绥宁县以竹代木的探讨

绥宁县是一个县域经济严重依赖林业的山区县。由于企业对原材料的大量需求,致使木材可伐资源日渐减少,材质越来越差,径级越来越小,到了只能依靠采伐中幼林来满足企业原材料需求的境地。如何保持县域经济快速、健康可持续发展？培育开发竹资源、推行以竹代木是适合绥宁县林情的最佳途径。     

Effect of board density and layer structure on the mechanical properties of bamboo oriented strandboard

This study examined the effects of density and layer structure on the mechanical properties and dimensional stability of strandboard manufactured from moso bamboo (Phyllostachys pubescens). The strandboard was fabricated in a laboratory at five densities and three different structures including a randomly oriented homogenous board, a unidirectionally oriented homogenous board, and a three-layered board with a cross-oriented core layer (BOSB). Bamboo strand alignment distribution could be predicted using the von Mises distribution function. Bending properties increased with increasing density and were affected by layer structure. The modulus of rupture (MOR) of the threelayered board in the parallel direction increased remarkably compared with the random board MOR; in the perpendicular direction, it exhibited less strength reduction. Elastic properties of the three-layered board could be predicted using elastic constants of the unidirectional board. Internal bond strength (IB) was greatly affected by density, but the layer structure effect did not appear in IB. Linear expansion per unit moisture change ranged from 0.017 to 0.022 for random and three-layered boards; these values are comparable with or lower than values for commercial board.     

大力开发竹资源，缓解我国木材供需矛盾

介绍了我国木材和竹材资源的基本情况,对我国木材供需矛盾作了分析,提出了如何加大竹材资源的开发力度的建议。     

Development and structure of the terminal layer in bamboo culms

In bamboo, the inner lining of the culm wall towards the lacuna is designated as a terminal layer. It develops during culm elongation by separation of pith cells. Subsequently, these cells collapse thus forming a skin-like structure to be attached to a transition layer of the culm wall. The transition layer between the skin-like structure and the ground tissue consists of a few cell rows of mostly radially and axially shortened cells with often thickened walls. Both the skin-like structure and the transition layer exhibit structural differences between species. These characteristics of the inner culm wall have significance for culm seasoning and especially for the diffusion treatment with preservatives.     

Relationships between avian richness and landscape structure at multiple scales using multiple landscapes

Little is known about factors that structure biodiversity on landscape scales, yet current land management protocols, such as forest certification programs, place an increasing emphasis on managing for sustainable biodiversity at landscape scales. We used a replicated landscape study to evaluate relationships between forest structure and avian diversity at both stand and landscape-levels. We used data on bird communities collected under comparable sampling protocols on four managed forests located across the Southeastern US to develop logistic regression models describing relationships between habitat factors and the distribution of overall richness and richness of selected guilds. Landscape models generated for eight of nine guilds showed a strong relationship between richness and both availability and configuration of landscape features. Diversity of topographic features and heterogeneity of forest structure were primary determinants of avian species richness. Forest heterogeneity, in both age and forest type, were strongly and positively associated with overall avian richness and richness for most guilds. Road density was associated positively but weakly with avian richness. Landscape variables dominated all models generated, but no consistent patterns in metrics or scale were evident. Model fit was strong for neotropical migrants and relatively weak for short-distance migrants and resident species. Our models provide a tool that will allow managers to evaluate and demonstrate quantitatively how management practices affect avian diversity on landscapes.     

The influence of timber harvest on the structure and composition of riparian forests in the Coastal Redwood region

The composition and structure of riparian forests in the coast redwood region were analyzed in relation to the length of time since timber harvest, and the width of riparian buffer zone. Ten sites were sampled in the central range of the coast redwood forest type within a variety of post-harvest age groups and riparian buffer zone widths. Data was collected using randomly selected sample plots adjacent to perennial coastal steams. Correlation Fisher's r to z tests and two-tailed t-test were used to examine the relationship between the sample variables and the experimental parameters “years since harvest”, and “width of buffer.” Results indicate that canopy cover was negatively correlated to “years since harvest” with the highest level of canopy cover found on the youngest sites and the lowest level found on the old-growth sites. The hardwood to conifer dominance ratio and the basal area of Alnus rubra (red alder) were correlated negatively to both “years since harvest” and “buffer width” indicating that timber harvest favored hardwood species. Late seral associates such as Oxalis oregana (redwood sorrel), Anthyrium filix-femina (lady fern), and Vaccinium parviflorum (billberry) were found preferentially in older forests and sites with wider buffer zones, while non-native species such as Hedera helix (English ivy), Pampas cortedaria (pampas grass), and Myosotis latifolia (forget-me-not) were found preferentially in younger forests and areas with smaller buffer zones.     

