Abstract

To examine possible effects of global change on soil fauna abundance and diversity, two long-term field experiments in Norway spruce stands in Sweden were studied. Soil fauna (Oribatida, Mesostigmata, Collembola, predatory macroarthropods and Enchytraeidae) were sampled in plots experimentally simulating altered precipitation patterns and increased soil temperature. Six years of summer drought caused large decreases in abundance in all faunal groups and a reduction in species diversity of Oribatida and Collembola. Summer drought and irrigation caused shifts in the community composition of Oribatida and Collembola, but drought affected soil fauna more than irrigation. Increased soil temperature during 5 years resulted in positive responses in several Oribatida species and negative in some Collembola species. Three years after the summer drought treatment had ceased, the soil arthropod communities had still not returned to control conditions. Total abundances recovered quickly, but species richness, diversity indices and community composition recovered slower. Mobile arthropod groups seemed to recover faster than groups with more limited dispersal ability, and Oribatida had the slowest recovery rate. Microarthropod species with wide habitat niche width recovered faster than those with narrow niche width, and parthenogenetic Oribatida recovered faster than sexually reproducing ones. Overall, Collembola were less affected by drought, and recovered faster than Oribatida. Soil fauna decreased in plots receiving repeated additions of solid nitrogen fertiliser for 13 years, whereas slight increases were found in plots receiving liquid fertiliser. The fertilisation treatments caused shifts in the community composition of Oribatida and Collembola but did not cause changes in species richness. In conclusion, climate change resulting in frequent summer droughts will probably decrease abundance and diversity of forest soil fauna. Moister conditions may primarily result in shifts in community structure. Intensive forest fertilisation for biofuel production will probably affect the composition of soil fauna communities. Oribatida communities seem to be particularly vulnerable to disturbances. Post-disturbance recovery of soil fauna seems to be slow and disturbances on a large spatial scale may affect the resilience of soil ecosystems, as disturbances may cause permanent changes in community composition.