Gastropod diversity in aspen stands in coastal northern Sweden


Forest management has actively reduced proportion of deciduous trees in Fennoscandian managed forests. Several species of cryptogams and invertebrates depend on deciduous trees, among which aspen (Populus tremula L.) is especially important. The occurrence and abundance of several terrestrial gastropod species are linked to aspen leaf litter. However, the impact of forestry practices on the gastropod communities is largely unknown. We examined difference in species richness, diversity (H’), and species composition in the gastropod fauna in aspen stands in a 400 km(2) managed boreal forest area in northern Sweden by collecting them with masonite boards from 20 selected stands. We contrasted isolated (>500 m from the neighboring stand) and aggregated (<300 m from neighboring stand) stands, stands close to arable land (<50 m) and stands in the forest, and used locations outside the aspen stands in the surrounding forest as controls. Stand sizes ranged from 100 to 3000 m(2). Gastropod species richness and diversity were high in aspen stands near arable land and in aggregated stands in the forest and low in controls. Both diversity and assembly composition of the gastropods in isolated aspen stands in the forest interior were intermediate between, and did not differ significantly from, controls and other aspen stands. Species diversity and richness increased with stand area up to an area of 700 m(2). We conclude that aspen stands in this managed boreal forest landscape are important for gastropods, even for species that are not strict habitat specialist connected to aspen. The total amount and the distribution of aspen in the landscape also may be important, since many species can be lost if area and connectivity of aspen stands drop to low levels. The positive species-area relationship suggests that future forestry practice should favor stands at least 500 m(2) (0.05 ha) preferably in connection to other stands. (C) 2002 Elsevier Science B.V. All rights reserved.