Recovery of soil macrofauna after wildfires in boreal forests

Forest wildfires can severely affect the soil faunal community. We hypothesised that the recovery of soil animals after a fire would occur through (1) immigration from the unburnt forest into the burnt area and (2) survival in less-burnt patches or deep soil layers. To test the rate of recovery, and whether immigration or survival was the main recovery factor, we studied soil macrofauna after two wildfires occurring in 2001 in central Sweden and north-western Russia. The animals were studied up to 2007 by taking soil and litter samples including unburnt and burnt forest plots 20 and 60 m from the edge of the unburnt forest. Total abundance and species richness was 1.5–5 times higher in the unburnt than in the burnt areas shortly after fire. Animals in deep soil layers had a better survival after fire than surface-dwelling species. The burnt area was colonised within a few months by flying insects, mostly dipterans. When the post-fire vegetation had established after 1–2 years, plant-feeding groups like aphids, cicadellids and thripses became even more abundant than in the unburnt forest. Millipedes established faster in the area close to the forest edge than in the central part of the fire area indicating migration from the forest edge, but most slow-dispersing soil animals seemed to recover through survival in the burnt area. The biomass of both microbi-detritivores and predators showed a delayed recovery in the burnt area and had only reached 40–60% of that in the unburnt forest six years after the wild-fire, indicating reduced habitat quality for the former and food shortage for the latter group.