THE EUCALYPT'S SURVIVAL SECRET

The eucalypt trees burnt in Australia's recent bushfires are already sprouting again — and one botanist has worked out how they do it.

Dr Geoff Burrows from the Department of Agriculture at Charles Sturt University has discovered that eucalypts regrow in a way unlike any other tree in the world.

His findings have overturned long held beliefs about eucalypts, which had always been assumed to ‘bud’ like all Northern Hemisphere trees.

"People just assumed that because all trees in the Northern Hemisphere are the same, eucalypts will be too," explained Dr Burrows, who has spent the past five years on the research.

Northern Hemisphere trees like oak and willow have buds near the bark surface. They can resprout from the ground if they are chopped down but, unlike eucalypts, are unable to regenerate if they are burnt in a fire, because the buds are killed.

Dr Burrows has found that the lumps on the bark of eucalypts are not actual buds but are connected to bud-forming tissue located beneath the bark. The connection is via tubes called "bud traces" which run from the centre of the tree through the wood to the bark.

"If you follow one of the lumps back in along the tube, when you get near to the bark or the inner wood, you find cells that will make buds if the tree gets the signal," he said.

While all trees have bud traces, including those in the Northern Hemisphere, eucalypts bud traces are the only ones that don't end in an actual bud.

The placement of the bud-forming tissue in the eucalypt bud trace means it can lose 2 cm of bark in a fire and still be able to regenerate.

"As long as the whole tree doesn’t get killed, there will still be some of this bud-forming tissue somewhere in what’s left of the bark," explained Dr Burrows.

The bud-forming tissue forms buds in response to signals such as a lack of photosynthesis, which happens when green leaves are burnt off a tree.

Unlike other trees, eucalypts are not restricted to sprouting from the ground. They can resprout from any point on the tree even five to 10 metres up in full sunshine.

"It gives them a real head-start on other plants that might be trying to restart after a fire," said Dr Burrows.

He said the difficult task of cutting thin sections of eucalypt involved the use of a new technique in which liquid plastic was poured into the wood and then set before cutting.

"It’s nice that eucalypts really are different," said Dr Burrows. "Because of the environmental pressures they have been under they have come up with something that has enabled them to get a competitive advantage on other plants."

Dr Burrows' research was published in the January 2002 issue of the journal New Phytologist.

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