The importance of being reliable – Local ecological knowledge and management of forage plants in a dryland pastoral system (Morocco)     

《Journal of Arid Environments》2013

In dryland rangelands with their high environmental variability, local ecological knowledge of forage plants is essential for management decisions. Ecological apparency hypothesis (EAH) predicts plants' availability and visibility to be important criteria for local valuation. However, EAH has mainly been tested in low-variability systems. We ask whether EAH is valid for forage plants in drylands; which other local criteria exist; and how criteria are connected to management decisions.In a Moroccan pastoral system, we applied a novel ethnobotanical method by calculating the Cognitive Salience Index (CSI) for plants' valuation (CSI_antro) and availability (CSI_eco). To evaluate explicit criteria, we correlated palatability and nutritive value to CSI_anthro. ANCOVAs related CSI_anthro to EAH criteria (CSI_eco and lifetime) and to plant occurrence on pasture types. We found EAH criteria to better predict CSI_antro than explicit criteria. Apparent plants from semi-arid pastures were more valued than those from arid pastures (HSD; p < 0.05). We introduce the criterion of reliability into EAH to explain this, and demonstrate how pastoralists adjust management decisions to resource reliability. Linking resource valuation to management decisions can thus improve our understanding of resilience mechanisms. Our study also confirms the validity of EAH for forage species and dryland environments.  相似文献   

Systems Theory in Physical Geography     

Arthur N. Strahler 《自然地理学》2013,34(1):1-27

Information used in systems is organized into a hierarchy of five levels, following W. H. Terjung; first, collected data; second, sets of morphological variables; third, flow systems of energy and matter; fourth, process-form systems; fifth, systems regulated by cybernetic feedback. System variables, rigorously defined by dimensional analysis, are grouped into four classes: A. dynamic variables related to energy force, and stress; B. mass-flow variables expressing rates of flow of matter; C. geometry variables describing size and form within systems; D. material-property variables, including environmental constants and regulator variables. The second level of systems analysis interrelates a set of morphological elements in a meaningful way in terms of system origin or function. Correlation and regression methods establish significant relationships among variables, which may be stated as empirical or rational equations based on field or laboratory observations. Open energy flow systems and open or closed material flow systems of the third level can be described by dimensionally correct equations or by schematic flow diagrams. Process-form systems of the fourth level are characterized by self-regulation through physical feedback loops. Cybernetic feedback characterizes the fifth level and links natural systems to those regulated or disturbed by human intervention.  相似文献   

Phase Changes in Linear Solar-Terrestrial Relationships and a Review of the Electrification Hypothesis     

John M. Harlin 《自然地理学》2013,34(2):108-125

It appears that relatively strong linear relationships between solar activity and various weather phenomena are forthcoming only if the analyses relate to specific solar periods or are con ducted for specific geographic locations. Solar periods in this instance are defined according to the amplitude of the 11-year sunspot cycle. The sign for correlation coefficients between weather ele ments under investigation and solar activity often change according to solar amplitude. However, these phase changes may not weaken arguments in favor of sun-weather hypotheses.

Atmospheric teleconnection provides a logical explanation for phase changes over space within specific time frames, and variations in solar-amplitude relate to reversals in phase with space held constant. Previous research of large pressure systems in the tropics and mid-latitudes as well as re gional variations in annual precipitation outlined in this research indicate that a change in sign for the linear sun-weather relationship occurred between 1930 and 1940. Between 1930 and 1940, the amplitude of the solar cycle also changed. The incredibly complex nature of the climatic change equation along with the lack of an explicit physical link between solar-activity and the lower atmo sphere are serious deterrents for broad acceptance of a solar-weather connection. It is suggested, however, that recent research on a possible electrical stimulus might go far in establishing the solar hypothesis as a credible one.  相似文献   

