Agriculture Reference
In-Depth Information
(a)
(b)
(c)
(d)
Fig. 2.2
Examples of a surface fire regime and a crown fire regime. North American (a) mixed
conifer forest historically burned by (b) low-intensity surface fires and (c) chaparral shrubland
historically burned by (d) high-intensity crown fires. (Photos by Jon Keeley, a,c; by U.S.
National Park Service, b; and U.S. Forest Service, d.)
woodlands and forests share many of the same fuel characteristics with closed-
canopy shrublands (i.e. high density of trees and accumulation of dead fuels in the
canopy), and thus are highly susceptible to crown fires (Bradstock
et al.
2002
;
Keeley
et al.
2009a
). In some forests, fires may spread by a combination of surface
and canopy fuels and are termed
active crown fires
. In more open forests where
fires are spread largely by surface fuels, localized accumulation of understory
“ladder” fuels may carry fires into the canopy of individual trees or small groups
of trees and these are termed
passive or dependent crown fires
(van Wagner
1977
).
Often times these crown fires are referred to as
stand-replacing fires
, although this
is largely a northern hemisphere perspective that describes crown fires in conifer
forests where entire stands burned in high-intensity fires are killed. Australian
Eucalyptus
forests and woodlands are an exception in that even when burned in
high-intensity crown fires, close to 100% of the trees resprout epicormically (Gill
1997
), rapidly returning the forest to its original state (see
Fig. 3.3d
). Northern
hemisphere oak woodlands have a similar capacity for epicormic resprouting and
resilience to high-intensity crown fires.
Ground fires
spread by smoldering combustion through duff and can be sus-
tained at relatively high fuel high moisture conditions (Miyanishi
2001
). In mires
