This thesis studies natural and anthropogenic determinants of grassland biodiversity in the Swiss Alps at the levels of plant communities within a landscape (Chapter 2), species diversity within plant communities (Chapter 2 and 3), biological interactions between plants and herbivores and pathogens (Chapter 4), and diversity within a species (Chapter 5-8). Within-species diversity is studied in the widespread and agriculturally important grass species Poa alpina L. Conclusion With our comprehensive study across 12 villages we could demonstrate that human land use affects biodiversity at all levels and has largely shaped present biodiversity during the hundreds of years of agricultural activity. Additionally, we showed that cultural traditions still affect man-made landscape diversity. Still persisting socio-economic differences among cultural traditions are likely to be responsible for this cultural effect. The reduction of labor for farmers by grazing of formerly unfertilized meadows or abandonment of pastures and meadows will reduce land use diversity, and the number of parcels of high biological value used at low intensity will decrease. Thus, biodiversity will decrease both between and within grassland parcels. Therefore, financial incentives are needed to stop the ongoing changes in agriculture in order not to risk losses in biodiversity. Financial incentives should promote high biodiversity within parcels of land, but as not all levels of biodiversity react in the same way a high landscape diversity at the village level is also necessary. Unfertilized meadows are the most laborious type of grassland, and therefore they are most likely to get abandoned, especially when they are steep and at high altitudes and thereby not easily accessible. Due to their significance for plant species richness and composition, financial incentives for the conservation of these unfertilized meadows are especially important. We showed that, in contrast to widespread reservations against grazing, particularly low-intensity grazing has several positive aspects at all levels of biodiversity, and from a biodiversity point of view, grazing is clearly preferable to abandonment of grasslands. In summary, to protect biodiversity at all levels of biological integration, a highly diverse landscape has to be promoted. Therefore, financial incentives should aim at high land use diversity, which is likely to be most successfully promoted at the village level. A reduced diversity of land use types or even abandonment of whole regions will severely reduce biodiversity. At the same time, landscape attractiveness for tourists will be reduced and the remnants of cultural heritage in the Swiss Alps will be endangered. The conservation of all levels of biodiversity and of their cultural, esthetical, ecological, and economic value requires the persistence of the diverse landscapes of the Alps.