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Im Kontext der Problematik von Fehlinformationen in der populärwissenschaftlichen Literatur widmet sich diese Arbeit in einer Fallstudie drei häufig verkauften Büchern Peter Wohllebens. Untersucht wird, wie nah diese Werke sich am aktuellen Stand der Forschung orientieren und wie gut die getätigten Aussagen nachvollziehbar sind. Für die Untersuchung wurde der Inhalt der Bücher codiert und die resultierenden 8899 Codiereinheiten quantitativ und qualitativ-vergleichend analysiert. Ergänzt wurde dies durch die qualitativ-vergleichende Analyse von drei Schwerpunktthemen. Aus den Ergebnissen wird geschlussfolgert, dass Wohllebens Nähe zum wissenschaftlichen Diskurs unter Einschränkungen ausreichend und die Nachvollziehbarkeit seiner Aussagen mangelhaft ist. Basierend auf diesen Erkenntnissen werden mögliche Maßnahmen und Handlungsfelder für eine Erhöhung der wissenschaftlichen Qualität populärwissenschaftlicher Werke diskutiert. Es werden weitere potentielle Forschungsmöglichkeiten für ein besseres Verständnis der Situation in den Populärwissenschaften identifiziert und vorgeschlagen.

The worldwide decline of plant and insect species during the last decades has far-reaching consequences for the functionality of ecosystems and their inherent processes. Pollination as one of them is an indispensable ecosystem service for human wellbeing. More than 85% of the worldwide flowering-plant species depend to some degree on pollination by insects (pollinators). Similarly, many pollinators depend on the flowers of the plants, as they need nectar and pollen as food resources for themselves and their offspring. However, an increasing number of pollinator and plant species are threatened by multiple, interacting, and sometimes synergistic causes (habitat loss, fragmentation, diseases, parasites, pesticides, monocultures) that are becoming a growing threat to ecosystem functioning. Given the loss of plant species diversity, it is increasingly difficult for pollinators to find food throughout the year. Therefore, this study analyses the influence of plant diversity on pollinators. The study was conducted in the course of the Jena Experiment, which is a long-term biodiversity experiment (since 2002) with 60 plant species, common to Central European Arrhenatherum grasslands. With a plant diversity gradient of 1, 2, 4, 8, 16, and 60 plant species per plot, time-series data resulted from a wide range of ecosystem processes, ranging from productivity, decomposition, C-storage, and N-storage to herbivory, and pollination. These were studied to investigate the mechanisms underlying the relationships between biodiversity and ecosystem processes. Chapter 2 studies the spatio-temporal distribution of pollinators on flowers along an experimental plant diversity gradient. For this purpose, the pollinators were divided into four different functional groups, i.e. honeybees, bumblebees, solitary bees and hoverflies. In particular, the spatial pollinator behaviour was examined, that is, in which flowering height the flowers were visited within the plant community. In order to study the temporal component, pollinator visits were observed over the course of the day and the season. As a result, an unprecedented high resolution of plant-pollinator interactions was found. For the first time it was possible to demonstrate that the different pollinator functional groups can complementarily use different spatio-temporal niches which was most pronounced in species-rich plant mixtures,. This leads to the conclusion that species-rich plant mixtures provide sufficient resources that can be used by generalists, such as honeybees and bumblebees, as well as other pollinator functional groups, such as hoverflies and solitary bees. Chapters 3 and 4 continues on the chemical composition of flower nectar (nectar) of various plant species. Nectar is used as food resource for adult pollinators, but is also largely used as a supply for their offspring, making it the most important pollinator reward. The chemical composition of the nectar was analysed for the two most important macronutrients, carbohydrates (C) and amino acids (AA), using high performance liquid chromatography (HPLC). Subsequently, their contents were analysed in terms of concentration, proportional content and the ratio of carbohydrates to amino acids (C:AA). In Chapter 3, the nectar of 34 plant species from the grasslands of the Jena Experiment was compared. In doing so, similarities and/or differences of the nectar compositions were investigated with respect to the most important macronutrients carbohydrates and amino acids between the individual species but also between the most