Australia: The Land Where Time Began
Aboriginal Exploitation of Toxic Nuts as a Subsistence Strategy in the Tropical Rainforests of Australia
The arid areas of central Australia and the glacial areas of Tasmania had been adapted to by 40,000 PB, and by this time the Aboriginal people had adapted to the tropics. An essential framework for examination of human responses to changing vegetation and the variable climate of Australia had been constructed by the groundbreaking palynological and palaeoecological work of Peter Kershaw. Kershaw demonstrated major climate changes at Lynch’s Crater on the Atherton Tableland, based on his study of changes in the concentrations of pollen and charcoal that fluctuated over the past about 120,000 years (Kershaw, 1986; Moss & Kershaw, 2000). Together with his team he has identified a time, about 45,000 BP, for the onset of burning on Atherton Tableland, by measuring increases in carbon particles that occurred around this time (Turney et al., 2001). It has been claimed that this evidence supports an argument for the early peopling of the region between 55,000 and 45,000 BP, which has heralded the initial impacts of humans on the ecosystems of Sahul, and including the megafauna extinction. Therefore, according to Ferrier & Cosgrove the archaeological data of the present run counter to suggestions of the peopling of the Atherton Tableland about 40,000 BP. It is possible, however, there was some occupation by Aboriginal people on the edge of the rainforest about 30,000 BP (Cosgrove et al., 2007), and it may be revealed by further work that there was some human occupation in the core rainforest area in the Late Pleistocene, as has been detected to the north of the study area (Haberle & David, 2004; Summerhayes et al., 2010.
The majority of archaeological material recovered from the Atherton-Evelyn Tableland region of north Queensland has been shown by wide-ranging research (Horsfall, 1987, 1996; Cosgrove and Raymont, 2002; Cosgrove, 2005; Cosgrove et al., 2007; Ferrier, 2010) to be from within the past 5,000 years, and human occupation was initially at very low levels, while it was only in the last 2,000 years that there was an intensification of occupation. In this paper Ferrier & Cosgrove expand on what appears to be an intensification of site occupation and use by Aboriginal people of toxic food plants in the Wet Tropics Bioregion of north Queensland in the Late Holocene, including an analysis of macrobotanical remains that were recovered from Urumbal Pocket, an open archaeological site on the Evelyn Tableland.
An ethnographic analogy of a modern botanical reference collection was used to understand techniques from the past for processing toxic plant food and the identification of archaeological specimens.
Exploitation of toxic food by Aboriginal people
There are a number of explanations that have been suggested to explain changes in Aboriginal subsistence patterns and the occupation of sites in the Middle to Late Holocene (Denham et al., 2009). Included among these are social intensification (Lourandos, 1997: 303, 305), and the use of broad-spectrum resources (Haberle & David, 2004), increased population and ceremonial activities (Beaton, 1983, 1985, 1990), Climate change on a large scale (Moorwood & Hobbs, 1995: 182) and high intensity El Niño Southern Oscillation (ENSO) activity (Rowland, 1999; Cosgrove, 2005; Turney & Hobbs, 2006; Cosgrove et al., 2007). In order to understand an increase in poisonous food plant use depends on the capacity to build a solid regional framework of archaeological and palaeoecological data that includes understanding:
i) Substantial archaeological evidence of the remains of ancient plants,
ii) Site formation and processes of taphonomy,
iii) An identification of associated changes in other cultural remains with matching palaeoenvironmental signals, and
iv) Commensurate comparisons of sites that have deposits that are stratigraphically intact.
It has been argued by previous studies that toxic plant processing techniques development occurred outside Australia and diffused into Australia about 4,000-3,000 BP (Beaton, 1983). The inclusion of significant amounts of tree nuts into the diets of hunter-gatherers in rainforests suggests it was part of a specific economic development of a region that occurred in the Holocene across Australia (Denham et al., 2009). It has been suggested that this development was associated with a much earlier generalist subsistence strategy in the Late Pleistocene of modification of habitat by fire and broad-spectrum exploitation of plants. The lack of evidence for early exploitation of plants that has been noted may have an underlying taphonomic explanation (Asmussen, 2008, 2009, 2010), and different from faunal remains in some sites dating to the Late Pleistocene (Cosgrove & Allen, 2001), organic materials preservation has possibly hampered investigations into early exploitation patterns of plant foods. In the Holocene there is more consistent evidence which predictions can be based on about dietary plant use by Aboriginal people.
