Disentangling the Influence of Past Fires on Subsequent Fires in Mediterranean Landscapes

Abstract

Understanding the interplay between climate, fuel and fire is necessary for developing strategies that minimize the negative impacts of fire on people and ecosystems. Here, we aim to investigate whether past fires limit fire activity by reducing fuel availability (‘fire leverage’) in Catalonia (NE Spain; 32,107 km2), a Mediterranean region encompassing diverse landscapes of agricultural plains and pine–oak mosaics. We built a hierarchical model to assess variations in annual burnt area in relation to weather, past fires and time for a 40-year period (1976–2015). The model also quantified how mean annual wind speed and the arrangement of forests modulated leverage. We found that the cumulated burnt area in the last 6–7 years reduced the re-occurrence of fires. Annual burnt area increased with both dry weather conditions and the number of hot days (≥ 30°C) and showed a moderate decline over the 40-year time series. Model outputs provided some evidence that landscapes with higher mean annual wind speed had lower fire leverage and landscapes with more continuous forest cover had higher fire leverage; however, the statistical uncertainty surrounding the effects of these two relationships was high. In summary, our results show that climate–fire relationships in Mediterranean landscapes are dynamic: fires create short-lived conditions where fuels limit future fire activity in fire regimes usually limited by weather. Our work highlights the multiple factors regulating leverage and helps to understand the interplay between climate, vegetation and recurrent fires in shaping fire regimes.