Aboriginal Occupation of South Central Tasmania in the Pleistocene

Australia: The Land Where Time Began

Aboriginal Occupation of South Central Tasmania in the Pleistocene - A palaeoecological model

A number of locations on the western coast of Tasmania have provided pollen data for analysis that indicates that the vegetation of the area was predominantly of a alpine-sub-alpine type of herb, heath and shrub species between earlier than 44,000 BP and 25,000 BP. The mean annual temperature was about 5^oC lower than at the present at this stage, with a wit climate (Colhoun & van de Geer, 1986; Colhoun, 1995a; 1985b). The dominant species were wet herb and heath communities 24,000-22,000 BP, with increasing herb and grass pollen appearing after 22,000 BP leading up to the last glacial maximum at 18,000 BP (MacPhail & Colhoun, 1985; Gibson et al., 1987), the geographical extent of these grasslands being important to the model, as the authors described later. About 21,000 BP the treeline was depressed about 230 m on the west coast, when the temperatures have been estimated to have been about 6^o cooler than the present average temperatures, and the climate was drier than the preceding period. Tree and shrub species were of increasing importance 14,000-11,000 BP, after 11,000 BP rainforest taxa became dominant (MacPhail, 1975, 1979; MacPhail and Peterson, 1975; Colhoun & Moon 1984), the climate at this period being warm and moist.

The vegetation cover in the east, 25,000-10,000 BP, is suggested by the pollen data, especially in the Midlands Valley, to have varied much less than it did in the west over the same period. It has been suggested that there had been a progression from grassy woodland to grasslands then back to grassy woodland in which Eucalyptus sp. was more dominant than in earlier periods (Sigleo & Colhoun, 1981). Alpine and sub-alpine grasslands were present at a lower altitude, at least 300 m lower than at the present altitude of about 1,000 m, on the southern edge of the
Tasmanian Central Plateau (MacPhail, 1975: 299). At about 18,000 BP the climate was relatively cold, dry and windier, especially in northeastern Tasmania, the average wind speeds being suggested to hAllen et al., 1988). ave been 8 km/hr higher than at present (Bowden, 1983). In southeast Tasmania the development of sand dunes has been dated to about 15,000 BP, shortly following the suggested period of maximum aridity (Sigleo & Colhoun, 1975). It has been found that the formation of lunettes continued in northeastern Tasmania up until about 8,300 BP (Cosgrove, 1985). According to the authors low sealevels resulted in these changes, the precipitation gradient between east and west was increased by the interception of most of the moisture by the mountains of the west coast (Bowden, 1983). It has been estimated that the mean annual precipitation on the west coast would have been at least 1000-1500 mm, whereas on the east coast it would have been 300-400 mm, even if the annual rainfall was 50 % lower during the Last Glacial Maximum (Galloway, 1986). During the glacial maximum eastern Tasmania would have experienced periods of drought stress, evidence of which is seen in the building episodes of inland dunes and lunettes (Bowden, 1978a, 1978b, 1983; Colhoun, 1978, 1982; Kirkpatrick, 1986: 239). The authors suggest that grasslands may have been restricted to areas with deeper soils by the climate of the area at this time that has been classed as glacial-arid (MacPhail, 1975) with higher moisture levels, areas with sandier substrates being more vulnerable to erosion.

The structure and distribution of exploitable energy, animal and plant, for hunter gatherers in the period before the Last Glacial Maximum to the period following it, were affected by the ecological variation (Foley, 1977: 71; 1981; Gamble, 1984: 224; 1986: 42, 64; Jockhim. 1979: 84). In southwest Tasmania, the distribution of productive grassy habitats are especially relevant for their suggested role in resource distribution and availability. Extensive areas of western and southwestern Tasmania covered by open herbfield and steppe (Kiernan et al., 1983: 30) has been described as a myth (Kirkpatrick, 1986: 235). He believes the dominant glacial vegetation complexes were almost certainly stunted woody, heath and sedge taxa, similar to those covering the alpine and treeless sub-alpine regions of the present, as a result of the soil infertility that is widespread in western and southwestern Tasmania (Kirkpatrick & Brown, 1984; Kirkpatrick, 1986: 239). Chenopod vegetation and short alpine herbfields have been extensive nly in the east and parts of the northwest, as well as the western continental shelf that was exposed (Hope, 1978; Sigleo & Colhoun, 1981; MacPhail & Colhoun, 1985; Colhoun et al., 1982).

