共查询到20条相似文献,搜索用时 109 毫秒
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<正>1选择适宜的物候期秋季树木大量落叶至土壤封冻是最适宜的栽植时间,即10月~12月份,并且在此时期内越早越好。秋季当树苗大量落叶后,苗木地上部水分蒸腾量减少,根系处在缓慢生长阶段,此时栽植,根系还有一个小的生长高峰,伤根极易愈合,并能生长出部分新根,春天发芽时较之春季栽植的苗木就少去了一个根系愈合的过程,生理活动的顺序是根系早,地上部晚,先由根供应水和养分,再生根发芽,养分供应早,生长早,成活率高,长势旺,而春季栽植的苗木是先发芽,再由根系供应养分,一旦根系愈合较晚,就有可能造成树体养分消耗殆尽,容易出现回芽现象,影响成活率,生长势也较差。 相似文献
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初雪 《绿色中国(A版)》2008,(24)
1乔桢推开门,一阵小北风先他一步吹进教室,有个女生忍不住咳嗽起来,最初轻咳,然后听起来就有些撕心裂肺。她坐在靠暖气的地方,身体裹得像一只小棕熊。乔桢站在讲台上,开始点名,喊到江恩美时,她举起手,没有抬头,整个人恹恹地缩在外套里,精神不振,这该死的感冒啊。乔桢首先记住了她,他每讲几句话,她就在下面咳,伴奏一样。后来,大家觉得实在有趣,就开始笑。乔桢的第一堂课,就这样匆匆结束了。她最后一个走出教室, 相似文献
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相传,在很久很久以前,一只美丽的凤凰从南方飞来,发现了一片绿洲:贺兰山雄距西北,重峦叠嶂,势若奔马;黄河襟带东南,不舍昼夜,款款北流;山河之间,稻针织绿,麦浪翻金,渠网平畴,水映晴光;满眼望去,是一片绵绵芊芊的鲜嫩绿色。于是,美丽的凤凰留下了,留在这风光秀美的塞上江南,变成 相似文献
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毛叶山桐子(Var vestita Diels),属大风子科,山桐子属,是山桐子(Idesia polycarpa Maxim.)的变种.落叶乔木,高8~15 m,树皮光滑,灰白色,皮孔大而明显.叶卵形至卵状心形,厚纸质,长8~16 cm,宽6~14 cm,先端锐尖至短渐尖,基部心形或近心形.叶缘有疏锯齿,表面光滑有光泽,背面密生灰色短柔毛,基部掌状5~7出脉,叶柄红色,长6~15 cm,圆柱形,幼具短柔毛,顶端有两个较大腺体.圆锥花序长15~30 cm,下垂,花黄绿色,芳香.浆果球形,红色、直径6~8mm,有多数种子,种子卵形,褐色,长1mm,径0.3 mm.花期5~6月,果熟期9~11月. 相似文献
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Alaa A. Bashandy Alaa E. El-Habashi Ahmed K. Dewedar 《Wood material science & engineering》2018,13(4):241-253
This research aims to study the feasibility of repair and strengthening of timber cantilever beams used in historic buildings. It is conducted to investigate the feasibility of using different valid materials and techniques to repair and strengthen timber cantilever beams in new and historic timber buildings. The study is performed in terms of structural performance as well as historic and architectural values. An experimental program of several different materials and techniques is executed. The results are driven in terms of initial cracking load, crack propagation for the tested samples at different loading stages, deflection values, and failure load for each repaired or strengthened material and technique. The main variables are timber types (new and historic), repair and strengthening materials (steel plates, Glass Fiber Reinforced Polymer wrap, and Carbon Fiber Reinforced Polymer laminates), repair or strengthening techniques (near surface mounted and externally bonded system), and cantilever length (1000 and 1250?mm). Test results indicated that using steel plates, glass fiber wrap, and carbon fiber laminates increases the value of failure loads and decreases the deflection at both; repaired and strengthened timber cantilever beams compared to control beams. 相似文献
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IntroductionMaskedciVet(Paguma18vata),Mammalia,Viverridae,ismainlydiStributedinShanxi,Sichuan,Tibet,Yunnanprovinces,etc..Itsmeatisdeliciousandhasspecialflavor.Itiseasytoberaisedartificially,withhighproduCtivity.Nutria(MyocasterCOypus),Rodentia,Capromyidae,originatedinArgentina,Chili,etc.insouthAmerica.Itisakindofherbivoresfur-bearer.itsartificialraisinghassuchmeritsasdurablefurandlowcostandhighproduCtivity.MaskedcivetandnutriahavehigheconomicvalueandwideprospeCtofutilization.Atpresen… 相似文献
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胡云楚 《中南林业科技大学学报(自然科学版)》1994,(2)
本文探讨了用苯芴酮萃取分光法测定微量锗的实验条件和步骤.结果表明,用此法测定微量锗灵敏度高、操作简便、准确,是测定微量锗的较好方法.可用于对植物和食品中的微量锗进行检测. 相似文献
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自然保护区合作管理(共管)理论研究综述 总被引:6,自引:0,他引:6
自然保护区合作管理自20世纪80年代末期开始逐步兴起,在资源管理中被广泛使用。文章介绍了共管的含义、共管实施原则、分析框架和评价指标。从公共部门和私有部门的互动模式、集体行动类型的不同、政府和资源使用者的参与管理方式三个方面论述了共管的模式。分析了政府和社区在共管实施过程中的作用,指出共管仍面临着分权不够、合作中的文化障碍、组织类型简单和信息交流不充分、社区参与能力和认识能力不足等挑战。 相似文献
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《Scandinavian Journal of Forest Research》2012,27(7):577-584
