Scott-Burgan Fuel Model Shifts

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Scott-Burgan Fuel Models (2005) The Scott-Burgan (SB) fuel models are a set of 40 standardized fuel descriptions used in wildland fire behavior modeling. They are categorized as follows: Model Description GR1 Short, sparse, dry climate grass (1 ft tall, 0.25 tons/acre) GR2 Low load, dry climate grass (1 ft tall, 0.75 tons/acre) GR3 Moderate load, dry climate grass (2 ft tall, 2 tons/acre) GR4 Tall, moderate load, dry climate grass (4 ft tall, 3 tons/acre) GR5 Tall, high load, humid climate grass (4 ft tall, 5 tons/acre) GR6 Moderate load, humid climate grass (2 ft tall, 2.5 tons/acre) GR7 Low load, humid climate grass (1 ft tall, 1 ton/acre) GR8 Very high load, humid climate grass (6 ft tall, 7 tons/acre) GR9 Extremely high load, humid climate grass (8 ft tall, 10 tons/acre) SH1 Low load, dry climate shrub (1 ft tall, 2 tons/acre) SH2 Moderate load, dry climate shrub (2 ft tall, 4 tons/acre) SH3 High load, dry climate shrub (4 ft tall, 6 tons/acre) SH4 Very high load, dry climate shrub (6 ft tall, 8 tons/acre) SH5 Low load, humid climate shrub (2 ft tall, 3 tons/acre) SH6 Moderate load, humid climate shrub (4 ft tall, 5 tons/acre) SH7 High load, humid climate shrub (6 ft tall, 7 tons/acre) SH8 Very high load, humid climate shrub (8 ft tall, 9 tons/acre) SH9 Extremely high load, humid climate shrub (10 ft tall, 11 tons/acre) TU1 Low load, activity fuel (timber with light surface fuels) TU2 Moderate load, activity fuel (timber with moderate surface fuels) TU3 High load, activity fuel (timber with heavy surface fuels) TU4 Very high load, activity fuel (timber with very heavy surface fuels) TU5 Extremely high load, activity fuel (timber with extremely heavy surface fuels) TL1 Low load, timber litter (light litter, no understory) TL2 Moderate load, timber litter (moderate litter, no understory) TL3 High load, timber litter (heavy litter, no understory) TL4 Very high load, timber litter (very heavy litter, no understory) TL5 Low load, timber-shrub (light litter, sparse shrub understory) TL6 Moderate load, timber-shrub (moderate litter, moderate shrub understory) TL7 High load, timber-shrub (heavy litter, dense shrub understory) TL8 Very high load, timber-shrub (very heavy litter, very dense shrub understory) TL9 Extremely high load, timber-shrub (extremely heavy litter, extremely dense shrub understory) SB1 Light logging slash (light fuels, low depth) SB2 Medium logging slash (medium fuels, medium depth) SB3 Heavy logging slash (heavy fuels, high depth) SB4 Very heavy logging slash (very heavy fuels, very high depth) GS1 Light grazing, low load grass (grass with some shrubs) GS2 Moderate grazing, moderate load grass (grass with some shrubs) GS3 Heavy grazing, high load grass (grass with some shrubs) GS4 Very heavy grazing, very high load grass (grass with some shrubs) NB1 Non-burnable, urban/agricultural (e.g., pavement, water, bare ground) NB2 Non-burnable, rock/soil (e.g., exposed rock, barren land) Impacts of Fuel Treatments Fuel treatments alter the amount, arrangement, and condition of fuels, which in turn changes fire behavior potential. Understanding how treatments shift fuel models is crucial for effective fire management planning. Thinning: Removes trees, reducing canopy bulk density and ladder fuels. Pruning: Removes lower branches, increasing crown base height and reducing ladder fuels. Mastication: Mechanically shreds vegetation, changing