Environmental zonation across the Australian arid region based on long-term vegetation dynamics     

E.F. Lawley  M.M. LewisB. Ostendorf 《Journal of Arid Environments》2011,75(6):576-585

Zonation of landscapes is generally based on broad scale biophysical data, field surveys, imagery and expert knowledge. Such zonation represents a static view of the environment and does not reflect dynamics and function. Arid environments are however often highly dynamic, and spatial and temporal patterns may be expressed over long periods of time. These dynamics need to be understood for management. Our aim is to understand the dynamics and functional response of vegetation in the Australian arid zone, and use this to inform and potentially improve the currently employed stratification. Principal component analysis of 25 years of satellite imagery identified underlying factors influencing patterns of arid vegetation growth, and regions of similar long-term response. Dominant factors of variation were identified as the spatial distribution of total vegetation growth, seasonality of growth, magnitude of seasonal variability in growth, and regularity of variation in growth. Additional variation resulted from episodic vegetation growth of limited spatial extent and duration. Classes expressing these functional components were compared with the existing biogeographical regions, revealing agreement in some instances, and in other cases adding information previously not available. The study demonstrates a new approach to Australian landscape zonation that has potential for much wider application.  相似文献   

Positive plant interactions in the Iberian Southeast: Mechanisms, environmental gradients, and ecosystem function     

F.I. Pugnaire  C. Armas  F.T. Maestre 《Journal of Arid Environments》2011,75(12):1310-1320

Semi-arid ecosystems are privileged sites to address the effects of plant interactions on community structure and dynamics because environmental conditions are demanding and may change quickly, altering in significant ways the balance between positive and negative effects among neighboring plants. Plant interaction processes have been well documented in the semi-arid region of Southeast Spain over the last 15 years. In this article we review the growing body of research on plant–plant interactions available from this area, highlighting its importance in increasing our knowledge on this field of study. This review has been organized in five sections, i) facilitation mechanisms; ii) the nurse effect; iii) the balance of interactions and environmental, ontogenic, temporal, and spatial gradients; iv) the effects of facilitation on biodiversity; and, v) facilitation and ecosystem functioning. Mechanisms of facilitation in these systems are relatively well known, but not completely explored. In these environments competition, mainly for water, is intense between neighbors and switches in intensity from belowground to aboveground as productivity increases. By contrast, facilitation may decrease quickly with increasing productivity, although the balance between facilitation and competition is not fully understood, and is further complicated because shifts can also be driven by factors such as life history or physiology of interacting species. Positive interactions are critical for maintaining biodiversity in some ecosystems in SE Spain, but their role as a driver of ecosystem functioning is less clear. Research on plant–plant interactions in this region has been highly influential and has contributed to our overall understanding of plant community dynamics. Despite the important progress achieved during the last 15 years, there is still substantial scope for exploring the effects of plant interactions at the ecosystem level, and their role as modulators of disturbances such as the current global environmental change.  相似文献   

中原城市群高速公路通达性及空间格局变化研究   总被引：2，自引：1，他引：1  

李红  李晓燕  吴春国 《地域研究与开发》2011,30(1):55-58

基于中原城市群2000,2003,2006,2009年高速公路网络建设情况,分别构建4个年份高速公路拓扑网络分析图和最短路径矩阵,对中原城市群高速公路10年来网络发育程度进行动态分析和空间格局变化的研究。结果表明:2000—2009年中原城市群高速公路网络发育程度明显改善,入网城市和线路数增加迅速,经历了由树状网络—回路网络—网络拓展阶段;区域交通中心形成6路回路网络连接;网络伸展程度逐年提高,区域网络直径变化虽然不明显,但是网络直径对应的城市却发生明显的空间位移;城市群高速公路网络发育在空间上已经开始打破"核心-边缘"的特点,呈现均衡化发展的趋势。  相似文献   

中部六省R&D经费投入与结构分析     

户万元  刘龙飞 《地域研究与开发》2011,30(5)

以中部六省为研究对象,对R&D经费投入总量及强度、R&D经费的支出结构与来源结构进行深入分析,并找出与先进地区或国家相比存在的差距。研究结果表明:中部六省之间,R&D经费投入与结构均存在较大差异。总体而言,中部六省R&D经费投入不足,强度偏低;对原始创新重视程度不够,R&D经费支出在科研机构与高校所占的比例以及在基础研究与应用研究所占的比例偏低;政府对R&D活动支持的力度有待进一步提升。  相似文献   

Interannual variability of tropical cyclone activity along the Pacific coast of North America     

