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A history and interpretation of fire frequency in dry eucalypt forests and woodlands of Eastern Tasmania.

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von Platen, J (2008) A history and interpretation of fire frequency in dry eucalypt forests and woodlands of Eastern Tasmania. PhD thesis, University of Tasmania.

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Abstract

There is scant information available on the occurrence of fire in the Eastern Tiers of
Tasmania. Whole, very large and fire scarred eucalypt cross sections were used as
source material for the reconstruction of a fire history for this region. Accurate
dating of fire scars in Eucalyptus has been problematic due to the unreliable nature
of the annuality of growth rings. Eucalypts have a proclivity for growth anomalies
such as false and or missing rings. The annuality of eucalypt tree rings was
assessed using dendrochronological techniques on a sub-set each of young trees
<140 yrs (n = 15) and old trees > 150 yrs (n = 27). A software program was
developed to assist with data capture and analysis. “Detect Rings” identified ring
boundaries and measured ring widths from high resolution photographs. However,
the seven sampled eucalypt species (E. amygdalina, E. obliqua, E. dalrympleana, E.
tenuiramis, E. delegatensis, E. pulchella, E. globulus), were not amenable to withinor
between-tree cross-dating.
Multiple radial ring counts from 104 large trees (photographs: n = 27, in situ: n =
77) were aggregated and tested for reliability with a mean error margin of ±7 rings
being calculated where tree age was estimated at > 200 years. Additional sources of
error were progressively eliminated. The integrity of fire scar capture from thirteen
sites, each with variable sample numbers, was addressed by the development and
application of a sample size adjustment procedure analogous to the bootstrap. This
process indicated that 9-10 sample trees per site were sufficient to detect a high
proportion of fire events large enough to generate injurious fire scars. There was no
effect on fire scar distribution resulting from tree age, species composition,
landscape position, bark thickness, diameter over bark, slope or elevation. The age
of the oldest sample tree was estimated to be ~570 years.
The sample size adjustment procedure was used to derive the mean decadal fire
years for each tree at each site. Temporal and spatial patterns were then discerned.
Temporal patterns were related to variation in annual rainfall. Approximately 29% of

fire years which occurred across three or more sites were related to years of low
rainfall indicating a relationship between low rainfall and widespread fires.
A composite fire scar chronology was developed 1740 – 2004 from which distinctly
different periods of fire years were defined. Fire years were recorded as mean fire
years per decade, per period, thus: 0.7 in the Aboriginal era 1740 – 1820, 0.4 in the
Transitional era 1820 – 1850, 1 in the 2nd European era 1850 – 1910, 1.5 in the 3rd
European era 1910 – 1990, and 0.7 in the Current or 4th European era 1990 – 2004.
Between-decade fire scar variability was highest in the Aboriginal era. The incidence
of fire scars massively increased across most sites from the 1850s and continued at
high levels until the late 1980s, although a reduced number of fire scars were
recorded in the first decade of the 20th C. Occurrence of fire scars in the most recent
period, 1990 – 2004, was shown to approximate that of the earliest period 1740 –
1820. These distinctly different temporal periods were interpreted as being caused
by cultural activity. Intensive use of the forests for timber-getting co-incided with
the Victorian gold-rush of the early 1850s and is the most likely explanation for the
sharp increase in fire years at this time. Land use analysis further defined
differences in fire years between public and private land with many more fire years
being recorded on private land in the first half of the 3rd European period. A
tradition of burning for fresh pick in sheep ‘run’ country, and cultural familiarity
with fire, are reflected in this distribution.

Item Type: Thesis (PhD)
Keywords: Fire, dry eucalypt woodlands and forest, fire history, dendrochronology, tree ring counting, fire regimes, Aboriginal fire, fire frequency, fire scars
Date Deposited: 10 Nov 2008 23:11
Last Modified: 11 Mar 2016 05:53
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