Agriculture Reference
In-Depth Information
(ENSO) events have been associated with a regional pattern of years with wide-
spread fires. There was increasing fire frequency during the latter half of
the nineteenth century coinciding with increased Native American occupation of
the area, followed by a sharp decline in fire frequency following the demise of the
Native American population in the late 1800s. Fire frequencies peaked again with
the arrival of Euro-Chilean settlers (Torrejon
et al.
2004
; Bustos-Schindler
et al.
2010
), but fire suppression was widely practiced and effective during the twentieth
century.
Fire in austral forest regions of the Los Lagos Regio´ n is heavily centered on
conifer-dominated ecosystems (Lara
et al.
2003
). The emergent conifer
Araucaria
araucana
grows with an understory of the shrubby
Nothofagus antarctica
in south-
central Chile and Argentina. Both species are well adapted to survive fire (Burns
1993
; Aagesen
2004
).
Araucaria araucana
possesses thick bark, readily sprouts
from epicormic buds, and protects terminal buds on high branches.
Nothofagus
antarctica
resprouts vigorously from root crowns after fire. Large
Araucaria
trees
survive fire without harm, and readily establish seedlings below the resprouting
canopies of
N. antarctica
. In the absence of fire, the shade-intolerant
N. antarctica
is eventually eliminated as canopies of
Araucaria
and arboreal species of
Nothofa-
gus
close over. Thus, fire acts as a medium for species coexistence between the
vigorously sprouting, shade-intolerant species (
N. antarctica
), and the more shade-
tolerant and fire-tolerant species (
A. araucana
).
Araucaria araucana
forms mixed stands with another tree,
Nothofagus pumilio
,
in the Andean cordillera of south-central Chile. Here fires are of mixed severity
and often high-intensity patches produce gaps that are filled with similar age
cohorts of one or the other species (Gonza´ lez
et al.
2010
). The occurrence of large
lightning-ignited fires covering thousands of hectares of
Araucaria
forest in the
summer of 2002 were the first historical fires over much of this region. However,
stands of
Araucaria araucana
studied near Lago Villarica have shown a 300-yr
chronology with a much more frequent fire regime (Gonza´ lez
et al.
2005
; Gonza´ lez
& Veblen
2006
,
2007
), indicating that fire has been an important disturbance
regime influencing these communities. The tree ring chronologies suggest that
the fire regime has included a mixture of mild surface fires and catastrophic crown
fires in past centuries. High-severity widespread fires were relatively infrequent
(e.g. 1827, 1909 and 1944). The mean fire interval over this period varied from
7 yrs for all fires to 62 yrs for intense fire events where
25% of recorder
trees were scarred. The spatial extent of fires ranged from small patchy events
to those that burned more than 40% of the entire landscape in the study area
(i.e.
>
1500 ha).
Dendrochronological studies with the long-lived
Fitzroya cupressoides
have
established a 600-yr chronology of fire occurrence in the coast range and central
valley of Los Lagos Regio
´
n. These studies show that
Fitzroya
is able to withstand
infrequent low-intensity fires. There was also evidence of even-aged stands
resulting from seedlings established after catastrophic stand-replacing fires (Lara
et al.
1999
; Silla
et al.
2002
).
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