Population trends of Finnish butterflies (Lepidoptera: Hesperioidea, Papilionoidea) in 1991–2000

The National Butterfly Recording Scheme in Finland (NAFI) is based on data collected using a uniform questionnaire for the whole country. During the first decade of the scheme (1991–2000), a total of 432 voluntary amateur and professional lepidopterists participated by providing data on 1.5 million individuals representing 94 indigenous and 11 non-resident species. Although the 10-year period is not long enough to provide extensive conclusions about changes in the fauna, changes in either the geographical distributions or population densities exhibited a downward trend for 15 species and an upward trend for 11 species. The decreased species were dominated by those inhabiting bogs and fens (4) and open sandy or rocky habitats (5), whereas the increased species were mainly typical of forest verges and clearings (8). The results indicated in particular the effects of drainage of peatlands and overgrowth of meadows. On the other hand, the distribution maps published in the national bulletin revealed northward expansion for seven species, which, together with some increasing migrants, may indicate the effects of possible climatic warming. By providing quantitative knowledge of possible changes in the distribution and abundance of butterflies, NAFI may be used to protect the Finnish butterfly fauna.