Soil fire severity is more relevant than fire frequency in explaining soil, carbon and nitrogen losses and vegetation recovery after wildfire in NW Spain

NW Spain is one of the regions of Europe most affected by rural fires and where there is a particularly high risk of increased soil erosion after fire. An increase in fire frequency is expected to enhance soil erosion and the asso-ciated carbon and nitrogen losses, impairing vegetation recovery and compromising ecosystem resilience. In this study, the influence of recurrent fires on soil erosion, carbon and nitrogen loss as well as on vegetation recovery was assessed in four shrubland areas dominated by Erica australis L. Pterospartum tridentatum (L.) Willk. And Ulex gallii Planch, burned in October 2017. Two of the areas were burned twice, between 2010 and 2017, and the other two areas were burned once, in 2017. Soil burn severity was moderate to high in all experimental sites. Soil erosion along with vegetation cover and diversity were monitored during the two years after fire, on 24 plots of 80 m2. In the first year after fire, the mean sediment yield was 24.1 Mg ha-1 in the areas burned twice and 17.4 Mg ha-1 in the areas burned once. Fire frequency did not significantly influenced soil loss unlike the carbon and nitrogen concentrations in eroded sediments. Sediment losses as well as carbon and nitrogen losses were significantly associated with soil burn severity. Vegetation recovery was not affected by fire frequency in the shrublands, which were dominated by resprouters. No alteration in species composition was observed, indicating the high degree of resilience of the communities. In summary, recurrent fires occurring within an interval of 10 years seemed to have little effect on sediment yield and vegetation recovery. The significant influence of soil burn severity on sediment yield and vegetation recovery highlighted the importance of considering this factor in fire prevention plans for fire-prone areas.