Landscape variables influencing forest fires in central Spain

In assessing fire risk, it is important to determine whether all areas in a landscape burn at similar rates. This goal is complicated by the limitations of burned-area data and the temporally dynamic nature of landscapes. We assessed the differential degree of forest-fire burning for six landscape variables (land-use-land-cover type, distances to roads and towns, topography (slope, aspect, elevation)), each comprising several categories. The study area (95 x 55 km) was located in central Spain, and the study period covered 16 years. Landsat multispectral scanner images were used to annually map fire perimeters and to classify the landscape. We calculated an annual resource selection index for each category within a variable. The sizes and shapes of all fires occurring within a year were randomly distributed into the landscape 1000 times, and the corresponding resource selection index was calculated. This provided a null random-burning model against which we tested the actual resource selection index of the fires in each year. Pine woodlands showed consistent and significant positive fire selectivity, whereas deciduous woodlands showed consistent and significant negative selectivity. No differences in the resource selection indices of land-use-land-cover types were found between large (>100 ha) and small fires (<100 ha). Fires positively selected (resource selection index >1) areas at small or intermediate distances to towns and intermediate distances to roads. Selectivity for topographic variables was less marked. Our study demonstrates that landscape variables defining composition (land-use-land-cover type) or proximity to human influence are important factors for fire risk.