The effects of land abandonment on biodiversity have received considerable attention by scholars, but results are far from conclusive. Different cultural traditions of scientists seem to underlie the contrasting ways in which land abandonment is understood. Although the forest transition (FT) framework considers land abandonment as an opportunity for biodiversity conservation, European landscape ecologists characterize it as a threat. We use insights from both traditions to analyze the effects of land abandonment on landscape and biodiversity in a mountain area of metropolitan Barcelona. We do so through an in-depth historical case study covering a period of 160 years. A set of landscape metrics was applied to land-cover maps derived from cadastral cartography to characterize the landscape ecological changes brought about by land abandonment. Cadastral data on land uses were used to understand how landscape ecological changes could be explained by changing socioeconomic activities. Information on past land-management practices from semistructured interviews was used to shed light on how peasants shaped the capacity of landscape to host biodiversity. Our results point to a remarkable landscape deterioration along with the disappearance of the peasant land-use mosaics and the ensuing forest expansion. By using insights from landscape ecology in a historically informed manner, we (1) question the alleged relationship between land abandonment and ecosystem recovery; (2) show that the assumed restorative character of the FT is based on the underestimation of the ecological importance of nonforest habitats; and (3) point at a remarkable trade-off between FT and biodiversity in the Mediterranean. Finally, the case study also serves to illustrate some of the strengths and challenges of using historical approaches to land abandonment.