Impacts of wood ants (Formica aquilonia Yarr.) on the invertebrate food web of the boreal forest floor

We studied the impact of wood ants on the structure and functioning of the invertebrate food web of boreal forest during a three-year period. Special emphasis was put on the detritus-based food web. The density of wood ants w as reduced > 90% by eliminating whole wood ant colonies from five areas in Central Finland, and leaving five areas as controls. We monitored the growt h of spruce, pine and birch seedlings planted on homogenised plots, and dev elopment of the invertebrate community in soil and vegetation. The ant remo val had little effects on the structure of the invertebrate food web. Howev er, biomasses of predators caught in pitfall traps were 60% smaller under h igh ant density than under low ant density. Also, at the end of the experim ent the biomass of the lumbricid earthworm Dendrobaena octaedra was reduced by 54% in the homogenised plots without ant nests. Removal of wood ants ha d no influence on soil microbial biomass, concentration of soil mineral nit rogen, plant N uptake, or plant growth.