Forest fires increase variability of soil macrofauna communities along a macrogeographic gradient

- We studied soil macrofauna in the burnt forests along a 3000-km-long transect in Russia.
- Fires increase within-forest type spatial variability of macrofauna community composition.
- Between-forest type variance of macrofauna community composition decreases after fires.
- Increased habitat heterogeneity in pyrogenic forests overrules macrogeographic differences.

We assessed the impact of forest fires on macrofauna taxonomic richness, abundance and total biomass in 20 forests burnt five years ago and 20 respective control plots along a 3000-km-long north-south transect in European Russia that covered five major forest types (Mediterranean and broadleaved forests, southern, middle, and northern taiga). In parallel we assessed basic soil abiotic parameters in these stands. Within forest type, the spatial variance of macrofauna total biomass was 1.8 times higher in the burnt forests than in the controls. Due to this increase of variance in the burnt forests, the main effect of forest type on soil macrofauna parameters was generally weaker. Among different soil abiotic parameters, higher level of uniformity of macrofaunal community parameters between different forest types was explained by the labile P and N content in the soil, water-holding capacity and soil moisture. Presence of open areas within the burnt forests seems to be the leading driver of the increased similarity of soil macrofauna communities across different forest types. Forest fires thus act as a powerful force that raises within-forest-type soil macroinvertebrate beta-diversity and associated biomass fluctuations. At the same time burning reduces soil macrofauna gamma-diversity due to increased faunistic similarity between different forest types. This has potentially important implications for the functioning of soil macroinvertebate communities in the pyrogenic forests and its dependency on macroclimatic conditions.