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The role of competition in tree communities is increasingly well understood, while little is known about the patterns and mechanisms of the interplay between above- and belowground competition in tree communities. This knowledge, however, is crucial for a better understanding of community dynamics and developing adaptive near-natural management strategies. We assessed neighbourhood interactions in an unmanaged old-growth European beech (Fagus sylvatica) forest by quantifying variation in the intensity of above- (shading) and belowground competition (crowding) among dominant and co-dominant canopy beech trees during tree maturation. Shading had on average a much larger impact on radial growth than crowding and the sensitivity to changes in competitive conditions was lowest for crowding effects. We found that each mode of competition reduced the effect of the other. Increasing crowding reduced the negative effect of shading, and at high levels of shading, crowding actually had a facilitative effect and increased growth. Our study demonstrates that complementarity in above- and belowground processes enable F. sylvatica to alter resource acquisition strategies, thus optimising tree radial growth. As a result, competition seemed to become less important in stands with a high growing stock and tree communities with a long continuity of anthropogenic undisturbed population dynamics. We suggest that growth rates do not exclusively depend on the density of potential competitors at the intraspecific level, but on the conspecific aggregation of large-diameter trees and their functional role for regulating biotic filtering processes. This finding highlights the potential importance of the rarely examined relationship between the spatial aggregation pattern of large-diameter trees and the outcome of neighbourhood interactions, which may be central to community dynamics and the related forest ecosystem services.

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Changes of habitats are amongst the main drivers of evolutionary processes. Corresponding shifts in the behaviour and life history traits of species might in turn also alter ecosystem attributes. The reproduction of Western European fire salamanders (Salamandra salamandra), in small pond habitats instead of first order streams, is one example of a recent local adaptation. Since fire salamander larvae are important top-predators in these fish free habitats, their presence likely changes various aspects of ecosystem functioning. Here, it was analysed how the ecological performance of salamander larvae in ponds in the Kottenforst in Western Germany changed in comparison to sympatric stream populations. Further, it was analysed how their presence in ponds influenced key ecosystem attributes such as prey density and diversity and aquatic-terrestrial linkage. To assess the impact of the life cycle shifts in salamanders on the pond functioning, detailed investigations of salamander larvae population dynamics, phenology, and macroinvertebrate community development in ponds were combined with experimental manipulations of the salamander presence. In the first part of this study, the impact of pond presence of fire salamanders in terms of ecosystem functioning focussing on aquatic terrestrial subsidy transfer was calculated. The study could show, that the adaptation of fire salamanders to breed in pools led to strong increases of animal-mediated import of terrestrial matter into the aquatic habitats. The hypothesis about the impact on macroinvertebrate communities derived from these calculations was then tested experimentally. It was shown, that presence of salamander larvae could influence some taxa of macroinvertebrates but they had only limited effects on the food web structure in their aquatic habitats. Yet, a high relevance of the subsidy exchange from aquatic to terrestrial and its high relevance for the predator persistence in the system could again be confirmed. Moreover, it was demonstrated, that the larval behaviour and performance could have a high inter-annual variability as a reaction to contrasting ecosystem constraints in comparison to the stream habitats. A fact that integrally separates the pond ecotype from stream ecotype conspecifics.

In north-western Germany, inland dunes and natural floodplains were widespread in the past. Due to the regulation of the natural course, large rivers have experienced serious anthropogenic influences resulting in a decline of adjacent natural floodplains. The realization of a restoration project in north-western Germany had the aim to restore a floodplain composed of inland dunes and seasonally flooded grasslands. Within this project, the response of wild bee communities to such restoration measures was evaluated. Therefore, an analysis of the succession and distribution patterns of wild bee communities in restored and target habitats was conducted. In chapter 1 and 2 the success of the restoration measures was evaluated by a comparative analysis of wild bee communities at restoration and target sites. The results show a rapid colonization of a species-rich wild bee community reflecting a community composition which is composed of generalists, specialists and parasitic species. The quantity of entomophilous plant species and the proportion of bare ground had a strong influence on wild bee species composition. To gain insight into the connectivity of wild bee populations, the population genetic structure of two wild bee species, Andrena vaga and Andrena fuscipes was analysed in chapter 3 and 4. Additionally, general intrinsic factors that maintain the genetic diversity and influence the degree of inbreeding were evaluated in chapter 5 on the basis of an extensive literature survey. These results reflect a high dispersal ability and inter-population movement of wild bees. For both species a high genetic diversity within populations and a low genetic differentiation among populations was found. In conclusion, wild bees proved to be useful indicators for monitoring the effects of restoration projects. The combination of population genetic analyses and community monitoring provides the opportunity to evaluate different aspects of restoration success.

