Change in spatial characteristics of forest openings in the Klamath Mountains of northwestern California,USA   总被引：4，自引：0，他引：4  

Carl N. Skinner 《Landscape Ecology》1995,10(4):219-228

Change in the spatial characteristics of forest openings was investigated in three forested watersheds in north-western Siskiyou County, California totalling approximately 24,600 hectares. Watersheds with minimal human disturbance were chosen for study. However, fire suppression has been pervasive throughout. Characteristics of forest openings (area, perimeter, distance between neighboring openings) were measured on aerial photographs taken 41 years apart. An index of regional form was determined for the landscape. Shape complexity for each opening was calculated using two indices based upon fractals. Significant differences were found using the Kolmogorov-Smirnov two-sample test between the perimeters, areas, distance from sample point to nearest opening, and distance between neighboring openings. The perimeters and areas became smaller, and the distances from the sample point to the nearest opening and between neighboring openings became greater over the 41 years between aerial photo sets. The estimated area occupied by openings decreased from 25.8 % to 15.6 % of the study area. No significant difference was found in the shape of the openings except as the shape indices were influenced by changes in size of the openings.This article was written and prepared by U.S. Government employees on official time, and it is therefore in the public domain and not subject to copyright.  相似文献   

试论福建省国营林场分类管理     

王光玉 《福建林学院学报》1989,(Z1)

本文分析了福建省110个国营林场的类型、目前管理体制、管理办法及存在的问题。指出了目前国营林场管理办法中存在着种种弊端,跟深化林业改革很不适应,必须改革和完善国营林场管理机制,理顺“省办地管县监督”的管理体制,实行分类指导。本文就分类管理的依据,原则和实施办法进行了探讨,并提出了一些建议。  相似文献   

Contribution to the taxonomy and pathogenicity of fungicolous Verticillium species. II. Pathogenicity     

Dr. A. van Zaayen  Dr. W. Gams 《European journal of plant pathology / European Foundation for Plant Pathology》1982,88(4):143-154

In recent years in the Netherlands a second mushroom species,Agaricus bitorquis, which prefers higher temperatures thanA. bisporus and is less susceptible to certain diseases, is often commercially grown.Verticillium fungicola var.fungicola, the causal agent of dry bubble, is responsible for considerable damage in crops ofA. bisporus. InA. bitorquis, however, dry bubble has hardly been noticed, but brown spots due toV. fungicola var.aleophilum resulted in inferior mushroom quality. The latter variety also caused brown spots ina. bisporus, but to a minor degree. In variety Les Miz 60 ofA. bisporus, however, it also induced fruit-body deformation in a way different from dry bubble. Verticillium psalliotae, isolated fromA. bitorquis in England, induced more confluent brown spots inA. bitorquis. In the netherlands, where moreA. bitorquis is grown than in other countries,V. psalliotae has not yet been encountered in crops ofA. bitorquis. V. psalliotae, which has a high temperature optimum for mycelial growth, likeV. fungicola var.aleophilum andA. bitorquis, did not infectA. bisporus in our trials.Artificial infection ofA. bisporus orA. bitorquis could not be accomplished with the following related and/or fungicolous fungi:Verticillium lamellicola, V. fungicola var.flavidum, V. biguttatum, Nectriopsis tubariicola, Acremonium crotocinigenum andAphanocladium album.Samenvatting Vooral in Nederland wordt sinds een aantal jaren naastAgaricus bisporus ook de warmteminnende champignonsoortAgaricus bitorquis geteeld, die minder vatbaar is voor bepaalde ziekten. TerwijlVerticillium fungicola varfungicola in de teelt vanA. bisporus droge mollen en daardoor veel schade veroorzaakt, komen in de teelt vanA. bitorquis geen droge mollen voor maar wel bruine vlekken, die tot kwaliteitsverlies en dus schade leiden. De vlekken bleken veroorzaakt te worden doorV. fungicola var.aleophilum. Deze schimmel veroorzaakte ook inA. bisporus bruine vlekken, hoewel in minder ernstige mate, maar in het ras Les Miz 60 vanA. bisporus bovendien misvormde champignons, die wel op droge mollen leken, maar daaraan niet gelijk waren.OokV. psalliotae, in Engeland geïsoleerd vanA. bitorquis met vlekken, veroorzaakte wat meer samenvloeiende, bruine vlekken inA. bitorquis. In Nederland, waar meerA. bitorquis geteeld wordt dan in andere landen, isV. psalliotae nog niet aangetroffen in teelten vanA. bitorquis. InA. bisporus kon geen kunstmatige infectie worden verkregen metV. psalliotae, die net alsV. fungicola var.aleophilum enA. bitorquis warmteminnend genoemd zou kunnen worden.Met de volgendeVerticillium-achtige of van paddestoelen geïsoleerde schimmels kon evenmin op kunstmatige wijze een infectie worden opgeroepen inA. bisporus ofA. bitorquis: Verticillium lamellicola, V. fungicola var.flavidum, V. biguttatum, Nectriopsis tubariicola, Acremonium crotocinigenum enAphanocladium album.  相似文献   

