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Eucalyptus regnans, known variously by the common names giant ash, mountain ash, Victorian ash, swamp gum, Tasmanian oak or stringy gum, is a species of Eucalyptus native to southeastern Australia, in Tasmania and Victoria. Historically, it has been known to attain heights over 114 metres (374 ft), making it one of the tallest tree species in the world and the tallest flowering plant.
An evergreen tree, Eucalyptus regnans is the tallest of the eucalypts, growing to 70–114.4 m (230–375 feet), with a straight, grey trunk, smooth-barked except for the rough basal 5–15 metres (16–49 ft). The leaves are falcate (sickle-shaped) to lanceolate, 9–14 centimetres (3.5–5.5 in) long and 1.5–2.5 centimetres (0.6–1.0 in) broad, with a long acuminate apex and smooth margin, green to grey-green with a reddish petiole. The flowers are produced in clusters of 9–15 together, each flower about 1 centimetre (0.4 in) diameter with a ring of numerous white stamens. The fruit is a capsule 5–9 millimetres (0.20–0.35 in) long and 4–7 millimetres (0.16–0.28 in) broad.
It occurs in cool, deep soiled, mostly mountainous areas to 1,000 metres (3,300 ft) altitude with high rainfall of over 1,200 millimetres (47 in) per year. They grow very quickly, at more than a metre a year, and can reach 65 metres (213 ft) in 50 years, with an average life-span of 400 years. The fallen logs continue supporting a rich variety of life for centuries more on the forest floor.
Unusually for a eucalyptus, it tends not to recover by re-shooting after fire, and regenerates only from seed. The seeds are released from their woody capsules (gumnuts) by heat and for successful germination the seedlings require a high level of light, much more than reaches the forest floor when there is a mature tree canopy. Severe fires can kill all the trees in a forest, prompting a massive release of seed to take advantage of the nutrients in the ash bed. Seedling densities of up to 2.5 million per hectare have been recorded after a major fire. Competition and natural thinning eventually reduces the mature tree density to about 30 to 40 individuals per hectare. Because it takes roughly 20 years for seedlings to reach sexual maturity, repeated fires in the same area can cause local extinctions. If, however, no fires regenerate an area, the trees die off after about 400 years and are replaced by other species.
Eucalyptus regnans is the tallest of all flowering plants, and possibly the tallest of all plants, although no living specimens can make that claim. The tallest measured living specimen, named Centurion, stands 100 metres (327 ft.) tall in Tasmania. Before the discovery of Centurion, the tallest known specimen was Icarus Dream, which was rediscovered in Tasmania in January, 2005 and is 97 metres (318 ft) high. It was first measured by surveyors at 98.8 metres (324 ft) in 1962 but the documentation had been lost. A total of 16 living trees in Tasmania have been reliably measured in excess of 90 metres (300 ft).
Historically, the tallest individual is claimed to be the Ferguson Tree, at 132.6 metres (435 ft), found in the Watts River region of Victoria in 1871 or 1872. This record is often disputed as unreliable, despite first-hand documentary evidence of it being measured on the ground with surveyor's tape by a senior forestry official (see below). Widespread agreement exists, however, that an exceptionally tall individual was reliably measured at 112.8 metres (370 ft) by theodolite in 1880 by a surveyor, George Cornthwaite, at Thorpdale, Victoria (the tree is known both as the Cornthwaite or Thorpdale Tree). When it was felled in 1881, Cornthwaite remeasured it on the ground by chain at 114.3 metres (375 ft). The stump was commemorated with a plaque that exists today. That tree was about 1 metre shorter than the world's current tallest living tree, a coast redwood, 115.55 metres (379.1 ft).
The tallest specimens of this and many other species encountered by early European settlers are now dead as a result of bushfires, logging and advanced age. Few living specimens exceed 90 metres (300 ft); old records of logged trees make varied claims of extreme heights, but these are difficult to verify today.
Most of those claims come from Victoria. Al Carder, notes that in 1888 a cash reward of 100 pounds was offered there for the discovery of any tree measuring more than 122 metres (400 ft). The fact that such a considerable reward was never claimed is taken as evidence that such large trees did not exist. Carder's historical research, however, revealed that the reward was offered under conditions that made it highly unlikely to be collected. First, it was made in the depths of winter and applied only for a very short time. Next, the tree had to be measured by an accredited surveyor. Since loggers had already taken the largest trees from the most accessible Victorian forests, finding very tall trees then would have demanded an arduous trek into remote wilderness and at considerable altitude. In turn, that meant that searchers also needed the services of experienced bushmen to be able to guide them and conduct an effective search. Only one expedition actually penetrated one of the strongholds of E. regnans at Mount Baw Baw but its search was rendered ineffectual by cold and snow and managed to measure only a single living tree — the New Turkey Tree: 99.4 metres (326 ft) — before appalling conditions forced a retreat, Carder notes.