The character of the rich deposits of Kutikina Cave have been found to be based on a general association between fauna & steppe (Jones, 1984; Kiernan et al., 1983). Valleys overlying limestone, and on soils that are relatively fertile, are the only places in the interior of the southwest where grass is likely to have been supported (Kirkpatrick & Harwood, 1980; Kirkpatrick, 1982: 268; 1986: 237; Kirkpatrick & Duncan, 1987).

The authors have proposed an alternative model based on the requirements of, and the interactions between the flora, fauna, soils, temperature and fire. The red-necked wallaby (Macropus rufogriseus) has been found to be the main animal exploited by humans in the southwest of Tasmania (Kiernan et al., 1983; Jones, 1984; Allen et al., 1988). At the present this animal occurs in open shrubland and sedgeland in very low numbers, being no longer common in the vegetation complexes of the southwest (Hocking & Guiler, 1982). It has been suggested that the sites in the southwest were abandoned when invading rainforest replaced the grasslands about 12,000 BP with the resulting reduction or elimination of the wallabies (Kiernan et al., 1983). An spect of red-necked wallaby behaviour is that they are extremely sedentary, having a home range that averages 15-20 ha, very unusual for macropods. They usually remain in a particular area of their home range for about 2-3 years, eventually moving to another one less than 30 m away (Johnson, 1987: 131), the range changing little from season to season and from year to year. In contrast, red kangaroos and grey kangaroos on the mainland of Australia have home ranges of about 10 km² or more, and when they moved to a new centre of activity it is 900-1060 m away (Priddle, 1988; Priddle et al., 1988). Another characteristic behaviour of red-necked wallabies is that most rest close to the edges of the forest where they have good protective cover, as well as escape routes and proximity to feeding areas (Southwell, 1987: 28; Johnson, 1987: 128). The major food source of these wallabies is grasslands and herbfields, which are essential for the support of large congregations of these animals (Jarman, et al., 1987; Kirkpatrick, 1983: 75; Strahan, 1983: 239; Gibson & Kirkpatrick, 1985: 96; Southwell, 1987). The apparently graze over a wide range of altitudes, a high correlation being found between the grazing of the wallabies and the distrribution of short alpine herbfields on snow patches at an altitude of 1200 m on Mt. Field (Gibsion & Kirkpatrick, 1985).

Fertile soils and reliable drainage are a requirement of grasses and herbs (Kirkpatrick Duncan, 1987; Bowman et al., 1986; Ellis, 1985, 1986; Ellis & Gravley, 1987). In southwestern Tasmania grasses are longer found on the siliceous soils, being restricted to sparse individual clumps of refugia on outcropping limestone in the Weld River, Franklin River and Maxwell River (Kirkpatrick & Harwood, 1980; Kirkwood & Brown, 1987). Grasses from these refugia would colonise the soils that were deeper and more fertile of alluvial flats or ground on restricted limestone geology, which, unfortunately for the wallabies that grazed the grass, also provided caves and Rockshelters that could be occupied by human hunters (Kirkpatrick, 1986: 237; Middleton, 1979).

