Forest structure, composition, and tree diversity response to a gradient of regeneration harvests in the mid-Cumberland Plateau escarpment region, USA

Upland hardwood stands on mesic, escarpment-oriented sites on the Cumberland Plateau region of northeastern Alabama provide a myriad management opportunities. Stands are primarily managed for Quercus, but the high species diversity allows for management that targets multiple species. Stand composition is unique in that dominant species include shade tolerant species such as Acer saccharum, intermediate tolerant Quercus spp. and Carya spp., and intolerant Liriodendron tulipifera. Three replications of five levels of disturbance were created to assess species compositional changes; disturbances included three levels of harvest intensity, a mid-story herbicide treatment, and a control. After eight growing seasons, there were no discernable differences in species richness, diversity or evenness. Importance values based on relative basal area and relative density also changed little, except for clearcuts where L. tulipifera greatly increased. An initial gradient in basal area, canopy cover, and light created by harvesting or thinning dissipated following five growing seasons. Options exist for future stand management, including promoting two-aged or uneven-aged systems. Maintenance of Quercus will require additional tending.     

Core subsets of base collections and priorities of national programmes: Indian perspective

Summary The establishment of representative core collections and back-up reserve collections was proposed to facilitate effective management and to promote utilization of large base collections. The priorities of the developing national PGR programmes, in the organization of components of their base collections, are different from those of IARCs since the strengths as well as limitations of the two systems vary. Unlike most IARCs, national programmes have the option of networking their active collections, maintained at several eco-sites, and linking this network to the base collection kept under long-term storage. This keeps open the option to develop situation-specific subsets for an effective germplasm utilization. There is a pressing need for a scientific re-examination of the concept of germplasm core in order better to apply it in developing core subsets in the national PGR programmes. The formulation of situation-specific subsets is advocated, as the system would be directed to users' requirements or addressed to gene bank managers' resource constraints. Arguments given in favour of developing core subsets, rather than a single core are: (i) logical; (ii) population genetic; and (iii) germplasm usage considerations. The Indian PGR programme and the emerging core context are briefly discussed, along with features of a programme designed to develop such core subsets.Abbreviations IARCs = International Agriculture Research Centers - NBPGR = National Bureau of Plant Genetic Resources - NAGS = National Active Germplasm Collection Site - NGSNs = National Germplasm Screening Nurseries - GACs = Germplasm Advisory Committees     

Litter decomposition and nitrogen mineralization in newly formed gaps in a Danish beech (Fagus sylvatica) forest

Gap formation is suggested as an alternative forest management approach to avoid extreme changes in the N cycle of forest ecosystems caused by traditional management practises. The present study aimed to investigate the effect of gap formation on N availability in beech litter and mineral soil on sites, which experienced only little soil disturbance during tree harvest. N pools, litter decomposition, and N mineralization rates in mineral soil were studied in two gaps (17 and 30 m in diameter) in a 75-year-old managed European beech (Fagus sylvatica L.) forest in Denmark and related to soil temperature (5 cm depth) and soil moisture (15 cm depth). Investigations were carried out during the first 2 years after gap formation in measurement plots located along the north-south transect running through the centre of each gap and into the surrounding forest.An effect of gap size was found only for soil temperatures and litter mass loss: soil temperatures were significantly increased in the northern part of the large gap during the first year after gap formation, and litter mass loss was significantly higher in the smaller gap. All other parameters investigated revealed no effect of gap size. Nitrification, net mineralization, and soil N concentrations tended to be increased in the gaps. Cumulative rates of net mineralization were two fold higher in the gaps during the growing season (June-October), but a statistically significant increase was found only for soil NH₄-N concentrations during this period. Forest floor parameters (C:N ratios, mass loss, N release) were not significantly modified during the first year after gap formation, neither were the total C content nor the C:N ratio in mineral soil at 0-10 cm depth.     

