Do trees always exist as single organisms, or can each tree also serve as part of a linked "superorganism?" A recent finding in New Zealand suggests the latter, as a tree stump there has apparently remained alive by joining roots with its neighbors.
The kauri tree stump in question was first discovered by Auckland University of Technology researchers Sebastian Leuzinger and Martin Bader, when they were hiking in a New Zealand forest. They noticed that even though the stump had no leaves – which are necessary for performing life-giving photosynthesis and gas-exchange – it was still alive, long after the main tree had fallen down.
By subsequently measuring sap flow in the stump and in surrounding kauri trees, they discovered that when the flow increased in the stump, it correspondingly dropped in the other trees. This, they determined, indicated that the stump's roots had grafted together with the roots of those trees, allowing the stump to receive water and nutrients from them.
While such root-grafting has previously been observed amongst trees of the same or similar species, it has usually been between a few trees that are all still complete and fully-functioning, which could each survive on their own. This arrangement makes sense, as not only does it allow them to draw resources from a wider area via their linked roots, it also increases their stability within the soil, lessening the chances of any one tree falling down.
In the case of the stump, which wouldn't have much to offer the other trees in its present state, it is believed that its roots were likely grafted when it was still a full tree. By the time that tree fell, what remained of it had already been "grandfathered in" to the root network, keeping the stump from dying off.
"This has far-reaching consequences for our perception of trees," says Leuzinger. "Possibly we are not really dealing with trees as individuals, but with the forest as a superorganism … This changes the way we look at the survival of trees and the ecology of forests."
The research is described in a paper that was recently published in the journal iScience.
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