FIRE EFFECTS GUIDE - National Wildfire Coordinating Group

viii. Fuel continuity. Fuel continuity is a description of the distribution of fuels. Fire
spread is most likely in continuously distributed fuels. The greater the fuel
discontinuity, the higher the fireline intensity required for fire spread. Fuel
continuity is described in terms of both horizontal and vertical continuity.
Horizontal continuity relates to the horizontal distances between fuel particles and
relates to percent cover. The proximity of tree or shrub crowns affects the ease
with which fire can spread in a live fuel strata. Vertical continuity describes the
proximity of surface fuels to aerial fuels and affects the likelihood that a fire can
move into the vegetative canopy.
ix. Heat content. The most important aspect of fuel chemistry influencing fire
behavior is heat content. This value expresses the net amount of heat that would
be given off if the material burns completely (or at 100 percent efficiency), rated
as Btu per pound of fuel. The heat content for all species of dead woody fuel is
essentially the same (Albini 1976). The presence of pitch in wood, and of volatile
compounds such as oils and waxes in some live fuels, increases heat content,
and thus flammability.
x. Live fuels. Some fuel types contain a significant component of live fuels in the
surface fuel layer, including shrubs, grasses, and forbs. The importance of live
fuels to fire behavior can change throughout the year. Their volume can increase
significantly during greenup and the early part of the growing season. They can
lose their foliage at the end of the growing season or during a drought. Seasonal
fluctuations in moisture content occur that significantly affect flammability. The
moisture cycles within live fuels are discussed in more detail in Chapter III.B.5.,
this Guide.
While technically live fuels, mosses and lichens do not have physiologically