Aboriginal pyromaniacs? - An Australian fire that rages on.

[Jacques Cinq-Mars]

The word (rage) is certainly a bit of an overstatement, but since researchers can be quite persistent, the debate regarding the exact cause(s) of Australia's megamarsupials (and a few other smaller biological entities) around the turn of the 50th millennium is still going on. This time, it has been fanned by a new report presented at the recent INQUA Congress in Reno, Nevada and is reported on by the New Scientist.

If you are interested in some historical background, here are two important references:

Miller, G.H., Hart, C.P., Roark, E.B. and Johnson, B.J. 2000: Isoleucine Epimerization in Eggshells of the Flightless Australian Birds, Genyornis and Dromaius. In, Perspectives in Amino Acid and Protein Geochemistry ed. by G.A. Goodfriend, M.J. Collins, M.L. Fogel, S.A. Macko, and J.F. Wehmiller, pp 161-181. New York: Oxford University Press.

Miller, G.H., Magee, J.W., Johnson, B.J., Fogel, M., Spooner, N.A., McCulloch, M.T., Ayliffe, L.K. 1999:. Pleistocene extinction of Genyornis newtoni: human impact on Australian megafauna. Science 283: 205-208.

Jacques Cinq-Mars

Big beast extinction blamed on prehistoric fire starters.

New Scientist 09:45 10 August 03

Prehistoric fire starters may have unwittingly killed off the big beasts that once roamed Australia. Analysis of ancient eggshells suggests that the animals suddenly became extinct about 50,000 years ago because people burned up their habitat.

Australia's giant carnivorous kangaroos, seven-metre-long lizards, marsupial lions and enormous flightless birds all died off between 45,000 and 55,000 years ago. Most scientists agree that people arrived in Australia somewhere between 50,000 and 55,000 years ago.

This suspicious coincidence of timing has led some to conclude that overzealous hunting by humans caused the extinctions. But others claim that we could not have cleared the entire continent of so many species in such a short time.

Geologist Gifford Miller of the University of Colorado at Boulder and an international team analysed hundreds of eggshell fragments of an extinct flightless bird called Genyornis, dating from 130,000 to 50,000 years ago. They compared them with the eggshells of emus, dating from 130,000 years ago to the present day.

For the full article, CLICK HERE.

[caldararo]

Miller's dates range from 130,000 to 50,000.  I think the older is more likely.  On the question of human control of fire I tend to be more conservative, see my article, "Human ecological intervention and the role of forest fires in human ecology", in Science of the Total Environment, v. 292, 2002:141-165.  You can download it from the Elsevier site free.

Niccolo Caldararo, Ph.D.
Dept. of Anthro
SFSU

[Iain Davidson]

This evidence is very difficult to interpret.  Once again, there is a claim for human involvement with environmental change much earlier than any other evidence for human presence in the region.

In this case, the most recent dates for Genyornis (a big bird, not a megamarsupial!) are close to the earliest dates on the continent, but there are no generally believed dates this early from further south.  Moreover, this evidence is from the driest, climatically most unpredictable part of Australia and the pattern of colonisation of different environments still seems to suggest that these were last to be occupied by people.

For what it is worth, one of the quiet revolutions in Australian Quaternary studies has been the retreat by Peter Kershaw from his espousal of early dates for colonisation.  In the past he has claimed early human presence on the basis of charcoal profiles in pollen cores, but he no longer does so.  This is a relief, because palaeoenvironmentalists were claiming dates back into the last Interglacial, while the consensus date for first human presence has been stuck between 50 thousand and 60 thousand for many years now.

Iain Davidson

[Jacques Cinq-Mars]

Miller's dates range from 130,000 to 50,000.  I think the older is more likely.  On the question of human control of fire I tend to be more conservative, see my article, "Human ecological intervention and the role of forest fires in human ecology", in Science of the Total Environment, v. 292, 2002:141-165.  You can download it from the Elsevier site free.

Niccolo Caldararo, Ph.D.
Dept. of Anthro
SFSU

Dear Niccolo,

Thanks for the info, but -- just a minor, annoying point, here, your article cannot be downloaded unless one is a subscriber or is willing to pay US$ 30 for the paper.

