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"Maintaining healthy soil is crucial," says Boggiss, who notes that the Tongan family farmers from whom Heilala sources have recently planted windbreaks of Pacific kauri trees and vetiver grass to prevent soil erosion.

Other teams confirmed the spike in samples from a German oak and a New Zealand kauri tree.

Through it all, one giant kauri tree stood tall — until, after nearly two millenniums, it died and fell in a swamp, where the chemical records embedded in its flesh were immaculately preserved.

The team used radiocarbon to date the kauri wood by lining it up with accurate, but coarse, radiocarbon cave records from China.

But he said he was concerned for the rainforest areas, where trees such as kauri pines were not well adapted to fire.