Environmental parameters and microspatial distribution of insects: a case study of carabids in an alluvial forest

The microspatial distribution of carabid beetles in a pristine alluvial Quercus-Ulmus forest along the river Elbe (north Germany) was investigated using 152 pitfall traps over a stud), period of 28 d. Traps were set in an area of only 100 x 120 in which comprised a wide range of microhabitats due to an extremely heterogeneous microrelief. Composition of the ground beetle assemblage was strongly influenced by microclimatic parameters and vegetation structure within it few metres: specifically soil moisture, light intensity, pH as well as cover of leaf litter and herbs. TWINSPAN analyses indicated a sensitive segregation or carabids into distinct microhabitats on a small scale. PCA and subsequent RDA distinguished two distinct species groups: species of wet deciduous woodland and species of wet open marsh habitats. The fringes of small temporary waters within the alluvial forest were of particular value for nature conservation. providing habitat for a high number of rare species. Although there was a shift in species composition over time and the assemblages reorganised spatially, the main environmental parameters governing the community remained the same as indicated by discriminant analyses. namely soil moisture, leaf litter cover and light intensity.