STORAGE OF MINING-RELATED ZINC IN FLOODPLAIN SEDIMENTS,BLUE RIVER,WISCONSIN     

Scott A. Lecce  Robert T. Pavlowsky 《自然地理学》2013,34(5):424-439

This study investigates spatial patterns of sediment-associated zinc (Zn) storage in floodplain deposits and the potential reintroduction of these metal-contaminated sediments to the active channel by bank erosion. We estimate patterns of Zn mass storage by combining longitudinal trends in Zn concentrations with measurements of sediment mass storage in overbank and point-bar deposits. Overbank deposits are the largest contaminant sink, storing five times more Zn than the point-bar deposits. While Zn concentrations decrease downstream because of dilution effects, the total mass of Zn stored in floodplains is greatest in both the upstream reaches and in the wider lower valleys where low channel gradients promote rapid sedimentation. Zn storage is low in middle reaches where steep, narrow valleys with high stream power favor sediment transport over deposition. Overall, more than half of the Zn released by mining remains stored in floodplain deposits within the watershed. The remobilization of Zn from storage is more likely in the upstream and mid-basin reaches where high stream power increases rates of lateral channel migration. Channels in the lower valley lack the stream power to migrate laterally and remobilize the large Zn mass stored in overbank sediments. [Key words: floodplains, Zn contamination, mining, stream power, Wisconsin.]  相似文献   

Synoptic Classification of Snowfall Events in the Great Smoky Mountains,USA     

《自然地理学》2013,34(2):156-171

Mean annual snowfall in the Great Smoky Mountains National Park (GSMNP) exhibits considerable spatial variability, ranging from 30 cm in the valleys to 254 cm at higher elevations. Snowfall can be tied to a variety of synoptic classes (e.g., Miller A or B cyclones, 500 hPa cutoff lows), but the frequency and significance of different synoptic classes have not been fully assessed, particularly at higher elevations. In this paper, we manually classify all snowfall events during the period 1991 to 2004 according to a synoptic classification scheme, calculate mean annual snowfall by 850 hPa wind direction and synoptic class, and develop composite plots of various synoptic fields. Hourly observations from nearby first-order stations and 24 hr snowfall totals from five sites within the GSMNP are used to define snowfall events. NCEP/NCAR reanalysis data are used to develop composite plots of various synoptic fields for cyclones passing south and then east of the area (e.g., Miller A cyclones). Results indicate that over 50% of the mean annual snowfall at higher elevations occurs in association with low-level northwest flow, and that Miller A cyclones contribute the greatest amount to mean annual snowfall at all elevations.  相似文献   

部分格罗夫山陨石的类型划分及其矿物岩石学特征          下载免费PDF全文

李世杰  王世杰刘燊 李雄耀李阳  尚颖丽 《极地研究》2013,25(4):369-377

对99块南极格罗夫山陨石的研究表明这些陨石分别属于普通球粒陨石H群、L群、LL群,橄辉无球粒陨石和碳质球粒陨石。其中普通球粒陨石H3为1块,H4为23块,H5为9块,H6为8块,L4为2块,L5为21块,L6为31块,LL4和LL6分别为一块。GRV 022888为橄榄石-易变辉石无球粒陨石,GRV 023159是一块CV3碳质球粒陨石。这些陨石的冲击程度普遍较高,冲击程度为S4的普通球粒陨石有15块,GRV 023138中出现了冲击熔融现象,该陨石的冲击程度为S5,这些样品为研究小行星早期的冲击作用提供了很好的素材。此外,这些陨石的风化程度普遍较低,风化程度为W1的陨石为75块,未见风化程度高于W4的陨石。  相似文献   

东南极格罗夫山：普里兹造山带中一个典型的泛非期变质地体   总被引：2，自引：0，他引：2       下载免费PDF全文

刘晓春  赵越  胡健民  刘小汉  曲玮 《极地研究》2013,25(1):7-24

提要：距我国中山站以南约400 km的格罗夫山是普里兹造山带向南极内陆的延伸部分,其基底地体由约在920?910 Ma期间侵入的镁铁质－长英质火成岩和少量中元古代的沉积岩构成,这些岩石仅在泛非期（约570?500 Ma）经历了单相变质－构造旋回,因此是一个典型的泛非期变质地体。泛非期高峰变质作用并不象前人所认为的那样仅为中低压麻粒岩相,而是高达770?840?C、1.18?1.40 GPa,并在随后经历了近等温减压（约0.6 GPa）的P-T演化过程。大规模的A型紫苏花岗岩和花岗岩在同造山－后造山阶段侵位,并造成了麻粒岩地体近等压降温的P-T轨迹。这些花岗质岩石是由长期富集地幔的底侵物质（碱性玄武质岩石）经部分溶融而形成的。结合相邻地质体的研究资料,我们认为普里兹造山带可能发育在太古宙－格林维尔期基底地体之上,这些基底地体可能与新元古代（？）盖层卷入到了统一的泛非期造山作用过程。在泛非期造山作用过程中,地壳曾被增厚约达40?50 km,而后又经历了厚约20 km的地壳伸展垮塌和剥蚀。所以,普里兹造山带应代表东冈瓦纳陆块内部由板块缝合作用所形成的一条泛非期碰撞造山带。  相似文献   

