广东博罗县小金河植物区系研究

本区计有野生维管束植物１７２科、５３２属、９７８种（包括变种、变型）。发现２新种，１新变种和３个广东新记录种。本区系的表征科为山茶科、壳斗科、桑科、芸香科、紫金牛科、樟科等，这些科大都是热带－亚热带分布式的，代表了本区系的性质。在属的地理成分中，本区以热带成分１７３属（占总数的３５．２％）和热带－亚热带成分１６９属（占总数的３４．４％）为主，说明了本区系具有由亚热带向热带过渡的南亚热带特征。本区与     

Vegetation and Community Changes of Elm （Ulmuspumila） Woodlands in Northeastern China in 1983-2011

Elm (Ulmus pumila), widely distributed in the north temperate zone, contributes to a special savanna-like woodland in typical grassland region in the northeastern China. This woodland performs a variety of ecological functions and environmental significance, such as decreasing soil erosion, stabilizing sand dunes, preserving species diversity. However, in the last approximate 30 years, the species composition, productivity and distribution area of elm woodland has decreased severely. A series of studies have been carried out to find out whether the climate changes or human disturbances caused the degradation of elm woodland and how these factors affected elm woodland. In this study, undisturbed, plowing and grazing elm woodland were investigated in 1983 and 2011 by using Point-Centered Quarter method. The relationship between vegetation changes and environmental factors was analyzed by Bray-Curtis ordination. The results show that in 2011, species diversity and understory productivity of undisturbed elm woodland decrease slightly compared to those of undisturbed elm woodland in 1983. However, nearly 60% of the species is lost in the plowing and grazing elm woodland relative to the species undisturbed elm woodland in 1983. Interestingly, plowing stimulates the growth of elm and certain understory species through furrowing soil and accelerating soil nutrient turnover rate. Grazing disturbance not only leads to species loss and productivity decrease, but also induces changes in elm growth (small, short and twisted). The mean age of the elm was 29 ± 2 yr in undisturbed and plowing elm woodland, while only 15 yr in the grazing elm woodland. The results of Bray-Curtis ordination analysis show that all sample stands clustered to three groups: Group I including the undisturbed sample stands of 83UE (undisturbed elm woodland in 1983) and 11UE (undisturbed elm woodland in 2011); Group II including sample stands of PE (elm woodland disturbed by plowing); Group III including samples stands of GE (elm woodland disturbed by grazing). The results indicate that the long time disturbance of the plowing and grazing have converted elm woodland to different community types. Climate change is not the primary reason causing the degradation of elm woodland, but plowing and grazing disturbance. Both plowing and grazing decrease the vegetation composition and species diversity. Grazing further decreases vegetation productivity and inhibits the growth of elm tree. Therefore, we suggest that reasonable plowing and exclusive grazing would be favorable for future regeneration of degraded elm woodland.     

呼伦湖表层沉积物花粉空间分布特征及影响因素探讨

对呼伦湖29个表层沉积物花粉组合和环境影响因子进行主成分分析(PCA)和冗余分析(RDA),探讨呼伦湖表层沉积物花粉组合的空间分布特征及造成空间分异的现代过程机制.研究结果表明,呼伦湖表层沉积物花粉组合空间分布差异显著,藜科和松属等花粉在湖泊东侧近岸地带百分含量较高,蒿属与桦属花粉在湖泊中部和西部百分含量较高.呼伦湖东岸盐生非地带性植被、主导风向形成的漂流、与水深相关的二次悬移再沉积过程以及河流搬运作用是影响呼伦湖表层沉积物花粉空间分异的主要因素,其中湖泊东岸盐生非地带性植被造成了藜科花粉百分含量在近东岸地带偏高,主导风向形成的由西向东的漂流作用可能导致了松属花粉百分含量在近东岸地带偏高.     

3D Diffraction of obliquely incident SH waves by twin infinitely long cylindrical cavities in layered poroelastic half-space

This paper studies three-dimensional diffraction of obliquely incident plane SH waves by twin infinitely long cylindrical cavities in layered poroelastic half-space using indirect boundary element method. The approach is validated by comparison with the literature, and the effects of cavity interval, incident frequency, and boundary drainage condition on the diffraction are studied through numerical examples. It is shown that, the interaction between two cavities is significant and surface displacement peaks become large when two cavities are close, and the surface displacement may be significantly amplified by twin cavities, and the influence range with large amplification can be as wide as 40 times of the cavity radius. Surface displacements in dry poroelastic case and saturated poroelastic cases with drained and undrained boundaries are evidently different under certain circumstances, and the differences may be much larger than those in the free-field response.     