Jacques Cinq-Mars

[Jacques Cinq-Mars]

All,

This is a follow up on my earlier post (and responses from other Forum members) on this “Aboriginal pyromaniacs” issue. I suppose it can be viewed as a “persist and sign” sort of statement on the part of Miller & al., regarding the role that ancient Australian aborigines are likely to (had to) have played, during their Late Pleistocene and Holocene tenure, in the desertification (and associated extinctions) of a large portion their own habitat, i.e., the whole interior of a continent! A bit much for my taste, but note, however, that in the authors’ own words, this can only be “implied”, and I don’t doubt that someone, somewhere, is getting ready to come up with an alternative explanation that will be more in “harmony with nature”.

Jacques Cinq-Mars

Arid Australian interior linked to landscape burning by ancient humans

Jim Scott
University of Colorado at Boulder

EurekAlert! - Public release date: 25-Jan-2005

Contact: Gifford Miller
gmiller@colorado.edu
303-492-6962

The image of a controlled burn in the interior of Australia today, featured on the cover of the January 2005 issue of Geology, illustrates how Australia might have looked 50,000 years ago. [Photo courtesy Gifford Miller, University of Colorado at Boulder
Click here for a high resolution photograph. -- see below - ed.]

Landscape burning by ancient hunters and gatherers may have triggered the failure of the annual Australian Monsoon some 12,000 years ago, resulting in the desertification of the country's interior that is evident today, according to a new study.

University of Colorado at Boulder Professor Gifford Miller said the study builds on his research group's previous findings that dozens of giant animal species went extinct in Australia roughly 50,000 years ago due to ecosystem changes caused by human burning. The new study indicates such burning may have altered the flora enough to decrease the exchange of water vapor between the biosphere and atmosphere, causing the failure of the Australian Monsoon over the interior.

"The question is whether localized burning 50,000 years ago could have had a continental-scale effect," said Miller, a fellow at CU-Boulder's Institute of Arctic and Alpine Research. "The implications are that the burning practices of early humans may have changed the climate of the Australian continent by weakening the penetration of monsoon moisture into the interior."

A paper on the subject by Miller appears in the January issue of Geology. Co-authors include CU-Boulder's Jennifer Mangan, David Pollard, Starley Thompson and Benjamin Felzer of the National Center for Atmospheric Research in Boulder and John Magee of Australian National University in Canberra.

Geologic evidence indicates the interior of Australia was much wetter about 125,000 years ago during the last interglacial period. Although planetary and meteorological conditions during the most recent ice age caused Earth's major monsoons to waver, all except the Australian Monsoon were "reinvigorated" to full force during the Holocene Period beginning about 12,000 years ago, he said.

Although the Australian Monsoon delivers about 39 inches of rain annually to the north coast as it moves south from Asia, only about 13 inches of rain now falls on the continent's interior each year, said Miller, also a CU-Boulder geological sciences professor. Lake Eyre, a deep-water lake in the continent's interior that was filled by regular monsoon rains about 60,000 years ago, is now a huge salt flat that is occasionally covered by a thin layer of salty water.

The earliest human colonizers are believed to have arrived in Australia by sea from Indonesia about 50,000 years ago, using fire as a tool to hunt, clear paths, signal each other and promote the growth of certain plants, he said. Fossil remains of browse-dependent birds and marsupials indicate the interior was made up of trees, shrubs and grasses rather than the desert scrub environment present today.

The researchers used global climate model simulations to evaluate the atmospheric and meteorological conditions in Australia over time, as well as the sensitivity of the monsoon to different vegetation and soil types. A climate model simulating a forested Australia produced twice as much annual monsoon precipitation over the continental interior as the model simulating arid scrub conditions, he said.

"Systematic burning across the semiarid zone, where nutrients are the lowest of any continental region, may have been responsible for the rapid transformation of a drought-tolerant ecosystem high in broad-leaf species to the modern desert scrub," he said. "In the process, vegetation feedbacks promoting the penetration of monsoon moisture into the continental interior would have been disrupted."

More than 85 percent of Australia's megafauna weighing more than 100 pounds went extinct roughly 50,000 years ago, including an ostrich-sized bird, 19 species of marsupials, a 25-foot-long lizard and a Volkswagen-sized tortoise, he said.

Evidence for burning includes increased charcoal deposits preserved in lake sediments at the boundary between rainforest and interior desert beginning about 50,000 years ago, Miller said. In addition, a number of rainforest gymnosperms -- plants whose seeds are not encased and protected and are therefore more vulnerable to fire -- went extinct at about that time.

Natural fires resulting from summer lightning strikes have played an integral part in the ecology of Australia's interior, and many plant species are adapted to regimes of frequent fires, he said. "But the systematic burning of the interior by the earliest colonizers differed enough from the natural fire cycle that key ecosystems may have been pushed past a threshold from which they could not recover."

