不同抚育方式对杉木幼林生长与地力维持的效果分析

对杉木二代幼林采用３种抚育方式：①全面劈草;②全面劈草,局部松土除草;③全面松土除草。通过３年试验观测,结果表明：①和②方式比③方式植被覆盖度分别大２４．３％～４１．３％和２２．８％～３４．６％,表层土壤的侵蚀度下降５０．１％和４０．６％,Ａ０层覆盖率分别提高５７．１％和５４．７％;３种抚育方式对杉木幼林的树高和冠幅生长无显著差异,但对胸径生长有极显著差异;抚育效果以②方式最佳。     

幼林抚育与管护

幼林抚育是造林结束后到幼林郁闭前进行的管理措施，也是巩固造林成果，确保“两率”的重要手段。俗话说：“三分造林，七分管”，说明了加强幼林抚育管护的重要性和必要性。 幼林抚育包括松土、除草、补植和保护；其原则是根据树种的生物学特性，立地条件和杂草生长情况，除早、除小、除了的原则，连续进行３—５年，每年１—３次。有冻害的地区，第一年以除草为主，可减少松土次数。松土除草应做到里浅外深，深度一般为５—１０厘米，干旱地区应深一些，丘陵山区可结合抚育进行扩穴，增加营养面积。 具体做法，先小苗后大苗；先是头年造的…     

皖东石质丘陵造林试验研究初报

５年的试验研究结果表明，土壤厚度、整地穴规格、适栽树种、造林用苗、抚育方法等都对石质丘陵造林成活率和保存率产生影响。土层越厚幼林保存率越高；整地穴规８０×８０×７０ｃｍ的造林平均保存率９６％，比整地穴规４０×４０×３０ｃｍ的造林保存率高２０％，比铲草皮后边挖小明穴边造林保存率高３７％；栽植火炬松容器苗幼林保存率７６．２％，比栽植火炬松裸根苗保存率高１７．２％；全面松土除草或以耕代抚幼林平均保存率９３％，比株周圆块状、规格为１００×１００ｃｍ抚育保存率高７．４％     

集粹

幼林的抚育管理幼树抚育的主要措施包括:松土、除草、灌水、施肥、修枝等。分殖造林还要适时定株摘芽去蘖。一、造林后及时转入幼林抚育管理。造林当年第一次幼林抚育要进行培土、扶正、扩穴、踩实等工作。二、除草、松土。造林初期每年抚     

林地化学除草：草甘膦

幼林抚育人工松土除草，用工多，劳动强度大，与采茶等农事活动掩时间、争劳力，往往影响抚育任务按时按质完成。祁门县1993、1994年在胥岭、大洪岭林场等地使用草甘膦除草剂进行幼林地化学除草试验，1995年在大洪岭林场、安凌站办林场等幼林地进行大田化学除草示范推广，面积3000余亩，节约幼林抚育资金4．2万多元，减少幼抚工日1．5万个。今年又购进10%草甘膦除草剂10吨，计划完成幼林地化学除草面积1．5万亩。     

不同抚育方式对巨尾桉幼林生长影响的试验研究

采用随机区组设计,对巨尾桉幼林进行了3种抚育方式对比试验:①全面劈草;②全面劈草,局部松培土;③全面松土锄草施肥。调查分析结果表明,不同抚育方式对巨尾桉幼林的胸径和树高生长均有显著影响。提高巨尾桉幼林抚育管理水平,有利于扩大林分营养空间的利用程度,促进林木生长,提高林分生物量和生产力,以充分发挥巨尾桉的速生丰产特性,提高短周期人工林经营的经济效益。各地可根据实际情况,选择合适的幼林抚育方式。     

谈谈人工幼林抚育管理

人工林从种植到郁闭以前的抚育管理工作,都叫幼林抚育管理。幼林抚育管理的目的,是为满足幼树对水、肥、气、光、热的要求,创造优越的环境条件,使幼树迅速成长,达到较高的成活率和保存率。幼林抚育管理,主要包括松土除草、灌溉追肥、林粮间作、修枝、补植、幼林保护等项作业。一、松土除草松土除草的作用是疏松土壤,减少林地水分燕发,改善土壤通气状况,防止杂草与幼树争夺水、肥。在松土除草过程中,有时与培土     

后山地区林木抚育管理技术

近十几年来，乌盟后山地区营造的大量林木，对防风固沙，保证农牧业稳产高产起到了一定的作用。但由于该地区土壤干旱缺水，再加上抚育工作跟不上，人们对天然降水利用不够，重造轻管，造成现有林木生长不良，提前衰退或枯梢死亡。为确保其造林成活后林木稳定生长，加强综合抚育管理技术措施是非常重要的。其主要技术措施如下： 一、中耕松土除草 1.中耕抚育季节 6月中旬至 7月上旬进行中耕抚育，既能做到去除杂草，又能提高土壤在雨季接纳天然降水能力，促进林木生长 。 2.中耕抚育方式及深度 中耕松土除草方法根据造林前整地方法而定。…     

对幼林传统抚育方式的改革

“三分造，七分管”是造林工作的指导原则。为了确保造林成林，尽快将传统幼林抚育方式进行改革，向所需资金少、抚育效果好的方式转变是当前造林工作迫在眉睫的任务。　　传统抚育方式有全垦锄抚和刀抚两种。全垦锄抚是对新造幼林每年进行2次全垦锄抚，连续抚育3年。主要对象是杉木人工林、经济林。每公顷全垦抚育1次耗费15个工作日，每次投资150元，3年共需投资900元。全垦抚育有利于幼林生长，但会造成林地水土大量流失。刀抚是用刀对新造林地内的杂草每年进行2次全面砍除，连续抚育3年，达到抚育目的。主要对象是新造松林和竹林，平均…     

FS—3型幼林抚育松土机受力分析

FS—3型幼林抚育松土机是一种小型手扶式旋耕松土除草机械,它的工作头旋耕刀既是耕作部件,又是作业时的行走机构,由操作手通过手柄上提或下压支承脚尖杆,控制机组前进速度,使之低于刀轴回转线速度,从而实现旋耕松土除草。松土机刀片在除草松土过程中,由于切削、破碎机和抛掷土壤,产生土壤切削阻力。又由于耕深、耕速、土壤比阻、刀片     

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.     

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。     

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.