Life History Traits Reflect Changes in Mediterranean Butterfly Communities Due to Forest Encroachment

The biodiversity of the Southern Balkans, part of the Mediterranean global biodiversity hot-spot, is threatened by land use intensification and abandonment, the latter causing forest encroachment of formerly open habitats. We investigated the impact of forest encroachment on butterfly species richness, community species composition and the representation of life history traits by repeated seasonal visits of 150 one-hectare sites in five separate regions in three countries—Greece, Bulgaria, and the Republic of Macedonia (FYROM—the Former Yugoslav Republic of Macedonia)— 10 replicates for each habitat type of grasslands, open formations and scrub forest within each region. Grasslands and open formations sites hosted in average more species and more red-listed species than scrub forest, while no pattern was found for numbers of Mediterranean species. As shown by ordination analyses, each of the three habitat types hosted distinct butterfly communities, with Mediterranean species inclining either towards grasslands or open formations. Analysing the representation of life history traits revealed that successional development from grasslands and open formations towards scrub forest shifts the community composition towards species overwintering in earlier stages, having fewer generations per year, and inhabiting large European or Eurosiberian (e.g. northern) ranges; it decreases the representation of Mediterranean endemics. The loss of grasslands and semi-open formations due to forest encroachment thus threatens exactly the species that should be the focus of conservation attention in the Mediterranean region, and innovative conservation actions to prevent ongoing forest encroachment are badly needed.