Nonlinear superposition model for the behavior of bolted joints

Summary A nonlinear superposition model was developed to assess the load-slip behavior of bolted joints consisting of a single bolt subjected to lateral loading at angles of load to grain. This model characterizes the bolted joint as a pair of orthogonal nonlinear springs aligned parallel and perpendicular to the grain of the wood members. The spring stiffnesses are quantified by a logarithmic or exponential function depending upon whether the connection softens or stiffens with increasing slip. The spring deformations are superimposed to determine the movement of each component of the connection. Deformations of connected members are added vectorially to determine their relative displacement. Spring constant were determined experimentally using metal-to-wood connections. Thick steel side plates were employed to limit the system deformation to the wood component. Wood members were evaluated at angles of load to grain ranging from zero to ninety degrees. Once the spring constants had been determined, the model was executed to predict the load-slip behavior of wood-to-wood connections. These predictions were compared to experimentally obtained load-slip values. The results indicate that the nonlinear superposition concept is a valid approach to predict joint deformation at angles of load to grain.The authors express their gratitude to the Fulbright-Hays Foundation and the Colorado State Agricultural Experiment Station for their financial support of this study     

Perceptions of Small Private Forest Owner’s Vulnerability and Adaptive Capacity to Environmental Disturbances and Climate Change: Views from a Heterogeneous Population in Southern Quebec,Canada

A study on the perception of vulnerability and adaptive capacity to climate change (CC) was realised among 27 small private forest owners (SPFOs) of a region in southern Quebec. In-depth semi-structured interviews were conducted with SPFOs of diverse profiles to better understand their perception of environmental disturbances and their needs to improve forest management in relation to global change and more precisely to CC. The main purpose of the research was to better understand whether perceptions of vulnerability and adaptive capacity to CC can constitute a barrier to proactive actions toward adaptation. Qualitative data shows a spectrum of attitudes and perceptions which highlight how SPFOs identify different potential and actual disturbances and assess the risk they represent for their forest-based activities. It shows how place-based experiences of environmental disturbances shape perceptions of vulnerability and capacity to adapt to disturbances. Factors such as access to financial resources and perceived resilience of forest ecosystem influence perceived adaptive capacity. Most SPFOs who participated in the research do not perceive their forest or forest-based activities to be vulnerable to CC, which may constitute a barrier to proactive adaptation to CC. The awareness of CC as a general phenomenon does necessarily translate into adaptation in forestry practices. Yet, many participants expressed a need for better access to knowledge and financial support to improve adaptive capacities to CC and broader environmental or economic stressors.     

柴达木盆地生态建设的思考

以对柴达木盆地退耕还林还草进展调研成果为基础,文中重点论述柴达木盆地生态现状及存在的问题,提出了柴达木盆地生态修复的若干对策:统筹规划,走可持续发展之路;严格保护,加强现有植被和野生动植物保护;因地制宜,加大生态修复力度;提质增效,推动生态环境高质量发展;以草定畜,发展盆地绿洲畜牧业;发展特色旅游,壮大绿色产业;开发与保护并重,走新型工业化和城镇化道路;宣传生态文化,做好生态监测预警。     

福建毛竹林生态培育与生态系统管理

针对福建毛竹林经营中存在的生态经济问题,提出毛竹林生态培育和生态系统管理的经营理念,旨在改变不合理的管理措施,因山因林制宜,切忌推广一种固定的经营模式.重建竹林生态系统的优化结构与功能体系,增加物种多样性,增强系统的自我调控能力,促进生物良性循环,提高竹林的抗逆性,确保毛竹林丰产、稳产,提高生态经济效益.     

林木低磷胁迫适应机制研究进展

土壤有效磷缺乏在自然环境中是一种非常普遍的现象,近年来世界各国针对植物的觅磷和耐磷机制进行了大量研究,然而目前相关的综述性报道多限于农作物,对林木低磷胁迫适应性的综述性报道尚不多见。在长期进化过程中,林木为利用土壤中现有的含量极低的有效磷,形成了各种适应低磷胁迫的机制。文中从林木根系的形态学变化、根系分泌物对土壤难溶性磷的活化作用、林木对土壤低浓度有效磷的吸收利用以及应对低磷胁迫的遗传调控等方面综述了低磷环境中林木的适应机制,为揭示林木对缺磷环境的适应机理、发掘林木自身对土壤有效磷高效率的吸收利用能力、以及进一步筛选林木的磷高效品种和合理经营管理人工林提供参考。     

集体林权制度改革的对策探讨

改革集体林权制度是解放林业生产力,增强林业活力的重要措施;是调整林业生产关系,进一步明晰林业产权,落实林业经营权,确保农民处置权的有效途径。通过改革集体林权制度,能充分调动各社会主体投资发展林业积极性,是我国林业发展的必经之路。     

浙江省花木蚧虫名录

在检索文献资料和调查的基础上,对浙江省花木蚧壳虫分布、种类和为害程度进行了补充整理,收录浙江省花木蚧虫12科97属258种.其中盾蚧科47属149种,仁蚧科1属1种,蚧科15属36种,球链蚧科1属1种,壶蚧科2属4种,链蚧科4属22种,绛蚧科1属3种,胶蚧科3属4种,绒蚧科1属7种,粉蚧科15属21种,珠蚧科6属9种,旌蚧科1属1种.     

