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What dictates fire behavior–the fire behavior triangle. Why do ecologists care? . 1. Weather 2. Fuels 3. Topography. Fire behavior largely determines fire effects!. Fuel Types- 4 Categories: where it is located.
What dictates fire behavior–the fire behavior triangle. Why do ecologists care? 1. Weather 2. Fuels 3. Topography Fire behavior largely determines fire effects!
Fuel Types- 4 Categories: where it is located Fire behavior is largely determined by which fuel strata is carrying the fire: • Ground • Surface • Ladder • Crown/ aerial
Fuel Types • Ground Fuels • Duff (partially decomposed) • Peat • Roots • Stumps litter fermentation layer Duff humus mineral soil
Fuel Types • Surface Fuels • Grasses • Shrubs • Litter (leaves) • Woody debris
Fuels • Aerial/ canopy Fuels • Crown or canopy of overstory • Ladder Fuels (located between crown and surface fuels) • Smaller trees • Vines
For each fire type: Fuel Characteristics influence fire behavior • Fuel Loading • Size and shape • Compaction • Chemistry • Arrangement • Vertical • Composition • Continuity • horizontal
Fuel loading- do we just weigh everything that can burn? • Fuel loading is simplified by categorizing fuels into similar groups • All fuels are characterized by their size category, called “timelag fuel class”. This is related to their capacity to absorb and lose water in relation to their environment. • The most important factor associated with fuel size is its surface area to volume ratio…why?
Timelag Fuel Class • EMC = equilibrium moisture content: the watever vapor pressure of the fuel is in equilibrium with the wvp of air. • Given a stable air mass, the “timelag” is time it takes for a particle of fuel to reach 63% of the difference between its initial moisture content and the equilibrium moisture content. • It is NOT how long the fuel will burn
Timelag= approaching equilibrium • It takes 5 timelags for 95% of the change to occur • But most of the change happens within the first timelag Difference http://stream2.cma.gov.cn/pub/comet/FireWeather/S290Unit10FuelMoisture/comet/fire/s290/unit10/print.htm#page_2.2.0
Larger fuels lose and absorb water less quickly http://stream2.cma.gov.cn/pub/comet/FireWeather/S290Unit10FuelMoisture/comet/fire/s290/unit10/print.htm#page_2.2.0
Timelag categories (know these!) • Size of fuel (diameter, inched) Timelag Class • 0” to ¼” 1 hour • ¼” to 1” 1o hour • 1” to 3” 100 hour • > 3” 1000 hour
Three ways to assess fuel loading • Fuel models • Photo series • Measure it
Fuel Loading – what do you include? Timber Brush
Fuel models use 4 fuel groupings- based on proportion in each timelag class Anderson, 1982 Fuel Models and Fire Behavior Prediction
Example BEHAVE outputs: Rate of spread Rate of Spread for Fuel models at 5 mph wind
6-10 tons/ acre FUEL MODEL 7: SOUTHERN ROUGH
3-5 tons/acre FUEL MODEL 8: CLOSED TIMBER LITTER
1-3 tons/acre FUEL MODEL 3: TALL GRASS
Photo series • Hundreds of field plots measured= averaged = photo series fuel loading values. • Digital photo series (USFS) • http://depts.washington.edu/nwfire/dps/
MEASURE IT: Today’s Lab! • Brown’s Planar Intercept