Three Principal Environmental Elements Affecting Wildland Fire Behavior
Fuels Fuel Type Fuel Moisture Size and Shape Fuel Loading Horizontal Continuity Vertical Arrangement
Fuel Moisture The amount of water in a fuel expressed as a percentage of the oven-dry weight of that fuel
Fuel Types Nonburnable Fuel Type Models (NB) Grass Fuel Type Models (GR) Grass-Shrub Fuel Type Models (GS) Shrub Fuel Type Models (SH) Timber-Understory Fuel Type Models (TU) Timber Litter Fuel Type Models (TL) Slash-Blowdown Fuel Type Models (SB)
Fuel moisture time lags: (Time it takes for a fuel to lose 63% of its moisture) Time lagFuel diameter 1-hour (fine fuels) <¼ inch (twigs, dead grass, leaves, needles) 10-hour ¼-1 inch (twigs, small branches, cones) 100-hour 1-3 inch (branches, tops) 1000-hour >3 inch (large branches, tops, logs) Fuel Size
Fuel Loading The quantity of fuels in an area Generally expressed in tons per acre
Topography Aspect Slope Position of Fire Shape of Country Elevation – Relates to curing of fuels, precipitation, length of fire season, etc. Aspect Slope Position of Fire Shape of Country Elevation – Relates to curing of fuels, precipitation, length of fire season, etc.
Running Types of Fire Behavior – spreading quickly Creeping – spreading slowly with low flames Smoldering– burns without flames; barely spreading Spotting– sparks/embers carried by wind or combustion column or moved by gravity Spot fires– new ignition points Fire brand– a piece of burning material
Torching Types of Extreme Fire Behavior – surface fire moves into crowns of individual trees Crowning – spreads from tree crown to tree crown (dependent, active, or independent) Flareup – sudden acceleration of fire spread or intensity (short duration, for portion of fire) Blowup– dramatic change in the behavior of the whole fire (rapid transition to a severe fire) Fire Whirls– vortex (gas mass with rotational motion)
Prescribe Fire Plan Burn prescription written Pre-burn site treatments completed Equipment designated & ready Personnel identified & trained Approvals & permits in hand Authorities & interested parties identified & notified* Latest forecasts checked* * Day before & day of burn
Principles of smoke management Have clear, defensible objectives Comply with local pollution regulations Notify local fire & law enforcement officials, nearby residents, & adjacent landowners Obtain the best available weather forecasts Don’t burn under highly stable conditions Burn during midday; avoid night burns Use caution near, upwind, or up-drainage of smoke sensitive areas
Principles of smoke management (continued) Use test fire to estimate smoke output & behavior Use backing fires if feasible Burn in small blocks if dispersion marginal Do not burn when fuel moisture high Don’t burn organic soils Mop-up along roads first Have an emergency plan!
The historic fire regime was thought to play a role in the maintenance of oak dominated forest prior to European settlement Prescribed fire has been suggested as a tool for regenerating oak Potential benefits included
Prescribed fires in late spring and summer are most lethal to oak competitors. – Prescribed Fire in the Central Hardwood Region
Generally, prescribed fire is best used in combination with reductions in overstory stocking (e.g. shelterwood, midstory removal) to release advance oak reproduction Repeated burning most effective at increase oak competitiveness Prescribed Fire in the Central Hardwood Region
The use of prescribed fire in oak forests has increased over the last four decades Results on oak regeneration has been highly variable
Prescribe Fire in the Central Hardwood Region Site Preparation Burn Fire can create conditions suitable for oak establishment by reducing litter layers and understory competition – Do not burn if acorn crop has just fallen or if new oak seedlings from recent crop are needed to regenerate the stand
Prescribe Fire in the Central Hardwood Region Site Preparation Burn Burning can be done in dormant or growing seasons High-intensity fires (flame lengths > 2 ft) in late spring decreases dense understory shaded more quickly Multiple fires over several years are commonly necessary to reduce dense understories to a level that improves oak seedling survival and growth
Prescribed Fire in the Central Hardwood Region Release Burn Burn used to free competitive oak reproduction from competition – Burning done after midstory removal, first removal cut of shelterwood or after final removal cut – Fire should occur after released oaks develop a more robust root system – Typically,
Prescribed Fire in the Central Hardwood Region Release Burn Moderate to high-intensity fires (flame lengths > 2 ft) to ensure topkill of understory layer Done in mid to late spring (April to May)
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