Swamp kauri providing a window to the past for scientists

Ancient swamp kauri is being used by NIWA scientists to reveal the secrets of past climates.

Ancient swamp kauri is being used by NIWA scientists to reveal the secrets of past climates.

Buried Kauri in Manukau Harbour

Dr Andrew Lorrey says 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 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 our past climate as well as clues about what might happen in the future. 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 says.

“There are a couple of outstanding questions in climate science at the moment – one is how the El Niño-Southern Oscillation will respond to global warming. A paleoclimate record can provide good information about that.”

In a paper just published in the Quaternary Science Reviews outlining the scientific potential of swamp kauri, Dr Lorrey explains 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 New Zealand can experience.”

There is currently a calendar-dated kauri tree ring record going back 4500 years.

“Further back than that we have segments of about 1000 or 2000 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.

Swamp Kauri at Johnston's Gumdiggers Park, Awanui.

In the paper Dr Lorrey says 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.”

Links between scientists and the swamp kauri industry have improved following a period of rapid market growth between 2011 and 2014 when things were very difficult to keep track of.

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 says 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.​

“That is one of its most exciting potentials,” he says.