D.S. Gutzler  K.M. Wood  E.A. Ritchie  A.V. Douglas  M.D. Lewis 《Atmósfera》2013,26(2):149-162

The interannual variability of near-coastal eastern North Pacific tropical cyclones is described using a data set of cyclone tracks constructed from U.S. and Mexican oceanic and atmospheric reports for the period 1951-2006. Near-coastal cyclone counts are enumerated monthly, allowing us to distinguish interannual variability during different phases of the May-November tropical cyclone season. In these data more tropical cyclones affect the Pacific coast in May-July, the early months of the tropical cyclone season, during La Niña years, when equatorial Pacific sea surface temperatures are anomalously cool, than during El Niño years. The difference in early season cyclone counts between La Niña and El Niño years was particularly pronounced during the mid-twentieth century epoch when cool equatorial temperatures were enhanced as described by an index of the Pacific Decadal Oscillation. Composite maps from years with high and low near-coastal cyclone counts show that the atmospheric circulation anomalies associated with cool sea surface temperatures in the eastern equatorial Pacific are consistent with preferential steering of tropical cyclones northeastward toward the west coast of Mexico.  相似文献   

Characteristics of tropical cyclones making landfall on the Pacific coast of Mexico: 1970-2010     

L.M. Farfán  E.J. Alfaro  T. Cavazos 《Atmósfera》2013,26(2):163-182

This study evaluates impacts from tropical cyclone (TC) landfalls on populated areas located along the Pacific Ocean coast of Mexico. The period of interest is from 1970 through 2010 and an international disaster database is used to identify the impact from the landfalling TCs. More than 30 landfall events occurred during the period; we examined the top 25 TCs based on rainfall accumulation, as well as the top 10 TC-related disasters based on the affected population. Each event resulted in affected population from 20 000 to more than 800 000. Strong winds and heavy rainfall, during periods of one to three days, are associated with property damage and loss of lives. Our results indicate that excessive rainfall accumulations and daily rates, over highly populated areas, are important elements associated with the occurrence of disasters. Six of the top 10 TC-related disasters occurred during El Niño and three during neutral conditions; however, looking at the top 25 events, 10 occurred during El Niño and 10 during neutral conditions. Three case studies that occurred during El Niño events (Liza in 1976, Pauline in 1997, and Lane in 2006) are documented in more detail as they affected areas with different population densities in the southern and northwestern coasts of Mexico.  相似文献   

Torremiroella hispanica Brun and Canérot, 1979 (benthic foraminifera) from the Lower Cretaceous of Central Iran and its palaeo-biogeographic significance     

《Cretaceous Research》2013

The larger benthic foraminifer Torremiroella hispanica Brun and Canérot, 1979, so far only known from its type-locality in southern Spain, is described from the Late Barremian–Early Aptian of Central Iran (Ardakan and Yazd areas). It is reported from foraminiferan pack- to grainstones associated with Balkhania balkhanica Mamontova, 1966, dated as early Aptian (Bedoulian). A review of the literature data suggests that both are typical northern Tethyan faunal components as indicated also by the assemblages of orbitolinid foraminifers and dasycladalean algae.  相似文献   

新疆祁漫塔格柯可卡尔德钨锡矿床控矿构造及 ⁴⁰Ar-³⁹Ar年代学研究   总被引：1，自引：0，他引：1  

丰成友  李国臣  李大新  周安顺  李洪茂 《矿床地质》2013,32(1):207-216

位处新疆东昆仑祁漫塔格地区的白干湖是中国西部最新探明的一个具超大型远景规模的钨锡矿田,柯可卡尔德是其中勘查程度最高、规模最大的钨锡矿床.文章在对柯可卡尔德钨锡矿地质特征详细野外调研和剖析的基础上,重点开展了控矿构造和白云母40Ar-39Ar定年研究.结果表明,该矿区内构造活动强烈且具多期次性,可划分为成矿前向西右旋剪切构造、成矿期以NE向为主的左旋张扭性断裂和成矿后近SN向正断层性质断裂等3期.应用白云母40 Ar-39 Ar同位素测年技术,分别测得了强云英岩化钨锡矿化花岗岩脉内白云母的积分年龄为(411.7±2.6) Ma,等时线年龄为(411.8±4.7) Ma(n=8,MSWD=0.21);黑钨矿-石英脉垂直脉壁生长的片状白云母的积分年龄为(412.8±2.4) Ma,等时线年龄为(414.6±3.9) Ma(n=10,MSWD=0.22),厘定了该矿床的成矿时代为晚志留世,认为其形成于东昆仑地区加里东造山旋回的后碰撞构造阶段.  相似文献   

