Farmland Abandonment and High Nature Value Farming in Mediterranean Landscapes: Plant Biodiversity Outcomes and Biocultural Trade-Offs

Mediterranean rural landscapes are globally important biocultural systems in which long-standing low-intensity farming, grazing, terracing, and agroforestry have historically maintained fine-grained habitat mosaics and high vascular-plant diversity. This review adopts a systematic scoping approach focused on farmland abandonment and High Nature Value (HNV) farming, with a search window extending from 1996 to April 2026. Following PRISMA 2020 and PRISMA-ScR principles, the review maps evidence on plant richness, diversity indices, floristic turnover, indicator species, and vegetation trajectories across Mediterranean agricultural and semi-natural systems. The literature shows that abandonment does not produce a single biodiversity outcome. Early abandonment can maintain or temporarily increase local richness through overlap among remnant grassland species, annuals, and colonizing shrubs, whereas prolonged abandonment more often drives shrub encroachment, woody dominance, and losses of open-habitat specialists. By contrast, HNV systems such as extensive grazing, agro-pastoral mosaics, wood pastures, and dehesa/montado-like agroforestry more consistently maintain habitat interfaces, beta diversity, and plant assemblages associated with cultural landscape continuity. The review argues that biodiversity-sensitive policy in the Mediterranean should move beyond the binary of abandonment versus conservation, and instead support landscape-specific combinations of passive succession, targeted grazing, agroforestry renewal, and rural livelihood viability.