In 1911, a previously unknown report was discovered: it was written by a licensed surveyor, G.W. Robinson, who had kept his personal forestry records from six decades earlier during the 1850s in the Dandenong Ranges, near Melbourne. Robinson had arranged with loggers to notify him when they found a very tall tree, and noted that every one he measured exceeded 91 metres (299 ft), the tallest being 104 metres (341 ft). Robinson noted that the tallest trees were felled first and had no doubt that "some of the trees felled earlier would have measured quite some 400 ft".
Victoria's early State botanist, Ferdinand von Mueller, claimed to have personally measured one tree near the headwaters of the Yarra River at 122 metres (400 ft). A government surveyor, David Boyle, claimed in 1862 to have measured a fallen tree in a deep gully in the Dandenongs at 119.5 metres (392 ft), and with a diameter at its broken tip that indicated it might have lost another eight metres of trunk when it broke, for 128 metres (420 ft).
Von Mueller's early records also mention two trees on the nearby Black Spur Range, one alive and measuring 128 metres (420 ft) and another fallen tree said to measure 146 metres (479 ft), but these were either based on hearsay or uncertain reliability. David Boyle also reported that a tree at Cape Otway measured 160 metres (520 ft), but this too was based on hearsay.
Many prominent botanists and tree enthusiasts have long been sceptical of such claims because they lacked first-hand evidence from a credible source. But Carder notes that nor can all the claims be considered imaginary: "The frequency, the persistence, and the wide occurrence of the reports leads to the belief that there was some basis of fact for the statements made."
None, however, had been verified by direct documentation until 1982 when Ken Simpendorfer, a Special Projects Officer for the Forests Commission, Victoria, directed a search of official Victorian archives. It unearthed a forgotten report from more than a century earlier, one that had not been referred to in other accounts of the species up to that time. It was written on 21 February 1872, by the Inspector of State Forests, William Ferguson, and was addressed to the Assistant Commissioner of Lands and Surveys, Clement Hodgkinson. Ferguson had been instructed to explore and inspect the watershed of the Watts River and reported trees in great number and exceptional size in areas where loggers had not yet reached. He wrote: "In one instance I measured with a tape line one huge specimen that lay prostrate across a tributary of the Watts, and found it to be 435 ft [133 metres] from its root to the top of its trunk. At 5 feet from the ground it measures 18 feet in diameter, and at the extreme end where it has broken in its fall, it is 3 feet in diameter. This tree has been much burnt by fire, and I fully believe that before it fell it must have been more than 500 ft [150 metres] high. As it now lies, it forms a complete bridge across a deep ravine."
It is also possible that individual trees will again attain such heights. Author Bob Beale has recorded that the tallest trees in the Black Spur Range now measure about 85 metres (279 ft) but — due to major bushfires in the 1920s and 30s — are less than 80 years old and have been growing consistently at the rate of about one metre a year.
In New Zealand
A Eucalyptus regnans stand in the Orokonui Ecosanctuary near Dunedin, New Zealand (where E. regnans is an introduced species) contains that country's tallest measured tree, standing 80.5 metres high in 2012.
Eucalyptus regnans is valued for its timber, and has been harvested in very large quantities. Primary uses are sawlogging and woodchipping. It was a major source of newsprint in the 20th century. Much of the present woodchip harvest is exported to Japan. While the area of natural stands with large old trees is rapidly decreasing, substantial areas of regrowth exist and it is increasingly grown in plantations, the long, straight, fast growing trunks being much more commercially valuable than the old growth timber.
It is a medium weight timber (about 680 kg/m³) and rather coarse (stringy) in texture. Gum veins are common. The wood is easy to work and the grain is straight with long, clear sections without knots. The wood works reasonably well for steam-bending. Primary uses for sawn wood are furniture, flooring (where its very pale blonde colour is highly prized), panelling, veneer, plywood, window frames, general construction. The wood has sometimes been used for wood wool and cooperage. However, the wood needs steam reconditioning for high value applications, due to a tendency to collapse on drying. This wood is highly regarded by builders, furniture makers and architects.
