fire Defining the Wildland–Urban Interface Susan I. Stewart, Volker C. Radeloff, Roger B. Hammer, and Todd J. Hawbaker Federal wildland fire policy in the United States has been substantially revised over the past 10 years (HFRA), which became law in 2003—reit- and new emphasis has been given to the wildland–urban interface (WUI), which creates a need for erated the need for resource managers to information about the WUI’s location and extent. We operationalized a policy definition published in work with communities and homeowners in the Federal Register (US Department of the Interior [USDI] and US Department of Agriculture [USDA]), the WUI to reduce the risks associated with 2001, Urban wildland interface communities within vicinity of federal lands that are at high risk from wildfire. wildfire. Fed. Regist. 66(3):751–777) to create national maps and statistics of the WUI to guide The increasing national fire policy fo- strategic planning. Using geographic information system analysis, we evaluate the national WUI by cus on the WUI came in response to recent altering the definition’s parameters to assess the influence of individual parameters (i.e., housing housing trends in the United States. Home- density, vegetation type and density, and interface buffer distance) and stability of outcomes. The most owners want to be near open space and in sensitive parameter was the housing density threshold. Changes in outputs (WUI homes and area) were close contact with nature. From 1940 to ABSTRACT much smaller than parameter variations suggesting the WUI definition generates stable results on most 2000, significant housing growth occurred landscapes. Overall, modifying the WUI definition resulted in a similar amount of WUI area and number in suburban and rural areas, especially in and of homes and affected the precise location of the WUI. near forests (Radeloff et al. 2005a). Housing growth was strong nationwide, including ar- Keywords: wildland–urban interface; wildland fire; housing growth; GIS sensitivity analysis; eas with short fire return intervals and high wildland fire policy departure from historic conditions such as the Rocky Mountains and the Sierra Nevada (Hammer et al. in press). The effects of re- he wildland–urban interface it clarified the role of the federal agencies in source management practices, climate (WUI) has become the central fo- fighting fires in the WUI (USDI and USDA changes, and insect and disease infestations, cus of wildland fire policy in the 1995). A 10-year overhaul of US wildland together with continued housing growth in T high fire-risk areas thus create an urgent United States. The tragic 1994 Storm King fire policy followed, spurred on by the ex- incident, in which 14 firefighters were killed, treme fire season of 2000. Each of the re- need to understand and manage fire risk in initiated intense scrutiny of wildfire policy ports and initiatives issued in successive the WUI (Pyne 2001). and management (US Department of the years—the Report to the President in Sep- Governments at all levels share respon- Interior [USDI] and US Department of Ag- tember of 2000, the 10-year Comprehensive sibility for wildland fire management in the riculture [USDA] 2006). When the Federal Strategy of 2001, its implementation plan WUI. The federal government’s role is to Wildland Fire Management Policy and Pro- and the Healthy Forest Initiative in 2002, provide leadership, coordination, and re- gram Review was issued the following year, and the Healthy Forest Restoration Act search across the country, a role that benefits Received June 20, 2006; accepted April 17, 2007. Susan I. Stewart ([email protected]) is research social scientist, Northern Research Station, USDA Forest Service, 1033 University Avenue, Suite 360, Evanston, IL 60201. Volker C. Radeloff ([email protected]) is associate professor, Department of Forest Ecology and Management, University of Wisconsin, Madison, Wisconsin. Roger B. Hammer ([email protected]) is assistant professor, Department of Sociology, Oregon State University, Corvallis, Oregon. Todd J. Hawbaker ([email protected]) is Ph.D. student, Department of Forest Ecology and Management, University of Wisconsin, Madison, Wisconsin. The authors are grateful for the comments of Pam Jakes and Don Field on an earlier version of this article. Support for this research was provided by the USDA Forest Service Northern Research Station under the National Fire Plan, and by the University of Wisconsin–Madison. Copyright © 2007 by the Society of American Foresters. Journal of Forestry • June 2007 201 from the ability to locate and compare the the Western Governor’s Association (Teie ulation data and determined vegetation WUI in different states and regions. To sup- and Weatherford 2000), with only minor proximity via detailed fuels mapping, al- port this aspect of WUI management and changes. The more recent HFRA moves though the Census data’s resolution, the strategic planning, we created a map of the away from this