The largest declines have occurred in grasslands and arid lands in North America and in farmed lands in Europe, whereas widespread forest specialists show fluctuating but stable trends. Actual protection levels and related trends are more difficult to evaluate, as protected areas change over time: new areas are designated, boundaries are revised and some sites may be destroyed or changed by pressures from economic development or natural processes. Environmental performance depends both on the designation of the area and on management effectiveness. Farmland bird populations declined over 1991-2004, but the decrease was less pronounced than over the 1980s, and for some countries populations have been rising since the late 1990s.