In the early contact period extensive records were kept by Europeans of occupation of tropical rainforest and the use of plant foods by Aboriginal people living in the rainforests, such as explorers, botanists, Aboriginal Protectors and naturalists (Lumholtz, 1889; Meston, 1889; Roth, 1900, 1901-1910; Coyyan, 1918; Mjӧberg, 1918). A number of authors (Harris, 1975, 1978, 1987) Horsfall, 1987, 1990) and Pedley, 1992, 1993), have summarised much of the ethno-historical literature, who have discussed Aboriginal foods of the rainforests. It is apparent from the historical literature that the rainforest provided a wealth of vegetable foods. Plant foods have been demonstrated by historical documents and Aboriginal oral histories to have comprised a significant proportion of the Aboriginal diet in rainforests, which included the collection, processing and consumption of a large number of rainforest nuts (e.g. Mjӧberg, 1918: 492-494; Pedley, 1993; M. Barlow pers. comm. to Ferrier & Cosgrove, 2004). There are 112 plants that have been identified as being consumed by rainforest Aboriginal people. Of these, 10%-13% required extensive processing to remove toxins (Horsfall, 1987; Pedley, 1993). Specific toxic tree nuts, that apparently formed an important source of food during the wet season from November to March, have been emphasised by most historical descriptions. It has been shown by experimental work (Pedley, 1993: 179-180; Teuchler, 2010) that the contribution of toxic nuts to the diet of rainforest Aboriginal people was significant, being an important source of carbohydrates, proteins and fats in various quantities. Toxic nuts have been estimated (Pedley, 1993) to have comprised about 10% to 14% of the diet of rainforest people at the time of European contact. In pre-contact times that total contribution to the diet of Aboriginal people is not known, though on the basis of early ethnographic observations and estimated nutritional values, Ferrier & Cosgrove suggest it was probably considerable.
Mick O’Leary, a gold prospector, observed the use of nuts in the early 1880s in the upper Tulley River area:
The principal food trees are the koah (yellow walnut), burra (black walnut), bean tree, tchupella (black pine) and a number of smaller varieties; there are also a few vines or tree climbers that at times bear edible fruits. The bean tree is not often used by those people on account of its poisonous nature and the amount of work that is attached to preparing it. The nuts are pared into very thin slices using a piece of sharp quartz, then there is a considerable time it has to go under the water process and fire before it is fit for consumption. The tchupella is a smaller nut and grows on the trees we know as black pine. When the season is on the food is eagerly sought for by those people and they will travel over miles of country to partake of it. They also grind those nuts, into fire, but it does not require the water treatment, baking in the hot ashes being sufficient. The tchupella is an annual bearer, but is not too plentiful and generally found on the high or tableland country. (Coyyan, 1918).
There are 2 types of walnut, Beilschmiedia bancroftii (yellow walnut) and Endiandra palmerstonii (black walnut), and the ‘black pine’ nut, Sundacarpus amara, and the black bean, Castanospermum australie, that were exploited by rainforest Aboriginal people are the types of toxic nuts that are most frequently mentioned in the historical descriptions of the diets of the Aboriginal people living in the rainforest. Many of the toxic species that were utilised by rainforest Aboriginal people are endemic to the Wet Tropics Bioregion of Australia (Hyland et al., 2002). The yellow and black walnuts are available for about 8 months of the year, mainly in the spring and summer months, and grow at altitudes that range from 0 m to 1,300 m. The black pine is available only between October and December, having a fruiting period that is considerably shorter, and has a more limited distribution, growing at altitudes of 600-1,200 m (Cooper & Cooper, 2004). The black bean fruits between March and November, growing at altitudes from 0 m to 840 m (Cooper & Cooper, 2004: 204). These toxic nut varieties have a high food value, high seasonal abundance and storage potential (both above and below ground) and were therefore sought after by rainforest animals and Aboriginal people. Cassowaries and bush rats eat yellow walnuts and the black walnut is liked by the white-tailed rat. For humans a particular attraction of the yellow walnut is that many of the fallen fruit can lie on the ground for short periods without attack from predators. Fallen black bean and black pine nuts are avoided by predators, though for a more limited time (Pedley, 1993: 193), though in order to avoid competition with the white-tailed rat black walnut needed to be collected immediately (Pedley, 1993: 193). The rainforest people could store these hard-shelled nuts for several months below ground to be consumed later (Coyyan, 1918; Mjӧberg, 1918; Harris, 1975).
