Immediate effects of fire-severity on soil invertebrates in cut and uncut pine forests

We studied how variations in fire severity and the degree of cutting before burning affected soil invertebrates in a Pinus sylvestris forest in central Sweden. A varied depth of burn in the mor layer was obtained by exclusion of rain and addition of fuel in small plots (1 m×2 m) in clear-cut, selectively cut and uncut part of the forest before large-scale prescribed burning took place. Soil samples were taken from the plots immediately before, the day after, and two months after the fire. The overall mortality of invertebrates depended on the proportion of organic soil consumed by the fire, and for individual taxa it ranged between 59 and 100%. Invertebrates that lived deeper in soil suffered lesser mortality than those in the vegetation and litter layers did. Greater mobility in soil (Staphylinidae) or a thick cuticle (Oribatediae, Elateridae) may have contributed to the higher survival observed in these taxa. The beetles Atomaria pulchra (Cryptophagidae), Corticaria rubripes (Lathridiidae), and other fire-favoured insects colonised the burned forest the very day the fire burned. These species preferred the hard-burned plots and the uncut stand for colonisation. Sixty days after the fire, the abundance of invertebrates was lower in the burned cut stands compared to the burned uncut stand. The species composition of beetles in the burned stands was then characterised by a few very abundant fire-favoured species.