We produced seven coarse-scale, 1-km 2 resolution, spatial data layers for the conterminous United States to support national-level fire planning and risk assessments. Four of these layers were developed to evaluate ecological conditions and risk to ecosystem components: Potential Natural Vegetation Groups, a layer of climax vegetation types representing site characteristics such as soils, climate, and topography; Current Cover Type, a layer of current vegetation types; Historical Natural Fire Regimes, a layer of fire frequency and severity; and Fire Regime Current Condition Class, a layer depicting the degree of departure from historical fire regimes, possibly resulting in alterations of key ecosystem components.The remaining three layers were developed to support assessments of potential hazards and risks to public health and safety: National Fire Occurrence, 1986 to 1996, a layer and database of Federal and non-Federal fire occurrences; Potential Fire Characteristics, a layer of the number of days of high or extreme fire danger calculated from 8 years of historical National Fire Danger Rating System (NFDRS) data; and Wildland Fire Risk to Flammable Structures, a layer of the potential risk of wildland fire burning flammable structures based on an integration of population density, fuel, and weather spatial data.This paper documents the methodology we used to develop these spatial data layers. In a Geographic Information System (GIS), we integrated biophysical and remote sensing data with disturbance and succession information by assigning characteristics to combinations of biophysical, current vegetation, and historical fire regime spatial datasets. Regional ecologists and fire managers reviewed and refined the data layers, developed succession diagrams, and assigned fire regime current condition classes. "Fire Regime Current Conditions" are qualitative measures describing the degree of departure from historical fire regimes, possibly resulting in alterations of key ecosystem components such as species composition, structural stage, stand age, canopy closure, and fuel loadings. For all Federal and non-Federal lands, excluding agricultural, barren, and urban/developed lands, 48 percent (2.4 million km 2 ) of the land area of the conterminous United States is within the historical range (Condition Class 1) in terms of vegetation composition, structure, and fuel loadings; 38 percent (1.9 million km 2 ) is moderately altered from the historical range (Condition Class 2); and 15 percent (736,000 km 2 ) is significantly altered from the historical range (Condition Class 3). Managers can use these spatial data to describe regional trends in current conditions and to support fire and fuel management program development and resource allocation.Keywords: current conditions, fire regimes, fuel management, fire occurrence, potential natural vegetation, cover type, GIS, wildland-urban interfaceYou may order additional copies of this publication by sending your mailing information in label form through one of the following...

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This paper was presented at the conference ‘Integrating spatial technologies and ecological principles for a new age in fire management’, Boise, Idaho, USA, June 1999 Maps of fire frequency, severity, size, and pattern are useful for strategically planning fire and natural resource management, assessing risk and ecological conditions, illustrating change in disturbance regimes through time, identifying knowledge gaps, and learning how climate, topography, vegetation, and land use influence fire regimes. We review and compare alternative data sources and approaches for mapping fire regimes at national, regional, and local spatial scales. Fire regimes, defined here as the nature of fires occurring over an extended period of time, are closely related to local site productivity and topography, but climate variability entrains fire regimes at regional to national scales. In response to fire exclusion policies, land use, and invasion of exotic plants over the last century, fire regimes have changed greatly, especially in dry forests, woodlands, and grasslands. Comparing among and within geographic regions, and across time, is a powerful way to understand the factors determining and constraining fire patterns. Assembling spatial databases of fire information using consistent protocols and standards will aid comparison between studies, and speed and strengthen analyses. Combining multiple types of data will increase the power and reliability of interpretations. Testing hypotheses about relationships between fire, climate, vegetation, land use, and topography will help to identify what determines fire regimes at multiple scales.

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