According to Ferrier & Cosgrove it is possible to reconstruct the processes involved in detoxification, based on historical accounts and ethnographic observations. Elaborate lawyer cane, Calamus australis, baskets were used to collect nuts on the ground and to climb trees to collect fresh nuts lawyer cane ropes were used (e.g. Roth, 1901-1910; Mjӧberg, 1918). Aboriginal rainforest people were observed by O’Leary to be using a sharp piece of quartz to slice nuts on the Tully River, and in other areas in the rainforest region, snail shell graters were used (Roth, 1900: Pedley, 1992: 51). Toxic nuts and other foods, as well as meat and fish, were steamed in earth ovens, and sometimes used river cobbles as well as ginger leaves, and finally placing hot coals on top. The nuts were cracked open using a small cobble as a nut cracking stone after this baking and steaming procedure. The last step was to grate the pulp then put the gratings into lawyer cane dilly bags and leach for 2-3 days in a small running creek. When the paste was leached of toxins, the pulp was chewed and formed into a paste that was eaten raw, and later in the period following contact, Aboriginal forest people made ‘Johnny cakes’ with it, or flat cakes that were baked on hot coals (Coyyan, 1918; Mjӧberg, 1918; Pedley, 1992). Carbonised fragments of the hard endocarp layer that encloses a single seed (nut) is what remains in the archaeological record.
The archaeological open site of Urumbal Pocket is situated high on the bank above the original course of the Tully River.
Urumbal Pocket is comprised of a series of patches of Eucalyptus among rainforest, which borders a stretch of the upper Tully River. There are in total 6 1m x 1m pits that were excavated at the site to investigate the density of the archaeological remains and the site stratigraphy, and to establish the spatial distribution of any cultural material present. The 2 main stratigraphic units are distinguished by the colour and structure of the soil, an upper dark humic layer, and an underlying lighter layer.
The soil type, the Yellow Kandosol, is common in the area (McKenzie et al., 2004: 246-247). Unit 1 is a black loam that is rich in artefacts, and has a Munsell that ranges from 10YR1/7 in the top layers to 7.5 YR4/6 in the bottom layers. In Unit 1 the sediments can be described as a sandy loam deposit that is homogenous and unconsolidated with fine grit distributed throughout it that was derived from the organic soil that surrounds it. There is a transition Layer that separates Unit 1 from Unit 2 (7.5YR 3/2) and consists of a light brown gritty soil that is distinguished by some orange mottling. The top of this layer begins at 40 cm depth and is approximately 10 cm thick. In Unit 2 (7.5YR 4/6) the sediments become increasingly gritty and less homogeneous with depth, with particles from the granite bedrock that is decomposing becoming incorporated in the soil.
All squares excavated produce charcoal. The in situ charcoal samples that were recovered gave 17 radiocarbon dates. A good chronological order is shown by the dates, which suggests the site is relatively undisturbed. At Urumbal Pocket the earliest dates, 7,445 ± 68 BP (8,273 ± 67 cal. BP [Wk-13578]) and 7,212 ± 46 BP (8.052 ± 65 cal. BP (Wk-13571) are from charcoal that was recovered from the lower spits of Unit 2, together with a small number of quartz artefacts. The dates correspond with an initial period of rainforest expansion in the Holocene, and correspond with increases in the amounts of microscopic charcoal in the pollen record (Haberle, 2005; Cosgrove et al., 2007). Another 6 AMS dates were obtained from in situ diagnostic endocarp fragments. The dates obtained from the fragments of nut shell correlate broadly with the dates obtained from the charcoal samples. A fragment of Lauraceae endocarp that was excavated, a yellow walnut (Beilschmiedia bancroftii) or a black walnut (Endiandra palmerstonii) was submitted for radiocarbon analysis. A date of 1,585 ± 40 BP (uncalibrated age; OZJ718) was returned which is consistent with evidence for the use of toxic plants from other archaeological sites in the region (Horsfall, 197: 268); Cosgrove et al., 2007). The Lauraceae fragment from Urumbal Pocket that was dated provided a minimum age for the appearance of the processing of toxic nut in the rainforest.
