Agriculture Reference
In-Depth Information
burning results although some of the success stories are based on short-term results.
Reports of successful changes in fire behavior need to be considered in the context
of sustainability of treatments. It is to be expected that areas treated within 1-2 yrs
will be effective but unless sites are to be continuously treated at this interval then it
is not possible to conclude that in the long run this fuel treatment is effective.
Most who advocate the use of prescription burning are realistic in the expect-
ations that these treatments will alter fire behavior by reducing fire intensity and
providing safer access to fire fighters (Conard & Weise
1998
). However, in
California for the last few decades of the twentieth century the U.S. Forest Service
(USFS) managed their chaparral landscapes with a strategy of prescription burn-
ing designed to create patch mosaics of different-aged vegetation that would
eliminate large fires (Rogers
1982
), as advocated by Minnich (
1983
; Minnich &
Franco-Vizcaino
1999
). The basis of the mosaic notion is that in the absence of
modern fire suppression on chaparral landscapes, mosaic fuel patterns developed
spontaneously from high frequency of lightning ignitions, and thus large fire
events were non-existent, and the theory further stipulated that modern cata-
strophic fires are an artifact of fire management (Minnich & Chou
1997
). How-
ever, there is a substantial body of evidence that disputes this model (Moritz
1997
;
Conard & Weise
1998
; Keeley
et al.
1999a
). In short, it is clear that massive high-
intensity wildfires are a natural feature of these landscapes and are not the result
of fire suppression (Keeley & Zedler
2009
). In 2005 the mosaic fuel strategy was
largely abandoned by the USFS for southern California chaparral landscapes
(USFS
2005
). Mosaic burning, however, has been proposed for other MTC
landscapes such as southwestern Australia (Burrows
2008
), where it could very
well be a viable strategy due to landscape and fire regime characteristics of
that region.
The mosaic model fails on landscapes prone to severe fire weather conditions,
where fires readily spread through young stands of reduced fuels or jump such
stands by spot fires. In California chaparral the early seral stages of the dense
highly flammable postfire ephemeral flora are incapable of stopping fires, often-
times even under moderate fire weather (see
Chapter 5
). In many Australian
Eucalyptus
forests fuel accumulates so rapidly that fires readily spread within
5-6 yrs of a fire (see
Chapter 8
). Even where there are clear discontinuities in fuels
due to stand age or topography, firebrands or embers of burning biomass are
responsible for generating spot fires that enable a fire to overcome such obstacles
(Cheney
1996
). Spot fires are common near the fire front and they decrease with
distance. Understanding spotting distance is important for predicting fire spread
as well as threats to downwind communities. Spotting distance is a complex
function of fuel structure and condition, fuel height, topography and winds
(Albini
1979
; Sardoy
et al.
2007
). Sometimes firebrands may be lofted high up in
plume-dominated fires with the potential of long-distance transport. The prob-
ability of whether or not these firebrands initiate a spot fire will depend on size
and material of firebrands, which determines how long it persists before extin-
guishing, and the fuels in which it lands. Typically in forested environments these
