FIRE BEHAVIOR: PNWCG

FIRE BEHAVIOR:

The behavior of a fire -- how fast and hot it burns -- is influenced by a number of factors, including the type of fuels burning, their moisture content, local topography, and weather. Five types of vegetation common to our region are illustrated here, with computer-generated estimates of how they would burn under certain conditions.

These predictions assume a wind speed of 20 mph, flat terrain, typical summertime moisture content of living and dead vegetation, and normal August weather for our region. It is important to note that fire size and rate of spread are largely determined by spotting (embers or firebrands that are thrown ahead and to the sides of actively burning fires). Spotting results in smaller fires that may contribute to the main fire size and rate of spread.

flame length of 8 feet CHEATGRASS: Cheatgrass is an invasive annual grass that usually occupies areas formerly vegetated with big sagebrush. It can dominate old burned areas, abandoned pastures, and other disturbed areas.

flame length of 55 feet BIG SAGEBRUSH/BITTERBRUSH: This is a heavy brush type consisting of large big sagebrush, bitterbrush, and sometimes mountain mahogany. Large amounts of dead woody material are usually present.

flame length of 10 feet OPEN PINE FOREST: This fuel type consists of open, park-like lodgepole and/or ponderosa pine, often interspersed with fir and other coniferous trees. The understory consists of pine needles and a variety of grasses, and often includes dense saplings.

flame length of 22 feet MIXED BRUSH: This represents a variety of brush species of varying heights with an understory of grasses and fuels litter. This type is very common in the foothills surrounding the valleys in the region.

flame length of 9 feet DENSE CONIFER FOREST: This vegetative type includes thick stands of mature pine, fir and other conifers. There are often mixed layers of vegetation among the young trees, seedlings and shrubs. There is a usually a large amount of dead or down woody material, needles and other organic matter on the forest floor.

flame length of 100 feet CROWN FIRES: Crown fires occur when a "ladder" of vegetation allows fire to climb to the tops of conifer trees. Flames can jump 100 feet high or more, sending burning embers more than a mile away.