standardized approach to de- rules for determining vegetation and popu- WUI across the lower 48 states (Radeloff et fining the WUI by allowing communities to lation proximity, and the types of vegetation al. 2005b). Unlike a community-level WUI establish a buffer zone around the town, the included were not specified, and the distinc- map that can be enriched by using detailed civic infrastructure, and evacuation routes, tion between interface and intermix WUI local data, this “big picture” national map including these areas in the WUI as well. was made based on population density required nationally consistent data and a sin- This more flexible definition is consistent alone. A coarse-scale map of the wildland gle standardized WUI definition. Here, we with the HFRA’s emphasis on empowering fire risk to structures was developed as a tool sought to understand how the national WUI local communities to develop Community for strategic planning (Schmidt et al. 2002). map is influenced by the WUI definition Wildfire Protection Plans. Ambient population data (USDE 2005) was used, the relative effect of each part of the Throughout its evolution, the WUI used to derive housing densities and com- definition, and the overall usefulness of the definition always includes three compo- bined with extreme fire potential (derived map in identifying homes likely to be af- nents: human presence, wildland vegeta- from climate data) and potential fire expo- fected by wildfire. We used geographic in- tion, and a distance that represents the po- sure data (derived from vegetation data) to formation system (GIS) analysis to address tential for effects (e.g., wildland fire and categorize threat levels at a 1-km resolution. these questions. human activity) to extend beyond bound- These examples illustrate that despite aries and impact neighboring lands. Beyond all that has been written about the WUI and Literature Review these three components, most WUI discus- its significance in fire policy, there is no sin- A good WUI map provides a graphic sions are imprecise regarding what is or is gle operational definition. A review by the representation that matches the conceptual not included. For example, human presence Government Accountability Office (GAO) understanding of what and where the WUI has been defined by housing density, popu- of NFP implementation criticized the fed- is. This conceptual understanding of the lation density, number of houses, or eral agencies responsible for wildland fire WUI has evolved over time; the area where configuration of housing developments and management on this point (Hill 2001). In a houses and forests meet has attracted atten- neighborhood characteristics. Wildland formal response included in the GAO re- tion for many years. Bradley’s book (Bradley vegetation is always mentioned, but the den- port, Forest Service Chief Bosworth reaf- 1984) on the resource management issues in sity, extent, and type of vegetation that firmed his agency’s commitment to main- the interface is a major early contribution. makes some vegetation “wildland vegeta- taining enough flexibility in defining the Even earlier, Henry Vaux characterized the tion” is not well defined. The distance that WUI to accommodate the many different WUI as the “hotseat of forestry” (Vaux the WUI extends into wildlands or into a kinds of landscapes it manages. 1982) and cautioned foresters not to under- housing development has been described in Flexibility is valuable for both forest- estimate its political and policy significance. many different ways, including the distance and community-level mapping and manage- Both authors discussed a wide range of WUI a golf ball will fly off the porch or the dis- ment but is counterproductive when issues and neither equated the WUI with tance from which flames or firebrands can comparing WUI across places or over time wildland fire. However, the focus of WUI reach a structure (Summerfelt 2003), but periods. Our research was intended to assess discussions had narrowed by the end of the specific distances are rarely given. the WUI across regions and to track its 1980s, when Davis (1990) characterized the Conceptually, these many definitions growth and change over time, two purposes WUI as a setting where wildland fire is a all refer to the same basic idea, that the WUI that required standardizing the WUI defini- problem and where conflicts arise over re- is where houses and wildlands meet or over- tion. With no previous standard definition sponsibility for protecting homes from wild- lap. However, operationally, they differ and of the WUI to draw from, we tested the def- fire. A 1997 issue of the Journal of Forestry in previous WUI maps, definitions vary de- inition we developed to ensure its consis- featured a cover photo of a wildland fire en- pending on data available at the time and tency with our research aims and with stra- croaching on a subdivision and included two across the extent of the map. For example, tegic wildland fire planning.