Gum tree’s budding talents

Gum tree’s budding talents

4 December 2008

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Australia — Australian eucalypts have again shown how well adapted they are to dealing with bushfires, according to collaborative research from Charles Darwin University (CDU) and Charles Sturt University (CSU).

The researchers had previously found that eucalypts have special “buds” that are buried within the bark of their trunks for recovery after intense fire. The researchers have now found primordial buds buried in the leafy canopies capable of fast recovery after lower intensity fires.

Research fellow with CDU’s School for Environmental Research, Dr Lynda Prior said it was quite amazing how well adapted NT eucalypts were to both low and high-intensity bushfires.

“Our research has shown that while fires may kill off the leaves of the eucalypts, it won’t spread further and consume the branches,” Dr Prior said.

“It is a great advantage to be able to reform the canopy from the well-protected buds at the ends of small branches.”

Senior Lecturer in Plant Science at the School of Environmental and Life Sciences, Dr Sean Bellairs said there was amazing variation in the different members of the eucalypt family that were examined.

“In the Turkey Bush which dominates the gravel road verges along the highway, the buds were very simple, whereas the bud structures are incredibly complex in the eucalypts.” Dr Bellairs said.

“Preparing the delicate bud material takes considerable skill.  Fortunately CDU Masters graduate Ms Sankham Hornby was available to collect the delicate bud material and embed it in resin for the detailed microscopic analyses required.”

Adjunct Professor at CDU’s School for Environmental Research, Professor David Bowman said the results were important in understanding why Australia has such a flammable landscape.

“Eucalypts which are the superstructure of the forests figured out how to live with fire millions of years ago and we are still learning some of their tricks,” he said.

For the past three years Dr Prior and colleagues from CDU and CSU, who are investigating how Northern Territory trees re-sprout after fire, have looked at bud structures in the canopy and under the bark in the trunks of a range of Territory trees, including rainforest and savannah species. The 20 species they are studying include seven eucalypts as well as three close relatives.

Plant research scientist with CSU, Dr Geoff Burrows said the adaptation in eucalypt trees in the north Australian savannas was quite remarkable.

“While scientists had already studied leaf buds (also known as axillary buds) in eucalypts, they had only looked at young seedlings and only to understand why some species formed woody swellings, or lignotubers, in the soil,” he said.

Dr Burrows said that all plants have axillary or leaf buds where the leaf meets the stem. All gardeners depend on these buds. After lightly pruning a plant, it is this reserve of buds that grows and covers the plant with new shoots and leaves.

“Although they appear tough and rugged, eucalypts initially produce an incredibly delicate ‘naked’ bud at the base of each leaf. In most cases this bud just dies and falls to the ground after a couple of weeks,” he said.

“In a few cases the bud grows and forms a new branch.”

When a ”naked” bud falls the eucalypt appears to have lost its ability to re-sprout. However, research has found that eucalypts have a number of minute, back-up or accessory buds – a main one with even smaller ones at its base – buried beneath the surface of the smallest branches. These buds are then protected from being eaten or killed by the heat of a ground fire.

“Most plants have strong, well-formed axillary buds,” Dr Burrows said.

“Eucalypts are the only trees I know that let a very delicate bud go out first, see what the situation is, in most cases lets it drop off, but then has a reserve of accessory buds hidden and protected within the smallest branches and twigs.

“In the Northern Territory most bushfires are grass-fires, so the eucalypt canopy doesn’t burst into flames – if it did these buds would be roasted. However, you get heat scorch and the leaves shrivel up but the protected buds can often survive. With this unique set-up, eucalypts are able to successfully re-sprout in the canopy of the tree.”

The eucalypts’ closest relatives have typical axillary buds that are long-lived and found on the surface, again showing just how remarkably different and fire-adapted eucalypts are.

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