适宜作家具材。此结果表明，可根据木材物理力学性质因子选取优良树种。     

浅议《木材学》专题化教学

浅议《木材学》专题化教学北京林业大学李启岭《木材学》作为木材加工专业的一门专业基础课，主要讲述木材的构造与识别，木材化学、物理与力学性质，木材缺陷和木材改性等内容。根据现行的教学大纲要求，总学时为６０，其中课堂讲授为４０学时，实验为２０学时，课堂讲授...     

中外木材物理力学数据的换算

根据中外木材物理力学性质试验方法标准的差异，提出了中外木材密度、干缩性和力学强度等试验数据的换算方法，以解决两类木材试验数据的对比问题。     

I──45杨木材基本性质的测定

Ｉ──４５杨木材基本性质的测定张家林，赵云，郑太晶，王军（吉林省林业科学研究院）张孟良（东丰县林业局）大量研究表明，木材密度是重要的木材性状，它与木材机械强度紧密相关，是判断木材物理力学性质、确定木材用途的有效措施。木材纤维长度在很大程度上决定着制浆...     

Browsing Damage on Pine (Pinus sylvestris and P. contorta) by a migrating moose (Alces alces) Population in Winter: Relation to Habitat Composition and Road Barriers

In Scandinavia, moose (Alces alces L.) sometimes cause severe browsing damage to economically-important pine. Moose-vehicle accidents have spurred construction of fences along roads, and these may interfere with moose migration between summer and winter ranges, or the road alone may be a barrier. If this happens and moose build up along roads, landowners may suffer economically. Therefore, this study investigated whether roads, fences or other factors influence the use of young pine stands by moose. Eighty stands along roads in northern Sweden were evaluated in which individually-browsed branches were counted on 9972 pines. Moose browsing was not significantly related to birch (Betula pendula Roth, B. pubescens Ehrh.) density, nor did it differ between pines (Pinus contorta Douglas or P. sylvestris L.). However, increased pine density, site productivity and proximity to a highway were associated with increased browsing. Further large-scale studies are needed to understand moose habitat selection and the effects of roads.     

Effects of Root Freezing on the Physiology and Growth of Picea glauca,Picea mariana and Pinus banksiana Seedlings Under Different Soil Moisture Regimes

The root systems of 2-yr-old Picea glauca, Picea mariana and Pinus banksiana seedlings were submitted to various frost temperatures during an artificial frost to induce different levels of root damage. Frost-damaged and control seedlings were placed in a greenhouse under high and low soil moisture regimes. Seedling growth and physiology were evaluated periodically. Seedling survival was reduced when root damage reached levels of 60-80%. Root systems of all three species showed partial to total recovery by the end of the experiment. In general, root freezing damage caused reductions in seedling growth, with these reductions becoming less significant over time. Root damage had little to no effect on black spruce and jack pine seedling physiology, while white spruce CO 2 uptake decreased with increasing root damage. Shoot nitrogen content of all three species decreased slightly with increasing root damage.     

Stand Structure in Pine,Spruce and Deciduous Forests: A Comparison Between Finnish and Russian Karelia

This study investigated the stand structure in pine, spruce and deciduous forests in the border district of Finland and Russia. A total of 46 mature forest stands was selected as pairs, the members of each pair being as similar as possible with respect to their forest site type, age, moisture and topography. The stands were then compared between the two countries by means of basal areas and number of stems. The proportions of dominating tree species were 2-12% lower, and correspondingly the proportions of secondary tree species higher, in Russian forests. The density of the forest stock was also higher in each forest type in Russia. The forests in the two countries differed most radically in terms of the abundance of dead trees. The amount was two to four times higher in Russian deciduous and spruce forests, and in pine forests the difference was 10-fold. The stand structures indicated that Russian coniferous stands, in particular, were more heterogeneous than intensively managed pine and spruce stands in Finland.     

Growth and Terminal Bud Formation in Picea abies Seedlings Grown with Alternating Diurnal Temperature and Different Light Qualities

The root collar diameter and the height:diameter ratio are of particular importance in container-grown seedlings where a high density in the containers may produce spindly seedlings. Temperature regimes and light quality are known to affect plant growth. The aim of this study was to identify responses in Picea abies (L.) Karst. seedlings grown with light providing different red:far-red ratios and under temperature regimes with alternating day (DT) and night temperature (NT) from negative (DT < NT) to positive (DT > NT) difference (DIF) between DT and NT. Experiments were conducted in controlled environment chambers and in a daylight phytotron. Only limited thermoperiodic responses appeared in P . abies seedlings with respect to seedling height and dry weight accumulation. The formation of terminal buds, however, was clearly delayed in seedlings grown at negative DIF. The results indicate a requirement for day extension light that is high in far-red, to prevent terminal bud formation under natural short-day conditions. An extended study should be conducted to clarify the minimum level of light intensity and the optimal light quality needed to prevent terminal bud formation under natural short-day conditions.     