西天山乌孙山地区大哈拉军山组火山岩LA-ICP-MS锆石U-Pb年龄及其构造环境   总被引：5，自引：0，他引：5  

茹艳娇  徐学义  李智佩  陈隽璐  白建科  李婷 《地质通报》2012,31(1):50-62

西天山乌孙山地区大哈拉军山组由玄武岩、安山岩、英安岩、流纹岩及相应的火山碎屑岩组成,安山岩和流纹岩分布最广。LA-ICP-MS锆石U-Pb定年结果表明,火山活动喷发的安山岩与安山质晶屑凝灰熔岩分别形成于353.9Ma±6.5Ma和356.3Ma±4.4Ma,属于早石炭世早期。通过区域对比,西天山大哈拉军山组的火山岩浆作用显示从伊犁中天山板块南北缘向伊犁盆地内部逐渐变年轻的特点,且火山岩喷发时代差别不大(约40Ma)。岩石地球化学研究表明,火山岩属钙碱性系列,富集轻稀土元素,相对亏损重稀土元素。中性火山岩富集大离子亲石元素(如Cs、Rb、Th、U),而相对亏损高场强元素,具有明显的Nb、Ta、Ti负异常,显示出岛弧火山岩的特征;酸性火山岩相对富集Rb、Th、U、Ta等元素,具有明显的Ba、Sr、P、Eu、Ti等元素的负异常。综合伊犁-中天山板块南缘的构造演化特征,认为大哈拉军山组形成于活动大陆边缘环境,产在板块俯冲-碰撞的最后阶段。  相似文献   

中条山同善地区虎坪杂岩锆石U-Pb年龄、Hf同位素特征及地质意义   总被引：1，自引：0，他引：1  

张晗  孙丰月 《吉林大学学报(地球科学版)》2012,42(3):733-746

中条山地区是华北克拉通中部造山带的重要组成部分,区内前寒武纪地层广泛出露,新太古代地质体主要分布在北东走向的中条山主山脉和近东西向王屋山"同善天窗"内。"同善天窗"中主要出露虎坪花岗质片麻杂岩及宋家山群。虎坪杂岩中黑云斜长片麻岩的锆石U-Pb上交点年龄为(2 530±13)Ma,εHf(2 530Ma)为3.89～7.12;英云闪长岩207 Pb/206 Pb加权平均年龄为(2 551.4±2.7)Ma,εHf(t)为5.49～9.67。结合近年来华北克拉通新太古代晚期中部造山带镁铁质火山岩Nd同位素及遵化二辉橄榄岩的Hf同位素特征,推测华北克拉通中部造山带新太古代晚期地幔εHf(t)与εNd(t)具有一定的线性关系,中条山新太古代晚期地幔εHf(2.55Ga)为8.2～9.5,显示华北克拉通地幔在2.55Ga之前即发生过大规模的分异。虎坪变英云闪长岩幔源Hf同位素的特征需要新生玄武质地壳俯冲熔融,类似特征的花岗岩往往存在于洋内俯冲带或是洋脊俯冲的特殊构造环境;因此,虎坪英云闪长岩的产出可能代表了中条山2.55Ga的洋脊俯冲或是年轻洋壳的壳内俯冲事件。  相似文献   

川西龙门山中段天然硅石资源地质特征及评价     

李广  刘奇川  刘文彦 《四川地质学报》2012,32(1):61-65

介绍了龙门山中段脉石英、石英砂岩等硅石矿产地质特征,分析其工业应用评价,提出勘查开发利用与保护的意义。  相似文献