Effects of immission load on spiders living on black pine

The effects of immission load on spiders living on black pine (Pinus nigra Arnold) were studied in a town in Western Hungary. In three sampling period s, trunk-trap catches of spiders from black pine trees planted in a control urban area were compared with those from black pines planted in an area wi th high immission load. In the first two sampling periods - when apart from the exclusive dwellers on or under bark of the black pine, foliage-dwellin g spiders overwintering under the bark (facultative bark-dwellers) could al so be trapped - the species richness and the Shannon diversity were signifi cantly higher in the control area than in the area highly affected by immis sion. In these sampling periods, the composition of spider assemblages also significantly differed in the studied areas. In the third sampling period - when only the exclusive bark-dwellers could be trapped because facultativ e bark-dwelling spiders returned to the foliage after the overwintering - t he species richness, Shannon diversity and the composition of spider assemb lages were similar in the differently affected areas. Our results suggest t hat spiders living exclusively on or under the bark are not significantly i nfluenced by immission load, while foliage-dwellers are sensitive to immiss ion. Indicator species analysis also proved the clear classification of the responses of spiders to immission load. The probable direct and indirect e ffects of immission, causing differences in the species richness, diversity and the composition of spider assemblages, are also discussed.