按树木材干燥特性与工艺及其皱缩研究现状

本文回顾和分析了桉树木材与干燥有关的材性和干燥特性，指出按木的密度、含水率和干缩率变异性大、渗透性差，在干燥过程中易产生皱缩、开裂等干燥缺陷，若采用预冻处理和前后期调温处理可减少木材的皱缩；同时建议研究各种桉木不同规格板材的干燥基准和两段式干燥工艺。     

桉树木材干燥特性与工艺及其皱缩研究现状

本文回顾和分析了桉树木材与干燥有关的材性和干燥特性 ,指出桉木的密度、含水率和干缩率变异性大、渗透性差 ,在干燥过程中易产生皱缩、开裂等干燥缺陷 ,若采用预冻处理和前后期调湿处理可减少木材的皱缩 ;同时建议研究各种桉木不同规格板材的干燥基准和两段式干燥工艺     

木材皱缩评价指标的研究

近年来 ,国内外学者对木材皱缩缺陷开始关注 ,澳大利亚学者Ｔ .ＣＩｎｎｅｓ( 1 995,1 996)、中国学者王喜明 ( 1 989)、刘　元 ( 1 994)等分别研究了澳大利亚产桉木如多枝桉、细叶桉和赤杨、山杨等木材的干燥皱缩缺陷。他们从调湿处理对皱缩的作用 ;皱缩材组织结构的变化 ;皱缩机理 ;皱缩极限温度 ;预冻处理对皱缩的作用等方面做了大量深入而细致的工作。所取得的成果公开发表后得到同行学者的认可 ,对进一步研究避免皱缩的干燥工艺打下了较好的基础。但在众多有关木材皱缩的研究报告中 ,普遍遇到一个同样的问题就是如何定量地去评价和测量…     

预冻处理减少木材皱缩的研究

以大青杨为试验材料，研究了预冻处理对木材干燥皱缩特性的影响，分析了木材在冰冻处理过程中木材细胞腔和细胞壁尺寸的变化规律，理论上计算了细胞壁强度的增加范围。并通过电子显微镜分析冰冻过程对木材细胞壁结构的影响，进而深入探讨预冻处理减小木材皱缩的机理，为减少木材皱缩提供理论基础。结果表明：预冻处理可以减少大青杨木材的皱缩。     

木材皱缩的研究现状及发展趋势

通过总结和分析国内外关于木材皱缩的研究现状，指出皱缩深度、皱缩因子、体积收缩率、干缩率等4项指标能够合理地评价木材皱缩的程度；采用预冻处理、热处理、加压或拉伸处理以及后期调湿处理能够在一定程度上减少皱缩的产生；并讨论了木材皱缩研究的发展趋势。     

热水处理对王桉木材干缩率和皱缩的影响

研究了热水处理的温度和时间对王桉（Eucalyptus regnans）木材全干干缩率和皱缩的影响。结果表明：随着处理温度的升高,王桉木材的全干干缩率呈增大的趋势,70℃和80℃时,处理时间对王桉木材的各向干缩率的影响不大;90℃和100℃时,处理时间对王桉木材的各向干缩率影响明显。经100℃热水处理6 h后王桉木材体积、弦向和径向全干干缩率分别增大了78.3%、116.1%和44.4%,分别达到25.5%,18.8%,7.8%。王桉木材的皱缩深度随处理温度的升高显著增大,处理时间对王桉皱缩深度的影响不明显。     

干燥工艺条件对木材皱缩特性的影响

以内蒙古西部产大青杨为研究树种,研究了干燥工艺条件对木材皱缩特性的影响,通过正交试验分析了温度、湿度对皱缩材的皱缩深度,体积收缩率和皱缩因子的影响,并探讨了影响的原因。     

木材干燥皱缩机理及其特性研究

本文从理论上探讨了木材干燥皱缩的机理．并通过对红柳桉和多枝桉进行干缩性试验，阐述了木材干燥皱缩的特征、特性及其影响因子．揭示了木材干燥皱缩受外界环境影响的规律，对在生产中克服和防止木材干燥皱缩有一定的参考价值．     

木材的皱缩

本文给出了木材皱缩的定义,分析了皱缩机理,木材细胞皱缩的基本条件和外界条件,探讨了皱缩的特性,皱缩的评价指标以及评价之间的关系。     

赤桉材干燥皱缩的热处理调控

以人工林赤桉材为研究对象,根据皱缩评价指标对比研究了热水浸泡和汽蒸预处理对皱缩发生程度的影响,以及干燥中的热处理对皱缩回复的影响。研究表明：包括4 h常压预汽蒸处理和80℃热水处理在内的预热处理可以有效地预防皱缩;在板材平均含水率18%时进行3 h的汽蒸处理可以有效回复皱缩材。     