representative plant families. This should lead to a better understanding about how plant diversity influences consuming pollinators and which factors, e.g. phylogenetics, morphology or ecology, can lead to different nectar compositions. We could show that each plant species differs in terms of carbohydrate content, amino acid content and C:AA-ratio. In addition, there were clear differences between the four representative plant families Apiaceae, Asteraceae, Fabaceae and Lamiaceae regarding the proportions of essential amino acids. The proportions of the individual sugars and the C:AA-ratios also differed greatly between the four plant families. Therefore, it can be assumed that these nectar contents are family-specific. The need for differences in carbohydrate content are probably due to the different morphology of the flowers, as plants with open flowers and exposed nectar, as in Apiaceae and Asteraceae, can protect their nectar from evaporation if the nectar has a higher osmolality, which can be achieved by a higher hexose (fructose and glucose) content. Thus, the nectar can remain dilute for a longer time and consequently remain consumable for pollinators, which in turn can contribute to the pollination of plants. Fabaceae and Lamiaceae showed different results. Here the nectar was probably protected from evaporation by closed flowers, which explains the high proportion of sucrose, leading to a lower osmolality that would enhance evaporation for exposed nectar. The metabolic pathways controlling the family-specific C:AA-ratios are yet to be explored. In conclusion, it can be suggested that this study contributes to elucidating the morphological and phylogenetic characteristics that control each plant species’ nectar composition. In Chapter 4, nectar was investigated in the context of diversity effects on the example of the plant species Field Scabious, Knautia arvensis. It was analysed to what extent the nectar quality (nutrient content) differs between plant individuals of one species. The underlying factors causing these differences in nectar composition have never been studied before. In order to investigate these coherences, plant communities in the Jena Experiment of different plant species richness levels containing the target plant species K. arvensis were used. In particular, we examined whether the nectar of K. arvensis is influenced by other neighbouring plant species, e.g. through competition for pollinators. The carbohydrate and amino acid content in nectar varied both between individuals of K. arvensis and between the different plant species richness levels. However, there were significant non-linear differences in the proportions of certain essential and phagostimulatory amino acids, which were produced proportionally more in the nectar of K. arvensis plants in species-rich plant communities, while histidine, one of the generally inhibiting amino acids tended to be less present. Our findings therefore suggest that the nectar of K. arvensis is more palatable when the plants grow in species-rich plant communities. Overall, these studies indicate how fragile plant-pollinator interactions are but also how important plant species-rich grasslands are to support plant-pollinator interactions. Increased plant species diversity is essential to ensure the availability of flowering resources throughout the year. Pollinators, such as honeybees, bumblebees, solitary bees, and hoverflies can use the niches in time and in vertical space complementarily. However, in plant species-poor grasslands there may be more niche overlaps, which is probably due to a reduced availability of resources. This points to the need to include different plant species belonging to different plant families, whose nectar may have evolved in response to morphological flower traits and metabolic pathways. Therefore plant species diversity can supply pollinators with nectar differing in carbohydrate and amino acid content and thus differing in quality. Also C-AA ratios have proven to be a useful measurement to reveal differences between plant species. In addition, C:AA ratios were not differing in nectar of K. arvensis individuals growing in different plant species richness levels, although their nectar seemed to be more attractive in mixtures with 16 plant species, likely due to higher content of essential and phagostimulatory amino acids than in plant species-poor mixtures. Thus further research investigating diversified farming systems, including pollinator-friendly practices to reveal the attractiveness of different plant species. More diversified field margins and grasslands, for the maintenance of pollinator services for sustainable provision of crop pollination.

