Spatial distribution of forest fires in Sierra de Gredos (Central Spain)

Understanding the impact of fire requires detailed knowledge about where fires occur, how they alter landscape patterns, and precise calculations of fire regime parameters. In this work, a reconstruction of the perimeters of fires that occurred during 1970-1990 was made by means of aerial photographs aided by field inspection in a 14km x 14km study area located in the southern slopes of Sierra de Gredos (Central Spain). Yearly fire perimeters, topographic attributes (slope, aspect and elevation) and the forest territory limits were incorporated to, and analyzed by means of, a raster-based GIS. The perimeters of 75 fires greater than or equal to4 ha were mapped, which were approximately 13% of the total number occur-red but accounted for 95% of the area burned. During this time, nearly 33% of the forest territory was burned and 22% of it was burned twice or more. Burning was not random in relation to topography, either when occurred for the first time or subsequently. Fires tended to aggregate spatially, which produced a set of increasingly larger interconnected burned patches. The fire rotation period was 51 years. A spatially explicit calculation of this parameter yielded 64 years, while for the areas that burned for the first time, in 15 years 50% of the area had burned again. Moreover, over half of the pine woodlands were 25 years old or older when they burned, while half of the reburned areas were less than 6 years old. These results indicate that fires, by concentrating in specific places, and by becoming more frequent in areas already burned could produce greater impacts than suspected and could further contribute to increase fire incidence in the area. (C) 2001 Elsevier Science B.V. All rights reserved.