Understanding and adding value to Eucalyptus fibre

Eucalyptus wood has become one of the most important hardwood resources for pulp mills worldwide. Furthermore, bleached Eucalyptus pulp is used extensively both in paper-making globally where it is included in such diverse products as tissue, packaging, as well as printing papers and in chemical cellulose products such as viscose, acetate and microcrystalline cellulose. This paper investigates and highlights the physical and chemical attributes of the wood and pulp fibre from Eucalyptus that contribute to its popularity in the pulp and paper-making industries and to suggest how these can be enhanced or conserved in the manufacturing process to add maximum value. The fibre properties of macerated wood samples from a range of Eucalyptus species used commercially in South Africa are compared with those of North American hardwoods such as birch, maple and aspen. In comparison to the American hardwoods, the Eucalyptus species were found to have short and thin fibres (on average, fibre length from 0.6 to 0.8 mm and fibre width between 15 and 17 μm, compared with 0.6–1.4 mm and 17–30 μm, respectively, for the American hardwoods. This particular combination of dimensions for the Eucalyptus fibre produces a low fibre coarseness, which is a highly desirable attribute for products such as coated and uncoated papers. The Eucalyptus fibre is therefore reasonably fragile and this makes it particularly vulnerable to damage during the pulp and bleaching processes. Fibre damage occurs throughout the pulp process but is most severe in the mechanical sections such as digester blowing, high shear mixers, medium- and high-consistency pumps as well as low-consistency refining. These areas are highlighted in this paper and possibilities for fibre conservation are discussed.     

An improved acetyl bromide procedure for determining lignin in woods and wood pulps

Summary The acetyl bromide procedure for spectrophotometrically determining lignin in wood and wood pulp samples has been modified by adding perchloric acid to the digestion medium. This enables faster dissolution of the materials and the use of coarser samples. Subsequent treatment of the digestion mixtures with larger amounts of sodium hydroxide than those used in the conventional procedure has obviated the need for treatment with hydroxylamine. The modified method has been successfully applied to woodmeals and pulps from Pinus radiata and Eucalyptus species.     

Productivity,soil fertility and soil erosion under cassava based agroforestry systems

The interactions between component species in three-tier agroforestry systems were studied on sloping laterite soils of South India for three years. The wood yield of Eucalyptus was found to increase in association with the intercrops, with cassava + groundnut resulting in the best growth of Eucalyptus. Green forage yield of Leucaena was adversely affected by cassava but was improved by inclusion of a short duration seasonal crop. Both spread and mean length of lateral roots of Eucalyptus and Leucaena were restricted by cassava intercropping. Both the tree species were found to reduce the tuber yield of cassava and also the pod yield of both the seasonal crops when grown in association. Monocropping with cassava was found to improve the fertility and an increase in phosphorus and potassium contents of the soil was observed when grown in association with Eucalyptus and Leucaena. Soil fertility fell considerably after three years of cultivation of the tree species. The nutrient uptake by cassava was low when grown in association with perennial species. Both run off and soil loss were effectively reduced when cassava was grown in staggered mounds under Eucalyptus and Leucaena.     

The coppice-with-standards silvicultural system as applied to Eucalyptus plantations — a review

We review the management of Eucalyptus species under a coppice-with-standards （CWS） silvicultural system. CWS management results in product diversification, permitting production of small and large scale timber from the same stand. Eucalyptus species are suitable candidates for CWS management because： there are large worldwide plantation areas, sprouting capacity is high, and eucalypts are multipur- pose species. We discuss （1） short rotation Eucalyptus coppice manage- ment for energy and pulping and （2） Eucalyptus seedling management for solid wood products. We review the literature and discuss experi- ences with Eucalyptus managed under the CWS system. We also assess projects dealing with Eucalyptus coppice management, stand density regulation, pruning, and stand and wood quality. The growth environ- ment of the standard trees （heavy competition up to the first harvest, free growth afterwards） coupled with long rotations （〉20 years） results in high quality logs for solid wood products. Early pruning should be ap- plied to enhance wood quality. We propose a system for the silvicultural management of Eucalyptus under the CWS system, elaborating on the consequences of initial planting density, site productivity, and standard tree densities as well as timing of basic silvicultural applications.     

Compressive deformation of wood impregnated with low molecular weight phenol formaldehyde (PF) resin IV: Species dependency

Flat-sawn specimens of eight wood species, albizia (Paraserianthes falkata, 0.23 g/cm³), Japanese cedar (Cryptomeria japonica, 0.31 g/cm³), red lauan (Shorea sp., 0.36 g/cm³), European spruce (Picea abies, 0.44 g/cm³), Douglas fir (Pseudotsuga douglasii, 0.50 g/cm³), elm (Ulmus sp., 0.51 g/cm³), Japanese beech (Fagus crenata, 0.64 g/cm³), and Japanese birch (Betula maximowicziana, 0.71 g/cm³), were impregnated with low molecular weight phenol-formaldehyde (PF) resin and their compressive deformations were compared. The volume gain (VG) and weight gain due to 20% resin solution impregnation were different among species. Furthermore, the specific volume gain (VG/specific gravity), indicating the degree of swelling of the cell wall, also varied from 17.7% for European spruce to 26.4% for elm. Oven-dried specimens of each species were compressed using hot plates fixed to an Instron testing machine. The deformation behavior of resin-impregnated wood up to 10MPa was significantly different among the species. Stress development during cell wall collapse for low density wood was minimal. As a consequence, a significant increment of density occurred up to 2MPa for low density wood such as albizia and Japanese cedar. When PF resin-impregnated wood was compressed up to 2MPa and the pressure was kept constant for 30min, the density of Japanese cedar reached 1.18g/cm³, about 30% higher than the density of compressed Japanese birch, which possesses an original density that is 2.5 times higher than that of Japanese cedar. The mechanical properties of resin-impregnated wood, especially low density wood, increased with density. Hence, it is manifested that low density wood species have an advantage as raw materials for obtaining high-strength wood at low pressing pressure.     

