• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1236
  • 323
  • 157
  • 112
  • 73
  • 40
  • 18
  • 15
  • 15
  • 13
  • 12
  • 11
  • 9
  • 8
  • 7
  • Tagged with
  • 2426
  • 707
  • 518
  • 423
  • 422
  • 249
  • 245
  • 216
  • 203
  • 198
  • 178
  • 160
  • 158
  • 158
  • 153
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1731

Trust and Reciprocity in the Market-Based Provision of Public Goods. Experimental Evidence and Applications to Conservation Tenders

Vogt, Nora 20 November 2013 (has links)
Zahlungen für Ökosystemdienstleistungen (Payments for Ecosystem Services – PES) und auktionsbasierte Vergabeverfahren sind ein wichtiges und innovatives Instrument im Kampf gegen den fortwährenden Verlust von biologischer Vielfalt. Basierend auf einem Vertrag zwischen einem Leistungserbringer und einem öffentlichen oder privaten Leistungsempfänger, der die Naturschutzleistung entlohnt, können bestimmte Vorgaben der Landschaftspflege oder der agrarwirtschaftlichen Bearbeitung verbindlich festgelegt werden. Die Vorteile von PES liegen in dem direkten monetären Anreiz zur Bereitstellung von Naturschutzleistungen und zudem in der Möglichkeit, ein Niveau an Umweltschutz und –qualität jenseits des von der Umweltgesetzgebung sichergestellten Mindestniveaus zu implementieren. Der Nachteil liegt in der hohen Informationsasymmetrie in der Vertragsbeziehung, welche einerseits dem Umweltgut als Vertragsgegenstand und andererseits der Natur ökonomischen Handelns geschuldet ist. Thema dieser Dissertation ist die Analyse der interdependenten Beziehung von Kompetitivität und Vertragserfüllung und das Aufzeigen der Relevanz von Vertrauen und Reziprozität in Verträgen über Umweltgüter. Auf diese Weise leistet sie einen Beitrag zu der umfangreichen und multidisziplinären Literatur über Zahlungen für Ökosystemdienstleistungen und Naturschutzauktionen. Während der vergangenen 25 Jahre habe Praktiker und Wissenschaftler unser Verständnis der Funktionsweise von Ausschreibungen zur Allokation von Zahlungen für Ökosystemdienstleistungen konstant verbessert und erweitert. Ein Großteil der Forschungsaktivität war jedoch auf die Auktionsmetrik und das Bieterverhalten gerichtet, wohingegen die resultierende Vertragsbeziehung zwischen Programmverwaltern (den Käufern) und Landbesitzern (den Ausführenden) weitgehend unbeachtet blieb. Wie in dieser Dissertation bewiesen wird, ist jedoch genau diese Beziehung der Schlüssel für ein erfolgreiches marktbasiertes Naturschutzprogramm. In der vorliegenden Arbeit wird in drei Artikeln argumentiert, dass Vertrauen und Reziprozität für die Überwindung von asymmetrischer Information in kompetitiv alloziierten PES-Verträgen von herausragender Bedeutung sind. Anhand eines für diese Arbeit entwickelten, zweistufigen experimentellen Testszenarios wird der Entscheidungsprozess in der inversen Auktion und in der anschließenden Vertragserfüllung in der kontrollierten Laborumgebung simuliert. In einem ersten Experiment kann auf Basis dieses Untersuchungsdesigns gezeigt werden, dass die Informations- und Anreizkonstellation in Naturschutzauktionen ein erhöhtes Risiko für vorvertragliche adverse Selektion, opportunistisches Verhalten bei Vertragserfüllung und somit suboptimale Ergebnisse birgt. Das Marktversagen kann jedoch durch eine vertrauensstiftende Institution, wie zum Beispiel Kommunikation zwischen Käufern und Verkäufern, verhindert werden. Persönliche Interaktion veranlasst Marktteilnehmer ihr individuell-rationales Verhalten zugunsten einer sozial-verträglicheren Verhaltensweise zu ändern. Dabei entsteht ein erhebliches Potential für die Bilateralisierung der Vertragsbeziehungen. Ein zweites Experiment verdeutlicht jedoch, wie wichtig vertrauensbasierte Vertragsbeziehungen insbesondere in Bereitstellungsumgebungen sind, die stark von externen, stochastischen Einflüssen verzerrt werden können. Ohne das nötige Vertrauen bricht die Kooperation in einem derartigen Szenario fast vollständig zusammen. Schließlich lässt der systematische Vergleich der Ergebnisse aus beiden Experimenten in einem dritten Aufsatz keinen Zweifel daran, dass stabile Langzeitvertragsbeziehungen in auktionsbasierten Vertragsnaturschutzprogrammen gefördert und nicht verhindert werden sollten. Langzeitverträge sind randomisierten Kurzzeitverträgen aus der Perspektive des Naturschutzes aber auch hinsichtlich der Kosteneffektivität überlegen. Daher liegt eine wesentliche Herausforderung für Programmentwickler darin, einerseits die Bildung von ausreichend Sozialkapital zu ermöglichen und andererseits faire Markt- und Vergabestrukturen zu erhalten.
1732

