The Production of Large and Small Wildfires

Natural large (catastrophic) disturbances are important because of their potential long-lasting impact on their surroundings, but underlying differences between frequent small and less common large disturbances are not well understood (Turner and Dale 1997, Romme et al. 1998, Turner and Dale 1998, chapter 4 of this book). Smaller disturbances may be better understood given their relative abundance, which lends itself more readily for study, but it is, perhaps, more useful to understand the forces driving damaging, catastrophic events. Wildland fires represent a perfect example. Nationwide, over 130,000 wildfires burn more than 4 million acres annually (1960–2002), these fires costing Federal agencies in excess of $768 million a year (1994–2002) in suppression alone (National Interagency Fire Center, http://www.nifc.gov/stats/index.html). Average wildfire size was 31 acres, with a suppression cost of $4800 per fire. The average wildfire does not appear a catastrophic threat, however this ignores the spatial distribution of these fires in relation to values at risk (an averaged size fire in a heavily populated area poses a different risk than a similarly size fire far removed from people and items of value). Catastrophic fire events, while relatively infrequent, do occur with some regularity—the 2000 Cerro Grande fire in New Mexico devastated 47,650 acres, two fire complexes in California in fall of 1999 each burned for three months and consumed a total of 227,647 acres, and during the 1998 Florida summer wildfire season, two fire complexes accounted for 205,786 acres or 9 percent of all wildfire acres, nationwide, in that year (National Interagency Fire Center, http://www.nifc.gov/stats/index.html).

Our objectives in this paper are to examine the wildfires that occurred in the St. Johns River Water Management District (SJRWMD) in Florida between 1996 and 2001. We explore four main questions: (1) Do small and large wildfires behave differently? (2) What are the implications for wildland management decisions? (3) Does spatial information enhance wildfire modeling? (4) Does spatio-temporal scale matter? We are interested in differences exhibited by large and small wildfire regimes-differences in fire damages (area), causes (arson, lightning, and accidents), ignition sources (dominant fuel source), climatic and weather influences, land use and wildland management (fuels management) strategies, landscape characteristics, and spatio-temporal factors (including fire and fuels management on neighboring areas) and their relevance for future mitigation. We use a scale fine enough to allow spatio-temporal effects to be observed, yet at the same time, a scale broad enough to be policy relevant to decision-makers interested in minimizing the damaging effects of wildfire.