The latest Carboniferous–Early Permian Dorud Group of the eastern Alborz (Iran): biostratigraphy and taxonomy of smaller foraminifers     

Zohreh Alipour  Seyyed Mahmood Hosseini‐Nezhad  Daniel Vachard  Koorosh Rashidi 《Geological Journal》2013,48(4):385-402

The latest Carboniferous–Early Permian Dorud Group in the Chaman‐Saver area of eastern Alborz, Iran is more than 222 m thick and includes thick sequences of oncolitic limestone, sandy limestone, sandstones and shales. The Emarat and Ghosnavi formations of this Group are dated here as latest Gzhelian to early Sakmarian Stages. During the Asselian Stage, the sea level fell abruptly and epeirogenic episodes occurred. These events generated a broad, shallow carbonate platform suitable for the growth and diversity of smaller foraminifers in the Chaman‐Saver area which, consequently, displays faunal differences with the rest of the Alborz Mountains. Three foraminiferal biozones are proposed: Nodosinelloides potievskayae–Vervilleina bradyi Zone (latest Gzhelian), Calcitornella heathi–Nodosinelloides sp. Zone (latest Gzhelian–Asselian), and Rectogordius iranicus n. gen. n. sp.–Hemigordius schlumbergeri Zone (early Sakmarian). The new taxa described herein include: Pseudovidalina iranica n. sp., P. damghanica n. sp., Rectogordius iranicus n. gen. n. sp. and Tezaquina sp. 1. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

豫西银家沟硫铁多金属矿床流体包裹体和同位素特征   总被引：6，自引：0，他引：6  

武广  陈毓川  李宗彦  刘军  杨鑫生  乔翠杰 《地质学报》2013,87(3):353-374

河南省银家沟硫铁多金属矿床位于华北克拉通南缘华熊地块内,是东秦岭地区最大的硫铁多金属矿床,以其硫铁储量大及共、伴生元素复杂区别于东秦岭其他以钼为主的矿床.成矿的全过程可以划分为矽卡岩期、硫化物期和表生期,包括磁铁矿阶段、脉状石英-辉钼矿阶段、石英-黄铁矿-黄铜矿-斑铜矿-闪锌矿阶段、网脉状石英辉钼矿阶段、石英绢云母-黄铁矿阶段、方解石-方铅矿闪锌矿阶段和玉髓褐铁矿阶段.流体包裹体研究表明,银家沟矿床主要发育气液两相水溶液包裹体(W型)、含CO2三相包裹体(C型)和含子矿物多相包裹体(S型).钾长花岗斑岩的石英斑晶中流体包裹体均一温度介于341～＞550℃之间,盐度介于0.4％～44.0％ NaCl eqv之间,属H2O-NaCl-CO2体系;脉状石英-辉钼矿阶段流体包裹体均一温度介于382～416℃之间,盐度介于3.6％～40.8％ NaCl eqv之间,属H2O-NaCl体系;石英-方解石-黄铁矿黄铜矿-斑铜矿-闪锌矿阶段流体包裹体均一温度介于318～436℃之间,盐度介于5.6％～42.4％ NaCl eqv之间,属H2O-NaCl体系;网脉状石英-辉钼矿阶段流体包裹体均一温度介于321～411℃之间,盐度介于6.3％～16.4％ NaCl eqv之间,属H2 O-NaCl体系;石英-绢云母黄铁矿阶段流体包裹体均一温度介于326～419℃之间,盐度介于4.7％～49.4％ NaCl eqv之间,属H2O-NaCl体系.银家沟矿床成矿流体主要为高温、高盐度流体,总体上属于H2O-NaCl±CO2体系.成矿热液的δ18 OH2O值为4.0‰～8.6‰,δ18 Dv-SMOW值为-64‰～-52‰,表明成矿流体来自岩浆水.矿石金属硫化物的δ18 SV-CDT值介于-0.2‰～6.3‰之间,平均为1.6‰,具深源硫特征,硫主要来自分异很差的由火成物质组成的下地壳,官道口群白云岩亦提供了部分重硫.矿床金属硫化物的206 Pb/204 Pb值介于17.331～18.043之间,207 Pb/204 Pb值变化于15.444～15.575之间,208 Pb/204 Pb值变化于37.783～38.236之间,总体上与银家沟岩体的铅同位素范围一致,暗示铅主要来自矿区内的燕山期中酸性岩体,地层在成矿过程中亦提供了少量物质.银家沟矿床属斑岩-矽卡岩型,形成于中生代EW向构造体制向NNE向构造体制转变阶段,成矿流体多期次的沸腾作用是矿质沉淀的主要机制.  相似文献