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28/2/2018 — Education, Science and Technology
Old swamp kauri in climate studies

Ancient swamp kauri is being used by scientists from the National Institute of Water and Atmospheric Research (NIWA) to reveal the secrets of past climates.

Swamp kauri hit the headlines late last year when it was revealed that the major Marsden refinery to Auckland oil pipeline rupture may have been precipitated by a machine operator looking for old kauri stumps in marshland near Ruakaka.

NIWA’s Dr Andrew Lorrey said kauri is a special species - mature trees live from 600 to 1000 years “if left to their own devices” - and provide important insight into long-term climate change.

Swamp kauri is predominantly found in Northland. There, the kauri trees have been preserved in relic peat bogs for tens to hundreds of centuries and contain vital information about past climate as well as clues about what might happen in the future.

NIWA said scientists use them to create a record of the weather going back centuries.

“These trees appeared to listen to what was going on with the El Niño-Southern Oscillation which is very important to our regional climate, as well as driving huge climate anomalies such as droughts and floods around the globe,” Dr Lorrey said.

In a paper just published in the Quaternary Science Reviews outlining the scientific potential of swamp kauri, Dr Lorrey explained scientists obtain climate data by taking a cross section of the trunk of swamp kauri excavated from the ground.

From that sample, scientists measure the width of the kauri tree rings after cutting the cross section into radial strips like the spokes on a bicycle wheel. After polishing, these tree ring samples are analysed under a microscope.

“One measurement after the other creates a ring width sequence that tells us about the environment the kauri grew in and how that varied through time, largely driven by climate. This provides us with a rich history of the range of natural variation NZ can experience.”

There is currently a calendar-dated kauri tree ring record going back 4,500 years. Further back than that we have segments of about 1,000 or 2,000 years scattered across 30,000 to 60,000 years ago, floating in time anchored by radiocarbon dates.”

Dr Lorrey says there is a concern that time periods could be lost if scientists are not told about swamp kauri excavation sites.

His paper said the accelerated rate of swamp kauri extraction and export is a paradox for science; it provides new material but also means wood can be lost from unknown excavations.

“For instance, we have a big gap of wood between 13,000 and 27,000 years old. If we were to get our hands on that we would have a shot at putting together an absolutely epic calendar-dated tree ring record.”

NIWA said links between scientists and the swamp kauri industry have improved following a period of rapid market growth between 2011 and 2014 when tracking data was more difficult.

Most practitioners will now advise scientists where they’re going to open-up a site to enable them to be there from the onset.

“There’s a lot of other information that we can record about trees at a site before they’re taken out of the ground. Even the direction the trees are pointing in can tell us about past storms.”

Dr Lorrey said New Zealand is the only place in the world that has preserved trees like this, creating the possibility to test some hypotheses about the role of the climate in major changes throughout history.

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Buried Kauri in Manukau Harbour. Photo: Andrew Lorrey, NIWA.
Swamp Kauri at Johnston's Gumdiggers Park, Awanui. Photo: Andrew Lorrey, NIWA.