Vielfältige Landschaften: Biodiversität, Ökosystemdienstleistungen und Lebensqualität

17 October 2013 (has links) (PDF)
Die Jahrestagung 2013 der deutschen Sektion der International Assiciation for Landscape Ecology (IALE) fand vom 10.-12.Oktober 2013 in Dresden statt. Motto der Tagung mit circa 70 Teilnehmern war "Vielfältige Landschaften: Biodiversität, Ökosystemdienstleistungen und Lebensqualität". Der Tagungsband entält die Kurzfassung der ca. 30 Tagungsbeiträge und 20 Poster.
1733

Bird community ecology and composition in afrotemperate forests of the Drakensberg Mountains, South Africa.

January 2009 (has links)
Recent research has emphasized the importance of understanding the consequences of species loss, not just for biodiversity per se, but also for ecosystem resilience and functioning. Firstly, a baseline analysis of the effects of a naturally patchy landscape on avian community composition and resilience in a high altitude Afrotemperate forest landscape in South Africa is presented. Bird data from a point count survey of 706 counts at 31 forest sites was used to test whether taxonomic species diversity, functional species richness and density of birds provide insight into community resilience in this historically patchy ecosystem. Bird species richness of forest patches ranged from 17 to 38, with a total species richness of 50. Density was slightly but negatively related to both area and species richness. That density compensation is occurring in these Afrotemperate forests suggests a level of resilience in this system. Following on from this, cumulative species-area and function-area graphs were derived to quantify the loss of forest area or taxonomic bird species richness that this landscape may potentially sustain before ecosystem functioning is negatively affected. The concept that species’ patterns of distribution, abundance and coexistence are the result of local ecological processes has recently been challenged by evidence that regionalscale processes are equally instrumental in shaping local community composition. The historically and naturally fragmented Afrotemperate forests of the uKhahlamba– Drakensberg Park, South Africa, offer an interesting test case. In this study the relative effects of local and regional-scale processes on species assemblages in a naturally patchy forest system were investigated. By employing species-area and species-isolation relationships, and nested subset analyses, we showed that isolation (regional-scale process) had a greater effect on bird species richness and composition than area (local-scale process), though the species-area relationship was significant. Using generalized linear models and an information-theoretic approach to model selection, patch area, the size of the regional species pool as well as the distance to the nearest Eastern Mistbelt forest were all influential in determining local bird species richness in these montane forests. Thus, localities are regionally enriched within the constraints on species occupancy provided by the available habitat. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.
1734

