How swamp kauri hides crucial climate clues

It's a prized commodity in the timber trade, but New Zealand's ancient swamp kauri also offers a crucial window into our prehistoric - and potential future - climate. Photo / File

It's a prized commodity in the timber trade, but New Zealand's ancient swamp kauri also offers a crucial window into our prehistoric – and potential future – climate.

Found mainly in Northland, swamp kauri has been preserved in relic peat bogs for tens to hundreds of centuries.

Its extraction and export as high-end timber products and stumps has fuelled a lucrative but controversial industry.

But these buried treasures also hide vital clues that scientists could use to reconstruct long-term changes in our prehistoric environment.

"These trees appeared to listen to what was going on with the El Nino-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," Niwa climate scientist Dr Drew Lorrey said.

"There are a couple of outstanding questions in climate science at the moment – one is how the El Nino-Southern Oscillation will respond to global warming.

"A paleoclimate record can provide good information about that."

In a just-published paper, Lorrey explained how scientists gathered climate data by taking a cross section of the trunk of swamp kauri excavated from the ground.

From that sample, scientists could 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 were 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 was 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."

Lorrey said there was concern that time periods could be lost if scientists are not told about swamp kauri excavation sites.

The accelerated rate of swamp kauri extraction and export was a paradox for science, as it provided new material, but also meant wood could be lost from unknown excavations.

"For instance, we have a big gap of wood between 13,000 and 27,000 years old," he said.

"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."

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

Most practitioners now advised 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."

Lorrey said New Zealand was 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."