云南松纵坑切梢小蠹成虫扬飞期测报研究

１９９２～１９９４年在玉溪市刺桐关林区对云南松纵坑切梢小蠹成虫进行了系统的调查。据系统观测，成虫梢转干历期约１４３天；干转梢历期约为１２９天；梢转干的高峰期为每年的１月２４日～２月１０日，计１８天，期间累计成虫数占总虫数的６６．６５％；干转梢高峰为每年的５月５～２５日，计２１天，期间累计成虫数占总虫数的６４．５６％。为便于监测测报，对成虫梢转干、干转梢过程中当地林木相应的物候期进行了观察     

Modeling the effects of introducing timber sales into volume-based tenure agreements

The problem of allocating cutting rights among competing licensees in Canada often entails assigning large discrete units of land to these licensees, typically for periods of fifteen to twenty-five years. The units of forest land are often large because it is economically infeasible for firms to maintain roads and operations widely dispersed across a forest. The assignment of these areas clearly frustrates the economic objective of sending the “right log to the right mill”. The objective of this research is to design a decision support model to evaluate the usefulness of incrementally introducing timber sales as an alternative method of allocation. An integer goal programming model was formulated to assign discrete units of land either to multiple competing mills or to timber sales — through which logs are then redistributed to these mills. The model is applied to a case study in British Columbia. Results from this case study indicate that the benefits of allocating forest land to timber sales decrease after approximately 40% of the annual allowable cut is redistributed through timber sales. The model can be used not only to evaluate but to plan for changes to Canada's forest tenure policy.     

培育森林资源要走内涵增长的新路子

本文提出了培育森林后备资源的指导思想要实现６个转变：（１）森林更新方式由营造成片人工纯林为主向“人天混”上转变，（２）森林培育方式由粗放经营向集约经营上转变；（３）森林培育重点由人工造林向抚育天然幼壮林上转变；（４）种苗工作由常规技术向生物遗传工程技术上转变；（５）经营机制由单一全民造林向多元化造林上转变；（６）营林机构单一职能部门向公司化转变。这些举措对森林经营和营林体制改革都具有现实意义。     

Current Research and Development on Deformation and Fixation of Bended Wood and Wood-based Composites

There are many advantages of bended wood,such as good-looking shape,simple process and low cost.The product,however,is easy to get recovery,which is urgent to be dealt with.This paper concludes the features of deformation and recovery of bended wood and wood-based composites and summarizes four treating methods to keep dimensional stability.Compared to bended solid wood,some elementary perspectives on the research of bended wood-based composites are presented.The purpose of this paper is to suggest:1)to investigate the optimum heating time and temperature that bended wood and wood-based composites need from the formation of deformation to the recovery and to the permanent fixation,according to its changes of dimensional stability such as curvature radius;2)to measure the composites comprised of wood and adhesives on the changes of stress relaxation,dynamic viscoelasticity and crystal1ization field;3)to quantitatively analyze changes of the major components in wood cell wall polymers as well as the composites under heat/steam treatment and untreated conditions.It will be helpful for subsequent research to clarify on the mechanisms of permanent fixation of bended wood and also contribute to that of wood-based composites.     

The Relationship of Oleoresin Exudation Pressure (or Lack Thereof) to Flow from Wounds

This paper reviews literature dealing with the measurement of oleoresin exudation pressure and the flow of resin from pine resin duct systems, with special reference to assessing tree resistance to bark beetle attack. The adequacy of a modification of Poiseuille's equation to predict resin flow is questioned, and resin pressure is judged to be an inadequate substitute for direct measurement of resin flow and estimation of tree resistance to bark beetle attack. Although direct measurement of resin flow is considered to be a superior method of eshating the relative resistance of trees to attack, it probably is not a totally satisfactory method for estimating resin flow, i.e., resistance to attack, associated with the progressive wounding done by bark beetles in their attempts to establish egg galleries. Multidisciplinary, integrated studies are needed to improve understanding of tree-bark beetle interactions.     

