Impact of Aboriginal burning practices

Margy Deveraux employs burning techniques in Marranungu country, Finnis River, NT. Photo: Deborah Rose

The environmental impact of Aboriginal landscape burning is one of the most complex and contentious issues in Australian ecology. Dr David Bowman , CRC researcher from the Parks and Wildlife Commission of the NT, has reviews the evidence.

Dr Bowman was invited to write his review by the prominent journal New Phytologist , as the 86th in their ongoing series of reviews honouring the great British ecologist Sir Arthur Tansley.

In his review, Dr Bowman showed how research on the issue of Aboriginal landscape burning has been uncoordinated and undertaken by people from different disciplines using different methods.

Although great uncertainty and gaps in knowledge remain, the available ethnographic evidence leaves little doubt that Aboriginal burning played a central role in the maintenance of the land subsequently colonised by Europeans.

Both 19th century European colonists and 20th century anthropologists have documented the indispensability of fire as a tool in traditional Aboriginal economies, a tool aptly described as ëfire-stick farmingí.

But it remains unclear as to whether or not Aborigines had a predictive ecological knowledge of the consequences of their use of fire, particularly on relatively long-term ecological processes.

Some evidence suggests that Aborigines used fire to achieve short term outcomes, such as providing favourable habitats for herbivores or increasing the local abundance of food plants.

However, much more ethnographic research into Aboriginal burning remains to be carried out to determine just how and why they used fire.

Given the enormous and ongoing cultural changes wrought by European colonisation, Dr Bowman suggests it is important to determine how the use of fire now differs between younger and older generations of Aboriginal people.

Otherwise, we might draw ecological conclusions from present practices, whereas past practices were those that really affected our flora and fauna.

Dr Bowman says that a lot of ecological evidence suggests that Aboriginal burning caused substantial changes in the geographic range and demographic structure of many vegetation types right across Australia.

The evidence also suggests that burning was important in creating habitat mosaics for small mammals in arid environments.

As well, burning created fire breaks, which helped to maintain some infrequently burnt habitats upon which about 10 per cent of Australia's terrestrial birds depend.

However, much of this evidence is circumstantial and is based on changes which were observed following the cessation of Aboriginal burning after European colonisation.

There have been very few experimental investigations of the possible ecological impacts of Aboriginal burning.

Use of modelling has helped to corroborate the importance of Aboriginal fire regimes in maintaining one tree species, Cypress pine (Callitris intratropica), in the monsoon tropics.

Dr Bowman suggests there may be great potential to use models to explore the long-term effects of the various fire regimes used by Aboriginal people prior to European colonisation.

The original impact of humans on the Australian environment is speculative. Unfortunately, we only have vague and disputed time frames proposed for the waves of colonisation and shifting settlement patterns of Aborigines over the last 100,000 years or so.

Charcoal and pollen evidence from long sedimentary cores is ambiguous and cannot be used to demonstrate unequivocally the initial impact of Aboriginal people on the Australian landscape.

There are very few studies that specifically link archaeological and palaeoecological data to determine the impact of Aboriginal burning. The studies that do so demonstrate localised impacts at most.

The sparse evidence available does not support at least four speculative hypotheses currently in vogue, namely that Aboriginal landscape burning:

• Caused the extinction of some Australian megafauna (large herbivorous and other carnivorous marsupials)
• Was critical in maintaining habitats of small mammals that have become extinct since European colonisation,
• Initiated widespread and accelerated soil erosion, and
• Forced the evolutionary diversification of the Australian biota.

However, Dr Bowman says that the available evidence does suggest that there were some evolutionary impacts of Aboriginal burning.

There may have been extinction of some fire sensitive species of plants as well as extinction of animals dependent upon infrequently burnt habitats, particularly during periods of climatic stress.

Also, it may have extended the range of fire adapted species, such as the eucalypts, into environments climatically suitable for rain forest. Lastly, it may have helped to maintain structurally open vegetation such as grasslands.

In concluding his review, Dr Bowman suggests that palaeoecological research (that is research using fossil evidence) has become too popular in considering the impact of Aboriginal burning on the Australian landscape.

He suggests it should give way to experimental studies of the role of the different fire regimes imposed by man in contemporary ecosystems which have not been destroyed by European colonisation.

Integrated studies using remote sensing, geographic information systems, mathematical modeling, experimental manipulation and autecological studies of key plant and animal groups would advance the our understanding of the impact of Aboriginal burning.

He feels there is an urgent need to include Aboriginal people in such research and we need to move beyond the poetic concept of 'fire-stick farming' to coherent scientific analysis.

Dr Bowman feels that his review is timely, because of as the increasing interest in the role of Aboriginal burning in the functioning and management of many Australian ecosystems.

Spin-offs from the review were invitations for Dr Bowman to give lectures on the topic at Harvard, Cambridge and Oxford Universities. As well, numerous questions have been raised by the work which have stimulated new research.

For example, Dr Bowman himself has recently collaborated on a predator-prey model to determine if Aboriginal over-hunting is a plausible explanation for the extinction of the marsupial megafauna. The results from this work will be presented later this year at a conference in Perth devoted to this issue.