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Enthusiasts measure the 76m mountain ash named 'Ada', which towers above Toolangi State Forest, VIC. (Credit: Bill Hatcher)

Australia’s tallest trees

  • BY Alyce Taylor |
  • February 05, 2013

Only trees in North America and Borneo rival the size of our native eucalypts, some almost 100m tall.

EVERYONE SEEMS TO KNOW about the soaring redwoods of California and their record height, the tallest measuring 115.6m. Australia's iconic eucalypt giants, however, receive far less attention, although they are close rivals for California's botany crown.

In total there are only 22 tree species worldwide known to reach over 80m tall. These trees are native to only three areas of the world; the west coast of North America, Borneo and Australia. All the Australian species are from the Eucalyptus family.

Australia's mountain ash (Eucalyptus regnans) is the second tallest growing tree species in the world. The tallest specimen – nicknamed 'Centurion' – stands at 99.6m in Tasmania's Arve Valley. It is the world's tallest flowering plant and known hardwood tree.

The species grows extraordinarily quickly, reaching its maximum height in 200 years, a rate five times faster than the redwoods.

"The eucalypts do not live long enough to rival the redwoods in size. However, there may have been genetic 'freaks' that may have – and could in the future – reach over 100m tall," says Brett Mifsud, a specialist in finding and measuring tall trees.

Historic records show that in 1880 a felled mountain ash was recorded at 114.5m in Thorpdale, 137km south-east of Melbourne, making it the tallest tree in the world at the time.

Are Australia's tall trees endangered?

Although scientists are unsure how successful tall tree species were in Australia thousands of years ago, the high rate of land clearing and the unregulated nature of the early timber industry suggests that the number of tall trees has declined significantly since European settlement.

Federal government data states that since settlement, Australia has lost 22 per cent of its forest and woodlands.

"There are most definitely less over the last 200 years, and that's because most of the tallest ones have been cleared," says Dr Dean Nicolle, director of Currency Creek Arboretum in South Australia. "Areas of tall trees are now much smaller, which makes them more prone to being wind-thrown and burnt."

How to measure a tall tree

The most accurate way to measure a tree is still to climb it and drop a measuring tape, which can record height to within a 10cm range.

"Generally surveyors can narrow which are the tallest trees or species using broader scale methods like remote sensing or geometry," says Dean. "But to pin down the exact height of a tall tree, it needs to be climbed."

Laser rangefinders, similar to those used by golfers to track the distance of their swing, are a far easier and safer way of measuring height, within the nearest metre or two.

Light detection and ranging (LiDAR) systems mounted on planes or satellites are a more advanced version of this technology. LiDAR instruments send pulses of light to both the ground and the tree's crown. By measuring the difference in time it takes for these two pulses to bounce back, an accurate measurement of height can be calculated.

Traditionally, a tree's height was calculated by using a clinometer and working with the angle made between a trees's crown and the ground.

"You would have to assume that the tree's top was directly below the base and that never was the case," says Brett. "It is the case for an electricity pole, it is the case for an MCG light tower, but it not the case with Eucalypts."

Dean and Brett say many of the older, inaccurate records that were calculated with this method are still being officially used today.

Finding Australia's biggest trees

"People are so interested in trees and big trees just add an extra dimension to it," says Derek McIntosh, director of Australia's national register of big trees.

Since its establishment in 2009 the public archive has recorded 580 large tree specimens spread over nearly 300 species. The size of a tree is gauged using a more holistic measurement than just height. Everyone from backpackers to university academics have contributed to the registry's list.

"It's not meant to be a clinical thing, or give too much detail about trees; you don't want to frighten people away with too much jargon," explains Derek, a tree enthusiast since his teenage years.

"It has brought me so much fun and enjoyment but what is so exciting is that it brings everyone else so much enjoyment, as more and more people start looking and then adding to it." 

View or add to the national register of big trees 

This list was complied with the assistance of eucalypt expert Dean Nicolle.

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