Butterflies in agricultural landscapes: impacts of agricultural land use and landscape structure across temporal and spatial scales

The decline of insect populations has raised global concerns regarding biodiversity loss and ecosystem stability. This thesis investigates the large-scale impacts of agricultural land use on butterfly populations by leveraging data from the German Butterfly Monitoring Scheme (DEBMS), one of the few nationwide, long-term citizen science monitoring programs in Germany. By integrating butterfly monitoring data with detailed datasets on land use and landscape structure, this research not only aims to assess key impacts on butterfly populations, but also evaluates the methodological potential and limitations of the DEBMS for large-scale biodiversity assessments. Through three complementary studies, this thesis demonstrates that both landscape structure and land-use intensity play a crucial role in shaping butterfly populations. The thesis highlights the sensitivity of butterfly communities to intensive grassland management regimes through livestock grazing and mowing. Further, it underscores the importance of the surrounding landscape matrix, as it shows positive effects of a high landscape heterogeneity, characterized by a high density of habitat boundaries, particularly in regions with low grassland cover. In contrast, in grassland-dominated landscapes where butterfly habitat availability is generally higher, improving habitat quality through less intensive grassland management emerges as most relevant to support butterfly populations. Besides ecological questions, this study also evaluates data quality for large-scale analyses of biodiversity patterns and the various factors influencing butterflies in agricultural landscapes. While the DEBMS provides a valuable dataset for large-scale biodiversity assessments, improving transect placement would help achieve a more comprehensive representation of land-use gradients in Germany's agricultural landscapes. For instance, integrating DEBMS data with data collected at systematic sampling sites could enhance spatial coverage, resulting in more robust biodiversity assessments. Additionally, incorporating high-resolution remote sensing and detailed agricultural data, such as data from the Integrated Administration and Control System (IACS), could refine future analyses of agricultural land-use impacts and biodiversity measures. These advancements would enable more precise habitat management recommendations to better conserve and restore butterfly populations in agricultural landscapes. By enhancing our understanding of large-scale land-use impacts on butterflies in agricultural landscapes, and by critically assessing the potentials and limitations of the DEBMS data, this thesis can help inform policy decisions aimed at increasing butterfly populations and improving monitoring efforts to evaluate agricultural impacts on biodiversity.