Evaluation of two emergency treatments for reducing post-fire runoff and sediment losses

A field experiment was conducted in a burnt area affected by a high severity fire located in Laza (Ourense) to evaluate the impact of fire and different post-fire stabilisation treatments like mulching and seeding on microbial biomass. Samples were collected from the A horizon (0-2 cm) immediately and 4, 8 and 12 months after the wildfire. Total biomass and biomass of specific groups (bacteria, fungi, actinomycetes, Gram-positive bacteria and Gram-negative bacteria) were determined in the fraction < 2mm by analysis of phospholipid fatty acids. Results showed that total biomass and biomass of specific groups decreased immediately after the wildfire and although this effect is was attenuated over time it still persisted after 1 year. Fungal/bacterial and G -/G+ ratios as well as actinomycetes abundance increased in burnt soil samples due to changes in soil pH and carbon content. The ratio of cyclopropyl fatty acid/monoeic precursors (cyclo/prec) tended to be higher in the burned soils than in the unburned control, indicating that the fire caused stress in soil microorganisms. There was no evidence of any significant difference on total biomass, biomass of specifics groups and microbial fatty acids indices (fungal/bacterial, G-/G+, cyclo/pre) between the two different post-fire treatments (QS, QM) and the corresponding burned treatment (Q).