Classification of natural forest communities of coastal British Columbia

Klinka, Karel January 2001 (has links)
Vegetation science, like any science, uses classification to organize knowledge about plants and plant communities. Classification is helpful for understanding how different plant communities relate to one another and their environments, for facilitating further studies of vegetation, and for conservation. To familiarize onself with vegetation of a large area, it is very convenient and efficient to begin with a few general units, such as plant orders rather than with many very detailed units, such as plant associations and subassociation. We offer such an approach and think that the information given in this series will be sufficient to assign any forested coastal community to one the orders or suborders. In spite of a history of vegetation studies in British Columbia, there has not yet been any attempt to develop a comprehensive hierarchical classification of plant communities for the province. As the culmination of fifty years of detailed surveys carried out by V.J. Krajina and his students, the Ecology Program Staff of the BC Forest Service, and other workers, we used tabular and multivariate analyses of 3,779 sample plots established in natural, old-growth, submontane, montane, and subalpine forest communities in coastal BC to develop a hierarchy of vegetation units according to the methods of biogeoclimatic ecosystem classification.
1735

Classification of high-elevation, non-forested plant communities in coastal British Columbia

Klinka, Karel, Chourmouzis, Christine, Brett, Bob, Qian, H. January 2001 (has links)
Non-forested ecosystems dominate high elevation sites in coastal British Columbia, yet there has never been a comprehensive classification or mapping of all high-elevation community types. The objective of this study is to collate and expand upon previous classifications, and thereby to increase our understanding of the habitats and composition of these plant communities.
1736

Classification of high-elevation, non-forested plant communities in coastal British Columbia. Full report.

Brett, Bob, Klinka, Karel, Qian, H., Chourmouzis, Christine 03 1900 (has links)
This report expands and clarifies previous classifications of non-forested plant communities from upper subalpine and alpine locations in coastal British Columbia. A total of 80 plots (releves) sampled specifically for this study were added to 202 releves from published and unpublished studies conducted since 1963. We used tabular and multivariate methods to synthesize and classify plant communities according to the Braun-Blanquet approach. Plant communities were classified into 37 vegetation units (associations or subassociations) which served as the basis of the resulting hierarchical classification. We describe the habitat and species composition of these vegetation units and their relationship to units recogized elsewhere in the Pacific Northwest. We then present eight generalized habitat types which we propose as the basic units for future ecosystem mapping. Each of these habitat types includes a predictable mosaic of vegetation units whose pattern occurs at too fine a scale to map individually.
1737

Great Lakes environmental policy : the ecosystem approach and an economic perspective

Jutlah, Russell Sean 11 1900 (has links)
This thesis is concerned with the conceptual foundations of environmental law and policy in the Great Lakes basin, the world's largest freshwater ecosystem. The Great Lakes regime is now widely recognized as one of the most advanced international environmental management regimes in existence. Over the past two decades, toxic contamination has emerged as a highly pressing ecological issue in the Great Lakes basin. In Canada and the United States, the ecosystem approach, a comprehensive and integrated approach to environmental management, has been adopted both bilaterally and domestically in the Great Lakes' complex environmental policy framework to guide the protection of ecological integrity. There has been extensive discussion of the ecosystem approach, particularly from scientific and managerial perspectives; however, the economic content of the concept has been largely neglected, despite the importance of considering all relevant perspectives in the development of law and policy. This thesis is divided into five chapters. After discussing in Chapter 1 the ecological and institutional contexts and methodological issues of the analysis, this thesis defends, in Chapter 2, the view that economic theory has relevance to issues of environmental law and policy. In addition to highlighting the main contours of welfare and environmental economic theory, a main conclusion, and an essential premise upon which the analysis proceeds, is that economics remains a useful analytical approach to environmental issues, despite some important criticisms. Subsequently, in Chapter 3, the analysis shifts to an examination of four bilateral and domestic Great Lakes instruments that form the core of Great Lakes toxic pollution policy: (i) the Great Lakes Water Quality Agreement; (ii) the Great Lakes Binational Toxics Strategy; (iii) the Canada-Ontario Agreement; and (iv) the Final Water Quality Guidance for the Great Lakes System. After outlining key principles underpinning each instrument, the thesis underscores common themes running through the collective policy framework. The ecosystem approach constitutes a unifying concept in this framework. The ecosystem approach is examined from an economic perspective in Chapter 4. After identifying key elements of the ecosystem approach, this chapter highlights important parallels between fundamental welfare and environmental economic notions. One main conclusion is that economic concepts and approaches, such as environmental valuation, externalities, and self-interest, form an integral part of the ecosystem approach. Finally, Chapter 5 identifies some directions for further research. Given that, as the thesis seeks to establish, economic theory constitutes an important, albeit not sole, perspective on the ecosystem approach, a key challenge will be to facilitate interdisciplinary analysis and cooperation leading to effective operationalization of the concept.
1738

