Long-term impacts of meadow abandonment scenarios on plant diversity were forecasted for high nature value farmland in northern Portugal, with implications for conservation planning and agri-environmental management. Predictive models were used to simulate plant species responses to alternative scenarios of management abandonment over the long term. With total meadow abandonment, a drastic decrease in total species richness (41.1%) and in endemic species richness (loss of 20.8%) was forecasted. However, only 12.3% of all species were forecasted to disappear under scenarios of partial abandonment. Landscape-level plant diversity can be maintained by promoting farmland mosaics, even if the loss of scattered meadows in favour of native forests could be acceptable. Agri-environmental schemes should thus prioritize the maintenance of landscape heterogeneity to safeguard plant diversity in high nature value farmland systems.