The Press

Wiggle technique improves accuracy

A new method more precisely dates Maori pa, Will Harvie says.

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Starting about AD1500, Maori started fortifying their villages. What had been open communitie­s became defensive pa. It was a huge constructi­on exercise that resulted in something like 7000 pa being built across Aotearoa in about 350 years.

This turn towards walls and protection – and their approximat­e age – has been known for years but now scientists have applied a technique that can date some pa with much higher precision.

If won’t necessaril­y answer ‘‘why’’ Maori needed to fortify their villages, but it gives a much clearer answer on ‘‘when’’.

The knowledge arises from a study of wood palisade posts found at Otahau Pa, north of Hamilton in the Waikato.

The builders planted posts upright in the ground and filled the spaces between them with beams and horizontal materials, much like today’s fences. Today, only the posts survive and even these are mostly stumps.

It’s now believed the fortificat­ion was constructe­d in AD1768 plus or minus four years, according to a recent paper in the Journal of Archaeolog­ical Science: Reports.

Radiocarbo­n dating has been used for years in New Zealand, says Associate Professor Alan Hogg, lead author of the paper and director of the radiocarbo­n dating lab at the University of Waikato.

But radiocarbo­n dating has limited value with materials that are not especially old, he says. Many Maori artifacts from about AD1500 and later fall into this category.

‘‘Radiocarbo­n ages don’t equate exactly to calendar ages. When you get a radiocarbo­n date, it might be very precise, for example it might be 350 years plus or minus 15 years,’’ he says.

‘‘But then you need to convert the radiocarbo­n age to a calendar age. When you do that, you can get a calendar age range of plus or minus 70 years. It’s no more precise than that.’’

To get through this problem, Hogg and colleagues used a technique called ‘‘wiggle matching’’ that compares radiocarbo­n deviations in wood of a known age to wood of an unknown age.

The technique produces ‘‘very accurate calendar ages’’, Hogg says.

Hogg and colleagues used wiggle matching to date posts from Otahau Pa.

The Waikato was a centre of Maori culture and among other things developed important kumara gardening techniques. But knowledge is limited.

‘‘At the moment it’s confusing,’’ says Hogg. Current knowledge is ‘‘mostly developed from Maori oral traditions. They know who lived in particular pa, who the chiefs were and there are details about the Maori wars and tribal movements and some informatio­n about gardening and kumara cultivatio­n’’.

This traditiona­l knowledge is supported by archaeolog­y and its supporter, radiocarbo­n dating.

But oral tradition and archaeolog­y don’t necessaril­y produce matching chronologi­es, he says. They don’t ‘‘align’’ well.

Wiggle matching could be ‘‘the touchstone or Rosetta Stone’’ of Waikato and Aotearoa history, he says. The Rosetta Stone unlocked ancient Egyptian hieroglyph­ics.

‘‘By getting really accurate and precise dates on various sites, then we can the align oral histories from the various hapu from within the Waikato and build a coherent history of what Maori have done since 1500,’’ Hogg says. ‘‘That’s the bigger picture.’’ Speaking on behalf of colleagues with expertise in the field, Hogg says the Otahau Pa posts were not carved or embellishe­d except for ‘‘skilfully sharpened points’’.

It appears pa inhabitant­s exploited a forest of newly growing trees, especially miro, and weren’t ‘‘fussy about what they took’’, Hogg says.

The evidence suggests the posts were chopped down and immediatel­y placed in the ground. ‘‘It looks like it was done quickly, perhaps in response to some perceived threat,’’ Hogg says. ‘‘We don’t know what.’’

The posts were planted in wet ground. Other sharpened posts were found in creek bottoms.

Wetness is important because it preserved the wood.

And for the purposes of wiggle matching, it was important that the preserved posts were still completely round and included sap wood and bark. Researcher­s needed all of the tree rings and bark to make use of wiggle matching.

The technique probably wouldn’t be valuable in dating a spear from the period, because the whole tree width wasn’t available, Hogg says.

The Otahau Pa project was a test case to see if accurate calendar ages could be calculated and whether the technique was cost effective.

It worked out in both cases and Hogg says wiggle matching could be used on pa sites across the country, provided they were swamp pa or the whole width of

"Radiocarbo­n ages don't equate exactly to calendar ages." Alan Hogg

wood had been preserved by water.

‘‘There will be lots of pa in New Zealand that have preserved palisades posts,’’ Hogg says.

‘‘We want to start in Waikato, where there are unusual relationsh­ips between pa constructi­on and [kumara] gardening. We expect to find preserved palisades posts anywhere there are swamp pa.’’

Maori living today near Otahau Pa were surprised by its age. They thought it was probably older, Hogg and colleagues reported in their paper.

 ?? WARREN GUMBLEY ?? Palisades posts from Otahau Pa were well preserved because they were immersed in swampy ground,
WARREN GUMBLEY Palisades posts from Otahau Pa were well preserved because they were immersed in swampy ground,
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 ?? WARREN GUMBLEY ?? Palisades posts from Otahau Pa, north of Hamilton. These have been radiocarbo­n dated, with unusual precision, to AD 1768 plus or minus four years.
WARREN GUMBLEY Palisades posts from Otahau Pa, north of Hamilton. These have been radiocarbo­n dated, with unusual precision, to AD 1768 plus or minus four years.
 ?? ALAN HOGG, WAIKATO UNIVERSITY ?? The posts were not embellishe­d beyond skillfully sharpened points. This suggests they were chopped and planted in the ground immediatel­y.
ALAN HOGG, WAIKATO UNIVERSITY The posts were not embellishe­d beyond skillfully sharpened points. This suggests they were chopped and planted in the ground immediatel­y.
 ??  ??

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