Great controversy surrounds the logging of old-growth Eucalyptus regnans in its natural range in both Victoria and Tasmania. Aside from its symbolic significance as the largest eucalypt of all, Eucalyptus regnans has value to conservationists in providing essential habitat to important birds and mammals (notably the wedge tailed eagle, the lyrebird and the endangered Victorian state animal emblem Leadbeater's possum). In a land of vast, arid plains and desert, the contrasting lush fertility of mountain-ash forest is particularly dear to nature lovers.
Although its status as a species is secure, old-growth forests of Eucalyptus regnans are particularly susceptible to destruction by forestry. For this reason stands of very old and very tall trees exist only in pockets. Very few such stands of trees fall within those areas that have been listed as National Park or World Heritage environments. Most lie within areas controlled by state forestry management authorities and their heritage value is balanced against the commercial value of harvesting and then planting fast-growing and more productive monoculture timber crops on these comparatively well-watered and fertile areas.
Political opposition to the logging of forests by the process known as clearfelling has grown very strong in recent years (particularly in the case of woodchipping), and the extent of future harvesting remains uncertain.
It has long been believed that while many species of eucalyptus successfully survived severe bushfires, forests of Eucalyptus regnans are highly susceptible to destruction by fire. While the process of recovery of most eucalyptus forests is rapid, so that trees that are devoid of leaves may be fully foliaged within two years, in the case of Eucalyptus regnans, the recovery of a forest after a severe fire might require the total regrowth from seed of the devastated area, taking perhaps 200 years or more.
It has been suggested that fire is necessary for the germination of Eucalyptus regnans, and that young Eucalyptus regnans trees flourish best where there is open space, allowing sunlight to penetrate. Prior to European intervention, indigenous land management practices involved controlled burning in order to maintain grassland. This resulted in cleared areas in forests, around the peripheries of which young trees could germinate and grow. It is probable that these indigenous practices were used within forests of Eucalyptus regnans. Cleared spaces also occur naturally in tall forests when an old tree falls, or dies and loses its foliage. These very tall trees do not survive independently of each other, as single trees are more subject to lightning strikes and wind damage.
The natural habitat of the Eucalyptus regnans is in general the areas of Australia with the highest and most reliable precipitation. These areas are less prone to catastrophic fires than other forested areas. Research has indicated that a stand of mountain ash in Victoria is actually a multi-age stand due to fire, having experienced seven fires since the 15th century, whereas, since European settlement, many of Australia's eucalyptus forests have suffered severe fires as often as every 20 years.
Studies conducted in the 20th by T. M. Cunningham and David H. Ashton suggest that the re-growth habit of Eucalyptus regnans requires open space, and an ash layer. For this reason clearfelling (as opposed to selective logging methods) are justified by the timber industry by claiming it is required for the successful germination and growth of seedlings, despite such intense burns not occurring naturally and the cleared land requiring reseeding from seed collected elsewhere. The clearfell process can lead to spectacular and uniform regrowth of commercially viable timber, if managed properly. Those who support clearfelling see it as an ideal method of land management but critics point to the impact of such activities on stream health, water yield of catchments, impacts on threatened forest fauna and flora, long term soil healthy and viability, and the loss of all biodiversity to the harvested area.
In addition to this, opponents of clearfelling point out that the forests survived for centuries without clearfelling and that it takes perhaps 300 years to replace a giant tree, commercially valuable only as woodchip, and therefore designated as "waste" by the harvesters. Opponents of clearfelling point out that the clearfell process was unavailable until the arrival of European settlers (indigenous people practised a mosaic burn system that kept the forest open but didn't remove large amounts of timber).
Half of Victoria's forested water catchment areas, which provides water requiring little treatment, are composed of E. regnans forest. Yields from these catchments fall significantly for 20 to 40 years after disturbance. These areas have an increased risk of bushfire due to smaller trees being more flammable, the risk increasing further with climate change.
Impact on the environment
ABC News reported on 17 June 2009 that a study has been carried out by environmental scientist Professor Brendan Mackey of the Australian National University which identified that mountain ash forests in Victoria’s Central Highlands as the best in the world at locking up carbon.
Mackey and colleagues found the highest amount of carbon was contained in a forest located in Victoria’s Central Highlands, which held 1900 tonnes of carbon per hectare.
This most “carbon-dense” forest was a stand of unlogged mountain ash over 100 years old. Mountain ash live for at least 350 years, according to Mackey.
- Eucalyptus delegatensis
- Eucalyptus globulus
- Manna gum
- For other trees named mountain ash, see Mountain ash
- List of superlative trees
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