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Human-caused declines in biodiversity have stimulated intensive research on the consequences of biodiversity loss for ecosystem services and policy initiatives to preserve the functioning of ecosystems. Short-term biodiversity experiments have documented positive effects of plant species richness on many ecosystem functions, and longer-term studies indicate, for some ecosystem functions, that biodiversity effects can become stronger over time. Theoretically, a biodiversity effect can strengthen over time by an increasing performance of high-diversity communities, by a decreasing performance of low-diversity communities, or a combination of both processes. Which of these two mechanisms prevail, and whether the increase in the biodiversity effect over time is a general property of many functions remains currently unclear. These questions are an important knowledge gap as a continuing decline in the performance of low-diversity communities would indicate an ecosystem-service debt resulting from delayed effects of species loss on ecosystem functioning. Conversely, an increased performance of high-diversity communities over time would indicate that the benefits of biodiversity are generally underestimated in short-term studies.Analyzing 50 ecosystem variables over 11 years in the world’s largest grassland biodiversity experiment, we show that overall plant diversity effects strengthened over time. Strengthening biodiversity effects were independent of the considered compartment (above- or belowground), organizational level (ecosystem variables associated with the abiotic habitat, primary producers, or higher trophic levels such as herbivores and pollinators), and variable type (measurements of pools or rates). We found evidence that biodiversity effects strengthened because of both a progressive decrease in functioning in species-poor and a progressive increase in functioning in species-rich communities. Our findings provide evidence that negative feedback effects at low biodiversity are as important for biodiversity effects as complementarityamong species at high biodiversity. Finally, our results indicate that a current loss of species will result in a future impairment of ecosystem functioning, potentially decades beyond the moment of species extinction. Human-caused declines in biodiversity have stimulated intensive research on the consequences of biodiversity loss for ecosystem services and policy initiatives to preserve the functioning of ecosystems. Short-term biodiversity experiments have documented positive effects of plant species richness on many ecosystem functions, and longer-term studies indicate, for some ecosystem functions, that biodiversity effects can become stronger over time. Theoretically, a biodiversity effect can strengthen over time by an increasing performance of high-diversity communities, by a decreasing performance of low-diversity communities, or a combination of both processes. Which of these two mechanisms prevail, and whether the increase in the biodiversity effect over time is a general property of many functions remains currently unclear. These questions are an important knowledge gap as a continuing decline in the performance of low-diversity communities would indicate an ecosystem-service debt resulting from delayed effects of species loss on ecosystem functioning. Conversely, an increased performance of high-diversity communities over time would indicate that the benefits of biodiversity are generally underestimated in short-term studies. Analyzing 50 ecosystem variables over 11 years in the world's largest grassland biodiversity experiment, we show that overall plant diversity effects strengthened over time. Strengthening biodiversity effects were independent of the considered compartment (above- or belowground), organizational level (ecosystem variables associated with the abiotic habitat, primary producers, or higher trophic levels such as herbivores and pollinators), and variable type (measurements of pools or rates). We found evidence that biodiversity effects strengthened because of both a progressive decrease in functioning in species-poor and a progressive increase in functioning in species-rich communities. Our findings provide evidence that negative feedback effects at low biodiversity are as important for biodiversity effects as complementarity among species at high biodiversity. Finally, our results indicate that a current loss of species will result in a future impairment of ecosystem functioning, potentially decades beyond the moment of species extinction.

Der projizierte Klimawandel könnte Verbreitungsgebiete von Arten sowohl auf globaler als auch nationaler Ebene beeinflussen. In dieser Dissertation wurden vier Analysen durchgeführt, um potentielle Auswirkungen des Klima- und Landnutzungswandels auf die Flora von Deutschland bis 2080 zu erfassen. Untersuchungen mit drei alternativen Szenarien ergaben einen negativen Einfluss auf die potentiellen Verbreitungsgebiete der Pflanzenarten in Deutschland. Es wurde gezeigt, dass eine Verschiebung von Klimatypen den gebietstypischen Artenpool ändern könnte. Für Arten aus Südeuropa ergaben die Szenarien einen Zuwachs an klimatisch geeigneten Gebieten in Deutschland. Diese Arbeit verdeutlicht, dass die Reduktion oder der Gewinn von möglichen Verbreitungsgebieten artspezifisch ist. Dennoch konnten Unterschiede der Auswirkungen auf Verbreitungsgebiete zwischen Biotoptypen und biologisch-ökologischen Eigenschaften der Pflanzenarten nachgewiesen werden. Ein neuartiges zweistufiges Verfahren testete die Eignung von biologisch-ökologischen Pflanzenmerkmalen als Diagnosewerkzeug für mögliche klimabedingte Reaktionen von Pflanzenarten. Insgesamt wurden in der vorliegenden Dissertation mögliche Einflüsse des projizierten Klimawandels für mehr als 1200 Pflanzenarten in Deutschland untersucht., Projected climate change could alter current plant species distribution at global as well as national level. This thesis was aimed in four different analyses at surveying the influence of alternative climate and land use change scenario on plant species in Germany up to 2080. Three different scenarios showed negative effect on species’ potential range changes in Germany. A shift of climate types in the scenarios resulted in a change of typical species’ pools. Species from southern Europe gained climatically suitable range in Germany. This study found species-specific rates of range loss or range gain. Nevertheless differences of range changes between species-specific habitats and biological-ecological traits were found. A novel two-step approach was developed to test the relationship between projected range changes and biological-ecological traits and used to predict climate sensitivity of plant species. Overall, this study provided results about potential impacts under projected climate change for more than 1200 plant species in Germany.

Human-caused declines in biodiversity have stimulated intensive research on the consequences of biodiversity loss for ecosystem services and policy initiatives to preserve the functioning of ecosystems. Short-term biodiversity experiments have documented positive effects of plant species richness on many ecosystem functions, and longer-term studies indicate, for some ecosystem functions, that biodiversity effects can become stronger over time. Theoretically, a biodiversity effect can strengthen over time by an increasing performance of high-diversity communities, by a decreasing performance of low-diversity communities, or a combination of both processes. Which of these two mechanisms prevail, and whether the increase in the biodiversity effect over time is a general property of many functions remains currently unclear. These questions are an important knowledge gap as a continuing decline in the performance of low-diversity communities would indicate an ecosystem-service debt resulting from delayed effects of species loss on ecosystem functioning. Conversely, an increased performance of high-diversity communities over time would indicate that the benefits of biodiversity are generally underestimated in short-term studies. Analyzing 50 ecosystem variables over 11 years in the world's largest grassland biodiversity experiment, we show that overall plant diversity effects strengthened over time. Strengthening biodiversity effects were independent of the considered compartment (above- or belowground), organizational level (ecosystem variables associated with the abiotic habitat, primary producers, or higher trophic levels such as herbivores and pollinators), and variable type (measurements of pools or rates). We found evidence that biodiversity effects strengthened because of both a progressive decrease in functioning in species-poor and a progressive increase in functioning in species-rich communities. Our findings provide evidence that negative feedback effects at low biodiversity are as important for biodiversity effects as complementarity among species at high biodiversity. Finally, our results indicate that a current loss of species will result in a future impairment of ecosystem functioning, potentially decades beyond the moment of species extinction.