Land snails in Estonian forests: numbers and species richness

. A drastic decline in land snail populations has been revealed in the oligotrophic areas of acidified regions of Europe. Since snail shells are an important calcium source for forest passerines, this decline causes severe reductions in forest passerine reproductive rates. In Estonia, about 40% of all woodlands consist of pine forests on poor, naturally acidic soils. It has been shown that birds breeding in such forests suffer calcium deficiency. A research project was carried out to estimate the current situation in Estonian forest land snail populations. This was the first large-scale quantitative investigation of forest snail fauna in the eastern Baltic area. Data about the abundance and species richness of snails are presented by geologically different regions and forest types of Estonia. The effect of industrial forest liming, occurring near some big oil-shale and cement works, was studied. Our data confirm that the number of snails in a substantial portion of Estonian forests is very low, and therefore birds breeding there may be vulnerable to possible increases in acidification. However, atmospheric pollution with calcareous materials in some ecologically problematic industrial regions seems to compensate for calcium deficiency for snail populations.