Disentangling large fire occurrence in Mediterranean forests: Management guidelines from a multiscale approach

1 Fire is one of the main disturbances in Mediterranenan ecosystems. In the recent decades, in 2 Catalonia (NE Spain), the number of fires has decreased while burnt area has increased. This is 3 related to changes in land use, climate and fire suppression policies which influenced 4 horizontal and vertical fuel continuity. From all the factors influencing fire risk only fuel load is 5 manageable by humans. For this reason it is important to understand the role of different land 6 covers and forest structure in fire occurrence. This study aimed to understand the 7 determinants of large fire occurrence at two different scales, 500m and 2000m around the 8 ignition point (local and landscape scale, respectively). A binary logistic regression model was 9 built using ignition points from the period 1989-2012 and considering 1000 control points. 10 Forest structure variables obtained through interpolation techniques throughout Catalonia and 11 land cover types were established as the independent variables at the two considered scales. A 12 risk map for large fire occurrence in Catalonia was also built. 13 Mediterranean pine forests and shrublands were the main variables influencing positively 14 large fire occurrence. Specifically, Mediterranean pine forests with intermediate values of 15 basal area and high understory increased the risk of large fires. Although large fires do not 16 usually start in mixed forests, these forests were important at the scale at the landscape scale 17 (2000m) probably because of their vertical continuity. Results showed that a multiscale 18 management would be necessary which should focus on the landscape mosaic of different 19 land cover types and less fire prone forest structures, particularly considering the uncertainty 20 associated with global change and the large fires’ risk increase throughout Catalonia. 21