Short drop amid the flames
Clever new research confirms that huge fires that burned across the South Island shortly after the arrival of Polynesians were indeed set by humans.
While it’s long been assumed that the fires were probably started by early arrivals, proof has been lacking and it was possible that humans and fires were coincidental.
But studies of sediments in two lakes near Wanaka and Queenstown turned up human faecal matter in the same layers as charcoal and ash from early fires.
‘‘Our data provide a direct record of local human presence in Lake Kirkpatrick and Lake Diamond watersheds at the time of deforestation and a new and stronger case of human agency linked with forest clearance,’’ reported lead author Elena Argiriadis of the University of Venice.
The team of nine researchers from Italy, the United States and New Zealand – including Janet Wilmshurst of Landcare Research and the University of Auckland – took sediment samples from the two relatively remote and undisturbed lakes.
As expected, they found little evidence of widespread burning before AD1280, the year western scientists date the first arrival of Polynesians in Aotearoa, plus or minus 20 years.
Before then, there were ‘‘nearly undetectable’’ samples of burning, presumably from fires set by lightning and ash blown across the Tasman Sea. But the podocarp forests of the area burned very little.
About 1350, however, that changes. Evidence of fire ‘‘abruptly and simultaneously increase[s] in sediments at about AD1345–1365 and mark[s] a period of intense or multiple fire events,’’ the authors reported in the paper published in the journal Scientific Reports.
‘‘The peaks occur shortly after Ma¯ ori arrival and during the Initial Burning Period.’’
The researchers also found coprostanol and related substances. Coprostanol is the most abundant sterol in human faeces and lasts for centuries in the right environment.
‘‘Prior to human settlement, fluxes of faecal sterols in both lakes were near zero,’’ the authors report.
There were substantial increases in human faecal sterols between 1310 and 1380, matching strong evidence of nearby fires.
It’s thought the faecal matter was deposited on the ground and runoff moved it into the lakes.
The record shows a shortlived peak of faecal sterols and ‘‘suggests that human activity in the watershed lasted only a few decades’’.
After that, faecal values remained about twice the level found in the pre-Polynesian era, the authors wrote.
‘‘This decline between about AD1400 and 1800 likely marks a reduced presence of people in the watershed prior to European colonisation, although humans may have been present sporadically or in low numbers.’’
Pollen and other plant markers were also examined and showed a dramatic change in the vegetation in the area. There was fewer native podocarps and more fire-adapted shrubs, grasses and ferns.
Lake sediments also showed greater erosion after the initial burning.
Archaeologist Atholl Anderson and other Ma¯ ori scholars have found evidence of ku¯ mara cultivation as far south as Kaiko¯ ura and possibly even Banks Peninsula, but inland Otago would have been too cold. Southern Ma¯ ori were foragers who continued to burn landscapes to ‘‘promote key carbohydrate resources, such as fire-adapted bracken fern’’, especially once food resources like moa birds were extinct.
Southern Ma¯ori were foragers who continued to burn landscapes to promote key carbohydrate resources.