This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Kauri are among Aotearoa New Zealand's tallest and longest-lived trees—and their place in our cultural landscape looms equally large. Centuries-old kauri such as Tāne Mahuta and Te Matua Ngahere are taonga, with deep cultural and spiritual significance to Māori.
Also remarkable is the amount of carbon these trees hold. Large kauri have gradually accumulated enormous amounts of biomass, leaving great quantities of carbon stored in their trunks, branches and roots. Over the past two decades, however, these giants of our forests have faced a growing threat from kauri dieback.
The disease is caused by the soilborne water mold Phytophthora agathidicida, which infects kauri through their roots and disrupts their ability to take up water and nutrients. As it progresses, trees can lose foliage and branches and eventually die. The toll has been significant.
Hundreds to thousands of kauri across New Zealand's upper North Island have died, with some of the heaviest losses recorded in Northland and Auckland's Waitākere Ranges. As dieback spreads and affected trees decline, some of the carbon held in their living biomass is lost from that store—with direct implications for carbon sequestration and the broader health of these forest ecosystems. Our latest research sheds some new light on these important impacts.
To build a clearer picture, we visited study plots in kauri forests in the Waitākere Ranges that had first been surveyed between 2011 and 2014. Our study co-author, Toby Elliot, revisited the plots to measure the trees again, assess the condition of their canopies and record which had died or become established. We then used the size of each tree, along with the typical wood density of each species, to estimate how much living biomass the plots contained.
This allowed us to see how the amount of carbon stored in living vegetation had changed over about a decade. We found that the more severe the kauri dieback, the less carbon forests gained through tree growth—and the more they lost as trees declined and died. The difference was notable.
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