高黎贡山南段4种典型植被类型枯落物层持水性能研究。

采用野外测定与室内实验分析相结合的方法,对高黎贡山南段4种典型植被类型枯落物层持水性能进行对比研究。研究结果表明,（1）枯落物总厚度为天然阔叶林＞旱冬瓜林＞杉木人工林＞次生阔叶林,其中未分解层枯落物厚度为旱冬瓜林＞天然阔叶林＞杉木人工林＞次生阔叶林,半分解层枯落物厚度为天然阔叶林＞杉木人工林＞旱冬瓜林＞次生阔叶林;枯落物总贮量为天然阔叶林＞次生阔叶林＞旱冬瓜林＞杉木人工林,其中未分解层枯落物贮量为次生阔叶林＞天然阔叶林＞杉木人工林＞旱冬瓜林,半分解层枯落物贮量为天然阔叶林＞旱冬瓜林＞次生阔叶林＞杉木人工林;（2）未分解层及半分解层最大持水量均为天然阔叶林＞杉木人工林＞旱冬瓜林＞次生阔叶林;（3）未分解层及半分解层持水速度均为天然阔叶林＞杉木人工林＞旱冬瓜林＞次生阔叶林。因此,4种植被类型枯落物层持水性能以天然阔叶林为最好。     

我国森林生态系统枯落物现存量研究进展

在参考大量相关文献的基础上,对我国森林生态系统枯落物现存量研究进展进行了归纳总结。我国枯落物现存量的研究主要集中在亚热带和温带,热带相对较少;枯落物现存量的研究主要采用收获法,但取样样方的布设、面积、数量及取样时间等尚没有统一的规定;在大区域尺度上,气候是影响森林枯落物现存量变化的主导因子,不同气候带森林枯落物现存量的大小顺序为温带>亚热带>热带;森林枯落物现存量还受林分起源、群落组成和结构、群落发育阶段、土壤、地形条件及干扰的影响。文中还针对全球变化背景下我国森林枯落物现存量研究中存在的问题及今后的研究方向进行了探讨。     

大沙河自然保护区森林枯落物水源涵养功能初步研究

为合理调整自然保护区内森林结构布局,充分发挥森林的水源涵养功能,对7种不同森林群落类型下的枯落物进行了储量、持水量及吸水速率的测定。结果表明:各森林群落类型枯落物储量排序为针阔混交林篦子三尖杉林人工杉木林阔叶林红豆杉林竹林灌木林;各森林群落类型枯落物最大持水量排序为:阔叶林针阔混交林竹林红豆杉林人工杉木林灌木林篦子三尖杉林;各森林群落类型枯落物在持水作用较强的前2h内,总吸水速率大小结果为阔叶林针阔混交林人工杉木林红豆杉林灌木林竹林篦子三尖杉林。0~2h各林分林下地表枯落物层持水量几乎呈直线上升,2h后吸水速率上升速度逐渐变缓并趋于最大值;0~2h各林分林下地表枯落物层吸水速率几乎都呈直线下降,2h后吸水速率下降速度逐渐变缓并趋于动态平衡。综合分析了7种不同森林群落类型下枯落物的水源涵养功能得出优势群落为针阔混交林和阔叶林,劣势群落为灌木林。     

湖州市主要林分类型枯落物和土壤持水能力

对湖州市7种主要林分类型植被的枯落物层持水性能和土壤层蓄水能力进行了研究.结果表明:7种林分类型林地枯落物层和土壤层的持水量存在差异,枯落物现存量变化范围为5.92～ 9.88 t/hm2,土壤总孔隙度的变化范围为49.00％ ～58.11％,土壤最大持水量的变化范围为1 934.8～2 324.4 t/hm2.枯落物最大持水量依次为针阔混交林＞常绿阔叶林＞疏林＞马尾松林＞灌木林＞杉木林＞毛竹林,林地水源涵养能力依次为针阔混交林＞常绿阔叶林＞疏林＞灌木林＞毛竹林＞马尾松林＞杉木林,毛竹林的林地持水能力要好于马尾松林和杉木林.全市非毛管总蓄水量为12 919.2万t,最大蓄水量为43 617.7万t.     