Nonlinear superposition model for the behavior of bolted joints

Summary A previously developed model to predict the load-slip relationship for mechanical joints using one bolt subjected to lateral loading (Part 1) was extended to incorporate the rotational resistance of joints containing two bolts. The rotation is about the long axis direction of the bolts, and considers the wood members oriented at arbitrary angles to the grain. The model utilizes nonlinear translational springs to represent the parallel and perpendicular to grain components of the reaction force present on each bolt resisting the applied moment. A series of experiments were conducted to determine the spring constants of bolted joints in axial loading and to verify the predictions of the mathematical model. Bolted joints subjected to a pure rotation were tested using combinations of steel plates and wood side members experiencing bolt reaction forces at various angles of load to grain. The results indicated an excellent agreement between theoretical predictions and experimentally obtained data.The authors wish to extend thanks to the Colorado State Agricultural Experiment Station for their financial support and to the Fulbright-Hayes Foundation for the educational scholarship and research funding provided to the project     

Adaptation of Asia-Pacific forests to climate change

Climate change is a threat to the stability and productivity of forest ecosystems throughout the Asia-Pacific region. The loss of forests due to climate-induced stress will have extensive adverse impacts on biodiversity and an array of ecosystem services that are essential for the maintenance of local economies and public health. Despite their importance, there is a lack of decision-support tools required to evaluate the potential effects of climate change on Asia-Pacific ecosystems and economies and to aid in the development of regionally appropriate adaptation and mitigation strategies. The project Adaptation of Asia-Pacific Forests to Climate Change, summarized herein, aims to address this lack of knowledge and tools and to provide support for regional managers to develop effective policy to increase the adaptive capacity of Asia-Pacific forest ecosystems. This objective has been achieved through the following activities: (1) development of a high-resolution climate downscaling model, ClimateAP, applicable to any location in the region; (2) development of climate niche models to evaluate how climate change might affect the distribution of suitable climatic conditions for regionally important tree species; (3) development and application of forest models to assess alternative management strategies in the context of management objectives and the projected impacts of climate change; (4) evaluation of models to assess forest fire risk and the relationship between forest fire and climate change; (5) development of a technique to assess ecosystem carbon storage using LiDAR; and (6) evaluation of how vegetation dynamics respond to climate change using remote sensing technology. All project outputs were developed with a focus on communication and extension to facilitate the dissemination of results to regional forest resource managers to support the development of effective mitigation and adaptation policy.     

板栗优质高产途径及其技术措施的研究

增加结果母枝粗度、减少生理落果、改善内腔光照条件、适当控制树冠体积、提高栗棚内的栗果数与栗果重、缩短由小年到大年的时间,以及适时防治病虫害是板栗优质高产的有效途径。同时提出了实现各途径的主要技术措施。     

Forest soils research and changing societal needs and values

The 10th North American Forest Soils Conference was held in Sault Ste. Marie, Canada, 20–24 July 2003. These conferences, held at 5-year intervals since 1958, are intended to provide a forum to discuss and summarize the state of knowledge on selected topics related to forest soils. Approximately 60 papers were presented on a variety of topics related to understanding and managing soils that support forests with particular emphasis given to field research, soil carbon, and site management/classification. We discuss the topics of this conference in relation to earlier ones and conclude that advances are made unevenly and that there is a need for new approaches to investigating many of the topics. We note the change in forest management that has occurred since the first of these conferences and the resulting changes needed in our approach to research and management. The need for interaction of scientists and clientele groups is noted as necessary for development of sound management and research policy. The interaction of scientific disciplines is needed to attack problems that have been difficult to elucidate. The challenge to forest soil scientists is to mesh their scientific interests with the needs of society to obtain the resources needed to advance science and provide information that will improve forest management.     

Field evolved resistance to carbamates,organophosphates, pyrethroids,and new chemistry insecticides in <Emphasis Type="Italic">Spodoptera litura</Emphasis> Fab. (Lepidoptera: Noctuidae)

Spodoptera litura Fab. (Lepidoptera, Noctuidae) is a polyphagous pest and has been shown to be resistant to a wide range of insecticides, which has led to sporadic out breaks of the pest and failure of crops. We were interested to establish if resistance to insecticides is diverse in different populations of S. litura collected from various areas with variable temperatures. We collected S. litura from eight different locations and compare the toxicity of insecticides. Resistance to the pyrethroids ranged from 20- to 11,700-fold compared with the Lab-PK (laboratory susceptible population). The resistance to bifenthrin was the lowest in a population collected from Multan and the highest to esfenvalerate in a population collected from Lodhran. Similarly, very high level of resistance to spinosad, indoxacarb, and methoxyfenozide was observed in all eight populations. In contrast, resistance to organophosphates was significantly lower than the pyrethroids, spinosad, indoxacarb, and methoxyfenozide, while toxicity of emamectin to field populations was similar to the Lab-Pk. The results are discussed in relation to integrated pest management (IPM) for S. litura with special reference to management of field evolved resistance to insecticides.     

