Plant species richness is essential for ecosystem functioning, resilience, and, ultimately, ecosystem services, yet it is globally threatened by anthropogenic land use including management and modification of natural environment. At very large scales land-use effects are often simply modelled by habitat loss assuming that transformed land becomes completely inhospitable for naturally occuring species. Further, estimates of species loss are flawed by the common assumption of a universal slope of the species-area curve, typically ranging from 0.15 to 0.25 or 0.35. This dissertation consists of a global species-area analysis, a meta-analysis about land-use effects on plant species richness and an approach to integrate these land-use effects in a countryside species-area model. It thereby contributes to a deeper understanding of species-area relationships and how patterns of species richness across spatial scales are driven by land use and suggests a model to predict species richness pattern of vascular plants that overcomes limitations of previous models.