fuelbed depth and particle size. Prescribed Fire: Consumes surface fuels, reducing fuel loading and modifying fuel structure. Grazing: Reduces fine herbaceous fuels. Chipping/Piling/Burning: Removes or consolidates fuels. Firebreaks: Strips of land cleared of flammable vegetation to stop or slow fires. Shaded Firebreaks: Firebreaks where some canopy is retained to reduce surface fuel regrowth and evaporation. Land Conversion: Changes in land use to non-vegetated surfaces. General Principles of Fuel Model Shifting Treatments generally aim to shift fuel models towards those with lower fire intensity, rate of spread, and crown fire potential. This often means moving from models with high fuel loads, continuous ladder fuels, or dense canopies to models with reduced surface fuels, higher crown base heights, and less continuous canopies. Reducing Surface Fuels: Often shifts to models with lower 1-hr fuel loads (e.g., from SH5 to SH1, or TU1 to GR2 if understory is significantly reduced). Increasing Crown Base Height / Reducing Ladder Fuels: Reduces potential for torching and crowning (e.g., from TL5 to TU1, or TU4 to TU1). Breaking Fuel Continuity: Reduces rate of spread and fire intensity. Changing Fuel Arrangement: Mastication can change dense shrub fuels into a more open, scattered fuel type. Common Fuel Model Shifts by Treatment Type 1. Thinning (Forests) Reduces tree density, canopy bulk density, and often ladder fuels. Surface fuels may initially increase due to slash, then decrease with decomposition or removal. Light Thinning: Reduces some smaller trees, minimal slash. Dense Conifer/Mixedwood with Ladder Fuels: TL5, TL6 $\rightarrow$ TU1, TL1, TL3 (slightly reduced understory) Moderate Thinning: Significant reduction in tree density, some slash. Heavy Timber-Understory with High Mortality: TL9 $\rightarrow$ TL5, TL6, TU5 (if significant slash) Dense Conifer/Mixedwood with Ladder Fuels: TL7, TL8 $\rightarrow$ TU1, TU2, TL1, TL3 Heavy Thinning: Drastic reduction in tree density, potentially large amounts of slash initially. Dense Conifer/Mixedwood: TL8, TL9 $\rightarrow$ GR1, GR2, TU1 (if understory is primarily grass and slash is removed) Open Ponderosa Pine: TU1 $\rightarrow$ GR1, GR2 (if understory is grass and thinning is severe) 2. Pruning (Forests) Primarily targets ladder fuels by raising crown base height. Forests with Low-Lying Branches: TL3, TL5, TU4 $\rightarrow$ TU1, TU2 (reduces crown fire potential) 3. Mastication (Shrublands, Forests) Shreds shrubs or small trees, creating a more uniform, often deeper, fuelbed of fine woody debris. Can initially increase surface fuel load but reduce continuity and flammability of live fuels. Dense Chaparral/Shrub: SH5, SH7, SH9 $\rightarrow$ SH1, SH2, SH8 (if significant deep litter) Brushy Understory in Forest: TL3, TL5 $\rightarrow$ TU1, TU2, GS1 (if understory is completely masticated to ground fuel) Aspen/Brush Mix: SH3, SH4 $\rightarrow$ GR2, GS1 4. Prescribed Fire (Surface & Understory) Consumes fine surface fuels, reduces litter depth, and can reduce small diameter woody fuels and ladder fuels. Low Intensity Burn: Primarily consumes fine surface fuels. Heavy Litter/Duff in Forests: TU1, TU2, TU4 $\rightarrow$ GR1, GR2, TU1 (lighter surface fuels) Shrub-Grasslands: SH1, SH2 $\rightarrow$ GR1, GR2 Moderate Intensity Burn: Consumes more surface fuels and some small shrubs/ladder fuels. Pine Flatwoods with Dense Palmetto: TL3 $\rightarrow$ GR2, GR3 Post-Fire/Rehab: