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 con iferous forest in the southern Finnish taiga. We sampled spiders with pitfall traps in the interiors and in the edges of the old-forest patc hes and in the surrounding managed forests. We surveyed assemblages of ground-dwelling spiders and the relation of species to formerly menti oned three forest-habitat categories. We analysed spider assemblages i n 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 tho se in the surrounding managed forests. The difference was attributable to habitat differences, mainly to reduced tree-canopy cover in manage d forests. Large hunting-spider species (Gnaphosidae, Lycosidae) benef itted from clearcutting and other management measures, whereas the cat ches of small forest-living species (Linyphiidae) decreased in plantat ions and open forests. The hunters colonized the edges of old-forest f ragments, and were seldom found in the interior of old forest. Size of old-forest fragment did not affect significantly the spider assemblag e. The results indicate that a buffer zone of mature forest with close d canopy should be left to surround the old-growth reserves in order t o minimize the edge effect in the fragments.