Leafless kauri stump found alive

A leafless kauri tree stump in a New Zealand forest has been found to remain alive due to a shared hydraulic network formed through fused roots with neighboring trees. The discovery was made by two botanists from the University of Technology in Auckland, who published their findings in a study in September 2019 in iScience.

Kauri tree's significance

The kauri tree, scientifically known as Agathis australis, is among the largest trees on the planet and can exceed fifty meters in height. Native to New Zealand, it is a symbol of the country’s unique flora and plays a vital role in its ecosystems.

Discovery during a hike

The researchers, Sebastian Leuzinger and Martin Bader, noticed the leafless kauri stump while resting along a hiking trail. Although the stump appeared dead at first glance, the tissue beneath the bark remained clear and full of sap, indicating real activity.

Sap flow measurements

To understand the phenomenon, the team installed sap flow sensors on the stump and on three neighboring kauri trees. These sensors allowed them to track how water and nutrients moved through the trees over time.

Unexpected water flow patterns

The measurements revealed an unexpected rhythm. In full sunlight, when the trees were transpiring at full capacity, almost nothing flowed in the stump. However, at night and on rainy days, when the neighbors slowed down, water began to rise again in the stump.

Root grafts explain the phenomenon

This reversed pattern can only be explained by variations in pressure in the roots, which the researchers suggest indicate natural root grafts that likely occurred when the stump still had leaves. The conducting wood of the stump and that of the neighbors then form a single network, in which water flows according to pressure differences.