The Effects of Inter-plant Interactions and Density-dependent Disturbances on Vegetation Pattern Formation     

Dan Malkinson  Ronen Kadmon 《Landscape Ecology》2006,21(2):259-270

Ecological interactions among individuals and disturbances are two important agents of pattern formation. In this study we investigated the interrelationships between interactions among individuals and large scale disturbances, and the resulting patterns. We categorized disturbances into three general classes, (1) those whose probability of occurrence increases with increased densities of vegetation, such as fire and disease, (2) those with a decreasing probability of occurrence with increasing vegetation densities, such as sand movement, and (3) disturbances that occur independently of vegetation densities, such as flooding. The ecological interactions among individuals were also divided to three classes: competition, facilitation and neutrality. We systematically investigated how these two types of processes interact to generate spatial patterns, using simulation models that were partially based on data collected from a shrub community in the Nizzana sand dune ecosystem. The results indicated that the different types of disturbances have fundamentally different effects on spatial patterns. Positive density-dependent disturbances, regardless of the type of interactions among individuals with which they were simulated, generated uniform spatial patterns. Patterns formed by interactions between decreasing or density independent disturbances with the different class interactions among individuals were more variable. These differences are attributed to the manner in which the difference disturbance types propagate in space.  相似文献   

Modelling forest recolonization by an epiphytic lichen using a landscape genetic approach     

Helene H. Wagner  Silke Werth  Jesse M. Kalwij  Jacqueline C. Bolli  Christoph Scheidegger 《Landscape Ecology》2006,21(6):849-865

The process of recolonization after disturbance is crucial for the persistence and dynamics of patch-tracking metapopulations. We developed a model to compare the spatial distribution and spatial genetic structure of the epiphytic lichen Lobaria pulmonaria within the perimeter of two reconstructed 19th century disturbances with a nearby reference area without stand-level disturbance. Population genetic data suggested that after stand-replacing disturbance, each plot was colonized by one or a few genotypes only, which subsequently spread clonally within a local neighborhood. The model (cellular automaton) aimed at testing the validity of this interpretation and at assessing the relative importance of local dispersal of clonal propagules vs. long-distance dispersal of clonal and/or sexual diaspores. A reasonable model fit was reached for the empirical data on host tree distribution, lichen distribution, and tree- and plot-level genotype diversity of the lichen in the reference area. Although model calibration suggested a predominance of local dispersal of clonal propagules, a substantial contribution of immigration of non-local genotypes by long-distance dispersal was needed to reach the observed levels of genotype diversity. The model could not fully explain the high degree of clonality after stand-replacing disturbance, suggesting that the dispersal process itself may not be stationary but depend on the ecological conditions related to disturbance.  相似文献   

Use of fourier transforms to define landscape scales of analysis for disturbances: a case study of thinned and unthinned forest stands   总被引：1，自引：0，他引：1  

Lundquist  J.E.  Sommerfeld  R.A. 《Landscape Ecology》2002,17(5):445-454

Various disturbances such as disease and management practices causecanopy gaps that change patterns of forest stand structure. This study examinedthe usefulness of digital image analysis using aerial photos, FourierTranforms,and cluster analysis to investigate how different spatial statistics areaffected by spatial scale. The specific aims were to: 1) evaluate how a Fourierfilter could be used to classify canopy gap sizes objectively, 2) determinewhich statistics might be useful for detecting and measuring disturbanceimpacts, and 3) examine the potential for this method to determine spatialdomains in a pair of ponderosa pine (Pinusponderosa) stands in the Black Hills of South Dakota,USA.The eventual goal is to develop an operational method of assessing the impactsof natural disturbances such as disease. Results indicated that several spatialmetrics discriminated between harvested and unharvested stands. We hypothesizethat these metrics will be useful as spatial measures of disease impact if theanalyses are performed on specific size classes of forest gaps.This revised version was published online in May 2005 with corrections to the Cover Date.  相似文献   

Effect of low‐dose N application and early mowing on plant species composition of mesophilous meadow grassland (Arrhenatherion) in Central Europe     

K. Čámská  H. Skálová 《Grass and Forage Science》2012,67(3):403-410

Semi‐natural temperate grasslands in Europe make an important contribution to biodiversity, but their existence has been endangered by both agricultural intensification and abandonment. In the Czech Republic, Arrhenatherion meadows are a typical example, with their conservation made difficult by the scarcity of research on effective management practices. We examined effects of two potentially useful approaches, application of 56 kg N ha^?1 and earlier first mowing (i.e. in the middle of May, about 2 weeks earlier than usual), on species composition of an Arrhenatherion grassland in central Bohemia over a 7‐year period (1998–2004). These treatments did not influence species richness, but resulted in small changes in canopy structure in terms of cover of individual species and particular plant functional groups. N application resulted in increases in nitrophilous species and tall graminoids, especially Alopecurus pratensis, Festuca pratensis, Heracleum sphondylium and Ranunculus acris, and in decreases in short graminoids. Earlier mowing decreased tall herbs, especially H. sphondylium, and might thus be useful in compensating for increases in some nitrophilous species owing to N application. However, earlier mowing had negative impacts on spring‐flowering species in terms of reduced cover.  相似文献   