Crop yields of rice and wheat grown in rotation as intercrops with three tree species in the outer hills of Western Himalaya

Studies on tree crop interaction under rainfed condition in Dehradun valley were conducted for 13 years during 1977 to 1990. Grewia optiva (Bhimal), Morus alba (Mulbery) and Eucalyptus hybrid were tried along with rice (CV: Akashi) — wheat (CV: RR-21) rotation. One-year-old tree seedlings of the above tree species were planted in line, 5 m apart in N-S direction, in July 1977, in the middle of the plot (size 20 m × 20 m). Eucalyptus was first harvested in 1987. Grewia optiva, Morus alba and coppice of Eucalyptus were harvested in 1990. All tree species had depressing effect on crop yields. Eucalyptus had maximum effect in depressing crop yield till the first harvest and had least effect thereafter. From 1987 onwards, Morus alba affected rice most, while wheat was mostly affected by Grewia optiva. The depressing effect on an average varied from 28 to 34% depending upon the species.Distance of tree line from the crop significantly affected the crop yield upto a distance of 5 m and there was 39% decrease in crop yield upto 1 m, 33% from 1–2 m, 25% from 2–3 m and 12% from 3–5 m distance. Annual removal of lops and tops from trees partly compensated the deficit. Grewia optiva could produce 1.08 t ha^–1 yr^–1 of branches and 0.26 t ha^–1 yr^–1 of leaves (air dry) and 1.28 t ha^–1 yr^–1 of branches and 0.28 t ha^–1 yr^–1 of leaves were obtained from Morus alba. Wood (ADT) produced by the trees was 33.6 t ha^–1 from Eucalyptus, 9.5 t ha^–1 from Grewia optiva and 11.6 t ha^–1 from Morus alba.     

Impact of Eucalyptus tereticornis Sm. shelterbelts on crops

The economic yield of chickpea, lentil, wheat, cauliflower, barseem, and toria in a 12-m-wide strip to the south of 8 ± 1-year-old Eucalyptus tereticornis shelterbelts (three different locations) was reduced by more than half. Among all the crops under study, the yield of chickpea was reduced by the maximum extent. The content of soil phytotoxins was maximum in the litter-free top soil surface, compared to that at 30 or 60 cm depths, at all distances from the Eucalyptus. Maximum content of phytotoxins was found at 1 m from the tree line for all depths. These soil phytotoxins impaired the germination of Lens esculentum, thus indicating an allelopathic effect. It is included that the poor perfornce of crops in the sheltered area is related to an allelopathic effect of the Eucalyptus.     

Relationships between nursery practices and field performance for Eucalyptus plantations in Brazil

The 3.5 million ha of Eucalyptus plantations in Brazil support many domestic and industrial activities. In the pulpwood sector, forest productivity has increased from 12 to 40 m³ ha^–1 year^–1 through breeding and silviculturalpractices. Nurseries have fostered thisevolution with changes in container/substratetypes, propagation methods and specificinfrastructure for each plant growth phase.Eucalyptus plants are mainly produced bycuttings, using rigid tube containers filledwith vermiculite-organic compound substrates.Stock quality is based on morphologicalcharacteristics of the plants, andenvironmental conditions are highly significantfor plant performance. Performance is dependenton physiological short-term effects related tosurvival and long-term effects of genotype/rootmorphology related to tree development. Currentsilvicultural trends are reducing establishmentcosts but increasing the risk of using lowquality plants. The development of fieldperformance models and nursery physiologicaltests is recommended for Eucalyptusplantations in Brazil. Improved experimentaldesigns are needed to capture the interactionbetween plant quality and field performance.     

广西桉树林下植被抚育现状调查与分析

林下植被抚育是桉树人工林经营中的关键环节。采用调查问卷的方式,在广西区直林场开展桉树林下植被抚育现状的调查,对林下草灌保留、除草方式、除草剂使用等情况进行汇总分析。结果显示,各林场通常采取人工和除草剂两种方式相结合进行桉树林下植被抚育;第一年抚育1~3次,第二年至第四年抚育0~1次,采伐前抚育1次;林下植被抚育时草灌保留高度在10~20 cm以下,部分林场林下灌木保留10%~30%;抚育成本675~1 275元/hm²;使用的除草剂主要是草甘膦、草舒、草乙疏等,均含有草甘膦成分,施用量为7.5~18.75 kg/hm²。采取多样化的桉树林下植被抚育方式,以平衡桉树生长和林下植被多样性的关系,促进桉树人工林可持续经营。