The BIOLOG and PLFA techniques were used to evaluate the short- and medium- term effects produced by high and low severity fires on microbial diversity. Two scrublands ecosystems from Galicia (NW Spain) with different post-fire treatments (seeding and mulching) were used, one affected by an experimental fire of low-severity and the other affected by a high-severity wildfire and the diversity indices (R, microbial richness; H, Shannon-Weaver diversity index; E, Shannon’s eveness) were determined in soil samples collected from the top layer (0-2 cm) immediately and 90, 180 and 365 days after the fire. The H values calculated with the PLFA technique were strongly correlated with those obtained with the Biolog technique; thus, information concerning taxonomic diversity given by H-PLFA is consistent with that provided by H-Biolog, metabolic diversity. The values for the R, H and E indices tended to be higher in the burned soils than in the respective unburned control, indicating that the diversity was slightly higher and the microbial groups were distributed more equitably following the fire. These effects were more marked in high severity wildfire than in low severity fire and they persisted even one year after the fire. Independently of the method used (PLFA, BIOLOG) there was no evidence of any significant difference in the diversity indices among the two different post-fire treatments and the corresponding burned treatment on both sampling areas.