It is suggested by the grouping of radiocarbon dates from Urumbal Pocket that there were 3 phases of Aboriginal occupation in the area, where about 70 % of the dates are later than 1,500 years BP. Increasingly high numbers of cultural materials over time correlates with the 3 phases of occupation. Increased human activity at the site over the last 1,000 years may explain mixing at some of the deposits in Unit 1. At a date of about 1,800 years ago for the initial very low intensity use of the site is pointed to by the chronology, with a hiatus between about 7,000 BP to 5,000 BP in use of the site. An occasional use of the site between 5,000 BP and 2,000 BP is indicated by the evidence. Cultural materials begin to increase at the end of Phase 2 (transition zone), and the site is rich in cultural materials in Phase 3, dating from about 2,000 BP to the late 1800s. From these upper levels thousands of stone artefacts, small amounts of ochre and Plant remains were recovered.
Robust endocarp fragments (or nutshells) comprise most of the plant assemblage from Urumbal Pocket. As a result of nut cracking during processing, and probably as well as human activities at the site, such as trampling and cleaning activities, the plant remains are highly fragmented. During excavations a number of seeds, complete and incomplete, that had diagnostic features were also recovered. The botanical remains are all carbonised inert charcoal, which has allowed them to survive in the archaeological record (Horsfall, 1987, 1990). It has been found by experiments that nutshell fragments that are put on coals produced from a small log fire burn fast and disintegrate to ash, but it is not yet clear how the plant remains were burnt. It is therefore considered to be most likely that the charring of nutshells most likely occurred in a low oxygen environment and the carbonisation is the result of anaerobic carbonisation during the steaming and baking of the nuts. This step in the process of detoxification has been described as ‘nuts roasted in hot ash’ (Mjӧberg, 1918: 494), which suggests that the nuts came into direct contact with hot ash and thereby became burnt. According to another explanation the nutshells were incorporated into coals in dying fires as waste products during cleaning up activities at the site. Ferrier & Causgrove suggest that experimental work may reveal an explanation for their survival in the archaeological record.
The pioneering work of Peter Kershaw on the Atherton Tableland in the tropical rainforest region of Far North Queensland over the past 40 years has established the important palaeoenvironmental backdrop to human interactions with the environment on the Atherton Tableland. Included among these is the palaeoenvironmental framework that he derived from pollen and charcoal studies from Lynch’s Crater. According to Ferrier& Cosgrove they benefitted from this important work as it allowed them to investigate the ecological relationship between people and changing patterns of subsistence in a unique part of Australia. The application of ethnographic analogy to the archaeological plant remains has provided clues to human subsistence patterns of the past, as is demonstrated by the results of analysis of archaeobotanical macrofossils that were excavated from the Urumbal Pocket open site in Far North Queensland’s Wet Tropics World Heritage Bioregion. Ferrier& Cosgrove have identified the use of toxic food plants extending back at least 1,600 years by applying this method. It appears, based on the evidence, that the Aboriginal people repeatedly collected rainforest walnuts at the Urumbal Pocket site over the period of about 2,000-1,600 years. It is also suggested by this evidence that this subsistence strategy was already being used on a much smaller scale prior to the shift towards occupation of the rainforest that was more permanent at some point in the last 2,000 years. This adaptive shift has been interpreted as the result of ENSO activity that was highly unstable beginning about 5,000 years ago (Turney & Hobbs, 2006; Cosgrove et al., 2007). It is demonstrated by the research of Ferrier & Causgrove that explanations of cultural change in the Middle to Late Holocene can be linked to broad scale environmental changes. Major reorganisations of social, political and economic structures were probably the result of processes of social intensification. Also, it appears that 2 languages developed during this time, Yidinj in the north, and in the south, Dyirbal (Dixon, 1991: 4). The emergence of a rainforest society that was fully functioning that was unique in Aboriginal Australia was facilitated by this.
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