###

The National Science Foundation and the Australian Research Council funded the study with additional support from Australian National University and CU-Boulder.

… and the actual paper:

Miller, Gifford, Jennifer Mangan, David Pollard, Starley Thompson, Benjamin Felzer, and John Magee. 2005. Sensitivity of the Australian Monsoon to insolation and vegetation: Implications for human impact on continental moisture balance. Geology33(1): 65–68.

Abstract:
General circulation model experiments test the geologically based correlation of high monsoon rainfall over interior Australia with Northern Hemisphere insolation and evaluate the sensitivity of the Australian Monsoon to ecosystem change. Our results suggest that Northern Hemisphere insolation control on the intensity of the Siberian High, rather than summer insolation over the Australian continent, determines the strength of the Australian Monsoon on millennial time scales, unlike a classic monsoon regime. Additional simulations show that the penetration of monsoon moisture into the interior is sensitive to biosphere-atmosphere feedbacks linked to vegetation type and soil properties. This sensitivity offers a resolution to the observed failure of the Australian Monsoon to penetrate the interior in the Holocene. Postulated regular burning practiced by early humans may have converted a tree-shrub-grassland mosaic across the semiarid zone to the modern desert scrub, thereby weakening biospheric feedbacks and resulting in long-term desertification of the continent.

Keywords:
Australia, monsoon, human, paleoclimate, climate models, biomass burning.

… with the Conclusion:

We hypothesize that lack of a strong early Holocene monsoon resulted from the conversion of a high-LAI, drought-adapted ecosystem that extended across the northern Australian semiarid zone to the modern desert scrub. We further hypothesize that this conversion was a result of systematic burning by early humans. Continued burning subsequent to colonization, coupled with nutrient-poor soils, maintained the changed ecosystem. Our GCM sensitivity tests show that such an ecosystem change would have reduced convective activity over the interior and the onshore flow ofmoist air, resulting in long-term desertification of the continental interior, even during periods with strong monsoon forcing. Our results imply that continental-scale changes in moisture balance may have been the outcome of low technology hunter-gatherer activities of early modern humans.

For full access to the article, click HERE.

[Robert Henvell]

  Circa 50Ka the population of Australia would have been relatively small and there were probably large tracts of land,where no one had ventured.Natural bush fires may have endangered fauna.The actions of a few early Australians are unlikely to have caused mass extinctions,unless they arrived downunder much earlier than the current evidence suggests.The solution to the problem may be more complex than has been suggested.

[Jacques Cinq-Mars]

All,

Here is a follow up to earlier posts dealing with the “Australian [palaeo] pyromaniacs issue: an original paper and accompanying commentary, and media coverage or releases indicating that Miller and colleagues persist with their notion that the first inhabitants of Australia were definitely not in “harmony with nature”

Fire-starters blamed for Australian extinctions
Early settlers accused of sending animal species crashing down in flames.

Michael Hopkin

news@nature.comm - published online: 7 July 2005

Australia's earliest settlers drove many animals to extinction through their use of fire, say palaeontologists who have studied the changing dietary habits of long-dead creatures.

Many large Australian animals are known to have died off after man first arrived on the continent around 50,000 years ago. But it has remained unclear exactly how, if at all, humanity caused this extinction.

Some experts have argued that early settlers unleashed a 'blitzkrieg' of hunting on the animals, wiping them out in a matter of generations. Others have argued that the aboriginals brought novel diseases with them from overseas.

Neither of those is the real story, argues Gifford Miller of the University of Colorado, Boulder. He says that humans' extensive use of fire altered the makeup of plant ecosystems, leading to a widespread die-off of creatures that fed on certain grasses.

Miller and his colleagues say they have found evidence that many animals changed their eating habits soon after humanity's arrival, and that those that were unable to adapt to new foods died out.

The researchers studied preserved eggshell fragments from Lake Eyre, Port Augusta and the Darling-Murray Lakes in southern Australia. Some of the eggs came from the emu (Dromaius novaehollandiae), which survives as a species today; others belonged to the similar, but extinct bird Genyornis newtoni.

Miller's team reconstructed the birds' diets over the past 140,000 years by studying the levels of radioactive carbon isotopes in the eggshells. They found that Dromaius shifted from nutritious grasses, which the team identified by its distinctive levels of radioactive carbon, to less nutritious shrubs and trees around 45,000 years ago.

