South European mountain butterflies at a high risk from land abandonment and amplified effects of climate change

Data from existing monitoring schemes point to a global crisis of butterflies across Europe, with habitat loss/degradation, climate change and chemical pollution as the main drivers of decline.The existing butterfly time series from Western Europe come from densely populated, relatively flat areas. However, population trends from less populated areas, such as mountain ranges in the south of Europe, have been less studied, despite these areas harbouring one of the highest butterfly biodiversity of the continent.Here, we analyse trends for butterfly populations in a Southwestern Europe mountain range (Picos de Europa, Northwest Spain), for the last 9 years (2013-2021), across an altitudinal gradient (80-2000 m). We show that this region, protected as National Park more than 100 years ago, is nonetheless under a great threat, with a decline in butterfly abundance of, on average, 5.7% per year (45.7% cumulative decline in the last 9 years).Species at higher elevations are faring worse than those at low elevations and communities at mid-elevations (below the tree line) are changing towards higher abundance of species with a preference from closed habitats. Combined effects of amplified climate change in mountains and habitat loss, due to abandonment of traditional management, appear to be affecting both individual species and community composition of butterflies in our study area.