Posted on 01/26/2005 12:28:52 PM PST by blam
Contact: Gifford Miller
gmiller@colorado.edu
303-492-6962
Jim Scott
303-492-3114
University of Colorado at Boulder
Arid Australian interior linked to landscape burning by ancient humans
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.
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.
Thanks for the spelling correction.
Lightening is mentioned at the bottom of the column, but it is downplayed.
Vegetation doesn't affect the weather all that much, although weather affects vegetation. If a rainforest were to be planted in Australia one year, the temporary moisture increase might affect the weather. But the weather would probably return to normal the next year with the death of the rainforest. Differences in topography, distances from poles and presence or lack of large bodies of water do affect weather, though.
"Mungo Man did it?"
I was thinking to write to the EPA to get a grant to study the effects of Yahoo Serious http://www.yahooserious.com/ on the desertification of Australia.
In a few hundred million years, when we can no longer see the planet Mercury in the heavens, the fire cycles will definitely be different and they will have changed many times between now and then.
That would be cultural desertification.
...er, lightning, even.
This is clearly wrong. I know from attending publik skool and consuming Hollyweird entertainment that the indigenous people who were displaced by the Evil White Man were themselves all sweetness and light, and that they lived in harmony with Mother Nature.
Oh no, a change in climate. Quick, blame it on Bushmen...
"Fire bad, Tree pretty"
Drat, you beat me to it.
Australia is drifiting at about the same rate as your fingernails grow.
Bushmen are in Africa not, Australia.
No beating around the bush allowed, 'eh?
No. 534:
AUSTRALIAN FIRE
by John H. Lienhard
Click here for audio of Episode 534.
Today, we suffer the loss of fire. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.
"I shiver at the taste of fire ..." writes poet Carol Drake. Take a close look at Australia's prehistory, and you might well shiver. For fire tells that land's story.
Great destructive brush fires have swept Australia several times during the 20th century. In 1983 one killed 71 people and a third of a million head of livestock.
Ecologists have taken stock of this destruction. They've found, as we so often do, that it's the complex fruit of human intervention. That story begins 40,000 years ago.
The Bushmen -- thinly distributed over Australia -- lived in a dry land of highly flammable brush. Fire became their constant companion. They all tended fire -- carried it about with them. They used it freely. They hunted by lighting huge horseshoe-shaped brush fires. Fire herded wild animals onto their weapons.
That was only one part of it. They cut highways in the impenetrable forests by burning off the scrub. They lit fires to get better access to edible roots. Burn, burn, burn! Fire was their way of life.
Fire both suited and shaped the ecology. The eucalyptus and gum trees have tough leaves and powerful root systems. They hoard water. They're not easily harmed by fire. If fire does hurt them, they quickly send up new shoots.
By the time the English dumped prisoners in Botany Bay in 1788, an ancient balance had been struck among Aborigines, fire, and the land. Then white settlement began. Settlers drove Bushmen, and their ever-present firesticks, out. Underbrush accumulated. It took over a century to create a real tinderbox.
Those settlers should have listened to the old myths. Listen as they tell the story of creation:
In the early Dreamtime, the creatures of the world did not look as they do today. ... The Father examined them and said, "You are not a proper people and not proper animals. We must change this." With his firestick he lit a ceremonial fire that spread until it encompassed the world. It swept over all creatures. It burned the earth and the stones. After the fire had passed, the creatures and the humans took their present form and character. The Bushmen knew perfectly well they were wed to fire. They knew that fire shaped them, and it shaped the world around them.
So the big destructive brushfires finally began in regions that hadn't been cleansed by fire for over a century. And we gaze at Aborigine art -- wild pointillist abstracts with titles like, "Fire Dreaming at Ngarna," and "Bushfire Dreaming."
As we look, we do indeed shiver at the taste of fire -- no longer there to daily cleanse and renew that vast land.
I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.
(Theme music)
Pyne, S.J., Fire Down Under. The Sciences, March/April, 1991, pp. 39-45.
The line of poetry is from one of the unpublished works of the poet Carol Christopher Drake.
Forgot to link the article:
http://www.uh.edu/engines/epi534.htm
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