River regulation and fish larvae: variation through space and time

1. Patterns in abundance and distribution of larval fish in a heavily regulated and a mildly regulated Australian lowland river were compared over four breeding seasons to gain some insight into how river regulation affects fish populations.
2. Larvae from a total of 13 species from nine families were recorded from the two rivers. The mildly regulated Broken River supported twice as many species as the heavily regulated Campaspe River. The two rivers shared three introduced species but only two native species. The dominant species in the Campaspe was not found in the Broken River.
3. The two most abundant species in the Campaspe were classified as `opportunists'. They are small, short-lived species, which spawn for up to 9 months, encompassing extremes in temperature and flow. The extended spawning period may place a subset of larvae in optimal conditions for recruitment and is hypothesised as being the key to the success of these species.
4. Most species spawned each year, despite large interannual variation in flow and temperature conditions. Poor recruitment over several decades, rather than a failure to spawn, is considered the most likely explanation for differences in the larval fish faunas between the two rivers.
5. The highly regulated section of the Campaspe River downstream of the regulating impoundment is thought to provide suboptimal habitat conditions for larvae relative to the less regulated downstream sections.
6. The timing of occurrence of larvae of the dominant species varied by breeding season and may be the result of flexibility in the timing of spawning.     

Land-Use History in Ecosystem Restoration: A 40-Year Study in the Prairie-Forest Ecotone

Land‐use history, recent management, and landscape position influence vegetation at the Rockefeller Experimental Tract (RET), a 40‐year‐old restoration experiment in northeast Kansas. RET is representative of the prairie‐forest ecotone, containing native tallgrass prairie and oak‐hickory forest, but unique in having tracts of replanted prairie, seeded in 1957, that have undergone long‐term restoration treatments: burned, grazed, mowed, or untreated. A land‐use history database for RET was compiled using a geographic information system to integrate historic and contemporary sources of information. Restoration management on the reseeded prairie has had a profound effect on forest development: mowing or burning precluded forest establishment (<3% forest cover), whereas portions of untreated or grazed areas became heavily forested (>97% forest cover). Forest colonization depends upon biotic and edaphic conditions at the time restoration was initiated: for areas replanted to prairie and managed by grazing, forestation was 6% on land in cultivation prior to replanting, 20% on former pastureland, and 98% on land deforested just before replanting. Patterns of forest colonization were also significantly associated with three landscape positions: near existing forest, along water courses, and along ridge tops. Additionally, land‐use history analyses showed that the presence of various prairie and forest species resulted from persistence and not from colonization following restoration. Because of the lasting imprint of historic land use on the landscape, our results indicate that it is essential that restoration studies be evaluated within a site‐specific historical context.     

Islands of water in a sea of dry land: hydrological regime predicts genetic diversity and dispersal in a widespread fish from Australia's arid zone, the golden perch (Macquaria ambigua)

Rivers provide an excellent system to study interactions between patterns of biodiversity structure and ecological processes. In these environments, gene flow is restricted by the spatial hierarchy and temporal variation of connectivity within the drainage network. In the Australian arid zone, this variability is high and rivers often exist as isolated waterholes connected during unpredictable floods. These conditions cause boom/bust cycles in the population dynamics of taxa, but their influence on spatial genetic diversity is largely unknown. We used a landscape genetics approach to assess the effect of hydrological variability on gene flow, spatial population structure and genetic diversity in an Australian freshwater fish, Macquaria ambigua. Our analysis is based on microsatellite data of 590 samples from 26 locations across the species range. Despite temporal isolation of populations, the species showed surprisingly high rates of dispersal, with population genetic structure only evident among major drainage basins. Within drainages, hydrological variability was a strong predictor of genetic diversity, being positively correlated with spring-time flow volume. We propose that increases in flow volume during spring stimulate recruitment booms and dispersal, boosting population size and genetic diversity. Although it is uncertain how the hydrological regime in arid Australia may change under future climate scenarios, management strategies for arid-zone fishes should mitigate barriers to dispersal and alterations to the natural flow regime to maintain connectivity and the species' evolutionary potential. This study contributes to our understanding of the influence of spatial and temporal heterogeneity on population and landscape processes.     

Long-term land-cover changes in the Belgian Ardennes (1775–1929): model-based reconstruction vs. historical maps

Understanding long‐term human‐environment interactions requires historical reconstruction of past land‐cover changes. The objective of this study is to reconstruct past land‐use and land‐cover changes in a rural municipality of the Belgian Ardennes over the last 250 years. Two approaches were compared. The first approach produced backward projections based on a mechanistic model which computes the demand for different land uses under the assumption of an equilibrium between the production and consumption of resources. The second approach involved using a series of historical maps to extract directly land‐use areas. A stochastic Markov chain model was also used to project backward missing land‐cover data in the time series. The consistency between the results obtained with the different approaches suggests that land‐use area can be successfully reconstructed on the basis of the mechanistic model, under conditions of a subsistence farming system and a closed economy. Land‐use/cover changes in the Belgian Ardennes from 1775 to 1929 were more driven by the interventionist measures of the Belgian government and by technological progress than by the ‘pressure’ of the growing population and livestock. Thanks to agricultural intensification, a decrease in land under human use was supporting increasing human and livestock populations from 1846 to 1880. Reforestation has accelerated since the mid‐19th century. This case study illustrates the highly dynamic and non‐linear character of land‐use change trajectories over long time periods and their strong interactions with the history of societies.     