Der Übergang vom fossilen Zeitalter hin zu einer kohlenstoffarmen Zukunft mit erneuerbaren Energien erfordert eine tiefgreifende Transformation, Reorganisation und Neukonfiguration des sozio-ökologischen Stoffwechsels, der insbesondere eine tiefgreifende raumzeitliche und politische Veränderung darstellt. Diese Arbeit analysiert diesen Wandel, indem sie die Rolle thermodynamischer Narrative untersucht, die im Zusammenhang mit der Elektrifizierung des Kapitalismus im Deutschland des endenden 19. Jahrhunderts aufgekommen sind. Sie geht der Frage nach, welche Bedeutung diese thermodynamischen Narrative für die lokale Umstrukturierung der Mensch-Umwelt-Beziehung in der kohlenstoffarmen Energiewende weiterhin haben. Anhand eines neuartigen Analyserahmens, genannt ‚kritische Thermodynamik‘, der diese miteinander verbundenen Beziehungen in einem historisch-materialistischen Kontext analysiert, werden drei Hauptargumente vorgebracht. Erstens führt eine thermodynamische Narration mit ihren materiellen Implikationen das menschliche Streben nach "grüner" Energie in einen gegenwärtigen Zustand, auf dem die wissenschaftlichen und politischen Einzelheiten eines zukünftigen Natur-Energie-Beziehung aufbauen. Zweitens, in der gegenwärtigen Phase der Energiewende produziert das Kapital aufgrund des Fokus auf die effiziente Verteilung erneuerbarer Energien neue ökonomische Formationen in Prozessen der ökologischen Modernisierung. Dabei wird die Energieflexibilität als zentrales Terrain für die Aufrechterhaltung eines Status Quos als Ausgleich infrastruktureller Defizite herausgearbeitet. Drittens steuert der Staat die Energiewende durch experimentelle Ansätze, die dem Kapital einen technokratischen Raum für seine notwendigen socio-ecological fixes bieten sollen. / The transition from the fossil fuel era to a low-carbon future of renewable energy requires profound transformation, reorganisation, and reconfiguration of the socio-ecological metabolism. Since this metabolism was initially built upon centralised thermal power plants, the move to a future system that predominantly lives of ‘green megawatts’ from decentralised renewable energy sources represents a major spatiotemporal and political shift. This thesis analyses such a shift by investigating the role of thermodynamic narratives, which emerged in the context of electrification of capitalism in Germany at the end of the 19th century. It addresses the question of how these thermodynamic narratives continue to matter for the localised restructuring of the human-environmental relationship in the low-carbon energy transition. Through a novel framework of ‘critical thermodynamics’, which analyses these interconnected relations through a historical materialist framework, the thesis makes three main arguments. First, a thermodynamic narrativity along with its material implications guides the human quest for abundant ‘green’ energy into the contemporary conjuncture on which the scientific and political specificities of the future nature-energy relationship are built. Second, because of a focus on the efficient distribution of renewable energy in the current phase of the energy transition, capital produces new economic formations in wider processes of ecological modernisation. Here, energy flexibility is exposed as a central terrain for maintaining a status quo despite infrastructural shortcomings. Third, the state guides the energy transition through experimental approaches, intended to provide a technocratic space for capital to perform its necessary socio-ecological fixes.

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