A similar trend was seen in wombat teeth, the researchers report in this week's Science1. But Genyornis showed much less variation in its diet, which may explain why it failed to adapt and survive into the present.

The change in diet is down to man's extensive burning of grasslands, to clear passageways, open up hunting grounds or signal over long distances, Miller argues.

"Our evidence suggests that the enterprise of the first colonists altered ecosystems at their lowest level: the vegetation," Miller says. "And as vegetation changed, those animals with flexible dietary tolerances were able to adjust to the changed food sources, whereas those with more specialized dietary needs became extinct."

Cold shoulder

The researchers add that no climate shift is known to have occurred in Australia during the time of that extinction. So they argue that humanity, rather than climate, caused a change in vegetation, and widespread extinctions.

Others are not so sure. Fossils found at Cuddie Springs, New South Wales, seem to indicate that ancient fauna lived side-by-side with humans for several thousand years before finally succumbing to encroaching desertification as little as 30,000 years ago (see "Did climate shift kill off giant Australian animals?").

But Miller argues that more accurately dated fossils are needed to support this theory. "The Cuddie Springs dating remains very contentious," he says. "Most agree that the extinction event occurred between 50,000 and 45,000 years ago."

Here are the reference and abstract:

Miller, Gifford H., Marilyn L. Fogel, John W. Magee, Michael K. Gagan, Simon J. Clarke, and  Beverly J. Johnson. 2005. Ecosystem Collapse in Pleistocene Australia and a Human Role in Megafaunal Extinction. Science 308: 287-290.

Abstract:
Most of Australia’s largest mammals became extinct 50,000 to 45,000 years ago, shortly after humans colonized the continent. Without exceptional climate change at that time, a human cause is inferred, but a mechanism remains elusive. A 140,000-year record of dietary d13C documents a permanent reduction in food sources available to the Australian emu, beginning about the time of human colonization; a change replicated at three widely separated sites and in the marsupial wombat. We speculate that human firing of landscapes rapidly converted a drought-adapted mosaic of trees, shrubs, and nutritious grasslands to the modern fire-adapted desert scrub. Animals that could adapt survived; those that could not, became extinct.

For full access to the material provided by Science, click HERE for the actual article, and HERE for the commentary.

Additional coverage can also be found HERE, HERE, and HERE.

Finally, John Hawks presents HERE, a very cogent review of this continuing story/debate, one with which I essentially agree. I would add that I am always  very worried -- as a matter of principle and a bit more -- by dramatic, monocausal explanations of this type, however elegant they may sound. At any rate, anyone interested in this particular story should also read the earlier posts.

Jacques Cinq-Mars

[Robert Henvell]

There is no definative evidence of Homo sapiens in Australia prior to circa  48Ka and for years after that date the population densities would have been relatively low.There were mega fauna at a number of NSW relict lacustrine sites about 20Ka.It is unlikely that the first Australians were entirely responsible for the demise of the mega-fauna.A broader research base on this topic might be warrented.

[Robert Henvell]

The reference senile one forgot to list is:

Prolonged coexistance of humans and megafauna in Pleistocene Australia   by Clive N G Trueman etc,2005.PNAS,June,7,vol 203,no23.

[Daryl Habel]

The reference senile one forgot to list is:

Prolonged coexistance of humans and megafauna in Pleistocene Australia   by Clive N G Trueman etc,2005.PNAS,June,7,vol 203,no23.

Ah yes, the Cuddie Springs publication.  Posted earlier on this forum HERE.  Apparently Miller et al. arbitrarily dismiss this site.  Miller is quoted in the nature.news article Jacques referenced above:  

"The Cuddie Springs dating remains very contentious," he says. "Most agree that the extinction event occurred between 50,000 and 45,000 years ago."

The dating 36-30 ka of the sediment layer containing both artifacts and megafauna at Cuddie Springs seems firm, but the argument against Cuddie Springs, as I understand it, is that the megafauna bones are secondarily derived from underlying non-cultural (older) bone deposits.  Trueman et al. directly addressed this argument in their PNAS article, comparing trace rare earth elements in the various Cuddie Springs sediment layer bone assemblages and arriving at a conclusion that the artifacts and megafauna were coeval.  Too "contentious" for Miller, I reckon.  
 
Oh well, this debate isn't about to end soon.  Stay tuned.    

Dar

[Dale Hoogeveen]

Wouldn't the Australian C4 floral community have had a firecycle before the extinctions like most other dryland and many not so dry areas ? 

Dale