Changes in soil properties after a wildfire in Fragas do Eume Natural Park (Galicia, NW Spain)

• Soil quality after a wildfire was evaluated in a forest under different vegetation.
• PCA was used to integrate a wide range of chemical and biological properties.
• Vegetation was the most important factor controlling soil quality.
• Wildfire was also an important source of variation in the quality of these soils.
• Fire provoked marked changes in microbial C, extractable C, pH and bacterial growth.

The impact of a wildfire on some selected physicochemical, chemical (water retention, pH, electrical conductivity, free Fe and Al oxides, total C, extractable C), biochemical (microbial C, soil respiration, bacterial activity, β-glucosidase, urease and phosphatase activities) and microbiological properties (analysis of phospholipid fatty acids, PLFA pattern) was evaluated in Fragas do Eume Natural Park (NW Spain). Soil samples were collected three months after the wildfire from the A horizon (0–2.5 and 2.55 cm) of the unburnt and burnt soil under climax vegetation (Quercus) and non-autochthonous vegetation (Eucalyptus). The results indicated that, independent of the vegetation considered, the wildfire induced short-term modifications of most soil properties analysed, more accentuated changes being those related to labile fractions of the soil organic matter (extractable C and microbial biomass C, negative effects) as well as those in pH and bacterial growth values (positive effects). The fire effect was often more noticeable in the 0–2.5 cm layer than in the 2.5–5 cm layer. The results of a principal component analysis performed with the matrix of the physicochemical and biochemical data showed that vegetation was the most important factor controlling the overall quality of these soils and that wildfire is also an important source of variation in soil quality. This is in agreement with the PLFA pattern, differentiating clearly the Quercus soil samples from the Eucalyptus ones and, to a lesser extent, the burnt soil samples from the corresponding unburnt ones. Medium- and long-term consequences of these microbial changes in the functioning of the plant–soil system should be investigated in order to preserve the biodiversity of the Natural Park.