Ecology - Wildland Fuel Fundamentals and Applications - page 81

Chapter 6
Ecology

The first law of ecology is that everything is related
to everything else.
Barry Commoner American Scientist

6.1 Fuel Dynamics

The most notable feature of wildland fuel beds is that they are always changing
in space and time because complex ecological processes are continuously inter-
acting with the fuelbed. Live and dead biomass is constantly being added and re-
moved by various ecological processes (Harmon et al. 1986 ). Spring snowstorms,
for example, may break tree and shrub branches and double fuel loadings in a few
hours, while decomposition may take decades to centuries to reduce coarse woody
debris (CWD) loadings. The annual shed of leaves and thousands of small woody
twigs from trees in forested stands creates significantly different fine woody debris
(FWD) spatial distributions than the infrequent toppling of large tree boles to cre-
ate logs or CWD fuel types. As a result, wildland fuel landscapes can be described
as shifting mosaics of hierarchically intersecting fuel characteristics. This dynamic
character of fuelbeds across space and time is perhaps the single most important
fuel characteristic to understand in fire management today because it influences
strategic fuel management considerations such as fuel treatment longevity and ef-
fectiveness, fire return intervals, and smoke potential. In fact, Anderson ( 1976 )
wrote, “recognizing fuel complexes as storehouses with irregular annual additions
and withdrawals of energy provides a basis for fire and smoke management.” There
are numerous processes that control fuel dynamics, but this chapter will present
four of the major processes that most influence spatial and temporal distributions of
fuels: biomass production, deposition, decomposition, and disturbance (Fig. 6.1 ). In
wildland fuel science, many have assumed that fuels are closely related to vegeta-
tion characteristics, but this only makes sense for the first two processes (production
and deposition) and completely ignores the role that decomposition and disturbance
play in fuel bed development.