Wildfire effects on soil organic matter in two forest types in central Portugal

Abstract

Forest fires are a frequent phenomenon in Mediterranean ecosystems, and are widely considered to be the main factor of disturbance in the Mediterranean basin. In particular the Iberian Peninsula has the highest risk of wildfire occurrence in Europe. In the case of continental Portugal, the total area that burnt during the period 1980-2003 amounted to approximately 2.500 million hectares, almost 29% of the country's total area. Wildfires can affect a wide range of physical, chemical, mineralogical and biological soil properties. The extend of such changes will depend to a large degree on the temperature ranges reached at different soil depths (severity) and the degree of heating that the different soil components can withstand before being altered (resilience). Wildfire impacts on selected soil properties are being studied by the EROSFIRE-II project (PTDC/AGR-CFL/70968/2006). The project's main aim is to predict soil erosion risk in recently burnt forest areas and therefore focus is on key soil properties determining runoff generation and the associated sediment/soil losses, in particular soil moisture content and water repellence. Nonetheless, fire-induced changes in soil organic matter content and composition are fully recognised to be of considerable potential importance for post-fire erosion phenomena. The present work aims to characterize physical and chemical changes in topsoil organic matter in two distinct forest types in the Colmeal study area. This area is located in the Lousã mountains in central Portugal and was affected by a wildfire in August 2008 that consumed a total area of about 70 ha. Within the area, two slopes were selected with maritime pine (Pinus pinaster) and eucalypt plantations (Eucayiptus globulus). In addition, two comparable but unburnt slopes in the immediate surroundings were selected as control sites. The fire effects on soil organic matter quantity and quality will be studied using complementary analytical approaches, such as elemental and isotopic analysis, and analytical pyrolysis (Py-GC/MS). Comparison of the results for the neighbouring burnt and unburnt sites will allow identifying the existence of typical patterns of fire-induced alterations and, thereby, contribute to a better knowledge base to optimise post-fire soil restoration efforts. In addition, the envisaged results will provide further insight into the effect of wildfire on soil ecological functions and on the soil's potential to act as a C-sink on a global scale.