The Conversation: How did this Kauri survive?

Wednesday 24 Feb 2021

The mysterious existence of a leafless kauri stump, kept alive by its forest neighbours - tect Plants use their leaves to make food from the sun’s energy and carbon dioxide. With very few exceptions of parasitic plants, no tree is known to grow without green foliage — or to be more precise, no tree can start life without leaves or some sort of green tissue containing chlorophyll.

But some may end up as “zombie trees” long after they lose all leaves and large parts of their trunk, either to disease or the chainsaw.

Such undead tree stumps have been observed for almost 200 years, but the evolutionary and physiological processes leading to their existence remain a mystery. One reason is because they are rare. Another is because whatever happens on their journey from feeding themselves to being fed happens out of sight — likely below ground.

American forest ecologist Suzanne Simard has shown that trees send each other signals through a network of fungi buried among their roots. This underground communication includes warning signals about environmental change and the transfer of nutrients to neighbouring trees before they die.

We suggest this supply can continue beyond the apparent death of an individual tree. By measuring water flow in the stem of a living kauri (Agathis australis) stump and its neighbouring trees, we show underground connections are indeed likely responsible for the survival of the stump.

A living tree stump is clearly a biological oddity, and our key question is why such root grafts form.

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