Butterfly monitoring in Sweden reveals changes in occurrences over a five-year period

Abstract: Many of the European butterfly species have declined rapidly over the past decades. The cause is thought to be habitat loss due to factors such as increased tree cover, afforestation and intensified agriculture. I analyzed nation-wide data on butterfly occurrences in Sweden, to explore whether occurrences of individual species, grassland dependent species, grassland specialists, red-listed species, and moths, have increased or declined over a period of five years. I found that four species had significantly declined and eight had increased. The results were in accordance with other finds from Sweden, as well as from the UK, regarding the declining species. In contrast, the results regarding the increasing species only partly confirmed previous studies. I also found that grassland specialists and red-listed species had increased, possibly reflecting the fact that Sweden has a relatively large amount of boreal landscapes containing patches of clear-cuts and semi-natural grasslands.