CAD与建筑设计的关系

本文分析了CAD在设计中引起的正面和负面影响,并进行了系统的阐述,从而使设计者在应用中能够保持客观的态度。     

Risk Perception Among Non-industrial Private Forest Owners

Based on an enquiry, risk perception among non-industrial private forest owners is described in relation to climate change and forestry hazards. Of the respondents, 11% took action to remedy the effects of climate change. Out of a given set, hazards were ranked according to each respondent's experience of recent substantial financial loss to the estate and in relation to his or her willingness to make investments aimed at risk reduction. For each hazard, the respondent assessed the risk in four classes ranging from very high to negligible risk. Six hazards were considered most problematic in all three aspects: browsing damage, falling timber prices, damage by wind, spruce bark beetle, root rot and pine weevil. A majority of the respondents claimed to take action to reduce the risk associated with at least one hazard, while 35% did not know whether they did. Excluding climate change, the need for decision support was the largest in relation to damage by wind owing to a combination of perceived high risk and a high level of ignorance in relation to whether risk-reducing measures were taken.     

Interactions in decomposition and N mineralization between tropical legume residue components

In situ produced plant residues contain a mixture of different plant components of varying quality. To assess synergistic or antagonistic interactions occurring during the decomposition and mineralization of such mixtures, individual plant parts (stems, leaves, leaf litter and roots) or the mixture of stems, leaves and leaf litter of the agroforestry species pigeonpea (Cajanus cajan) or of crop residues of peanut (Arachis hypogaea) or of the weed hairy indigo (Indigofera hirsuta) were incubated in pots for 19 weeks. Periodically, remaining plant residues were sieved out (>2 mm), weighed and N content as well as soil mineral N determined. Above- and below-ground residues of peanut decomposed fastest and showed the largest N release in agreement with their high N concentration and low-acid detergent fibre (ADF) : N ratio. Hairy indigo was hypothesized to be of lower quality than pigeonpea because of its high-polyphenol content. However, it decomposed faster than pigeonpea, largely because of the higher N and lower lignin concentration of its components. Ranking of individual plant components for N mineralization resulted in the following pattern, leaves > leaf litter > roots > stems. In mixtures of the different plant components a similar species order in decomposition was obtained, e.g. peanut > hairy indigo > pigeonpea. The amount of N released from the mixture was dominated by stem material that comprised 46–61% of the mixture. The interactions in mixtures were relatively small for peanut (generally high-quality components) as well as for pigeonpea (low proportion of high-quality components, i.e. N rich leaf material). However, a positive interaction occurred during later stages of N mineralization in the mixture of hairy indigo as it had a significant proportion of N rich components and absence of highly reactive polyphenols. Thus, for plants with low to intermediate chemical quality attributes, manipulating plant composition (e.g. by varying harvest age, affecting stem and leaf proportions) will be important to obtain significant interactions during decomposition when its components are mixed.     

Pasture production and tree growth in a young pine plantation fertilized with inorganic fertilizers and milk sewage in northwestern Spain

The use of organic waste materials such as milk sewage as an organic fertilizer could have the dual advantages of organic-waste disposal and reduced dependence on inorganic fertilizers. The effects of fertilization with (1) conventional mineral fertilization, (2) milk sewage sludge at 40 kg N ha⁻¹ target rate and (3) no fertilization on pasture production and tree growth were examined in an experiment consisting of two pasture mixtures under a one-year-old Pinus radiata plantation with a density of 2500 trees ha⁻¹. The two pasture mixtures were: (1) Dactylis glomerata L. var. saborto (25 kg ha⁻¹) + Trifolium repens L. group Ladino (4 kg ha⁻¹) + Trifolium pratense L. var. Marino (1 kg ha⁻¹); (2) Lolium perenne L. var. Tove (25 kg ha⁻¹) + Trifolium repens L. group Ladino (4 kg ha⁻¹) + Trifolium pratense L. var. Marino (1 kg ha⁻¹). The experiment began in the spring of 1995 using a randomized block design with three replicates in Castro Riberas de Lea (Lugo, Galicia, north-western Spain). Plot size was 12 × 8 m², with a 1 m buffer strip between plots. Two-year data showed that fertilization with either material had a positive effect on pasture production, with no significant difference between the two fertilization treatments. Tree growth in the milk sewage sludge plot was significantly higher than in the control plots. Inorganic fertilization increased pasture production, but affected tree growth negatively. The results show that milk sewage sludge could be used as a fertilizer in silvo-pastoral systems. This revised version was published online in June 2006 with corrections to the Cover Date.     

Key Habitats in the Norwegian Production Forest: A Case Study

This study investigated the forest history, structural characteristics, the presence of fungal species suggested to indicate ecological continuity in old-growth forest, and the species composition of saproxylic beetles in 30 old forest ''woodland key habitats'' (WKHs), and compared them with production forest in the same age-class in south-eastern Norway. No statistically significant differences in forest characteristics, community of saproxylic beetles or number of red-listed beetles were found between the WKHs and the production forest, probably owing to a combination of profound long-term logging and a lack of will to delineate sufficiently large WKHs in the one area with significantly less forestry impact. The study indicates the advantage of including forest history information in WKH selection where such data exist, and the importance of restoring habitats in heavily exploited forest landscapes.