燕山东段森林群落及灌木群落枯落物的研究

燕山东段森林群落枯落物现存量平均为４．３５－２８．６７ｔ／ｈｍ＾２，以山杨混交林、松栎混交林、椴树混交林最高，栎林和油松林次之，侧柏林最低。灌木群落枯落物现存量平均为４．１５－１８．９４ｔ／ｈｍ＾２，低于森林群落。森林枯落物现存量受树种组成、年龄、立地条件及人为干扰的影响。其中，人为干扰影响最大，几乎使枯落物损失殆尽。森林枯落物营养元素总贮量０．１７６－１．５３４ｔ／ｈｍ＾２，最大贮水量３．９－５     

高黎贡山南段4种典型植被类型枯落物层持水性能研究

采用野外测定与室内实验分析相结合的方法,对高黎贡山南段4种典型植被类型枯落物层持水性能进行对比研究。研究结果表明,(1)枯落物总厚度为天然阔叶林>旱冬瓜林>杉木人工林>次生阔叶林,其中未分解层枯落物厚度为旱冬瓜林>天然阔叶林>杉木人工林>次生阔叶林,半分解层枯落物厚度为天然阔叶林>杉木人工林>旱冬瓜林>次生阔叶林;枯落物总贮量为天然阔叶林>次生阔叶林>旱冬瓜林>杉木人工林,其中未分解层枯落物贮量为次生阔叶林>天然阔叶林>杉木人工林>旱冬瓜林,半分解层枯落物贮量为天然阔叶林>旱冬瓜林>次生阔叶林>杉木人工林;(2)未分解层及半分解层最大持水量均为天然阔叶林>杉木人工林>旱冬瓜林>次生阔叶林;(3)未分解层及半分解层持水速度均为天然阔叶林>杉木人工林>旱冬瓜林>次生阔叶林。因此,4种植被类型枯落物层持水性能以天然阔叶林为最好。     

内蒙古林科院树木园华北落叶松人工林枯落物和土壤层的水文效应

森林枯落物和土壤层具有重要水文功能,对内蒙古林科院树木园华北落叶松人工林林下枯落物现存量、持水特征、有效拦蓄量及林地土壤的物理性质、贮水特征进行了研究.研究结果显示:华北落叶松人工林枯落物未分解层、半分解层的最大持水深分别为0.88 mm、1.63 mm,林分枯落物的有效拦蓄量为1.64 mm.不同土层深度的土壤有效贮...     

喀斯特地区不同森林类型枯落物储量及其持水特性比较

对施秉县白云岩区4种森林类型枯落物的存储量和持水特性进行研究。结果表明:所有森林类型的总枯落物现存量变动范围为8.6t/hm~2~37.1t/hm~2,枯落物总现存量大小依次为水竹林(37.1t/hm~2)﹥针阔混交林(28.9t/hm~2)﹥阔叶林(26.7t/hm~2)﹥针叶林(8.6t/hm~2);阔叶林持水率最大(543.16%),针叶林最小(357.92%);枯落物层的持水率与浸泡时间呈显著对数关系,而吸水速率与浸泡时间呈显著幂函数关系。本研究结果可为喀斯特石漠化治理和植被恢复提供重要科学依据。     

毛竹林等不同森林类型枯落物水文特性的研究

2002年12月采集位于浙江省富阳市毛竹产区试验林分枯落物,测定毛竹纯林、竹阔混交林枯落物的水文特性并与阔叶林对照,结果表明:24h内枯落物持水进程可以分为两个阶段:阶段Ⅰ(0～8h)和阶段Ⅱ(8～24h)。阶段Ⅰ不同林分枯落物持水量约占饱和持水量(24h)的比例范围为:23.85%～30.39%。枯落物持水量随浸泡时间延长而增加,6～8h后基本趋于稳定。枯落物浸泡1h的平均持水率为1.958g·g-1·h-1,浸泡4h后降低为0.419g·g-1·h-1,降低至初始值的22%。在浸泡2～8h后,毛竹纯林枯落物持水率是竹阔混交林的1/3～1/8。阶段Ⅱ各林分枯落物在不同时段的持水量表现出相似规律,即在8～12h呈现下降趋势,12h后各时段枯落物持水量又有所回升至24h达到饱和。相比之下竹阔混交林枯落物持水量下降幅度最快。各森林类型枯落物对降水的拦蓄能力依此排序为:常绿阔叶林>竹阔混交林>未垦复毛竹纯林>垦复毛竹纯林。从林地枯落物的现存量及饱和持水量着眼,竹阔混交林的水文生态效应优于毛竹纯林而次于常绿阔叶林,垦复毛竹林不利于枯落物水文效应的发挥。     

