木兰林区落叶松人工林可持续发展探讨

该文指出按可持续发展理论衡量,木兰林区大面积高密度落叶松人工纯林存在着严重的生态弊端:病虫害防治困难;森林防火困难;土壤理化性质恶化;林内太阳辐射严重受影响;林间地被植物减少。最后根据可持续发展理论,提出了对木兰林区落叶松人工纯林的改造对策。     

危害落叶松的两种线小卷蛾发生规律及监测策略

落叶松线小卷蛾和松线小卷蛾在塞罕坝林场混杂发生,主要危害华北落叶松嫩芽及枝梢。海拔1600m以上林区是其主要危害区,在沟顶阳坡最先成灾。成虫期降水量少利于其增殖。监测的重点是海拔1600m以上的华北落叶松纯林。     

塞罕坝人工落叶松用材林营养面积初探

<正>塞罕坝是个大型人工林林场,是我省落叶松人工林生产基地。目前大面积人工用材林均已郁闭,林场的任务由造林为主转入了全面经营为主。近年来,林业科技人员对林场各种经营措施做了很多调查研究,提出了不少新的见解。笔者试图通过对落叶松人工林营养面积的研究,探讨林分保留密度的问题,以便为其合理经营提供理论依据,更好地指导生产。 林木营养面积是人工林尤其是人工用材林经营中的一个关键问题,直接关系到木材生产的数量和质量。在用材林经营中,若能根据林     

长白落叶松人工用材林培育经济效益分析

长白落叶松 (Larixolgensis)是东北林区的乡土树种 ,其适应性强、生长快、用途广 ,在造林树种中占有重要位置。现根据经营水平 ,把长白落叶松人工用材林划分为现实林、丰产林和模式林 ,并从各年龄段的人工用材林培育投入和产出数据入手 ,采用国际上通行的 3种经济分析评价方法 ,对 3种人工用材林进行比较分析 ,以便为长白落叶松人工用材林栽培技术的推广及建立工业用材林基地提供决策依据。1　资料的收集与整理研究数据取自黑龙江省林业科学研究所的研究成果。在整理数据的过程中 ,对原始数据进行了认真的审查 ,各林龄的收获数据分布于Ⅱ产…     

塞罕坝林区森林可燃物含水率及火险预报

通过对塞罕坝林区9月至翌年6月中旬整个森林防火期枯草、落叶松枯落物、樟子松枯落物、落叶松嫩枝、樟子松嫩枝含水率的观测,研究了含水率随时间变化的动态规律;以当日气象因子中的温度、湿度与连续无降水日为自变量,利用多元统计的方法建立了3种可燃物类型的含水率回归方程,并编制了适合塞罕坝林区的森林火险预报系统.     

不同整地方式对落叶松人工林更新效果的影响

落叶松是华北北部塞罕坝地区的主要用材林树种,近几年来,随着用材林经营性采伐面积的逐渐增加,伐后更新的任务也随之加大。为探索不同整地方式对落叶松人工林生长的影响,对不同整地方式的人工更新进行了试验。试验结果表明,机械整地造林成活率、当年生长量都明显优于人工穴状整地方式。因此,建议在平坦、开阔的人工林皆伐作业地块上进行落叶松人工更新,最好在造林的前一年雨季之前采用机械整地,在坡度陡峭、狭窄地段结合人工整地,可以有效提高造林成活率、年生长量,节约投资,确保一次成林。     

坝上落叶松人工林主要害虫的发生与防治

塞罕坝机械林场大面积的落叶松人工纯林，自８０年代中以来虫害加剧，主要为落叶松尺蠖与落叶松腮扁叶蜂。经两年的调查研究，已摸索出它们在该林区的发生发展规律，并采取了有效的防治措施。     

落叶松锉叶蜂发生与环境因子的关系

落叶松锉叶蜂Pristiphora laricis(Hartig)是危害塞罕坝人工落叶松林的主要害虫,为控制其危害,掌握其发生规律,对影响落叶松锉叶蜂发生的环境因子进行了调查研究.结果表明,该虫的发生与林分、地形及气候因子关系密切,发生程度一般表现为纯林重于混交林,林缘重于林内,成熟林重于中幼龄林,树冠下层重于中上层,高海拔区重于低海拔区,阳坡重于阴坡,山脊重于山谷;温度越高越有利于幼虫的生长发育,幼虫孵化越早.     

施尿素二胺肥对华北落叶松生长的影响探讨

指出了华北落叶松是塞罕坝地区三大针叶用材林树种之一,也是塞罕坝地区栽植面积最大的树种,在维护塞罕坝地区生态环境方面起着重要作用。对6年生华北落叶松苗木施1∶1比例的尿素和二胺肥料,分析施肥对其生长发育的影响。结果表明:施尿素二胺后华北落叶松苗木的树高、基径、冠幅以及枝条的长度和基径都显著好于未施肥的苗木。提出了在华北落叶松幼林阶段可以适当施尿素二胺肥料来促进苗木的快速生长。     

林区落叶松育苗丰产试验小结

落叶松是针叶树种中的速生树种。材质优良、分布广、适应性强、为营造速生丰产用材林的主要树种之一。目前落叶松造林还是以人工植苗为主,直播尚有一定困难,因此落叶松的育苗工作还是一项重要的课题。特别是在林区环境由于地势高寒、无霜期短、落叶松育苗受自然条件及技术措施所限,当年生苗高平均不超过5厘米;同时产量也低,每平方米只有400—600株。这不仅大大的提     

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.     

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.     

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。     

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.