Agriculture Reference
In-Depth Information
Fire-scar dendrochronology studies show that these forests historically burned at
short intervals of
10 yrs until government-sponsored fire suppression began in
the early 1900s, after which fires were successfully excluded (Swetnam
1993
). The
largest groves in national parks have been routinely maintained for the last several
decades with understory burning done under prescriptions that are sufficient to
consume substantial quantities of dead surface fuels but not escape into the
crowns of these majestic trees (Parsons
1995
). Success is largely measured by the
reduction of surface fuels and tree density to presumed pre-management levels
(Keifer
1998
). In similar conifer forests in California other metrics of success have
modeled fire behavior and tree mortality (Vaillant
et al.
2009
). However, despite
the apparent success of 50 yrs of prescription burning in this and other parks,
there are socio-economic problems that limit its effectiveness. Due to air drainage
patterns into populated foothill communities, windows of burning opportunity
are limited by air quality restrictions and it is doubtful that the bulk of the
landscape can be treated under current air quality and budget restrictions.
Australian
Eucalyptus
have an equally long record of prescription burning but
on a much grander scale that allows one to investigate impacts on fire behavior. In
southwestern Australian open forests, prescription burning has been widely prac-
ticed since the mid 1900s; a total of
c
. 114 000 ha in the 1950s to 314 000 ha in the
1970s (Gill
1986
). In one of the longest running studies in southwestern Australia,
over 50 yrs of prescription burning has changed the frequency and intensity of
unplanned fires (Boer
et al.
2009
). Indeed, in most years the number of prescrip-
tion burns outnumbered the unplanned ignitions. However, the impact of these
planned fires on incidence and size of unplanned fires was short lived and barely
evident after 6 yrs. While this program seems to be an important part of fire
management in Western Australia, there are many reasons for questioning
whether it is something readily implemented on other landscapes. The low popu-
lation density in the region, coupled with flat landscapes and an extensive road
network, plus relatively long periods of stable weather in spring and autumn may
make this policy ideal for that region. All of these effects contribute to magnifying
the effect of these treatments on unplanned fire incidence and size, relative to
regions of high population density, rugged terrain and less stable weather. The fact
that it is relatively ineffective after 6 yrs would be a concern if there are flora and
fauna that require longer intervals between fires in order to maintain sustainable
populations.
Prescription burning has been variably successful in other MTC regions. Two
decades of prescription burning in South African mountain fynbos has not pro-
duced any obvious changes in wildfire regimes (Brown
et al.
1991
). Modeling
results suggest that prescription burning would have little impact on the total area
burned in Mediterranean shrublands (Pin
˜
ol
et al.
2007
). In California chaparral
the massive reburning of burned scars by fires only 4 yrs apart strongly suggests
that prescription burning designed to create young fuels is not likely to be effective
under severe fire weather on these landscapes (Keeley
et al.
2004
,
2009b
).
Fernandes & Botelho (
2003
) provide a comprehensive review of prescription