百花山5种典型林分枯落物蓄积量及持水特征

以北京百花山国家级自然保护区5种典型林分类型为研究对象,对其枯落物层的蓄积量及持水特性进行定量分析。结果表明:5种林分枯落物蓄积量中华北落叶松林(15.75t/hm^2)>核桃楸林(9.99t/hm^2)和白杄林(10.27t/hm^2)>蒙古栎林(7.34t/hm^2)>黑桦(7.04t/hm^2),针叶林枯落物层中未分解层蓄积量占比明显高于阔叶林分;枯落物蓄积量总持水量中华北落叶松林(2.91mm)>核桃楸林(2.77mm)>黑桦(1.90mm)与蒙古栎林(1.83mm)>白杄林(1.29mm),针叶林枯落物层中未分解层持水量大于半分解层,而阔叶林枯落物层则表现为半分解层大于未分解层。针叶林未分解层枯落物的蓄积及水文效应高于半分解层,而阔叶林半分解层枯落物的蓄积及水文效应高于未分解层。     

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.     

Decomposition and nutrient loss from prunings of different contour hedgerow species in tea plantations in the sloping highlands of Sri Lanka

Contour hedgerows of multipurpose tree species in the sloping tea lands of Sri Lanka are expected to reduce soil erosion and also add significant amounts of plant nutrients to the soil via periodic prunings. The objective of this experiment was to characterize the biomass decomposition pattern and quantify the amount of nutrients added through prunings of six tree species (Calliandra calothyrsus, Senna spectabilis, Euphatorium innulifolium, Flemingia congesta, Gliricidia sepium and Tithonia diversifolia) currently being used in hedgerows associated with tea. Withered leaf and stem prunings (50 g) were enclosed in 2-mm litter bags, placed at 5-cm depth and retrieved after one, three, six, nine and 12 weeks. Loss of initial dry weight, N, P and K was measured. Single exponential decay function adequately described both dry weight and nutrient loss. Tree species differed significantly in their rate of breakdown with decomposition constants (k) varying from 0.0299 to 0.2006 week⁻¹ for leaves and from 0.0225 to 0.0633 week⁻¹ for stems. Gliricidia showed the highest k for leaves with the rest in the following descending order: Senna > Tithonia ≥ Euphatorium > Calliandra > Flemingia. A similar pattern was observed for loss of all nutrients with Calliandra and Flemingia always having lower k values than the rest. Although N immobilization was not observed, immobilization of P and K was observed during the first week of incubation in some species, particularly in stem prunings. Annual biomass of prunings differed significantly between tree species in the following descending order: Calliandra > Senna > Flemingia > Tithonia > Gliricidia > Euphatorium. Calliandra added the greatest amount of nutrients annually to the soil with Euphatorium adding the least. Calliandra prunings provided the annual total K requirement and 49% of the N requirement of mature tea. However, none of the species provided more than 5% of the P requirement. It is concluded that among the tree species tested, Calliandra and Flemingia are the most suitable for contour hedgerows in tea plantations of this agroclimatic region because of their higher soil nutrient enrichment capacity and slower decomposition rates which would minimize leaching losses. This revised version was published online in June 2006 with corrections to the Cover Date.     

Growth of Phlebiopsis gigantea in wood of seven conifer species

Heterobasidion parviporum and Heterobasidion annosum are widely distributed root‐rot fungi that infect conifers throughout Europe. Infection of conifer stumps by spores of these pathogens can be controlled by treating fresh stumps with a competing non‐pathogenic fungus, Phlebiopsis gigantea. In this study, growth of three Latvian strains of P. gigantea and the biological control agent ‘Rotstop’ strain was evaluated in stem pieces of Norway spruce, Scots pine, lodgepole pine, Douglas‐fir, Weymouth pine, Siberian larch and Sitka spruce. The growth rates of one H. parviporum and one H. annosum isolate were also measured in the same stem pieces. The growth rate of P. gigantea varied greatly in wood of different conifer species. It was higher in the three pine species, lower in Norway spruce and lowest in Sitka spruce and Siberian larch, and in Douglas‐fir, this fungus did not grow. The largest area of wood occupied by P. gigantea was in lodgepole pine. Growth of Latvian isolates of P. gigantea in the wood of Pinus and Picea species was comparable to that of the Rotstop isolate. Consequently, stump treatment with local P. gigantea isolates should be recommended. However, our results suggest that Douglas‐fir stump treatment against Heterobasidion by P. gigantea may be ineffective and other stump treatment methods should be considered.     