Land use sustainability on the South-Eastern Amazon agricultural frontier: Recent progress and the challenges ahead

The recent decoupling of deforestation and soybean production has raised optimistic expectations towards enhanced land use sustainability in the South-Eastern Amazon agricultural frontier. Nonetheless, assessing land use sustainability implies not only the consideration of how agricultural activities affect natural ecosystems but also how they impact on society and how society can cope with them. We review some of the forthcoming challenges that the agricultural sector should address to confirm its significant progress towards land use sustainability. Firstly, we assess the recent efforts to adopt environmentally friendly practices with regard to the ongoing intensification process mainly based on double cropping systems. Secondly, while rapid agricultural development has brought major social advances, we evidence a recent trend towards a decoupling of soy production and the Human Development Index at municipality level. We then put this result into perspective considering that the trend towards agricultural intensification based on the use of large amounts of agrochemicals could lead to major health concerns which are still too rarely considered. Finally, we discuss how the recent efficient policies to contain deforestation in the Amazon can cause indirect land use changes in the Brazilian Cerrados and in African Savannas, thus potentially leading to an “illusion of preservation” at global scale. We conclude that new indicators involving social sciences are necessary to better address the complexity of land use sustainability on the still very dynamic agricultural frontier in the South-Eastern Amazon.     

利用GPS水准点加强和改善天文重力水准网

介绍如何利用GPS水准点加强和改善天文重力水准网的原理、方法及实现的途径。以单线推进路线为例,一般证明GPS水准点的控制作用。还着重讨论并验证间接平差方法的有效性,能够满足当前需要。     

The influence of geological fabric and scale on drainage pattern analysis in a catchment of metamorphic terrain: Laceys Creek, southeast Queensland, Australia

The relationship between geological fabric and drainage patterns in the 81.8 km² Laceys Creek sub-catchment of the North Pine River catchment, southeast Queensland, Australia, is analysed using a new channel–ordination system. The Laceys Creek catchment is situated on the South D'Aguilar Block, which underwent metamorphism, faulting and uplift from the Late Carboniferous to Late Triassic. The catchment drains exposures of two main rock units, the Neranleigh–Fernvale Beds and the Bunya Phyllite. Both units are composed of metamorphosed deep-sea sediments that accumulated as an accretionary wedge during late Palaeozoic subduction of the palaeo-Pacific plate under the eastern margin of the Australian craton. The new channel ordination system used in this study allows improved classification of stream segments of equal prominence or rank in comparison to previous schemes. A 10 m contour digital elevation model (DEM) was produced within which drainage channels were digitised. Planar geological features, including bedding, faults, joints and cleavage, were mapped in the field and collated with data from previous geological mapping programs.Regional and local trends of geological fabric are reflected in the variable orientation of channels of different rank in the catchment. Cleavage and fractures are the dominant planar features of the Bunya Phyllite and these correlate most closely with the orientation of middle-order incised stream segments. In contrast, middle-order channels on the Neranleigh–Fernvale Beds most closely correlate with bedding, which dominates the fabric of this unit. Although anthropogenic factors exert local influence and climatic processes exert broad influence on the catchment, this study focuses on structural and lithological fabrics, which are the apparent dominant controls on middle-order channel orientations. Identification of congruent patterns between bedrock fabric and channel ranks is variable, depending on the scale and number of channels included in the analysis. Many low-rank channels correspond closely to the orientation of fine-scale bedding and foliation and these influences may not be detected by coarse-scale mapping. Understanding the extent of geological controls on the morphology of a catchment may assist geo-hazard identification, land-use planning and civil-engineering projects.     

阿拉善高原荒漠植被组成分布特征及其环境解释Ⅰ.典型荒漠植被分布格局的环境解释

阿拉善高原是亚洲中部荒漠亚区的一个植物地理区域,特殊的地理位置和严酷的气候条件形成了该区独特的植被组成。目前由于气候的干暖化、黑河断流、森林草原的过度开采利用以及人口的激增等,给当地的农牧业发展、生态环境的可持续发展和利用带来严重障碍。如何有效地管理和利用当地的草场资源是当地政府和科研人员面临的首要问题。通过分析环境因子和植被分布的相互关系,来确定影响该区草场资源分布的主要环境因子。通过对52个样地的植被调查资料进行分析,发现所调查到的70种植物包括16个科和46个属,其中一年生植物占7.1%,灌木和小灌木占52.9%。种数最多的4个科是豆科(Leguminosae)、蓼科(Polygonaceae)、禾本科(Gramineae)和菊科(Compositae),分别占到总种数的20.0%、15.7%、14.3%和14.3%。高位芽和地面芽是主要的生活型,这代表了沙漠植物典型的生活型谱。采用二歧双向指示种分析（TWINSPAN）,将所调查植被分为6个类型,每个植被类型及相应的土壤特征代表了特定的地理单元。此外采用除趋势分析（DCA）和典范对应分析（CCA）方法研究了植被分布和环境变量二者的关系。环境因子主要有29个:其中包括18个土壤因子、8个气候因子和3个地理位置因子。DCA和CCA分析的结果一致,都表明植被分布和环境因子之间相关性较强。其中,CCA的第一轴主要代表了土壤有机质、全氮、沙黏粒含量、海拔、Kira湿度指数以及相对湿度,而CCA第二轴主要和Cl-、K+、Mg2+和电导率相关。这两轴在解释植物-环境关系的过程中累积贡献率达到60%,说明前两轴代表的环境因子是决定该区荒漠植被分布的主要因子。这一结果阐明了阿拉善干旱荒漠区植被分布的独特性,以及与关键环境因子之间的作用机制,这为该区域荒漠草场的恢复和管理提供了一定理论基础。