1. Prescribed Fire in the Forest Ecosystem FORS 5610 / 7610 Location: Joseph W. Jones Ecological Research Center For more information: Dr. Pete Bettinger Phone: 542-1187 E-mail: pbettinger@warnell.uga.edu Dates: May 14-20, 2006 Course Credits: 2

2. Fire Models Fire spread can be thought of as a series of ignitions, where heat from a fire raises successive strips of fuel to the ignition temperature. A fire model evaluates the energy generated by a fire, the heat transfer from a fire to the fuel ahead of it, and the energy absorbed by that fuel. Live and dead fuels are considered. Fine fuels (less than 1/4 inch diameter) generally carry a fire, so these have the most weight in a fuel model. A fire model is intended to describe a flame front advancing towards unburned fuel.

3. Predicting Fire Behavior Three areas of emphasis: 1. Describe the fuels (using a fuel model), fuel moisture, wind speed, and slope of the ground. 2. Calculate fire descriptors: rate of spread, fireline intensity, flame length 3. Interpret the results and translate into potential spread distance, fire perimeter, fire area, and flame length

4. Predicting Fire Behavior Describe the Fuels - Fuel models

5. Predicting Fire Behavior Describe the Fuels - Fuel models Components: 1. Fuel loading - the mass of fuel per unit area, live and dead, by size class (1 hour, 10 hour, 100 hour, and live fuel) 2. Surface area to volume ratio 3. Fuel depth 4. Fuel particle density 5. Heat content of fuel 6. Moisture of extinction - the upper limit on fuel moisture content, beyond which a fire will no longer spread.

6. Predicting Fire Behavior Describe the Fuels - Fuel models

7. Predicting Fire Behavior Describe the Fuels - Fuel models Which one to use? 1. Determine the general vegetation type (grass, brush, slash, etc.) 2. Estimate which stratum of the surface fuel is likely to carry the fire 3. Note the depth and compactness of the fuel 4. Determine which fuel classes are present and estimate their influence on fire behavior 5. Select a model

8. Predicting Fire Behavior Describe the Fuels - Fuel models - Selection process  Primary carrier of fire is grass  Fine, below knee level, cured, continuous.  Coarse, above knee level (3 ft or so), difficult to walk through.  Under open timber, brush, or other overstory, litter from overstory is expected to play a role.

9. Predicting Fire Behavior Describe the Fuels - Fuel models - Selection process  Primary carrier of fire is brush, or litter beneath the brush  Vegetative type is southern rough, or low pocosin. Brush is 2-4 feet high.  Live fuels are absent or sparse. Brush is 2-4 feet high. Brush requires moderate winds to carry a fire.  Brush is 2 feet high. There is a light loading of litter, which can carry a fire at low wind speeds.  Brush is 6 feet high. There is a heavy loading of dead fuel.  Vegetative type is high pocosin.

10. Predicting Fire Behavior Describe the Fuels - Fuel models - Selection process  Primary carrier of fire is litter beneath a timber stand  Surface fuels are mostly foliage litter - tightly compacted (short needles).  Surface fuels are mostly foliage litter - loosely compacted (longer needles, leaves).  There is a significant amount of larger fuel present, and well-distributed.

11. Predicting Fire Behavior Describe the Fuels - Fuel models - Selection process  Primary carrier of fire is logging slash - aged and overgrown  From hardwoods.  From Conifers.

12. Predicting Fire Behavior Describe the Fuels - Fuel models - Selection process  Primary carrier of fire is logging slash - fresh (less than 3 years)  Depth 1 foot. Not continuous. Needs help from grass or litter to carry the fire.  Depth 2 feet. Somewhat continuous. 1/2 of needles still on branches, but are not red. If needle are red -   Depth 3 feet. Continuous coverage. 1/2 of needles still on branches and are red, or all needles still on branches and are green.

13. Predicting Fire Behavior Describe the Fuels - Fuel moisture

14. Predicting Fire Behavior Describe the Fuels - Fuel moisture Need to determine this for both live and dead fuels. These conditions impact: (a) Fireline intensity (b) The heat required to bring the fuel ahead of a spreading fire to the ignition point Fuel moisture is a measure of the amount of water contained in a fuel, and expressed as a percentage of the oven-dry weight of a fuel. It is influenced by weather events.

15. Predicting Fire Behavior Describe the Fuels - Fuel moisture - Live fuels Favored method is to estimate it using stages of plant development.

16. Predicting Fire Behavior Describe the Fuels - Fuel moisture - Dead fuels Fuel moisture in these fuels responds to temperature, humidity, and solar radiation. One classification system is based on the length of time required for a fuel to change moisture by a specified amount when subjected to changes in the environment (temperature, humidity, solar radiation). 1-hour fuels up to 0.25 inches in diameter 10-hour fuels 0.25 to 1 inch in diameter 100- hour fuels 1 inch to 3 inches in diameter 1000-hour fuels3 to 8 inches in diameter

17. Predicting Fire Behavior Describe the Fuels - Fuel moisture - Dead fuels To estimate actual fuel moisture percent, tables can be employed. They require measures of temperature and relative humidity. The result, when using the tables, is a worst-case fuel moisture content for fine fuels.

18. Predicting Fire Behavior Describe the Fuels - Fuel moisture - Dead fuels

19. Predicting Fire Behavior Describe the Fuels - Fuel moisture - Dead fuels

20. Predicting Fire Behavior Describe the Fuels - Mid-Flame Wind Speed

21. Predicting Fire Behavior Describe the Fuels - Mid-Flame Wind Speed Wind is the most variable factor required to predict fire behavior. It can change in both the horizontal and vertical directions. Most winds have a repeatable pattern that can be used to make reliable predictions of fire behavior. These are general winds and convective winds. Other winds are not so reliable - winds associated with thunderstorms, whirlwinds, and nighttime high elevation winds.

22. Predicting Fire Behavior Describe the Fuels - Mid-Flame Wind Speed

23. Predicting Fire Behavior Describe the Fuels - Mid-Flame Wind Speed The standard height for wind measurements aloft used by land management agencies is 20 feet above the surface of the ground. The mid-flame wind speed is adjusted for vegetation depth.

24. Predicting Fire Behavior Describe the Fuels - Mid-Flame Wind Speed Step 1. Contact fire weather meteorologist - get the forecast for 12-24 hours Step 2. Consider the possibility of spurious (unreliable) winds Step 3. Determine speed and direction of winds aloft Step 4. Determine if these winds are likely to reach the ground surface, or whether convective winds will be active Step 5. Determine the speed and direction of the local 20-foot winds Step 6. Estimate mid-flame wind speed Step 7. Determine upslope or downslope convective winds, if necessary

25. Predicting Fire Behavior Describe the Fuels - Mid-Flame Wind Speed

26. Predicting Fire Behavior Describe the Fuels - Mid-Flame Wind Speed

27. Predicting Fire Behavior Describe the Fuels - Mid-Flame Wind Speed

28. Predicting Fire Behavior Describe the Fuels - Ground slope

29. Predicting Fire Behavior Describe the Fuels - Ground slope Two general methods....

30. Predicting Fire Behavior Describe the Fuels - Ground slope

31. Predicting Fire Behavior Calculate Fire Descriptors - Rate of spread, fireline intensity, flame length

32. Predicting Fire Behavior Calculate Fire Descriptors - Rate of spread, fireline intensity, flame length To do this, we will use a nomogram. Nomogram: a group of interconnecting graphs that can be used to solve a mathematical problem.