Patterns of fuel types and crown fire potential in Pinus halepensis forests in the Western Mediterranean Basin

Using the databases from the Spanish Forest Inventories, we have classified the forest structures of Pinus halepensis plots across the Iberian Peninsula into different fuel types as a function of the most common fire types that can be supported. The purposes of this study are to determine (i) the proportion of the different fuel types and fire type associated with different disturbance scenarios (undisturbed, after a recent wildfire, after an old wildfire and after thinning), (ii) the effect of climate and soil type on the distribution of fuel types and (iii) the effect of the different disturbance scenarios on the transitions between these fuel types. After a recent wildfire the risk of spreading active crown fires was reduced but the risk increased with time since last fire and in undisturbed areas. Climate and stoniness influenced the spatial distribution of fuel types and the potential crown fire risk. There was a lower risk of active crown fires when there was higher aridity and higher stoniness. Disturbances modify the transitions between fuel types; after a wildfire there was the highest change in fuel types with an increase of fuel type one with open forest structures and the presence of plots without trees that are linked to lower risk of active crown fires. There was also a reduction of fuel types 3 and 4, which burn with high intensity during a wildfire. In the absence of disturbances or after an old wildfire, changes between fuel types were slow, usually leading to increasing canopy closure and higher risk of active crown fires. After thinning there were also important changes in fuel types, with a reduction of active crown fire risk after thinning from below and heavy thinning. Fire plays an important role in maintaining landscape heterogeneity. As a consequence of climate warming, new areas with high structural continuity will increase the risk of extreme fire behavior, and for this reason, small wildfires and specific thinning treatments are the key to reduce crown fire potential. (C) 2011 Elsevier B.V. All rights reserved.