Detecting temporal changes in the extent of High Nature Value farmlands: The case-study of the Entre-Douro-e-Minho Region, Portugal

•High Nature Value farmlands (HNVf) were assessed in space and time.•HNVf areas decreased between 1989 and 2009.•HNVf loss (1989–2009) was mainly due to the replacement by forests and heathlands.•HNVf loss was observed both inside and outside of areas designated for nature conservation.•This provides an early warning that nature conservation designation does not ensure HNVf persistence.