Living Tree Stump That Survives by Feasting From Its Neighbors Discovered in New Zealand

A tree stump that should be dead—but isn't—has been discovered in a forest in New Zealand. The kauri tree stump appears to be surviving by feeding on its neighbors resources, holding onto their roots and extracting water from them.

Sebastian Leuzinger and Martin Bader, from the Auckland University of Technology, were hiking when they came across the "odd" tree stump. They decided to study the nearby trees to find out how it was being kept alive.

Their findings, published in iScience, revealed that the roots of the stump were grafted to the trees surrounding it, with the movement of water between them and the stump having a strong negative correlation—as the surrounding trees lost water, the stump gained it.

In an email interview with Newsweek, Leuzinger said they were very surprised at their discovery: "A tight water coupling between trees and living stumps (and presumably between intact trees) is a new finding that challenges our view on trees as individuals."

Researchers know resources can be passed between plant life through a fungus that grows on the roots. However, although there are a few reports of sightings globally, there is little scientific research on the phenomenon. "As for kauri, reports are anecdotal. No forester nor New Zealand ecologist could direct us to a specific place where such leafless stumps exist. We only found one single living stump so far," Leuzinger said.

The scientists say the kauri stump roots grafted to the roots of other, surrounding trees—something that can happen once one tree recognizes the other as the same species.

tree stump
View of the front and back of the living tree stump. Sebastian Leuzinger

The discovery of the tree may suggest that root grafting is reasonably common, Leuzinger said. However, the physiological implications are not really known: "If other species show such tight hydraulic coupling, the theory on tree water supply, tree mortality under drought, and forest mortality need to be completely revised."

The team next plan to find out more about how the root grafts form and which organisms benefit from it: "Why support a leafless trunk that's obviously not contributing to carbon assimilation?" Leuzinger asked. "How many other species show similar root connections?"

Potentially, Leuzinger and Bader argue, the discovery could mean trees do not operate as single entities, but that forests are "superorganisms"—a group that interacts synergically, operating as an organic whole. "The idea of superorganism arises when we imagine all trees of the same species in a forest are connected underground," Leuzinger said.

"That this is the case for carbon that is exchanged via mycorrhizae [through the roots] is already known. If, as our study suggests, this is also true for the exchange of water, we have to rethink the definition of 'tree' and 'forest.' Potentially we'll have to look at them a bit like huge insect colonies, that only exist as the entirety of all individuals—an entirely new concept of forests."