A bizarre insight from our kauri means we should view forests as ‘super-organisms’.
Kiwi scientists have been astonished to find how kauri stumps can keep themselves alive by feeding off water from neighbouring trees.
The AUT researchers behind the ground-breaking discovery say it should mean we view trees not as individuals, but members of a forest ecosystem that’s essentially a “super-organism”.
Further, their findings could have big implications for tackling the disease killing kauri across the upper North Island.
In the new study, published in iScience this week, AUT’s Dr Martin Bader and Associate Professor Sebastian Leuzinger described how trees surrounding kauri stumps offer them a form of life support, possibly in exchange for access to larger root systems.
It was an insight the pair stumbled across while hiking in West Auckland, and spotting an unusual-looking stump.
“It was odd, because even though the stump didn’t have any foliage, it was alive,” Leuzinger said.
They decided to investigate how the nearby trees were keeping the tree stump alive by measuring water flow in both the stump and the surrounding trees belonging to the same species.
They found that the water movement in the tree stump was strongly negatively correlated with that in the other trees.
These measurements suggest the roots of the stump and surrounding conspecific trees were grafted together, Leuzinger said.
Root grafts can form between trees once a tree recognises that a nearby root tissue, although genetically different, is similar enough to allow for the exchange of resources.
“This is different from how normal trees operate, where the water flow is driven by the water potential of the atmosphere,” Leuzinger said.
“In this case, the stump has to follow what the rest of the trees do or else use osmotic pressure to drive water flow, because since it lacks transpiring leaves, it escapes the atmospheric pull.”
But while root grafts are common between living trees of the same species, the pair were interested in why a living kauri tree would want to keep a nearby stump alive.
“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?”
One explanation, Leuzinger said, is that the root grafts formed before one of the trees lost its leaves and became a stump.
The grafted roots expand the root systems of the trees, allowing them to access more resources such as water and nutrients.
They also increased the stability of the trees on the steep forest slope.