The distribution of carabid beetles in fragments of old coniferous taiga and adjacent managed forest

Abstract

Carabid beetles were sampled by using pitfall traps in 35 fragments of old coniferous taiga (area range 0.4-101 ha) and in managed forest in their immediate surroundings in southern Finland in 1984 and 1985. The pooled sample comprised 1986 individuals from 42 species. Species number, standardized by rarefaction, was greater in the forest sur roundings than in the forest fragments, but the difference is due to great between-site variability in the surrounding areas. Marked differences in the composition of the carabid samples between the fragment interiors and their surroundings were mainly caused by species that are scarce or occasional in coniferous forests. Nine abundant forest generalists comprised about 90% of the pooled sample, and they were widely (although not uniformly) distributed over successional stages of forest. In order to detect possible area effects the pooled data sets of fragments larger than 30 ha and smaller than 5 ha were compared. No differences were detected in the species assemblage characteristics, and of the nine most abundant species seven were more abundant in the small fragments than in the large ones, and two species were equally abundant in the two fragment size classes. We discuss the significance of the results concerning the preservation of faunal diversity in coniferous taiga, using carabids as an example, and we support the maximization of habitat heterogeneity on the regional scale as an appropriate conservation strategy.