GROUND-DWELLING SPIDERS (ARACHNIDA, ARANEAE) IN FRAGMENTED OLD FORESTS AND SURROUNDING MANAGED FORESTS IN SOUTHERN FINLAND

We studied the structure of spider assemblages in fragments of old coniferous forest in the southern Finnish taiga. We sampled spiders with pitfall traps in the interiors and in the edges of the old-forest patches and in the surrounding managed forests. We surveyed assemblages of ground-dwelling spiders and the relation of species to formerly mentioned three forest-habitat categories. We analysed spider assemblages in relation to vegetation structure as well. As in forest spiders there are no habitat specialists, no strict old-forest species were found. However, the spider assemblages of old forests were different from those in the surrounding managed forests. The difference was attributable to habitat differences, mainly to reduced tree-canopy cover in managed forests. Large hunting-spider species (Gnaphosidae, Lycosidae) benefitted from clearcutting and other management measures, whereas the catches of small forest-living species (Linyphiidae) decreased in plantations and open forests. The hunters colonized the edges of old-forest fragments, and were seldom found in the interior of old forest. Size of old-forest fragment did not affect significantly the spider assemblage. The results indicate that a buffer zone of mature forest with closed canopy should be left to surround the old-growth reserves in order to minimize the edge effect in the fragments.