Post-fire evolution of water repellency and aggregate stability in Mediterranean calcareous soils: A 6-year study

- Water repellency and aggregate stability were studied in burnt soils during 6 years.
- Water repellency almost disappeared in the coarser aggregates (1-2 mm) after 6 years.
- Water repellency persisted in finer aggregates (0.25-1 mm) after 6 years.
- Aggregate stability was not affected severely by moderate-severity burning.
- High soil resilience to low-moderate fire disturbance was observed

Water repellency (WR) and aggregate stability (AS) are two soil properties generally modified after burning which show several hydrological and soil functioning consequences and may be used as indices for assessing burn severity. Both properties are strongly related and have major impacts on soil functioning and post-fire hydrologic and geomorphological processes. In many cases, the impact of fire on these properties has been analyzed in the short term. However, it is also necessary to investigate the magnitude of these changes and their implications for longer periods under specific conditions. In this work, we have investigated [1] the fire-induced changes on soil WR and AS in the medium term (6-year period after burning) and its distribution within aggregate size fractions (1-2, 0.5-1 and 0.25-0.5 mm), [2] the relations between post-fire AS and WR, and [3] the interactions between AS, WR and different factors (site, time since burning, lithology and vegetation type) in Mediterranean calcareous soils. Five areas burned during the summer 2006 in southern Spain were selected for this study. The study sites were characterized by wettable or slightly water-repellent calcareous soils with loam to clayey texture under herbaceous vegetation and shrubs. Soils were characterized chemically and physically, while the WR and AS of the fine earth and aggregate sieve fractions were determined annually between 2006 and 2011. Results show that soil WR was induced in previously wettable or enhanced in slightly or moderately water-repellent calcareous soils after moderate severity burning. Severity of WR from finer aggregates (0.5-1 and 0.25-0.5 mm) varied or remained stable but did not contribute to general soil WR assessed in the fine earth fraction. AS was slightly increased in some cases, and both properties returned progressively to pre-fire conditions during the study period. Soil resilience to low-moderate severity burning in the study area was very high.