Globalization with its increasing emergence of global value chains is one of the main driving forces behind persisting unsustainable production and consumption patterns. The global coffee market provides a fitting example, as it is connected to many sustainability issues like the persisting poverty of coffee farmers, and degrading ecosystems. Many interventions, from state-led regulation to industry-led certification processes, exist, that try to change global value chains to shift societies back on more sustainable trajectories. However, due to the complexity and manifold connections between social and ecological factors, global value chains pose a wicked problem. To this date, it is still under debate if these interventions are an effective means to change global value chains. With climate change and persisting issues of social justice as strong accelerators, calls are increasingly made for a radical transformation of global production and consumption patterns. Many frameworks try to inform research and real-world policies for a transformation of global value chains. In this dissertation, I use the framework of the practical, political and personal sphere proposed by O’Brien and Sygna (2013). The authors highlight that the interactions between these three spheres bare the greatest potential for a transformation towards sustainability. however, in this dissertation, I argue that it is exactly at the nexus between the three spheres of transformation where barriers towards a fundamental shift of systems occur. I, therefore, use three perspectives to bring empirical nuance to the problems that arise on the interplay between the different spheres of transformation. These perspectives are: (1) the scientific perspective: using a systematic review of alternative trade arrangements; (2) the producer perspective: facilitating a participatory network analysis of social-ecological challenges of Ugandan coffee farmers and their adaptive management practices; (3) the consumer perspective: through the use of a German consumer survey and a structural equation model to investigate into the Knowledge-Doing-Gap end-consumers are facing. These three perspectives bring empirical nuance to the interplay between the different spheres as they highlight the real-world barriers that arise within and at the nexus of the three spheres. Through the results from the scientific perspective, I am able to show that most of the research is investigating the certified market and that the effectiveness of labels rarely exceeding the practical sphere. My empirical research on the producer perspective highlights that Ugandan coffee farmers facilitate a variety of on-farm crop management (practical sphere) but their support structures rarely exceed informal exchange with neighboring communities (political sphere). Exchange with governmental actors and global traders is happening but has been assessed as not sufficient to cope with the social-ecological challenges the producers are facing. Through the results of the consumer perspective, I am able to highlight that even though end-consumers have pro-sustainable attitudes (personal sphere) they are facing situational constraints (political sphere) that create a gap between their attitudes and the respective behavior. Using these empirical insights about drivers and barriers for a transformation I propose that frameworks, aiming to inform research and policies, need to include two aspects: (1) the notion of a forced transformation as one of the major influencing factors for a deliberative transformation; and (2) the translational capacity of the frameworks to create meaningful interdisciplinary discourses in different contexts. I, therefore, propose two approaches that should function as a starting point for further development of transformation frameworks (1) a fourth sphere, called the “planetary force” to include the notion of a forced transformation that is already happening in different contexts, highlighted by the producer perspective in this dissertation; and (2) the consequent use of methods that create interdisciplinary exchange and rigorous testing.

Global environmental changes and the subsequent biodiversity loss has raised concerns over the consequences for the functioning of ecosystems and human well-being. This thesis provides new mechanistic insights into the role of tree diversity in regulating forest productivity and forests’ responses to climate change. The thesis also addresses the overlooked functional role of ecological continuity in mediating ecosystem processes in the context of multiple global environmental changes. The findings of the thesis emphasize the need to retain the functional integrity of forest ecosystem by preserving biodiversity and acknowledging the ecological memory forests.

Der Klimawandel gehört zu den globalen Herausforderungen des 21. Jahrhunderts. Die Folgen des Klimawandels machen sich u.a. in Form von Hitze, Stürmen oder Starkregen bemerkbar. Dem Klimawandel kann sowohl mithilfe des Klimaschutzes (Mitigation) in Form der Ursachenbekämpfung als auch mithilfe der Klimaanpassung (Adaption), welche sich in Form von Anpassungsmaßnahmen an das sich ändernde Klima darstellt, begegnet werden. Aufgrund ihrer Struktur sind insbesondere urbane Strukturen von Klimafolgen betroffen. Der Raum- und Umweltplanung komme dabei hinsichtlich der sozial-ökologischen Naturverhältnisse eine wichtige Rolle zu, sofern sie die Aufgaben der Krisenbewältigung annehmen und verantwortungsvoll wahrnehmen will. Auch die Hansestadt Lüneburg steht zukünftig vor einigen Herausforderungen. Durch den allgemeinen Trend der Urbanisierung und als Teil der Metropolregion Hamburg gilt Lüneburg als beliebter Wohnraum. Folglich werden auch zukünftig neue Baugebiete erschlossen, Wohnraum geschaffen und Verdichtung sowie Flächenversiegelung vorgenommen. Im aktuell bearbeiteten Klimagutachten für Lüneburg werden bereits bisherige Risikogebiete bezüglich Hitze und Frischluft aufgezeigt. In der vorliegenden Arbeit werden zunächst die der Ausarbeitung zugrungegelegten Begriffe sowie die Bedeutung von Starkregenereignissen in der Stadtplanung definiert und näher erläutert. Darauf folgt die Darstellung der zur Beantwortung der Forschungsfrage verwendeten Methoden. Anschließend werden in der empirischen Forschung das bisherige Auftreten von Starkregen analysiert, bestehende Adaptionsstrategien norddeutscher Städte und Regionen aufgezeigt, ein Zukunftsausblick auf Grundlage wissenschaftlicher Prognosen gegeben und konkrete, auf die Hansestadt Lüneburg bezogene, Analysen und Szenarien erstellt, bevor ein Resümee der empirischen Forschung gezogen werden kann. Abschließend wird das methodische Vorgehen reflektiert, die Ergebnisse diskutiert und ein kurzer Ausblick auf zukünftige Herausforderungen gegeben.