According to the authors, to understand the reasons the Aboriginal population of southwest Tasmania abandoned the region at the end of the Pleistocene it is important to find mechanisms involved in the maintenance of grasslands in the long-term. It has been suggested (Ellis, 1985, 1986) that under model conditions when fire frequency increases on grasslands the result can be a grassland sub-climax, but a colonisation sequence from heathland, tea-tree to eucalypt, and possibly to rainforest, can result from a cessation of burning, as has been observed to have occurred in less than 150 years in parts of northeastern Tasmania (Ellis, 1986). It has been suggested that in higher alpine areas, where plant cover possibly approximates palaeo-vegetation characteristics, in the short term fire increases the dominance of herbaceous species like poa grasses, though the shallow fertile soils are degraded in the long-term, while the deeper substrates may suffer less (Kirkpatrick, 1983; Kirkpatrick & Dickinson, 1984). The invasion of these grasslands by rainforest species at the end of the Pleistocene, about 12,9000 BP, as the climate became wetter and warmer, has been the explanation of the disappearance of the grasslands at this time (Kiernan et al., 1983; Jones, 1988).

The authors claim that on anthropogenic grounds this is difficult to sustain, a significant point being the extreme fire sensitivity of rainforest, that can be effectively excluded from its former range by firing that is systematic and regular (Bowman & Jackson, 1981; Jarman et al., 1982; Hill & read, 1984). In recent decades large areas of Tasmanian rainforest have been destroyed in short periods of time by fires that were human-induced (Jackson, 1978: 98-101). There is uncertainty as to why in some areas, such as the Florentine Valley, that is a fertile area close to the eastern boundary of the southwestern zone, grasslands were not maintained with fire, as they would probably have been able to be utilised well into the Holocene. It has been noted that at the present any fires in the Florentine Valley will be severe in summer when hot, dry, northerly winds are blowing (Gilbert, 1949). It has been suggested that the replacement of progressive grassland by eucalypt forest in the Florentine Valley resulted from the end of firing that had previously been carried out by the Aboriginal people until 200 years ago (Gilbert, 1959). The authors say this suggest that the abandonment that occurred 12,000 BP was probably of a single type of Pleistocene economic strategy that was centred on cave sites.

The authors suggest that a large quartzite core and several hornfels flakes that were found in the Nunamira Cave (Bluff Cave), that were lying on the floor surface, could indicate that following the sealing of the surface by calcite about 12,000 BP the cave was used for ephemeral visits. Additional evidence that the area had been used by Aboriginal people is seen in open sites (Kiernan et al., 1983: 28), but these sites were still to be investigated in 1998.

The authors suggest hat in the southwest of Tasmania resource patch-richness, with sedentary animals and plant food being interspersed among low trees and shrubs in the river valleys, where the moisture input was consistent and effective, is indicated by the palaeoecology of the region to have characterised the region at any point in time Kirkpatrick & Brown, 1987: 548). Contrasting with the southwestern region, the southeastern region was characterised by widespread grasslands, that were drier and drought-prone, and in which the resources were probably widely dispersed, and at times unpredictable, and distributed across the landscape more generally (MacPhaill & Jackson, 1978; Sigleo & Colhoun, 1981; Kirkpatrick & Duncan, 1987). These patterns are illustrated in Fig. 6a.2, Source 1.

According to the authors they have assumed that these conditions were not stable, almost certainly varying on micro-scales and meso-scales with time and from place to place, the magnitude of such shifts being unknown. Theories of ecosystem dynamics, both at the present and in the past, that involve complex influences that include climatic, edaphic and anthropogenic factors that contribute to variability in the long-term as well as the short-term (Kirkpatrick & Brown, 1984; Bowman & Brown, 1986; Foley, 1981; Pickett & White, 1985: 374; Delcourt & Delcourt, 1983: Dodson, 1989). The authors claim the basing of their model mainly on evidence makes it useful, and to a large extent being independent of archaeological data. They say it forms an ecological framework in which it is possible to investigate variability, inter-regionally as well as intra-regionally, and the concomitant behaviour of the humans in the regions in question.

See Aboriginal Occupation of South Central Tasmania During the Pleistocene

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