Effects of Seed Weight and Seed Type on Early Seedling Growth of Pinus sylvestris under Harsh and Optimal Conditions

The effects of seed weight and seed type on seedling growth of Pinus sylvestris (L.) were studied by seeding individually weighed orchard and stand seed in different mixtures under harsh (direct seeding in field) and optimal (seeding in nursery) conditions. In the nursery experiment an increase in the seed weight from 3 to 7 mg increased the seedling height by 10-27% and total weight by 27-113%, and decreased the height/diameter ratio by 5-6% after 2 yrs. With elimination of seed weight effects, orchard seedlings were 2% taller than stand seedlings in year 2. Without elimination of seed weight effects, orchard seedlings were 7-13% taller. In the field experiment an increase in the seed weight from 3 to 7 mg increased seedling height by 18-65%, stem volume by 81-274% and the number of top-buds by 23-34% in year 5. After elimination of seed weight effects, orchard seedlings were 7-13% taller than stand seedlings and without elimination of seed weight effects 20-21% taller after 5 yrs. Even after elimination of both seed weight and genetic effects orchard seedlings were 3-9% larger than stand seedlings in the field experiment. In conclusion, the influence of seed weight and seed type on growth traits and slenderness is highly significant and the influence seems to be greater in harsh conditions.     

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.     

Potential to harness superior nutritional qualities of exotic baobabs if local adaptation can be conferred through grafting

Baobab leaves form an important part of the local diet in Sahel countries and elsewhere in Africa. Existing leaf nutritional data and agroforestry performance information are based solely on Adansonia digitata L., the baobab of continental Africa. The introduction potential of Adansonia species from the center of diversity in Madagascar and from Australia remains untapped. To assess this potential, the mineral contents and B₁ and B₂ vitamin levels of dried baobab leaves were determined for five-year old trees of A. digitata, A. gibbosa (A. Cunn.) Guymer ex D. Baum, A. rubrostipa Jum. & H. Perrier (syn. A. fony Baill.), A. perrieri Capuron and A. za Baill. grown in an introduction trial in Mali. Nutritional data were evaluated against survival and vigor to identify promising germplasm. Leaf vitamin and crude protein contents were highest in the Madagascar species, especially A. rubrostipa (B₁ 88 mg 100 g⁻¹, B₂ 187 mg 100 g⁻¹, protein 20.7% dry weight). However, the local species far outperformed the introductions in survival, tree height, basal diameter and resistance to termites. We suggest grafting as a way of harnessing the vigor of well-adapted local baobab varieties to the superior nutritional profiles of A. rubrostipa and others. Cross-species grafting tests in Adansonia were successful, thus creating new agroforestry possibilities with different scion/rootstock combinations.     

Modelling of adequate pretwist for obtaining straight timber

Abstract

Wood in general and wooden studs in particular are often distorted owing to uneven shrinkage during the drying process in the sawmill. Twist is often the most detrimental of all types of distortion, and it is caused by spiral grain in combination with variations in moisture content. For sawmills, the objective is to produce dried, straight boards, and one method of dealing with boards with excessive spiral grain is to sort them out and then dry them in a pretwisted position to obtain straight boards after drying. A model using the finite element (FE) method for the simulation of drying twist distortions was first calibrated against laboratory experiments in which boards were dried with and without restraints and pretwists. After the calibration, the FE results were compared with industrial test results for boards that were dried without restraints or with restraints with zero pretwist, i.e. straight restraints. The FE model used an elastic–ideally plastic material model to obtain permanent deformations. The calibration was to set the yield stresses so that there was a good match between FE results and results from the laboratory experiments. The comparison between the industrial test results and the FE results showed that the FE model is capable of realistic simulations of drying boards with and without restraints and presumably also pretwists.     

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。