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331.
Contrasting structure and composition of the understory in species-rich tropical rain forests 总被引:1,自引:0,他引:1
LaFrankie JV Ashton PS Chuyong GB Co L Condit R Davies SJ Foster R Hubbell SP Kenfack D Lagunzad D Losos EC Nor NS Tan S Thomas DW Valencia R Villa G 《Ecology》2006,87(9):2298-2305
In large samples of trees > or = 1 cm dbh (more than 1 million trees and 3000 species), in six lowland tropical forests on three continents, we assigned species with >30 individuals to one of six classes of stature at maturity (SAM). We then compared the proportional representation of understory trees (1-2 cm dbh) among these classes. The understory of the three Asian sites was predominantly composed of the saplings of large-canopy trees whereas the African and American sites were more richly stocked with trees of the smaller SAM classes. Differences in class representation were related to taxonomic families that were present exclusively in one continent or another. Families found in the Asian plots but not in the American plot (e.g., Dipterocarpaceae, Fagaceae) were predominantly species of the largest SAM classes, whereas families exclusive to the American plots (e.g., Melastomataceae sensu stricto, Piperaceae, and Malvaceae [Bombacacoidea]) were predominantly species of small classes. The African plot was similar to Asia in the absence of those American families rich in understory species, while similar to America in lacking the Asian families rich in canopy species. The numerous understory species of Africa were chiefly derived from families shared with Asia and/or America. The ratio of saplings (1-2 cm dbh) to conspecific canopy trees (>40 cm dbh) was lower in American plots than in the Asian plots. Possible explanations for these differences include phenology, moisture and soil fertility regimes, phyletic constraints, and the role of early successional plants in forest development. These results demonstrate that tropical forests that appear similar in tree number, basal area, and the family taxonomy of canopy trees nonetheless differ in ecological structure in ways that may impact the ecology of pollinators, dispersers, and herbivores and might reflect fundamental differences in canopy tree regeneration. 相似文献
332.
Anthropogenic nitrogen sources and exports in a village-scale catchment
in Southeast China 总被引:6,自引:0,他引:6
An experimental village-scale catchment was selected for investigation of nitrogen (N) sources and exports. The mean N application rate over the catchment was 350.2 kg N ha−1, but this rate varied spatially and temporally. The N leaching loss rate varied from 8.1 to 52.7 kg N ha−1 under different land use regimes. The average N leaching loss rate was 13.4 kg N ha−1 over the whole catchment, representing about 3.8% of the total N inputs. The N export rate through stormflows was 28.8 kg N ha−1, about 8.2% of the total N inputs. Seasonal patterns showed that 95% of N exports through stormflows occurred during July to September in 2002. Overall, the maximum riverine N exports were 12.1% of total N inputs and 15.5% of the inorganic fertilizer N applied. Understanding N sources and exports in a village-scale catchment can provide a knowledge base for amelioration of diffuse agricultural pollution. 相似文献
333.
Application of SO(4)(2-)/TiO2 solid superacid in decontaminating radioactive pollutants 总被引:4,自引:0,他引:4
Polyaniline doped with SO(4)(2-)/TiO(2) superacid shows good conductive ability. When used in a strippable coating film for decontaminating radioactive pollutants, the SO(4)(2-)/TiO(2) solid superacid replacing HCl exhibits higher electrical conductivity (7.01 s/cm) and a decontamination ratio higher than 97%. Coating and electrolyzing the film in solution or in dry medium were effective methods, the latter was more promising for decontaminating radioactive pollutants which were attached to the surface or within the body of equipments used in nuclear industry. 相似文献
334.
某厂氩气纯化器是由1Cr18Ni9不锈钢制成,在使用过程中出现致密性的网状裂纹开裂。详细论述了氩气纯化器开裂失效的原因,并通过理论分析及实践摸索,找出了应对氩气纯化器失效的对策。并在实际运行中得到了验证,确保了新制氩气纯化器的安全可靠运行。 相似文献
335.
多元可燃性混合气体临界氧浓度的测定 总被引:7,自引:0,他引:7
可燃性气体(蒸气)的临界氧浓度目前只限于对单元气体混合物的研究,且影响因素较少提及。通过实验测定了人工煤气、液化石油气的爆炸极限和临界氧浓度,对可燃性气体(蒸气)临界氧浓度的影响因素进行了研究,所测定的数据为煤气、液化石油气的安全防爆工作提供了依据。 相似文献
336.
本文借鉴杜邦公司安全管理的理念与经验,提出了在企业安全管理上,能否实现"有感领导"是决定企业安全管理水平的关键,并从领导者承诺、安全工作优先级、安全管理体制机制、安全人员配备等7个方面具体阐释了企业安全管理如何做到"有感领导"。 相似文献
337.
为研究我国城市安全生产的影响因素及预测城市安全生产的发展趋势,以上海市为例,对2004—2010年期间与安全生产相关的数据进行灰色关联度分析,提取影响安全生产状况的主要经济社会因素,并与工矿商贸死亡人数之间建立回归模型。研究结果表明,工矿商贸死亡人数与第二产业比重、GDP增长率、教育支出占GDP比重以及私营及个体工商户比例均呈现负相关。基于2007—2011年各月份上海市的安全生产死亡人数,运用Winters乘法模型,预测上海市安全生产发展趋势。 相似文献
338.
瞬态径向热流法测定松散煤体变导热系数 总被引:3,自引:1,他引:2
松散煤体的导热系数是指在单位梯度作用下,松散煤体单位时间内通过单位面积的热量,表征了松散煤体导热性能的强弱,是研究煤自燃的重要参数。目前,使用最广泛的热线法,测试结果易受电阻升温变化影响。针对当前测试方法的不足,本文在二维径向导热模型的基础上,设计了瞬态径向热流法测定松散煤体变导热系数测试装置,并建立了相应的导热系数解算模型。通过测定不同煤样随温度变化的变导热系数。结果表明,随着温度的升高,松散煤体的导热系数不断上升,两者之间基本成线性关系,测试结果符合松散煤体的导热特性。 相似文献
339.
Caiyun Hou Sen Qiao Yue Yang Jiti Zhou 《Frontiers of Environmental Science & Engineering》2019,13(6):92
340.