Mysteries of the "Vampire Parasite" Stump

At one point, a kauri tree fell somewhere in New Zealand. The tree rotted away leaving behind just the stump, “leafless and apparently dead”, writes Ed Yong. But when botanist Martin Bader knocked on the stump, it didn’t sound like deadwood. Was it alive? If so, how?

They found the stump is connected to other kauri trees, probably via its roots:

“The water flowing through the full-size trees also drives water through the stump, keeping it alive. It will never green again, never make cones or seeds or pollen, never unfall, never reclaim its towering verticality. But at least for now, it’s not going to die, either.”

And that just raised questions:

“How best to think about the living stump? Is it a vampiric parasite that sustains its undead existence by leeching the supplies of its fellow trees? Is it a beneficial partner that extends the root network of those other kauri in exchange for water? Is it even an individual entity anymore, or just a part of its neighbors?”

It has been known that trees are often connected… underground. Researchers think this allows trees to “share resources during times of hardship”. Ok, that makes sense. But that raises a question:

“Why would the intact trees keep their connections to a partner that’s no longer contributing anything itself?”

Possible answers for that question include:

1. The stump does extend the range over which roots can find water;
2. Trees can’t identify freeloaders in their midst, like the stump;
3. Even if they identify freeloaders, they don’t have a way to disconnect.

Another mystery with the stump is: How does the water flow in a stump?

“Water isn’t pumped through trees, but pulled. The water that evaporates from leaves drags more water up through stems and from roots—a process called transpiration. But without leaves, that pulling force is absent. Water doesn’t flow, and neither do the nutrients dissolved within it. The innards of a leafless stump should be stagnant. Instead, they’re still on the move.”

Solving these questions hasn’t been easy, because they haven’t found other such vampire zombie stumps for kauri trees. So they don’t know if this is a one-off exception, or a not too uncommon phenomenon.

All of which is why botanist Sebastian Leuzinger says:

“That really changes our view on forest mortality. If living, intact trees regularly share water through connected supplies, we need to look at forests as superorganisms.”