初冬早春南昌郊区灯下常见蛾类活动情况纪实     

章士美  赵凤霞 《江西农业大学学报》1994,16(1):47-51

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水土保持是山丘区经济发展的根本出路     

肖秧 《中国水土保持》1994,(10):1-2

水土保持是山丘区经济发展的根本出路肖秧（四川省人民政府，成都６１００００）四川地处长江上游，幅员辽阔，境内高山峻岭，江河纵横，是一个有一亿多人口的农业大省。由于历史原因，森林曾遭严重破坏，加之人口众多，人均耕地数量少，垦殖指数高，水土流失十分严重。遥...  相似文献   

Deforestation patterns and their effects on forest patches     

Wayne C. Zipperer 《Landscape Ecology》1993,8(3):177-184

Five identifiable patterns of deforestation are recognized - internal, indentation, cropping, fragmentation, and removal - and each has a distinct effect on habitat quality of forest patches in the eastern United States. By overlaying land use maps from 1973 and 1981 for three counties in the State of Maryland (Prince Georges, Anne Arundel, and Wicomico), changes in the interior core area and edge length of individual patches were measured. Forest interior declined by 23.8 km² in Anne Arundel, 16.3 km² in Prince Georges, and 8.4 km² in Wicomico. Within Anne Arundel and Prince Georges Counties, deforestation increased edge length by 52.1 km and 31.2 km, respectively, whereas, within Wicomico, it decreased edge length by 8.7 km. Differences among counties resulted from current land use patterns, percentage of forest cover, and the dominant deforestation pattern.  相似文献   

辽宁西部半干旱地区油松纯林改造的研究   总被引：3，自引：0，他引：3  

吴生广 《沈阳农业大学学报》2005,36(3):320-323

喀左县位于辽宁西部地区，现存大面积油松人工纯林，不仅改善地力和水土保持效益差，而且火险性强、虫害蔓延成灾、生长早期衰退。为改善其林分生态条件，提高林木生长量和综合效益，在中三家镇对25年生油松人工纯林进行改造试验。结果表明，选择山杏、刺槐、沙棘等乔、灌木树种，利用林间空地、林缘隙地、侵蚀沟壑和疏林地造林，在大面积油松纯林连片地区进行窄带状或块状砍伐后造林，5年后效益显著，林分相对湿度提高了2．2％，土壤有机质含量提高5．4％，土壤含水量提高9．8％，减轻土壤容重３％,林分虫害明显下降，油松树高、胸径生长量分别提高22．6％、19．8％。  相似文献   

Quasi-non-linear fracture mechanics analysis of splitting failure in simply supported beams loaded perpendicular to grain by dowel joints     

Jørgen Lauritzen Jensen 《Journal of Wood Science》2005,51(6):577-582

A quasi-non-linear fracture mechanics model based on beam on elastic foundation theory is applied for analysis of the splitting failure of dowel joints loaded perpendicular to grain. Simply supported beams symmetrically loaded by two dowels are considered, and the effects of edge distance, dowel spacing, and distance between dowels and supports are accounted for. The foundation modulus used in the beam on elastic foundation model is chosen so that the perpendicular-to-grain tensile strength and fracture energy properties of the wood are correctly represented. This ensures that a conventional stress analysis and failure criterion lead to the same solution as the compliance method of fracture mechanics. A semiempirical efficiency factor is proposed to account for the influence of the total beam depth, which does not enter the beam on elastic foundation model, but the effect of which is evident from tests. It is shown that the so-called Van der Put/Leijten model, which recently has been adopted in Eurocode 5, appears as a special case of the model presented. Tests on simply supported beams with a single dowel joint at midspan are compared with the theoretical predictions. Various edge distances, beam depths, and spans were tested.  相似文献   

RESEARCH ON THE CONTROL OF FOREST RAT USINGCOUMATETRALYL     

苏元吉 《林业研究》1996,7(3):8-12

lNTRODUCTlONThcdan1egcoftheforestratsisbecomingmorcal1dmoreserioustviththeincreaseoftI1cartificlaIforestinrccentvears.Theratscatsccds.}'oungseedIlngsandbarklnspringandxvintcr.t`l1ichcauscatyrgcnumberofsccd-lingsand}oungtrcestodie.Forthcsakeofthedct'cloplllclltofforestryandtl1cprotcctiol1oftllcrcscri'eforcstrcsourcc-thecontrolortl1cllarl11f[lIforcstratsappcarstobe\'cryi111por-tant.Cl1ch1icalcontrolisthcmostcfficicl1tmcthodthatiscas\'tobehandle.lou'cost.Itoccupicsa\'ery'lmportantpositio11i…  相似文献   

澳门海岸防护林多树种配置造林效果分析     

刘凯昌  叶渭贤 《防护林科技》2001,(4):9-11

对澳门凼仔岛海岸山地防护林造林地 (8年生 )进行调查 ,分析了林分保存率、林分生长量、各树种平均胸径、平均树高、林分土壤肥力和林分植被变化情况。认为海岸山地防护林营造多树种阔叶混交林是一种值得研究推广的林分改造模式  相似文献   

商品林分类指标体系的研究     

郑小贤  王伟 《北京林业大学学报》2001,23(3):20-25

在综合分析影响商品林经营的社会、经济、自然、生态、法律等因子基础上 ,提出商品林分类标准和指标体系 ,并以山西管涔林业局杜家村林场为例 ,验证商品林分类指标 ,为商品林建设提供依据  相似文献   

浅谈林地资源保护管理与生态林业建设   总被引：4，自引：0，他引：4  

陈日红  余峰 《浙江林业科技》2001,21(4):68-70

论述了建德市林地资源保护和生态林业建设现状以及他们间的相互关系，并提出要搞好生态林业建设必须建立林地资源保护管理体系，对林地资源要实行总体规划，合理使用。  相似文献   

哈尼族传统人居环境体系中森林要素之作用评述     

管旸 《西部林业科学》2004,33(4):96-99

从不同角度评述了森林在哈尼族传统人居环境体系中的作用和地位，阐述了未来山区村镇发展中保留周边森林的重要性。  相似文献