卫闽光皮桦林优势种群的种间联结性研究

应用方差比率VR、种间联结系数AC及X2检验等方法,对福建卫闽光皮桦林优势种群的种间联结性进行了定量研究,结果表明,在卫闽光皮桦林8个优势种组成的28个种对中,正联结种对有12个,占联结种对总数的42．9％,负联结种对16个,占57．1％。正联结种对中,呈显著正联结种对有3个,占总种对数的10．7％;负联结种对中,是显著负联结种对有1个,占总种对数的3．6％。多数种群间联结性不显著说明卫闽光皮桦林还不成熟,群落结构种和种类组成还不完善和稳定,整个林地仍处于变化和演替中。     

光皮桦不同造林密度林分生长效应分析

对6年生光皮桦不同造林密度林分生长效应进行了分析,结果表明：光皮桦不同造林密度对林木胸径、冠幅及材积生长差异极显著,树高生长差异不显著。不同造林密度对林分生长的影响,6年生时光皮桦林分蓄积量与造林密度大小成正相关,密度越大,林木分化越早,影响了光皮桦后期的生长。因此,选择合理的造林密度对林分正常生长发育及综合利用是十分重要的。此试验对光皮桦4个不同造林密度处理,以1100株／hm2最好。     

光皮桦生长与环境因子的关系研究

以雅长林场九龙分场13 a光皮桦纯林作为研究对象,探索土壤酶活性、土壤化学元素以及林分温度对光皮桦生长的影响,采用相关性分析探究影响光皮桦生长的主要环境因子。结果表明,土壤酶活性与光皮桦树高、胸径、冠幅呈正相关,且相关性均较高,光皮桦生长受土壤酶活性的影响作用较大;除速效磷外,土壤中其他化学元素含量与光皮桦生长量相关性较高,其中总氮含量相关性最高,对光皮桦的生长起主导作用;光皮桦林分内地表温度、空气温度与其生长量的相关系数均较低,其与光皮桦的生长没有直接影响;土壤中的蔗糖酶活性、酸性磷酸酶活性、土壤总氮与光皮桦的相关性相对较高,因此,土壤蔗糖酶活性、酸性磷酸酶活性、总氮含量可能是影响光皮桦生长的主导环境因子。     

黔西北地区光皮桦次生林主要群落类型初步研究

按照典型抽样方法,调查了贵州西北部地区28个光皮桦天然次生林样地,根据样地乔木、灌木树种优势种、亚优势种的构成情况进行群落的初步分类。结果表明,该地区光皮桦次生林主要有光皮桦纯林、川榛-光皮桦林、光皮桦响叶杨混交林、光皮桦杉木混交林和光皮桦马尾松混交林5种类型。各类型林分光皮桦的密度较大,树高和胸径生长多处于中等至偏低水平,蓄积量生长则处于偏低至很低水平,绝大多数达不到用材林的生长指标和经济价值。现有光皮桦天然次生林的保护和利用目标,宜以水土保持林为主。如要培育生产力水平较高、经济价值较大的光皮桦用材林,应当选择立地条件较好的造林地,采用人工植苗造林的方式。     

低效灌木林地改种光皮桦人工林后地力状况分析

通过研究低效灌木林改种光皮桦人工林后的地力状况，结果表明：经过改种后形成的光皮桦林分对土壤的物理性状具有改良作用；且光皮桦林分各项肥力指标均比灌木林地高，表明该树种林分对地力具有较好的改良作用；同时，各种土壤酶活性均随林龄增大而增强，表明光皮桦林分林地养分的转化、利用和归还处于一个良好循环过程中。研究结果可为低效灌木林的改造和光皮桦人工林的经营管理提供参考。     

施肥对光皮桦生长量影响初探

在福建安溪虎邱官埔林场对4a生光皮桦林分进行施肥试验。1a后,调查光皮桦的胸径和树高,计算不同施肥试验对光皮桦生长量的影响。结果表明:施肥对4a生光皮桦的生长有明显促进作用,不同施肥处理对光皮桦胸径、树高、材积生长量影响都达到显著水平,与对照(未施肥)相比,胸径增幅为21.07%～32.23%,树高增幅为19.78%～32.23%,单株材积增幅达86.58%～115.72%,本试验以尿素(N含量46%)和洋丰复合肥(N:P:K=15:15:15)各75g混合施肥方式效果最好,单株材积平均增幅达115.72%。     

乡土绿化树种——野生光皮桦生长状况研究

进行了野生光皮桦的生态学特征、用途、分布及开展野生光皮桦研究,针对引种的意义及在对野生光皮桦进行树干解析分析后,对野生光皮桦高生长、径生长特点进行了论述,并对培育和经营光皮桦提出了建议。     

红桦扦插育苗

<正>红桦又名红皮桦、纸皮桦、鳞皮桦,属桦木属桦木科,落叶乔木,主要生长在中国西部的大森林中,山西、甘肃、陕西、河南、河北、湖北、云南及四川等均有分布。甘肃省主要分布在小陇山、白龙     

不同造林密度和混交树种对光皮桦幼林生长的影响

通过对光皮桦不同造林密度、不同混交树种的试验研究,结果表明:光皮桦不同造林密度林分的生长有较大差异,其胸径、冠幅由大到小依次为:1 100株.hm-2、800株.hm-2、1 600株.hm-2、2 500株.hm-2,树高以1 100株.hm-2的林分最大,其余比较相近。光皮桦与不同树种混交生长有较大差异,各生长指标以杉木×光皮桦混交林最好,其余依次为:福建柏×光皮桦、木荷×光皮桦、马尾松×光皮桦;光皮桦纯林生长指标与福建柏光皮桦混交林比较接近。杉木×光皮桦和福建柏×光皮桦是较好的混交组合。     

光皮桦引种栽培试验研究

2007年开始引种光皮桦,栽植后对其生长量在不同立地条件下进行对比试验。结果表明:光皮桦造林成活率、初生长等表现良好;不同海拔、不同坡向对光皮桦的高生长影响不大;不同坡位、不同土层厚度对光皮桦的高生长影响显著。因此,光皮桦造林应选择中、下坡位,土层深厚的地段为好,光皮桦在该区域可以推广种植。     

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.     

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.     

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.     

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.     

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.     

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。