Agriculture Reference
In-Depth Information
where fire suppression policy has been effective at excluding fire, some species
populations may die out. As fuel loads increase with time since fire, they can
lead to a fire regime shift toward higher intensity crown fire that could extirpate
some species.
Fire hazard reduction treatments are sometimes incompatible with resource
issues. One of the biggest threats to many plants and animals is the fact that
prescriptions often require frequent rotations of burning in order to maintain fuel
levels within specified limits (Morrison et al. 1996 ). Forest types with historical fire
regimes of frequent surface fire may be amenable to this treatment as most species
in these systems are adapted to such a regime (Keeley et al. 2009a ). In such forest
types fuel treatments may even enhance the habitat for some animal species (Craig
et al. 2010 ).
However, crown fire regimes in general are more vulnerable to frequent fires.
Nonetheless, even on these landscapes there are examples of prescription burning
programs that have played an important role in protecting natural resources
(Conroy 1996 ). In short, in some surface fire regimes, fire hazard reduction
objectives may be compatible with resource objectives, whereas in crown fire
regimes the best rotation for hazard reduction oftentimes is not compatible with
resource sustainability. Factors other than frequency also may have impacts on
resources. Sometimes safe prescriptions call for out-of-season burns in winter or
early spring. This treatment may result in poor recruitment of postfire seeders
(Bond 1984 ; Parker 1987 ; Brown et al. 1991 ) and increased mortality of resprout-
ing species (Rundel et al. 1987 ). Poor out-of-season recruitment has been tied to
heating effects on moist seeds (Rogers et al. 1989 ) and more intensive seed preda-
tion (Heeleman et al. 2008 ), but the truncated growing season prior to summer
drought has to be a critical factor as well.
Where there is a necessity for applying prescription burning, managing sensitive
ecosystems can take different courses. An approach widely applied to conifer
forests of the western USA is restoration of fire regimes present prior to the
nineteenth-century colonization by Europeans (Covington & Moore 1992 ). This
is justified on the basis that these fire regimes were appropriate for maintaining
sustainable populations of native flora and fauna (Millar 1996 ), and there is a vast
database on historical fire regimes inferred from fire-scar dendrochronology for
forests with surface fire regimes (Swetnam et al. 1999 ).
A related approach possible in wilderness areas where risks are lower is to allow
naturally occurring fires to burn unchecked (Kilgore & Briggs 1972 ; van Wilgen
et al. 1990a ; Seydack et al. 2007 ). Since this approximates the “natural” fire regime
it is presumed that these fires are conducive to long-term sustainable biodiversity.
This seems to be a reasonable strategy in forests with surface fire regimes, or
remote fynbos-dominated mountain ranges, but advocating it for southern
California chaparral (e.g. Childers & Piirto 1989 ; Minnich 2001 ) seems dubious.
Not only would this be an extreme fire safety hazard, but it is not justifiable based
on the fact that the bulk of this landscape has experienced more burning during
the twentieth century than historically was the case (Safford & Schmidt 2010 ).
Search WWH ::




Custom Search