Designating a greenbelt around the city of Riga, Latvia     

Janis Donis   《Urban Forestry & Urban Greening》2003,2(1):31-39

Latvian legislation demands that forest protection belts are established around all cities and towns. The main goal of a protection belt is to provide suitable opportunities for recreation to urban dwellers and to minimise any negative impacts caused by urban areas on the surrounding environment. Legislation states the main principles to be adopted, which include the maximum area of protection belts, their integration in territorial development plans and restrictions placed on forest management activities. The largest part of the forest area around Riga is owned by the municipality of Riga, which, as a result, has two competing interests: to satisfy the recreational needs of the inhabitants of Riga, and to maximise the income from its property. In order to compile sufficient background information to solve this problem, the Board of Forests of Riga Municipality initiated the preparation of a proposal for the designation of a new protection belt.The proposal was based on the development and application of a theoretical framework developed during the 1980s. The analysis of the recreational value of the forest (5 classes of attractiveness) was carried out based on categories of forest type, dominant tree species, dominant age, stand density, distance from urban areas and the presence of attractive objects. Information was derived from forest inventory databases, digital forest maps and topographic maps. Additional information was digitised and processed using ArcView GIS 3.2. Local foresters were asked about the recreation factors unique to different locations, such as the number of visitors and the main recreation activities. From a recreational point of view and taking into account legal restrictions and development plans for the Riga region, it was proposed to create three types of zones in the forest: a protection belt, visually sensitive areas and non-restricted areas.  相似文献   

不同覆盖方式对旱地棉田土壤环境及棉花产量的影响   总被引：10，自引：1，他引：10  

刘冬青  辛淑荣  张世贵 《干旱地区农业研究》2003,21(2):18-21

分析普通地膜覆盖、小麦秸秆覆盖、地膜 秸秆覆盖3种覆盖物对旱地棉田土壤环境、棉花产量构成因素的影响,结果表明:覆盖栽培能改善土壤环境,降低土壤容重,提高土壤水分利用率,调节土壤温、湿度,协调水热资源利用的同步性;秸秆覆盖能增加土壤养分含量,特别是速效钾含量;在棉花生长后期,提高叶面积指数,延长叶片功能期,提高棉株的光合能力从而防止棉花早衰,增加铃重,提高棉花产量。  相似文献   

水稻旱作对其生长量和经济产量的影响   总被引：11，自引：0，他引：11  

黄文江  黄义德  王纪华  李金才 《干旱地区农业研究》2003,21(4):15-19

1998～1999年，研究了水稻旱作条件下，不同生育时期受水分胁迫后对作物生长量的影响。结果表明：不同指标对水分胁迫时期的敏感性不一，植株高度对抽穗期水分胁迫最敏感；单株绿叶面积和单株地上部干重对幼穗分化后期水分胁迫最敏感；根系干重和根冠比对幼穗分化前期水分胁迫最敏感；幼穗分化后期水分胁迫对经济产量影响程度最大，无效分蘖期水分胁迫对产量影响程度最小。  相似文献   

Integrated Pest Management in Cocoa Agroforests in Southern Cameroon: Constraints and Overview     

Denis J. Sonwa  Ousmane Coulibaly  A. Akinwumi Adesina  Stephan F. Weise  Mathurin Tchatat 《Integrated Pest Management Reviews》2002,7(3):191-199

Imports of pesticides have long been subsidised for use in the cocoa agroforests of the humid forest zone of southern Cameroon. With the liberalisation of the cocoa and pesticides sectors and the devaluation of the local currency (CFA franc), farmers are facing fluctuations in the price paid for cocoa and the high cost of farm inputs. Without the support of the extension services, they themselves have developed traditional integrated control methods based on the use of plant extracts mixed with conventional pesticides. From a survey of 300 cocoa farmers, the study assesses the farmers' command of these methods, the pests controlled, the problems encountered and the institutional constraints in the definition and dissemination of integrated control methods. The study concludes with recommendations for research and development towards the better definition and dissemination of integrated control methods. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

以固氮树种发展食用菌专用林的建议     

刘福平 《食用菌学报》2002,9(4):33-39

许多固氮树种速生丰产，萌生能力强，叶片，木屑含氮率较高，可为食用菌栽培提供理想原料，而且固氮树种在绿花荒山，保持水土，提高地力方面作用显著，以固氮树种发展短轮伐期食用菌专用林，具有较高的经济效益和生态效益，本文介绍了银合欢，黑荆，大叶相思，银荆，桤木，南洋楹和马占相思等在食用菌栽培上的应用概况，各地可因地制宜栽培合适的固氮树种作为食用菌专用林。  相似文献   

超干贮存对番茄种子活力的影响   总被引：17，自引：1，他引：17  

张海英  孟淑春  孔祥辉 《园艺学报》2002,29(1):35-38

 研究了超干含水量、贮存温度对番茄种子生活力和活力的影响, 结果表明: 含水量为4. 6 %、2. 4 %的番茄种子在20 ℃下密封贮存13 年后, 发芽率、苗长、脱氢酶活性、SOD 活性与对照(0 ℃、6. 2 %)相比均无明显差异, 但含水量为1. 9 %的种子上述指标却显著下降, 说明含水量为4. 6 %、2. 4 %的超干番茄种子在常温下具有良好的耐藏性, 含水量过低(1. 9 %) 不利于长期贮存, 但上述三种含水量(4. 6 %、2. 4 %、1. 9 %) 的番茄种子在0 ℃下密封贮存13 年后, 均有着较高的种子活力、生活力和酶活性。  相似文献   

新疆淡水藻类研究：乌鲁木齐南山八一林场绿藻初报     

王克勤 《干旱区研究》1997,14(4):26-29

本文首镒报道乌鲁木齐南山八一林场山区的绿藻１１属，１２种，其中１０属，１０种为新疆新记录。这些结果是对１９９１年７月采集的２０号标本经鉴定后获得的。  相似文献