The Holocene archaeology and Palaeoecology of NortheasternTasmania, Australia

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.