What if the best option for managing burnt forest areas was not managing them at all? A modelling approach to evaluate different post-fire management scenarios

Scars left by wildfires are easily noticeable in the Mediterranean landscape, turning these events a major issue for forest management. Like any wound, even those left by fires must be treated to properly regenerate.

In a burned area the vegetation cover is often destroyed by the fire, leaving the soil unprotected and vulnerable to erosion. The alterations of soil properties induced by fires lead to an increase in surface runoff, promoting the detachment of sediments and consequently endangering the water quality of downstream aquatic systems. If left unmanaged, the spontaneous regeneration of vegetation will eventually cover the affected area, restoring its natural hydrological cycle. After a wildfire, in Portugal, following an economical based perspective, the burned areas are normally reforested with selected plants species, namely Eucalypt and Maritime Pine, not infrequently by resorting to the implementation of bench terraces.

To define the best management strategy to adopt after a fire, the scientific community is continuously assessing the effects of these forestry practices on soils and the downstream water bodies. In this study, the Soil and Water Assessment Tool (SWAT) was used to simulate three different post-fire land management scenarios for a small catchment (21.9 ha) in central Portugal. The choice of this basin relates to the implementation of terraces to create a eucalyptus forest production area, 6 months after a fire burned the catchment completely. The model was calibrated for streamflow and water quality at the catchment outlet, both for the short post-fire period and the following eucalyptus cycle. In this study two post-fire scenarios were created, one with the recovery of the vegetation, and another in which a highly effective erosion mitigation measure (mulching) was applied to the high and moderate fire severity burned areas. The third scenario corresponded to the implementation of the terraces and the actual eucalyptus cycle.

Both the mulch application and the eucalyptus cycle scenario showed an important reduction in soil loss and sediment transport when compared with the post-fire spontaneous recovery scenario. A smaller reduction in the total runoff, as well as a negligible change in total flow, was found in the mulching scenario when compared with the spontaneous recovery one. Despite the eucalyptus cycle presented the highest flow discharge for the overall period, it presents smaller discharge peaks when compared with the two post-fire management scenarios.