森林生态系统稳定性研究进展

笔者简述了森林生态系统稳定性概念,介绍了天然林生态系统稳定性研究进展,并从人工林自身特性与稳定性、人工林生态系统稳定性的研究方法和人工林生态系统稳定性指标3方面综述了人工林生态系统稳定性的研究进展。人工林生态系统稳定性的研究需要对一定时间跨度内,特定空间的特定目标树种(纯林、混交林)进行研究,长远考虑,综合评价。     

公路边坡稳定性分析及治理

边坡稳定性的分析和评价是边坡工程的核心问题,是岩土工程领域的一个重要课题。文章分析了影响公路边坡稳定性的因素,并结合某公路段中的边坡进行稳定性状况分析,采用极限平衡传递系数法计算边坡稳定系数,同时针对其稳定性提出了治理方法。     

基于有限元分析的椅类家具稳定性研究

【目的】该文撰写的主要目的是为引起读者对椅类家具稳定性的重视,从设计阶段提升椅类稳定性。【方法】以弓形椅为例,运用建模法、有限元分析法以及试验验证法分析评估稳定性。【结果】分析评估的结果为弓形椅稳定性不合格,结合理论分析,提出了优化设计方案,有限元分析结果显示该优化方案稳定性显著提升,将优化后的设计方案制作样品并进行试验,试验结果再次验证了稳定性显著提升。【结论】基于两次有限元分析和试验验证得出运用有限元分析提升椅类稳定性是可行的结论。     

基于样地调查和森林资源数据的森林稳定性评价

摘要：森林稳定性是森林群落结构与功能的综合特征,是制定森林经营和管理方案的基础。本研究采用Delphi法从演替稳定性、抵抗力稳定性、恢复力稳定性、功能稳定性和环境稳定性等5个方面筛选出16个指标构成稳定性评价指标体系,利用秭归县9类不同森林类型157个样地调查数据确定指标权重,并基于森林资源调查数据,对区域森林稳定性进行了综合评价。结果表明：①建立的森林稳定性评价指标体系可以利用森林资源调查数据反映林分稳定性状态,值得推广;②秭归县有面积超过2/3的森林综合稳定性指数在0.4以上,仅约10%森林的综合稳定性指数低于0.3;③在各森林类型中,阔叶混交林平均稳定性指数最高,达到0.558,其后依次为针阔混交林、灌木林、针叶混交林、马尾松纯林、阔叶纯林、其他针叶纯林、经济林、柏木林,其综合稳定性分别为0.545,0.510,0.473,0.427,0.403,0.341,0.324,0.307。     

基于RBF神经网络方法的铀尾矿坝稳定性分析

为研究分析我国某铀尾矿坝的稳定性,以影响尾矿坝稳定性的14个指标为参数,运用MATLAB实现RBF神经网络的方法,采用实际数据对网络进行训练,结果得出了该铀尾矿坝的稳定性参数为3,属于一般安全铀尾矿坝,这对研究尾矿坝稳定性提供了重要的参考作用。     

杉木二种源核型和带型的比较研究

分析结果表明：两种源的核型、Ｃ－带、Ｃ－带带型均具有明显的杂合性。通过分析各种源的杂合稳定性，发现两者存在差异及两种源杂合稳定性差异产生的原因，并对染色体杂合稳定性与遗传稳定性的关系进行了讨论。     

干旱瘠薄山地侧柏人工林生态稳定性评价技术研究

乔木层、土壤和林下灌草层是侧柏人工林生态系统的重要组成部分,其质量优劣决定了生态系统的稳定性。以鲁中山地3个试验地的23个典型侧柏人工林为研究对象,通过野外调查和室内分析,采用因子分析法分别研究了侧柏林乔木层、土壤和林下灌草层的综合质量,进而计算得出侧柏人工林生态稳定性指数,从而对其生态稳定性进行了评价。按稳定性指数大小将侧柏林生态系统分为四个稳定性等级,分别为"高度稳定""中度稳定""低度稳定"和"不稳定"。通过相关性分析,筛选出14个观测指标共同组成侧柏林稳定性评价指标集。采用这些指标,可利用多元回归方程和逐步回归方程对侧柏林稳定性指数进行预测,推荐在侧柏林生态系统稳定性评价时选择使用。     

国外结构人造板尺寸稳定性的研究技术

国外结构人造板(如定向结构板、大片刨花板、华夫刨花板等)主要用作建筑材料,对产品的尺寸稳定性要求很高,许多研究者在如何提高产品尺寸稳定性方面作了大量的研究工作。文中综述了大量的科研成果,介绍了国外结构人造板尺寸稳定性的研究技术,包括引起结构人造板尺寸不稳定的缘由,结构人造板尺寸稳定性的评价方法,影响结构人造板尺寸稳定性的工艺因素以及提高结构人造板尺寸稳定性的措施。     

填土高度对高填方路堤稳定性影响分析

针对高填方路堤的稳定性进行分析,重点探讨了填土高度对路堤稳定性的影响.通过Geo-Slope有限元软件,建立了七种不同填土高度的路堤模型,分析稳定性系数.分析结果表明:路堤静力稳定系数随填土高度大致呈线性变化.     

城市地面沉降水准监测网基准点稳定性分析

地面沉降监测基岩起算点的稳定性是相对的,目前判断其相对稳定性的方法较多。作者依据工程实践,介绍了用最简单方便的方法对基岩点的相对稳定性进行判断、评价的成功经验。     

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。     

Natural Regeneration in Clear-cuts: Effects of Scarification,Slash Removal and Clear-cut Age

The effects of soil scarification (mounding), slash removal and clear-cut age on the natural regeneration in clear-cuts was evaluated using data from four sites in southern Sweden. The treatments were carried out during a good seed and establishment year for birch ( Betula pubescens Ehrh. and B. pendula Roth). Scarification had the strongest positive effect on the density of naturally regenerated seedlings, especially in birch, but also in pine ( Pinus sylvestris L.) and spruce [ Picea abies (L.) Karst]. Slash removal had a positive effect on birch density. No statistically significant effect of clear-cut age was found. In addition, no statistically significant interactions between clear-cut age and scarification or slash removal were found. The ingrowth of field vegetation was the fastest in areas that were not scarified, less rapid in areas scarified on old clear-cuts, and the slowest after scarification in fresh clear-cuts. In conclusion, it may be possible to control the density of birch during a good establishment year for birch. If birch is desired, the best combination of treatments is to remove the slash and scarify; otherwise, these treatments should be avoided.     

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.