Simultaneous determination of shear strength and shear modulus in glued-laminated timber using a full-scale shear block specimen

A newly developed full-scale shear block specimen was used to simultaneously determine the shear strength and shear modulus of glued-laminated timber. The shear modulus was calculated using the shear strain distribution measured by means of digital image correlation. To obtain the exact relationship between shear modulus and shear strength, the shear strain in the intended shear plane was measured. A relatively high correlation coefficient of 0.75 was found between the shear modulus and nominal shear strength in two types of glued-laminated timber tested: sugi (Cryptomeria japonica) and Douglas-fir (Pseudotsuga menziesii). Good correlation was also found between the density of middle lamina and shear strength. However, the relationships to density showed species dependence, which was not observed in the relationship between shear modulus and shear strength.     

The Summerwood: Springwood Ratio in Conifers: How it arises, varies, and affects end use for timber, board, and paper

A theoretical discussion of variation in summerwood and springwoodcontents among conifers. Three methods of measuring these, bycross-sectional area of logs, by dryweight fibre percentage,and by nominal specific gravity, are compared. High-summerwood tissues have a nominal specific gravity of 0?45or over; low-summerwood tissues have a specific gravity below0?45. All conifers have a low summerwood content in their juvenilewood or core wood formed towards their stem-tips. In Pinus,Larix, and Pseudotsuga the summerwood percentage increases markedlywith age, but only in the outer layers towards the butt; inPicea, Abies, and Tsuga similar increases occur, but high-summerwoodtissues are seldom found. Within any species, and for any particulargrowth rate, low-summerwood tissues are characteristic of regionsof high relative humidity where summer water deficits rarelyoccur, such as high altitudes, far northern latitudes, and themaritime climate of western Britain. High-summerwood tissuesdevelop where summer temperatures are high, with associatedstrong sunshine, low relative humidity, and frequent summerwater deficits. High-summerwood tissues have greater strength in compressionand bending, relative to volume; but low-summerwood tissueshave greater strength relative to their weight. Low-summerwoodmaterial has proved satisfactory for most structural purposes,and for the manufacture of several kinds of artificial board.Its technical properties for the making of many types of paperare excellent, provided high resistance to tearing is not required.Likely summerwood content should guide planting programmes andmarketing policies.     

Biomass,harvestable area,and forest structure estimated from commercial timber inventories and remotely sensed imagery in southern Amazonia

The purpose of this study was to determine if spatially-explicit commercial timber inventories (CTI) could be used in conjunction with satellite imagery to improve timber assessments and forest biomass estimates in Amazonia. As part of a CTI, all commercial trees ≥45 cm DBH were measured and georeferenced in 3500 ha of a logging concession in NW Mato Grosso, Brazil. A scientific inventory was conducted of all trees and palms ≥10 cm DBH in 11.1 ha of this area. A total of >20,000 trees were sampled for both inventories. To characterize vegetation radiance and topographic features, regional LANDSAT TM and ASTER images were obtained. Using a stream network derived from the ASTER-based 30 m digital elevation model (DEM), a procedure was developed to predict areas excluded from logging based on reduced impact logging (RIL) criteria. A topographic index (TI) computed from the DEM was used to identify areas with similar hydrologic regimes and to distinguish upland and lowland areas. Some timber species were associated with convergent landscape positions (i.e., higher TI values). There were significant differences in timber density and aboveground biomass (AGB) in upland (6.0 stems ha⁻¹, 33 Mg ha⁻¹) versus lowland (5.4 stems ha⁻¹, 29 Mg ha⁻¹) areas. Upland and lowland, and timber and non-timber areas could be distinguished through single and principal component analysis of LANDSAT bands. However, radiance differences between areas with and without commercial timber on a sub-hectare scale were small, indicating LANDSAT images would have limited utility for assessing commercial timber distribution at this scale. Assuming a 50 m stream buffer, areas protected from logging ranged from 7% (third order streams and above) to 28% (first order and above) of the total area. There was a strong positive relationship between AGB based on the scientific inventory of all trees and from the commercial timber, indicating that the CTI could be used in conjunction with limited additional sampling to predict total AGB (276 Mg ha⁻¹). The methods developed in this study could be useful for facilitating commercial inventory practices, understanding the relationship of tree species distribution to landscape features, and improving the novel use of CTIs to estimate AGB.     

关于加快发展我国竹材制浆造纸的一些看法

我国木材资源匮乏，每年都要耗费大量外汇进口纸和纸浆，进口量占了我国纸和纸板产量的一半以上。竹材是制浆造纸的优质原料，充分利用我国产竹大国的优势，发展竹材制浆造纸，有利于缓解我国严重的木材供需矛盾和造纸工业的可持续发展，有利于森林资源和生态环境的保护，认为竹材制浆造纸亏本的观点是不符合实际的。当前，随着我国经济建设的快速发展和经济结构调整，竹材制浆造纸正在跨入一个大发展的新时期，需要统一认识，顺应市场发展的需要，努力建设好竹材制浆原料基地，推动我国竹材制浆造纸快速发展。