GS2, GS4 $\rightarrow$ GR1, GR2 (as vegetation recovers) 5. Mechanical Removal/Chipping/Piling & Burning Removes significant fuel loads from the site or consolidates them for burning. Heavy Slash/Logging Residue: SB1, SB2, SB3, SB4 $\rightarrow$ GR1, GR2, TU1 (after removal/burning) Dense Shrub/Brush: SH5, SH7 $\rightarrow$ GR1, GR2 6. Grazing Reduces fine herbaceous fuels (grasses, forbs). Tall Grass/Heavy Grass: GR3, GR4 $\rightarrow$ GR1, GR2 Shrub-Grassland: SH1, SH2 $\rightarrow$ SH1 (but lower herbaceous fuel load) or GR1 7. Firebreaks / Shaded Firebreaks Creation of fuel-reduced or fuel-free zones. Firebreak (Cleared to Mineral Soil): Any burnable model $\rightarrow$ NB1, NB2 (depending on underlying soil/rock) Shaded Firebreak (Fuel Reduction, Canopy Retained): TLx, TUx, SHx $\rightarrow$ TU1, TL1, GR1 (Reduced surface and ladder fuels, but not completely barren) 8. Land Conversion/Development Changes land use to non-vegetated surfaces. Any Burnable Model: GRx, SHx, TUx, TLx, SBx, GSx $\rightarrow$ NB1, NB2 Considerations for Fuel Model Selection Residual Fuels: Always account for post-treatment fuels (e.g., slash from thinning, masticated debris). Regrowth: Fuel models can shift back over time as vegetation regrows. Heterogeneity: Treatments often result in mosaic patterns; multiple fuel models may be needed. Expert Judgment: Field observation and local knowledge are critical for accurate selection. Fuel Moisture: Treatment effectiveness can vary with fuel moisture conditions. Fuel Bed Depth: Mastication can increase fuel bed depth, affecting fire behavior even if overall load is reduced. Example Shift Table Initial Fuel Model Treatment Type Likely Post-Treatment Model(s) Rationale GR3 (Moderate Load Grass) Grazing GR1, GR2 Reduction in fine fuel loading and height. GR5 (Tall, High Load Humid Grass) Prescribed Fire (Moderate Intensity) GR1, GR7 Removal of standing dead and live herbaceous fuels. SH3 (High Load Dry Shrub) Mastication SH1, SH2, SH8 Reduced live fuel continuity, increased fine dead fuelbed. SH7 (High Load Humid Shrub) Mechanical Removal GR1, SH1 Significant reduction in shrub biomass, potentially exposing grass. TU3 (High Load Activity Fuel) Thinning (Moderate) & Piling TU1, TL1, GR2 Removal of heavy surface fuels and ladder fuels, reducing fuel load. TL6 (Moderate Load Timber-Shrub) Thinning (Light) & Pruning TU1, TL1, TL2 Reduced tree density, increased crown base height, less ladder fuel, reduced understory. TL9 (Extremely Heavy Timber-Shrub) Heavy Thinning + Prescribed Fire (Moderate) TU1, TL5, GR2 Significant reduction of overstory and understory fuels. SB2 (Medium Logging Slash) Piling & Burning GR1, GR2, TU1 Removal of slash, exposed mineral soil, potential for grass regrowth. SB4 (Very Heavy Logging Slash) Chipping & Removal TU1, TL1 Complete removal of heavy slash, leaving only timber litter. GS3 (Heavy Grazing, High Load Grass) No Treatment (Recovery) GS1, GR3 Potential for grass recovery and increased fuel load without continued grazing. SH9 (Extremely High Load Humid Shrub) Land Conversion (Development) NB1 Area converted to urban/agricultural land. TL8 (Very Heavy Timber-Shrub) Land Conversion (Mining/Quarry) NB2 Area converted to exposed rock or barren land. TU4 (Very High Load Activity Fuel) Firebreak (Cleared) NB1, NB2 Complete removal of all fuels to mineral soil. TL7 (High Load Timber-Shrub) Shaded Firebreak TU1, TL1 Surface and ladder fuels reduced, but canopy retained.