基于核心力量导向差异的贵州乡村旅游开发模式比较与剖析——以贵州天龙屯堡、郎德苗寨和西江苗寨为例

贵州是中国较早开展乡村旅游的区域之一。在众多乡村旅游地中,贵州天龙屯堡、郎德苗寨、西江苗寨因核心力量导向差异而形成3种不同的乡村旅游开发模式,即公司主导型、社区主导型和政府主导型模式。作为贵州乡村旅游开发的典型代表,3种模式各具特色,值得关注。通过对3种不同乡村旅游开发模式下的市场开拓能力、社区居民获益方式与状况、传统文化保护与传承及其乡村旅游开发模式的形成原因进行横向比较分析,为国内乡村旅游开发提供经验借鉴和理论指导,推动乡村旅游研究的深入。     

早期断奶应激(EWS)对仔猪影响的研究——对血液生理指数和血清蛋白成分变化影响的试验观察

试验检测了ＥＷＳ对仔猪在断奶前和断奶后的血液生理指数和血清蛋白质指数的变化情况，结果表明：（１）在血液生理指数方面，断奶１０ｄ后，红细胞、血红蛋白和白细胞数均有所减少，特别是白细胞减少２５．３２％（Ｐ＜０．０１），在白细胞分类比值中，断奶１０ｄ后，淋巴细胞和嗜酸性白细胞分别减少１０．８６％（Ｐ＜０．０５）和３６．３６％（Ｐ＜０．０１），嗜中性白细胞增加１８．３４％（Ｐ＜０．０５），这是机体抵抗力降低的标志。至断奶２０～３０ｄ后，上述各项指数基本恢复和超过断奶前原有水平。（２）在血清蛋白质成分指数变化方面，断奶１０ｄ后，血清总蛋白量减少２２．５４％（Ｐ＜０．０１），白蛋白比值增加３．９４％（Ｐ＞０．０５），而γ－球蛋白则减少１２．３９％（Ｐ＜０．０５），这也是机体抵抗力降低的标志。至断奶３０ｄ后，血清总蛋白量已恢复至断奶前原有水平，白蛋白减少７．３９％（Ｐ＜０．０５），γ－球蛋白则增加１５．６０％（Ｐ＜０．０５），表明仔猪已适应于新环境生活，机体抵抗力已获得恢复和提高     

玉米芯添加量对黄伞栽培的影响

研究玉米芯添加量对黄伞栽培的影响.玉米芯添加量70%时,黄伞菌丝长速最快,达到2.80 mm/d.玉米芯添加量20%时,黄伞生物学效率为81.1%,未见明显降低.     

The cultural model of “the good farmer” and the environmental question in Finland

Farmers' relationship with nature isdetermined by the significance of agriculturefor human beings. When agriculture is definedas human activity that uses renewable naturalresources and aims to produce usable food andfiber products, agriculture is explicitlydefined as production. Farmers' relationshipwith nature is based on the principle ofproduction. This article discusses thecontradiction between the peasant values ofprotection of nature that many farmers inFinland still have and the environmental harmtheir production-oriented farming style causes.When farmers interpret their farming practicesas harmonious co-operation with nature, it isdifficult for them to see the polluting effectsof their work. Paul B. Thompson's suggestionthat three religious–philosophical doctrines(hard work, the doctrine of grace, and the mythof garden) have made it easy for farmers toadopt productionist farming strategy is used asa framework to interpret farmers' narrativesconcerning their relationship with nature. Theresearch is qualitative and biographical. Thedata include life stories and biographicaltexts farmers wrote for a competition in1997.     

苹果霉心病的研究Ⅰ致病菌种类的调查鉴定

自苹果花期至贮藏期定期从花器、幼果、成熟果实和贮藏过程中的果实分离获得菌株。用孢子悬浮液经果实的萼筒注射接种红星苹果的成熟果实，发病后分离获得病原菌纯培养物。根据培养性状、子实体和孢子的形态共鉴定出１１属的１２种及８个类型的致病真菌。     

1994～2001年板栗研究文献计量分析

作者对1994～2001年专业期刊公开发表的板栗文献做了计量分析。总文献量为1666篇，其中署名文献有1616篇。核心作者49人。确定了12种核心期刊。