Lake Ladoga Region: human impacts and recent environmental changes

This paper presents a landscape-ecological analysis of Ladoga Region, a 30 000 km² territory around Lake Ladoga, which is the largest lake in Europe. The Region includes the contact zone between the crystalline bedrock of Baltic Shield and the sedimentary rocks of the East European plain, and the transition from Boreonemoral to Southern Boreal (Taiga) forest vegetation; it is characterized by abundance of lakes. The Region is divided into 17 discrete landscape areas that are classified in 6 groups.The author uses the landscape-dynamcal approach to the analysis of recent (from 2–3 to 40–50 yr) environmental changes in the region, caused by human activities: forest felling, fires, peat excavation, agriculture, recreational development etc. The following processes are observed: vegetation successions after clearcutting and selective logging; effects of forest fires on the spreading and conservation of pine forests; consequences of peatland drainage; landscape effects of collective farming and gardening; forest succession from pine and deciduous tree dominance towards spruce dominance (observable in all landscape regions); natural vegetation succession on former Finnish arable lands (two types of scenarios: forest succession or development of sedge meadows).     

From bobolinks to bears: interjecting geographical history into ecological studies, environmental interpretation, and conservation planning

In these days of supercomputer‐based global climate models, large ecosystem experiments including Biosphere II, and aircraft‐borne sensors of ozone holes it is often overlooked that many fundamental insights into ecological processes and major environmental issues come not through reductionist or high‐tech studies of modern conditions but from thoughtful consideration of nature’s history. In fact, it is foolhardy to make any ecological interpretation of modern landscapes or environments or to formulate policy in conservation or natural resource management without an historical context that extends back decades, at least, but preferably centuries or millennia. Oftentimes, the ecological and conservation communities, in their search for more detail on the present and simulation of the future, appear to have forgotten the value of a deep historical perspective in research and application. However, the willingness of the geographical sciences to embrace broad temporal and spatial perspectives and to consider cultural as well as natural processes is worth emulating as we address environmental subjects in the new millennium.     

粤北古驿道重点线路沿线传统聚落景观比较研究

粤北古驿道沿线传统聚落是古驿道“文化线路”遗产的有机组成部分,一些学者已开展沿线传统聚落的研究,但未从景观视角确立聚落中的观测指征。结合Google earth和ArcGis软件以及实地调研,对粤北古驿道中的连州丰阳—东陂古道、西京古道、梅岭古道沿线的传统聚落进行定点采样和定量分析。采用比较研究的方法研究其宏观层面的聚落高程、聚落规模,中观层面的聚落景观格局、居住地内部肌理、坑塘布局特点以及微观层面的民居平面形制。结合移民史和地方志等史料进行环境作用机制分析,得出不同层面的聚落景观差异分别受不同的主导因子影响,自然地理条件主要影响其宏观层面,民族民系与移民文化主要作用于中观、微观层面。通过对比研究,明确粤北不同古驿道沿线聚落景观资源的差异,以期为各条古驿道保护提供更有针对性的建议。     

文化景观维护视野下德国历史性文化景观的两种方法论：清单盘点与空间区划

中欧国家当前面临诸多发展问题,诸如地区差异化、农业土地面积矛盾加剧、高密度区域土壤退化及多样性丧失等,引发了学术界的关注。从20世纪90年代开始,德语背景下的 “文化景观维护”概念建立。利用历史地理学、考古学与遗产保护学以及空间与区域规划等学科的综合方法,对国土和区域空间内的文化景观进行分析和研究。文化景观维护概念以“永恒的圆环”理论模型体现,并分为分析与评价、保护与阐释、规划与管理3个主要步骤。基于此基本概念,文化景观维护大致分为2个研究方法范本：清单盘点与空间区划。范本一：历史性文化景观的对象清单盘点,就是对一定的限定区域内的文化景观要素和结构的系统化收集分类和评价方法。又分两种不同类型： Gunzelmann的复杂型“历史性文化景观”的分析法与Burggraaff和Kleefeld的 “文化景观物质分析”法。范本二：文化景观的区域化,旨在从专家角度对历史性文化景观进行标记、注释、分类和简要的特征化。又细分为类型化和个性化2个类型,并结合案例说明。最后指出：对两种研究方法的应用,不仅要客观地分析各种因素,而且还要考证在特定政治背景下的适用性。