Fire behavior is dependent on many different environmental factors, including vegetation. Because plant communities reflect complex interactions of biological and physical factors such as seral stage, soils, moisture, temperature, slope, aspect and elevation, plants are good indicators of potential fuel combustibility and fire behavior.
Cover Types Fire monitors in Yellowstone use a system of vegetation cover types to quickly describe a fire start and assess its potential to spread (Despain 1990). Cover types are based on the dominant tree species and time since the last disturbance (e.g., LP for lodgepole pine, 0 for a young stand = LP0). Cover types are useful to fire monitors because they are easily and quickly identified in the field and are general indicators of fuel load, dominant vegetation and time since the last wildfire or other disturbance. Other than lodgepole pine cover types (LP0-LP3) which are most common in Yellowstone, there are spruce-fir (SF), whitebark pine (WB), and Douglas-fir (DF) cover types. Generally the most flammable cover types are older. Older stands have accumulated downed logs and thick litter layers on the forest floor, and have a well developed understory of shade tolerant trees and shrubs. The fuels on the ground promote ignition and fire spread while the understory forms a “ladder” which provides the potential for a ground fire to reach into the canopy. In Yellowstone the LP3 cover type (old-growth lodgepole pine) may be 300 years or older and is particularly flammable and prone to ignition by lightning (Renkin and Despain 1991).
Habitat Types In addition to cover types there are more specific habitat types that describe the vegetation and environmental conditions in greater detail (Despain 1990). Habitat types are used primarily by the fire effects monitoring staff when a more detailed description of vegetation is needed for research purposes. For example, fire effects technicians quantify the vegetation and assign a habitat type in order to monitor the effects of fire on specific plant communities in a prescribed burn. Forest habitat types are generally named after the dominant tree species followed by the dominant shrub or forb. For example, there are Whitebark pine/grouse whortleberry and Douglas-fir/pinegrass habitat types.
Fuel Models While cover types and habitat types describe the vegetation specific to Yellowstone, wildland fire staff also use a system of fuel models which are standardized throughout the United States (Anderson 1982). There are thirteen fuel models that range from grasslands to forests. In Yellowstone most wildfires burn in fuel models 8 and 10 which represent conifer forests with varying fuel loads. For example, a mature lodgepole stand ( LP2) generally fits fuel model 8 while older stands (LP3) fit fuel model 10 because they have accumulated more fuels. Other fuel models describe grass- and shrublands. Fuel models are another way to predict fire behavior and rates of spread.
Anderson, H.E. 1982. Aids to determining fuel models for estimating fire behavior. National Wildfire Coordinating Group General Technical Report INT-122.
Despain, D.G. 1990. Yellowstone Vegetation: Consequences of environment and history in a natural setting. Roberts Rinehart Publishers, Inc.
Renkin and Despain. 1992. Fuel moisture, forest type, and lightning caused fire in Yellowstone National Park. Canadian Journal of Forest Research 22(1):37-45.