ABSTRACTThe connection between chemical composition and anatomy of wood is poorly studied. Abiotic and biotic growth conditions affect the synthesis of structural compounds and the anatomy of wood at the same time as they affect growth. In this study, the wood chemical composition, and connections between wood chemistry and anatomy were studied in downy birch (Betula pubescens Ehrh.) grown on four growth sites possessing mineral and peat soils. Lignin, holocellulose, extractive and ash contents, and effective heating value were analysed and compared with libriform fibre double wall thickness and lumen diameter, vessel size and number, and ray and axial parenchyma numbers. Measured lignin and extractive contents were exceptionally high and holocellulose content low. Correlations between wood anatomy and effective heating value were partly different on different soils. Correlations between holocellulose and anatomy were the opposite of the correlations between other chemical compounds and anatomy. The significant correlations between chemical composition and anatomy were commonly opposite in trees grown on peat than in trees grown on mineral soil. Particularly, vessel characteristics and fibre wall thickness correlated significantly with wood chemistry in trees grown on mineral soil. The connections between wood anatomy and chemistry proved to be soil-dependent. 相似文献
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Temuulen Tsagaan Sankey 《New Forests》2008,35(1):45-55
Spatial patterns, rates, and density of encroaching forests into adjacent grasslands have important implications for long-term
land use management and resource planning. This study examines the effects of Douglas-fir (Pseudotsuga menzeisii) and aspen (Populus tremuloides) regeneration mechanisms on sucker and seedling spatial patterns, distance from adult trees, and density in encroaching forests.
A total of 8,924 aspen suckers and 1,244 Douglas-fir seedlings were counted and mapped in 2,920 quadrats (5 m × 5 m) in 106
plots along a lower forest-grassland ecotone in the Centennial Valley, MT, USA. Sucker and seedling spatial patterns were
analyzed using Morisita’s I index. Average sucker and seedling density per quadrat and distance from adult trees were estimated for each plot and compared
between aspen-dominated plots and Douglas-fir-dominated plots using ANOVA tests. Aspen suckers were established in a clustered
spatial pattern at a significantly higher density and a significantly shorter distance from the adult trees. In contrast,
Douglas-fir seedlings were established in varying spatial patterns at a significantly lower density and a significantly greater
distance from the adult trees. Forest encroachment into the adjacent grassland in the Centennial Valley is occurring in contrasting
patterns and at varying rates and densities due to the difference in aspen and Douglas-fir regeneration mechanisms. 相似文献
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G.W.W. Wamelink H.J.J. Wieggers G.J. Reinds J. Kros J.P. Mol-Dijkstra M. van Oijen W. de Vries 《Forest Ecology and Management》2009
Changes in the Earth's atmosphere are expected to influence the growth, and therefore, carbon accumulation of European forests. We identify three major changes: (1) a rise in carbon dioxide concentration, (2) climate change, resulting in higher temperatures and changes in precipitation and (3) a decrease in nitrogen deposition. We adjusted and applied the hydrological model Watbal, the soil model SMART2 and the vegetation model SUMO2 to asses the effect of expected changes in the period 1990 up to 2070 on the carbon accumulation in trees and soils of 166 European forest plots. The models were parameterized using measured soil and vegetation parameters and site-specific changes in temperature, precipitation and nitrogen deposition. The carbon dioxide concentration was assumed to rise uniformly across Europe. The results were compared to a reference scenario consisting of a constant CO2 concentration and deposition scenario. The temperature and precipitation scenario was a repetition of the period between 1960 and 1990. All scenarios were compared to the reference scenario for biomass growth and carbon sequestration for both the soil and the trees. 相似文献