当今杨树发展之我见

藁城市位于华北平原腹地、省会石家庄东侧 30 km,地理坐标为北纬 37°51′～38°1 9′,东经 1 1 4°39′～ 1 1 4°59′,年平均气温1 2 .5℃ ,无霜期 1 89d,平均降水量 4 98mm,既是农业高产区 ,又是平原绿化和农田林网化及河北省省会周围绿化重点地带。杨树是藁城市平原绿化和农田林网化主栽树种 ,6 0年代主要推广品种为加拿大杨 ,由于病虫危害严重、生长缓慢和材质较差 ,70年代改推品种为大官杨和北京杨。大官杨由于天牛危害严重 ,很快被淘汰。北京杨在北京地区表现较好 ,干形通直 ,前期和后期生长速度均较快 ,由于区域限制 ,北京杨在藁城…     

藁城市平原绿化发展情况调查

藁城市位于华北平原腹地 ,省会石家庄东侧 30km处 ,地理坐标为北纬 37°5 1′～ 38°19′ ,东经 114°39′～ 114°5 9′ ,年平均气温 12 .5℃ ,无霜期 189d ,平均降水量4 98mm。全市东西横距 2 6km ,南北纵向 5 1km ,总面积836km2 。全市 14个乡镇 ,1个经济技术开发区 ,2 4 0个行政村 ,总人口 73万 ,耕地面积 5 .5万hm2 ,基本农田面积4 .3万hm2 。全市四旁植树统计数据为 90 0万株 ,其中农田林网约占 35 %左右 ,约 32 0万株 ,农田林网折合占地面积约 2 0 0 0hm2 ,保护农田面积 5 .3万hm2 ,林网控制率95 %以上。平原绿化尤其是农田林网化在…     

沭阳杨树速生丰产的几项措施

江苏沭阳位于苏北平原,地处南北气候交汇地带,属暖温带半湿润季风气候,四季分明,日照充足,雨量充沛,具备杨树生长的良好自然环境条件。沭阳杨树栽植历史悠长,全县现有杨树成片林87万亩、农田林网200万亩。杨树是优良的平原造林树种之一。在沭阳,杨树在改善生     

农田林网更新改造技术的研究

山东省十分重视农田林网的营造和发展 ,已取得较好生态、经济和社会效益。但由于种种原因 ,造成部分林网出现树龄过大、生长衰退 ,树种单一、结构不善 ,品种老化、病虫害严重等问题 ,严重地影响其防护功能和经济效益。因此 ,开展农田林网更新改造技术的研究 ,对提高林网更新质量和经营水平 ,实现其防护功能和综合效益的持续性和稳定性均具有重要意义。为此 ,我们采用定位试验和调查研究相结合的方法 ,对位于鲁西南黄泛平原区成武县的农田林网的更新年龄、更新方式和改造技术等作了系统研究 ,取得一些进展 ,现将研究结果总结如下。1　主要树…     

山东经济林树种资源调查与发展规划

山东地处中国东部 ,北纬 3 4°2 2′～ 2 8°2 3′和东经 114°47′～ 12 2°43′之间 ,东临海洋 ,西接大陆 ,总面积为15 .67km2 。地形中部突起 ,为山区丘陵区 ;东部半岛大部分是起伏和缓的波状丘陵区 ;西部 ,北部是黄河冲积而成的鲁西北平原。山东气候属暖温带季风气候类型 ,     

藁城市农田林网的发展状况与建议

农田林网是农业现代化的重要组成部分 ,生态体系的主体 ,也是农业基本建设中一项极其重要的内容 ,所以 ,它的效益是多方面的。为使林网建设较好的发展 ,现就藁城市林网发展状况和今后如何营建高标准、高质量的农田林网 ,谈以下几点意见 :1　基本情况概述河北省藁城市 ,位于北京西南 2 6 4km、石家庄正东 31 km。地理座标为东经 1 1 4°39′～ 1 1 4°59′,北纬 37°51′～ 38°1 8′。属太行山洪积平原。土壤有褐土与潮土两大类。海拔 39～ 6 5m,地势向东南倾斜缓降。由于过去境内的滹沱河等 3条河流的改道和变迁 ,形成一些沙丘、洼地、河岗…     

农田林网更新改造技术与效果评价

农田林网是平原农区构成农田防护林体系的重要组成部分。目前,山东省部分林网存在树龄过大、结构不合理、树种品种老化、病虫害严重等问题,迫切需要更新改造,提高林网质量,实现其防护功能和综合效益的持续性和稳定性。为此,山东省科委于１９９１年下达《农田林网更新...     

中潜3号杨山区壮苗培育技术

渝东南地区的黔江区属山区 ,位于北纬 2 9°0 4′2 7″～ 2 9°5 2′10″,东经 10 8°2 8′0 4″～ 10 8°5 6′5 6″,年均温度 15 4℃ ,年均降水1194ｍｍ ,最低海拔 32 0ｍ ,最高海拔 1938.5ｍ。当地乡土造林树种主要是马尾松、杉木、柏木。为了给退耕还林工程、天然林资源保护工程、速生丰产用材林工程等提供更多的树种选择 ,本区于 1999年 10月开始中潜 3号杨树引种育苗试验 ,效果较好 ,1年生苗平均高 2 .9ｍ ,平均地径 1.8ｃｍ。笔者将在中低山丘陵地区培育中潜 3号杨树壮苗技术介绍如后。1　圃地选择通过育苗试验 ,中潜 3号杨树在光照…     

杨树简介

杨树简介毛白杨是我省农区农田林网、防护林、用材林和四旁绿化的速生乡土树种，深受群众喜爱而且被纳入国家攻关树种。特别在我省运城、晋城、临汾、长治地区大面积栽树，前途十分广阔。目前毛白杨约有１０４７个无性系，经我省林业科技工作者从塞外平原到黄河之滨，广为...     

农田林网杨树生物量的研究

目前我国对农田林网的研究多集中在防护效益和粮食产量方面,对农田林网中林木的物质生产、积累与分配以及光能利用等则研究较少。揭示农田林网生态系统中林木的物质生产、积累、分配、循环的规律有助于挖掘土地生产潜力,提高光能利用率,进一步提高农田林网生态系统的生产力。杨树是华北平原农田林网的主要树种,所以我们对杨树生物量进行了初步研究。     

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.     

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.     

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。