Kiwi scientists have found a kauri tree stump being kept alive by neighbouring trees.

It’s raised questions about just what constitutes a tree, and whether we should be treating forests as single ‘superorganisms’.

AUT Associate Professor Sebastian Leuzinger told Newshub a stump no longer contributes to the carbon economy of a forest, “yet it’s being fed by possibly genetically related, but possibly non-related individuals. Why would they do that? That’s a very fundamental question.”

Leuzinger was hiking in west Auckland when he and a colleauge stumbled on a stump that was clearly still alive, despite not having any foliage. They investigated, and discovered it was exchanging water and resources through its roots, which were grafted onto nearby trees.

“For the stump, the advantages are obvious – it would be dead without the grafts, because it doesn’t have any green tissue of its own,” Leuzinger said. “But why would the green trees keep their grandpa tree alive on the forest floor while it doesn’t seem to provide anything for its host trees?”

They propose it’s because trees that have roots connected to the stump are able to trade resources with each other.

“This has far-reaching consequences for our perception of trees – possibly we are not really dealing with trees as individuals, but with the forest as a superorganism.”

While this might sound cool, it’s bad news for the fight against kauri dieback disease, which is decimating the native species.

“I’ve just spoken to a pathologist, and they can confirm it’s a major worry to know that these potential root grafts exchanging water may have carried the pathogen as well, which is not good news for kauri dieback.”

Leuzinger hopes to find more living stumps so we can learn more, “particularly in a changing climate and a risk of more frequent and more severe droughts”.

“This changes the way we look at the survival of trees and the ecology of forests.”

The research was published Friday in journal iScience.

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