Kauri trees are copper-skinned conifers endemic to New Zealand. They’re held sacred by the indigenous Māori and have been used for carvings and canoes for thousands of years. They also hold invaluable information about the world’s climate history.  

The trees can live for more than two millennia and grow to be more than 16 feet in diameter. One tree, recently discovered by an energy company building a geothermal platform, was 65 feet long, 8 feet across, and weighed 65 tons. What the excavators that dug it up didn’t know at the time was that this is the only unearthed kauri tree that existed between 13,000 years ago and 25,000 years ago. That roughly 12,000-year span was a glacial period in which scientists believe the trees’ population shrunk or moved to lower elevations, so researchers have yet to find a tree dating to that period. 

So why is the tree so valuable? Much like ice cores, lake sediments, and stalactites, and stalagmites, tree trunks offer a glimpse into the past and a record of our planet’s climate. Tree rings show not only how old a trunk is, but also what the climate was like each year that it lived. According to Andrew Lorrey, a climate scientist at New Zealand’s National Institute of Water and Atmospheric Research, these trees directly sample the atmosphere and record it, providing a “high-resolution time-capsule.”

Analyzing this specific kauri trunk, Lorrey’s team was able to decipher that the tree lived for 1,600 years. The rings show relative humidity, rainfall patterns, and soil moisture for each of those years. Cross-referencing this data with research from University of Auckland dendrochronologist Gretel Boswijk, the team was able to create a 700-year reconstruction of a specific climatic period in Northern New Zealand. 

Researchers like Lorrey continue to search for unearthed kauri trees. Each one provides a snapshot in time and Lorrey says he hopes to one day connect these chains of climate chronology. Unfortunately, many of the trees, which are often buried deep in wetlands, were dug up by 19th-century gum diggers who sought the tree’s resin to preserve jewelry or by excavators in the early 2000s looking to sell the wood for luxury furniture. New Zealand finally put a limit on kauri exports in 2018, but there’s no telling what evidence was lost forever. 

As the scientists work on collecting more data from kauri trees, they’re using the current samples to continue dating other plant, human, and animal artifacts, from as far back as tens of thousands of years ago and fighting to protect the endangered kauri groves that still stand.