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61.
The interaction between landscape structure and spatial patterns of plant invasion has been little addressed by ecologists
despite the new insights it can provide. Because of their spatial configuration as highly connected networks, linear wetlands
such as roadside or agricultural ditches, can serve as corridors facilitating invasion at the landscape scale, but species
dynamics in these important habitats are not well known. We conducted a landscape scale analysis of Phragmites australis invasion patterns (1985–2002 and 1987–2002) in two periurban areas of southern Québec (Canada) focusing on the interaction
between the network of linear wetlands and the adjacent land-uses. Results show that, at the beginning of the reference period,
the two landscapes were relatively non-invaded and populations occurred mostly in roadside habitats which then served as invasion
foci into other parts of the landscape. The intrinsic rates of increase of P. australis populations in linear anthropogenic habitats were generally higher than those reported for natural wetlands. Riparian habitats
along streams and rivers were little invaded compared to anthropogenic linear wetlands, except when they intersected transportation
rights-of-way. Bivariate spatial point pattern analysis of colonization events using both Euclidian and network distances
generally showed spatial dependence (association) to source populations. An autologistic regression model that included landscape
and edaphic variables selected transportation rights-of-way as the best predictor of P. australis occurrence patterns in one of the landscapes. Given the high invasion rates observed, managers of linear wetlands should
carefully monitor expansion patterns especially when roads intersect landscapes of conservation or economic value. 相似文献
62.
输油管道添加降凝剂是改善原油代温流变性的一种物理化学方法,从降凝剂的筛选和复配,处理条件,应用方式,配套设施、应用效果等方面系统地介绍了含蜡原油添加降凝剂输送工艺的研究及应用现状,指出了降凝剂在研究和应用中存在的问题,对添加降凝剂的输油技术进行了客观评价,展望了降凝输油技术的发展方向。 相似文献
63.
64.
蒋月评 《湖南农业大学学报(自然科学版)》1999,26(4)
研究了4 种高维 Mobius 群的初等子群定义之间的关系⒚得到了高维 Mobius 群是初等群的充要条件;在离散的条件下,给出了这种初等子群的结构性定理⒚ 相似文献
65.
点是现代景观设计中一个重要的视觉造型元素。现就景观设计中点的涵义、形态视觉特性等方面进行论述,并通过应用实例来阐述景观设计中点的几种表达方式,不同"点"的造型要素在不同应用情况下产生的不同景观效果。 相似文献
66.
渠道是农田水利建设的一个重要工程,渠道测量在渠道兴、改、扩建中具有重要的地位和作用。仅就施工过程中如何快捷恢复渠道中线的测量方法作了探讨,并对恢复中线的精度作了相应分析。 相似文献
67.
68.
Nitrate leaching in a silage maize field under different irrigation and nitrogen fertilizer rates 总被引:4,自引:0,他引:4
Mahdi Gheysari Seyed Majid Mirlatifi Mehdi Homaee Gerrit Hoogenboom 《Agricultural Water Management》2009,96(6):946-954
Quantification of the interactive effects of nitrogen (N) and water on nitrate (NO3) loss provides an important insight for more effective N and water management. The goal of this study was to evaluate the effect of different irrigation and nitrogen fertilizer levels on nitrate-nitrogen (NO3-N) leaching in a silage maize field. The experiment included four irrigation levels (0.7, 0.85, 1.0, and 1.13 of soil moisture depletion, SMD) and three N fertilization levels (0, 142, and 189 kg N ha−1), with three replications. Ceramic suction cups were used to extract soil solution at 30 and 60 cm soil depths for all 36 experimental plots. Soil NO3-N content of 0-30 and 30-60-cm layers were evaluated at planting and harvest maturity. Total N uptake (NU) by the crop was also determined. Maximum NO3-N leaching out of the 60-cm soil layer was 8.43 kg N ha−1, for the 142 kg N ha−1 and over irrigation (1.13 SMD) treatment. The minimum and maximum seasonal average NO3 concentration at the 60 cm depth was 46 and 138 mg l−1, respectively. Based on our findings, it is possible to control NO3 leaching out of the root zone during the growing season with a proper combination of irrigation and fertilizer management. 相似文献
69.
70.
本文详细推导了质点系对于任意点的动量矩定理,该定理具有普遍性,由它可以导出质点系对于定点、质心、刚体作平面运动时速度瞬心的动量矩定理。运用这些定理可以很方便地求解某些问题。 相似文献