Surface and Ground Fuels - Wildland Fuel Fundamentals and Applications - page 49

3.2.5.3 Disturbance Origin

Many distinctive fuel beds were created by exogenous disturbances. Exogenous
disturbances are disturbance events that originate from outside of the stand or fuel
bed, such as fires, hurricanes, and avalanches, and spread through the area to alter
fuel bed characteristics (see Chap. 6). High wind events can topple trees over large
areas and create unique blowdown of fuel beds where logs are aligned along wind
direction (Woodall and Nagel 2007 ). Hurricanes can blow trees and branches down
to the ground and create fuel beds that may foster other disturbances, such as fire
and insect outbreaks (Busing et al. 2009 ; Fig. 1.2b). While many insects and dis-
eases may damage or kill occasional plants when at low population levels (endemic
level), outbreaks of these insects and pathogens can occur under the right climatic
and vegetation conditions and these outbreaks can severely damage or kill plants
to create fuel beds that many consider hazardous (Jenkins et al. 2008 ). Mountain
pine beetles, for example, bore into the cambium of host pines and lay their eggs
and also introduce fungus in tree tissue. Both the fungus and the larvae that hatch
from the eggs damage or kill the tree, and if the beetle population is at epidemic
levels, many trees will be killed to alter both canopy and surface fuels, from both
falling dead biomass and the facilitation of canopy growth of surviving competitors
(Fig. 1.2c). It would be impossible to describe the fuel beds created by all possible
exogenous disturbances since it would greatly depend on pre-disturbance stand con-
ditions, antecedent climate, disturbance intensity, and a host of other biophysical
factors. However, it is critical to acknowledge the importance of severe exogenous
disturbances in influencing fuel dynamics (Chap. 6).

3.2.5.4 Human Origin

Several important fuel complexes result from land management activities. First, the
slash fuel bed is created when the vegetation is treated using a wide variety of tech-
niques depending on land management objectives (Fig. 3.3e ). Slash is the biomass
left on a treated site. It is often branches, needles, and other material that isn't mer-
chantable or of little valuable to society. The amount of slash left after harvesting or
silvicultural activities greatly depends on the density of the treated vegetation, the
specifics of the slashing treatment, the amount of material removed from the site,
and the equipment used to treat the site.
The second important human-made fuel complex is a special class of slash fu-
els created by unique fuel management activities that are becoming common on
fire-prone landscapes of the world. The masticated fuelbed is created as a result of
mechanical treatments that break canopy fuels and large surface fuels into smaller
particles in an effort to decrease fire hazard by reducing canopy bulk densities and
heights and decreasing surface fuel depths (Fig. 3.3f ). Properties of the masticated
fuel particles and fuel beds are unlike any observed in nature or documented in the
past in that particles remaining after mastication treatments are shards of wood of
odd shapes and sizes depending on the technique used to fragment the canopy and
surface fuels (Kane et al. 2009 ). Diverse mechanical equipment and approaches are