Estado y propuesta de manejo de los recursos naturales de la cuenca del Arroyo Grande, Tierra del Fuego

Cellini, Juan Manuel January 2005 (has links)
Los análisis morfométricos realizados en la cuenca del Arroyo Grande indican que la misma tiene forma alargada, oval y oblonga, con pendientes abruptas en las cabeceras y moderadas en la zona de valle y desembocadura, con una superficie de 129,5 km². La vegetación esta compuesta por pastizales, turberas y bosques de Nothofagus pumilio y N. betuloides factibles de ser aprovechados comercialmente. La cuenca presenta una degradación de los ambientes naturales debido al impacto de especies exóticas, el aprovechamiento forestal no planificado y el turismo no regulado. Los principales problemas encontrados son la falta de planificación en el uso del suelo y la falta de manejo en áreas naturales frágiles. A través de una ordenación en la cuenca, se analizaron alternativas de manejo para aumentar la eficiencia de las actividades productivas tradicionales. Es necesaria la exclusión del ganado, debido al impacto sobre la regeneración del bosque y a la introducción de especies exóticas, concentradas en los sitios de pastoreo. Asimismo se propone la utilización del método de retención dispersa y agregada para el manejo forestal, siendo su objetivo principal mantener la biodiversidad del bosque dentro de niveles aceptables, logrando una posibilidad de 1.082,2 m³/año, siendo suficiente para abastecer un aserradero. Se plantea el ordenamiento de la actividad turística y el restablecimiento de las funciones del ecosistema de turberas explotadas mediante técnicas de recuperación específicas.
1739

Fish harvest and replacement of top piscivorous predators in aquatic food webs: implications for restoration and fisheries management

McGregor, Andrea M Unknown Date
No description available.
1740

The effect of land use on the species composition of amphibians in North Eastern KwaZulu-Natal.

Russell, Charlene. January 2010 (has links)
Global declines in amphibian species have directed research towards investigating why this is happening. One of the major causes of these declines is the fragmentation and loss of habitat. This study examined the effect of land use on the species composition of frogs within North Eastern KwaZulu-Natal, and the use of buffer zones to facilitate the protection of these species. Three land use types were investigated: sugar cane (Saccharum officinarum), gum (Eucalyptus sp.) plantations and conservation areas. The average number of frog species differed between areas: conservation 13.2 ± 6.6; plantations 3.8 ± 1.3; and sugar cane 2.8 ± 1.4. Sugar and gum plantation were found to be lacking the wetland and grassland/woodland habitats. In addition to this, the frog species that were not present on these land use types were those that are totally dependent on water as well as those that are not dependent on a water source. Two species were highlighted as possible indicator species of land use: Amietophrynus gutturalis and Hyperolius marmoratus. To mitigate the effect of these land use types, the use of buffer zones was explored in a desktop study. A range of buffer zones were applied to wetlands in a sample study area, using a range of distances including the distances of 290 m and 159 m recommended by Semlitsch and Bodie (2003), and the recommended distances for wetlands in South Africa of 10-20 m. The application of a 290 m and 159 m buffer zone on a conglomerate of wetlands connected by a 100m buffer was the most feasible as it incorporated a percentage of the total study (6.4% and 4.3%) area similar to the percentage occupied by the recommended 20m buffer zone (5.5%) around all wetlands, and still incorporated the range under protection put forward by Semlitsch and Bodie (2003). Management implications of these findings are discussed. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

Page generated in 0.0889 seconds