Agriculture Reference
In-Depth Information
In other MTC regions annual fire records generally do not extend back more
than a few decades; however, other historical records may be useful. For example,
a 130-yr fire history was compiled for the Valencia region of Spain based on an
extensive review of old forest administration dossiers and newspapers (Pausas &
Ferna´ ndez-Mun˜ oz 2011 ). Given the high population density of the area during the
period 1873-2006, and the importance of fires in the media, the compiled fire
history is considered a reliable estimate of area burned, but perhaps less reliable in
terms of the number of fires.
A widely applied technique for estimating fire histories in North American
coniferous forests is fire scar dendrochronology (Dieterich & Swetnam 1984 ). It
is primarily applicable in surface fire regimes where trees are scarred but
survive low intensity understory fires. Like written records it can provide
annual and even seasonal resolution of past fires but has the added advantage
of recording fire histories over a span of hundreds or sometimes thousands of
years (Swetnam 1993 ). The primary limitation of this methodology is that it
provides a point record of some but not all past fires and requires some
untested assumptions in drawing conclusions about spatial patterns of past
fires (Baker & Ehle 2001 ; Falk & Swetnam 2003 ;Veblen 2003 ;Hessl et al.
2004 ;vanHorne&F ´ le 2006 ). It also is unable to capture the past history on
landscapes previously subjected to logging, which makes highly managed
forests, such as those in the Mediterranean Basin or portions of the western
USA, unsuitable for characterizing fire regime. The primary limitation to this
technique in the study of MTC regions is that it requires forests with a history
of surface fire regimes and thus it has not received wide application in most
MTC regions.
Fire scar dendrochronology has been used in some Western Australia forests,
although sometimes utilizing different assumptions in the interpretation of fire
scars (e.g. Burrows et al. 1995 ). These investigators interpreted an increase in fire
scars following European colonization to be the result of less frequent fires. They
reasoned that prior to colonization high rates of burning by Aboriginal people
kept fuel loads so low that they rarely scarred trees. However, tests of this
interpretation of fire scar data failed to support it (Richards 2000 ) and other
studies have found that fire scars are a consistent indicator of fire frequency in
Western Australian Callitris trees (O'Donnell et al. 2010 ). More widely used on
these landscapes are fire scars left in the leaf base patterns in grasstrees ( Xanthor-
rhoea species). Although lacking the precision and reliability of tree ring fire scar
records, they are apparently useful in drawing broad generalizations about past
fires (Miller et al. 2007 ).
Charcoal and pollen deposits can provide fire frequency estimates covering the
past 10 000 yrs or longer, but typically at temporal resolutions of decades to
centuries (Clark & Robinson 1993 ; Millspaugh et al. 2004 ). Fire frequency esti-
mates based on charcoal deposition are affected by wind patterns that affect
dispersion of particles, which in turn are affected by particle size, which in turn
is a function of fuel type, as well as sediment movement. Charcoal abundances in
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