Definition of priority areas for forest conservation through the ordered weighted averaging method

The general objective of this study was to evaluate the ordered weighted averaging (OWA) method, integrated to a geographic information systems (GIS), in the definition of priority areas for forest conservation in a Brazilian river basin, aiming at to increase the regional biodiversity. We demonstrated how one could obtain a range of alternatives by applying OWA, including the one obtained by the weighted linear combination method and, also the use of the analytic hierarchy process (AHP) to structure the decision problem and to assign the importance to each criterion. The criteria considered important to this study were: proximity to forest patches; proximity among forest patches with larger core area; proximity to surface water; distance from roads; distance from urban areas; and vulnerability to erosion. OWA requires two sets of criteria weights: the weights of relative criterion importance and the order weights. Thus, Participatory Technique was used to define the criteria set and the criterion importance (based in AHP). In order to obtain the second set of weights we considered the influence of each criterion, as well as the importance of each one, on this decision-making process. The sensitivity analysis indicated coherence among the criterion importance weights, the order weights, and the solution. According to this analysis, only the proximity to surface water criterion is not important to identify priority areas for forest conservation. Finally, we can highlight that the OWA method is flexible, easy to be implemented and, mainly, it facilitates a better understanding of the alternative land-use suitability patterns.     

Determination of embedding strength of wood for dowel-type fasteners

Embedding tests parallel and perpendicular to the grain were conducted to produce a database of embedding strength of wood for the design of dowel-type joints. Dowel diameters were 8,12,16, and 20mm. Embedding strength was evaluated by the 5% off-set method and a maximum load up to 5mm displacement according to EN383. The embedding strength parallel to the grain evaluated by the former method showed values close to those obtained with the latter method, but they showed a significant difference in tests conducted perpendicular to the grain. The embedding strength parallel to the grain was 0.9 times as large as the compressive strength parallel to the grain regardless of the evaluation method. The embedding strength perpendicular to the grain evaluated by the 5% off-set method was four times as large as the compressive strength perpendicular to the grain. When the embedding strength perpendicular to the grain was evaluated by a maximum load up to 5mm displacement according to EN383, the ratio of embedding strength perpendicular to the grain to the compressive strength perpendicular to the grain decreased as the dowel diameter increased.Part of this paper was presented at the annual meeting of the Architectural Institute of Japan 1999, Hiroshima, September 1999; the 50^th annual meeting of the Japan Wood Research Society, Kyoto, April 2000; and the World Conference on Timber Engineering 2000, Whistler, Canada, July–August, 2000     

Does growth temperature affect the temperature responses of photosynthesis and internal conductance to CO2? A test with Eucalyptus regnans

Internal conductance to CO(2) transfer from intercellular spaces to chloroplasts (g(i)) poses a major limitation to photosynthesis, but only three studies have investigated the temperature dependance of g(i). The aim of this study was to determine whether acclimation to 15 versus 30 degrees C affects the temperature response of photosynthesis and g(i) in seedlings of the evergreen tree species Eucalyptus regnans F. Muell. Six-month-old seedlings were acclimated to 15 or 30 degrees C for 6 weeks before g(i) was estimated by simultaneous measurements of gas exchange and chlorophyll fluorescence (variable J method). There was little evidence for acclimation of photosynthesis to growth temperature. In seedlings acclimated to either 15 or 30 degrees C, the maximum rate of net photosynthesis peaked at around 30 or 35 degrees C. Such lack of temperature acclimation may be related to the constant day and night temperature acclimation regime, which differed from most other studies in which night temperatures were lower than day temperatures. Internal conductance averaged 0.25 mol m(-2) s(-1) at 25 degrees C and increased threefold from 10 to 35 degrees C. There was some evidence that g(i) was greater in seedlings acclimated to 15 than to 30 degrees C, which resulted in seedlings acclimated to 15 degrees C having, if anything, a smaller relative limitation due to g(i) than seedlings acclimated to 30 degrees C. Stomatal limitations were also smaller in seedlings acclimated to 15 degrees C than in seedlings acclimated to 30 degrees C. Based on chloroplast CO(2) concentration, neither maximum rates of carboxylation nor RuBP-limited rate of electron transport peaked between 10 and 35 degrees C. Both were described well by an Arrhenius function and had similar activation energies (57-70 kJ mol(-1)). These findings confirm previous studies showing g(i) to be positively related to measurement temperature.