Effects of experimental irrigation and drought on the composition and diversity of soil fauna in a coniferous stand

1. The effects of experimental long-term summer drought and irrigation on soil fauna were studied in a Norway spruce stand in south-western Sweden. The treatments, carried out over 8 and 10 years respectively, were chosen to simulate two scenarios of climate change, involving drier and wetter summers. 2. Different microarthropod communities developed in the different treatments. The abundances of enchytraeids, mesostigmatid mites and macroarthropod predators were all lowest in the drought plots. Drought decreased and irrigation increased the abundance and diversity of Oribatida. Drought decreased the abundance of Collembola. 3. The dominance structure of Oribatida and Collembola also changed, but less markedly. Drought affected community composition of both groups more than irrigation. 4. The study confirms that soil microarthropods can be useful environmental indicators, but their responses did not support the widely held view that deviations from a log-normal dominance structure indicates a stressed community. 5. The results also indicate that a drier climate with summer drought will lead to the local extinction of some soil animal species in this region.