Fluctuations in European eel (Anguilla anguilla) recruitment resulting from environmental changes in the Sargasso Sea     

SYLVAIN BONHOMMEAU  EMMANUEL CHASSOT  ETIENNE RIVOT 《Fisheries Oceanography》2008,17(1):32-44

European eel decline is now widely observed and involves a large number of factors such as overfishing, pollution, habitat loss, dam construction, river obstruction, parasitism and environmental changes. In the present study, we analyzed the influence of environmental conditions in the Sargasso Sea and Atlantic ocean circulation on European glass eel recruitment success. Over a recent 11‐yr period, we showed a strong positive correlation between an original index of glass eel recruitment and primary production (PP) in eel spawning area. Moreover, PP was negatively correlated with temperature in the Sargasso Sea. Therefore, we used sea temperature as an inverse proxy of marine production. A close negative relationship has been found over the last four decades between long‐term fluctuations in recruitment and in sea temperature. These findings were reinforced by the detection of a regime shift in sea temperature that preceded the start of the decline in glass eel recruitment in the early 1980s. By contrast, variations in integrative indices measuring ocean circulation, i.e. latitude and strength of the Gulf Stream, did not seem to explain variations in glass eel recruitment. Our results support the hypothesis of a strong bottom‐up control of leptocephali survival and growth by PP in the Sargasso Sea on short and long time scales. We argue that sea warming in the eel spawning area since the early 1980s has modified marine production and eventually affected the survival rate of European eels at early life stages.  相似文献   

巴氐人的起源与成汉政权的建立     

程刚 《信阳农业高等专科学校学报》2005,15(4):48-50

巴氐人的祖先最早居住在四川西部宕渠,称为板盾蛮,后迁至天水、略阳一带。那里原为氐人的居住地,故称之为巴氐人。巴氐人保持着纯正的板盾蛮血统和风俗,他们和廪君蛮并非同宗同源,是他们奠定了成汉政权的基础。  相似文献   

林火管理对火动态的影响   总被引：1，自引：0，他引：1  

苗庆林  刘耀香  田晓瑞 《世界林业研究》2014,27(4):42-47

火是森林生态系统最主要的干扰因子之一。火动态研究是开展科学林火管理的基础。文中总结了当前全球各种植被类型的火动态,分析了不同林火管理政策对林火动态的影响,根据当前火动态恢复与重建的理论与技术发展提出了综合林火管理技术的发展趋势与技术难点。  相似文献   

南北极渔业管理机制的对比研究   总被引：2，自引：1，他引：1  

邹磊磊  黄硕琳  付玉 《水产学报》2014,38(9):1611-1617

极地权益成为新兴的国际关注热点,而开展极地渔业活动并参与极地渔业管理机制构建是实现极地海域"实质性存在"及权益的重要切入点。本文采用对比研究的方法,从渔业管理协议、渔业管理组织、渔业管理理念、与其他国际协议及组织的互动性、以及渔业管理职责等方面分析南北极渔业管理机制中的各项举措,并剖析各自管理举措中的亮点与瓶颈,且以此进一步讨论南北极渔业管理机制的相互借鉴作用。对比研究为南北极渔业管理实践经验提供了交流的平台,同时有助于深刻解析南北渔业管理机制的特色,从而为制定中国极地渔业政策提供相应的背景资料。  相似文献   

历史政权遗址资源在园林绿地建设中的利用——以南京为例          下载免费PDF全文

陈鸣跃 《中国城市林业》2013,11(6):60-61

南京朝代多,10个朝代跨度长达1 700多年,各朝都城和宫城遗址资源丰富。南京政区及治所变更频繁,主要古称数十,历代衙门遗址资源丰富。将南京历代政权遗址纪念园林建设纳入南京绿地系统建设规划,使绿化与文化联姻,可以让游人在游园的同时感受南京厚重的历史与文化。    相似文献   

围封与放牧措施下生物土壤结皮发育及其微生境土壤养分特征   总被引：2，自引：0，他引：2  

韩炳宏  牛得草  袁晓波  任运涛  石明明  吴让  傅华 《草地学报》2016,24(6):1218-1225

为了探讨围封与放牧措施下生物土壤结皮发育及其与微生境土壤养分的对应关系,本研究以黄土高原天然草地两类生物土壤结皮（藻类和藓类）为研究对象,调查了生物土壤结皮发育的形态指标,并就不同措施下生物土壤结皮层及其下层土壤养分特征进行了比较分析。结果表明,两类生物土壤结皮对围封与放牧干扰的响应一致,盖度均表现为围封显著高于放牧,而厚度和生物量无显著差异。然而,围封与放牧对生物土壤结皮层及其结皮下层养分含量的影响不尽相同,围封藻结皮层及其结皮下层SOC,TN和Zn含量显著高于放牧,而TP和Na则显著低于放牧。另外,生物土壤结皮层与结皮下层养分间的关系均存在差异,其藻结皮层土壤SOC与TN,TP,Na,K,Fe,Mn和Zn均呈正相关,与Ca呈负相关;藓结皮层SOC分别与Mn和Zn呈正相关,而与Ca和Fe呈负相关。  相似文献