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The Holocene archaeology and Palaeoecology of Northeastern Tasmania, Australia

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Thomas, I (1991) The Holocene archaeology and Palaeoecology of Northeastern Tasmania, Australia. PhD thesis, University of Tasmania.

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Abstract

An analysis of ethnohistorical sources, modem pollen rain, fossil pollen, contemporary
vegetation patterns and.thedistribution of Aboriginal sites enabled a moc;tel of Holocene
vegetation change in northeastern Tasmania to be developed. The influential
hypotheses of fire stick farming and ecological drift are shown to be generally resiliant
and worthwhile but in need of adjustment to account for local and regional variations in
environmental and cultural practices. A more recent theory in which Aborigines were
forced out of southwestern Tasmania at about 12,000 BP by expanding Holocene
forests is re-evaluated in the light of evidence which suggests that forests may have
developed earlier than previously thought and that Aborigines, forests and fire in
Tasmania have had a long co-existence.
A study of all available Tasmanian ethnohistorical sources pertaining to Aboriginal
burning of vegetation revealed a pattern of Aboriginal land use from ca. 1 n3 - 1830
which was more complex than previously thought. In northeastern Tasmania, fire was
used in a fashion corresponding to the position of sites along an altitudinal gradient from
sea level to 1,500m.
A close reading of the available information reveals that present day ecologists and
archaeologists often use ethnohistorical references concerning fire in an uncritical
manner. A number of crucial historical incidents in which European mariners sighted
devastating fires and dense clouds of smoke are reinterpreted as defensive responses
by Aborigines to the presence of Europeans, rather than a normal modus operandi.
These sources cannot therefore be taken to indicate a traditional use of fire.
Historical sources suggest that Aboriginal life in Tasmania revolved around a complete
familiarity with forests. Previous research has highlighted the importance of coastlines for
settlement, and that forests, especially wet forests, were inimical to Aboriginal settlement
objectives. The analysis emphasises that Aboriginal fire regimes differed across the state
according to social perogatives as well as to environmental determinants.
Archaeological surveys and limited excavations were conducted in order to date the
commencement of Aboriginal site formation in coastal, inland and mountainous
environments. It was discovered that coastal sites in the northeast date to the last 3,000
years of the Holocene. Sites which are located on the margins of lunette fringed lagoons
and shallow freshwater lagoons date from about 6,000 years BP to ca. 8,500 BP. In the
highlands of the northeast, rockshelters are dated to 1,600 years BP.
Prior to an investigation of fossil pollen to determine vegetation changes over the same range of times, Tauber pollen traps were placed in a selection of representative
vegetation communities in the northeast. The results of this study were used to form
analogues against which fossil pollen assemblages were compared. In this way it was
possible to reconstruct past vegetation associations with a degree of precision not
available by the analysis of fossil pollen alone.
Analyses from a coastal lagoon, an inland marsh, two highland bogs and sediment from
an Aboriginal site revealed patterns of vegetation change which drew attention to the
effects of Aboriginal burning on the landscape.
A 10,500 year old pollen sequence from the coastal lagoon suggested that the
vegetation had changed from a pre-Holocene Poaceae dominated steppe complex, to a
Eucalyptus forest, and finally to an Allocasuarina dominated coastal heathland. The
final change to heathland occurred at 6,500 years BP. This date is synchronous with the
stabilization of sea levels, increases in inorganic input into lagoon sediments, major
peaks in Typha spp. pollen and the commencement of Aboriginal occupation on lagoon
margins. The present day structure of the vegetation is likely to have resulted from a
complex interaction between environmental variables and the burning of forests and
heathlands by Aborigines.
Eucalyptus forests surrounding a small closed basin at 80 m altitude in the hinterland
have existed virtually unchanged for 4,000 years. Further evidence suggests that these
forests may have been extant for at least 13,000 years. Increases in regional wet forest
and rainforest pollen taxa point to a change in climate at about 3,500 BP which allowed
an expansion of wet forest communities. This is supported by increases in local spore
percentages which show that the hydrology of the basin changed to allow the
development of a Sphagnum bog. The humid phase is thought to have continued for a
maximum of about 1,000 years, after which time drier climates prevailed. It is possible that
decreases in temperature rather than increases in precipitation were responsible for the
perturbation. Throughout the 4,000 year long sequence, high levels of carbonized
particles indicates that burning by Aborigines was continuous.
Pollen from a short core obtained from a highland bog surrounded by wet eucalypt and
rainforest communities, showed a transition from grassland or grassy woodland to wet
forest at about 3,000 BP. It is thought that burning of local forests by Aborigines altered
the local hydrology sufficiently to create a mire at about 5,500 years BP. Continued
burning maintained an open grassy formation for 2,000 years. The abandonment of the
site by Aborigines as a place for frequent burning led to the development of forests in
which wet forest taxa predominated and where fires were less frequent but more intense.
Sediment from a highland buttongrass moor adjacent to a 1,600 year old Aboriginal site
was analysed for pollen. The sequence displays little vegetation change since the onset
of organic accumulation 1,600 years ago. Synchrony between the two dates provides
the first direct palaeoecological evidence that Aboriginal burning practices were involved
in the creation and maintainence of buttongrass moorlands in Tasmania.
The pollen and archaeological evidence, in combination with the analysis of
ethnohistorical sources demonstrate that forests and Aborigines have a long history of
coexistence. Aboriginal fires had major effects on delicately poised coastal ecosystems
and lesser effects on inland lowland forests. In elevated locations with high rainfall and
fertile soil, fire was employed to produce small treeless patches. Burning on poorly
drained infertile sites is thought to have initiated hydrological changes which resulted in
the creation of limited areas of sedgeland.

Item Type: Thesis (PhD)
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Date Deposited: 17 Dec 2013 03:30
Last Modified: 15 Sep 2017 01:06
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