Tasmanian Plants

Eucalyptus viminalis (White Knight)

It is common knowledge that the Mountain Ash (Eucalyptus regnans) is the worlds tallest flowering tree and that Tasmania has some of Australia’s tallest old growth forests. So magnificent are the Mountain Ashes that significant individuals  have earned appellations such as ‘Centurion’ and ‘Methuselah’. Alas, the legend of the Mountain Ashes have overshadowed the other giants that reside in Tasmania. There are other giants among the eucalypts that are worthy of more general recognition, and it may come as a surprise to some that the White Gum (Eucalyptus viminalis) is one of them.

Practically every plant enthusiast in Tasmania and many tourists who visit the state has seen the grand Mountain Ashes of the Styx or the Tarkine. Few however, even among Tasmanian botanists, have met or are even aware of the giant White Gums of Tasmania’s Northeast. This is because White Gums are often thought of as average sized trees  associated with dry forest. Yet, in the Evercreech Forest Reserve just 10km from Fingal, a forest of giantic white gums, locally called White Knights, preside over the wet forests. For centuries they have watched, like silent sentinels from their statuesque vantage point, the changing landscape of Tasmania’s Northeast. The time is nigh for the White Knights to take their rightful place in the annals of Tasmania’s rich botanical heritage, for nowhere else in the world does one encounter white colossuses such as these.

Another magnificent White Gum in stark contrast to the verdant wet forest understorey

In the 1970s a forester named Des Howe was carrying out a routine survey in the forest about to be fell when he noticed that one of the trees that was to be felled was very tall. A surveyor came in and measured the tree to be an incredible 91m. A more accurate measurement of 89m was later given in the gianttrees website. Girth-wise, the White Knight is just as impressive, being 3.3m in diameter. The White Knight is also believed to be over 300 years old. Due to the presence of the White Knight, 52 hectares in the area was made a forest reserve to preserve the White Knight and other giant White Gums that reside there.

The story goes that botanists initially did not believe that the tall tree reported by the Forestry Commission was a White Gum until leaf and fruit specimens were brought before them. Likewise for me, my experience of the white gum being a average size tree of dry forest was so ingrained that I would have scarcely believed that the White Knights were White Gums until I saw the characteristic seed capsules myself.

It is not difficult to see how the first foresters who came before the presence of the giant white gums likened the trees to Knights, perhaps spotting shiny-clad armour. White has always been the colour of purity and goodness, and there is nothing quite like the sight of Brobdingnagian white boles standing in blazing contrast to a deep green forest understorey. And I am properly awed and impressed, just as the visitors before me that have come to pay their obeisance to the White Knights.

The elephantine girth of the White Knight

A rather recent trend in molecular science has been to use the technique to extort genes to reveal the history of how a plant has extended it’s geographical distribution throughout time.

I have written about how researcher James Worth used molecular techniques to pinpoint the locations (refugia) where Myrtle Beeches (Nothofagus cunninghamii) survived during the last glacial period. Just earlier this year, researchers Paul Nevill, Gerd Bossinger and Peter Ades published a paper in the Journal of Biogeography doing the same for the Mountain Ash (Eucalyptus regnans).

As in James Worth’s Myrtle Beech study, the researchers looked for variations at specific locations in the chloroplast DNA in Mountain Ash individuals distributed throughout the species natural geographical range. Different individuals may exhibit specific sequences which may differ from region to region and these are known as haplotypes.

A large amount of haplotypes found in a population an any given area would suggest that the area is a glacial refugium as we would expect a species to have persisted for longer periods of time in a refugium, thereby accumulating genetic changes. Conversely, places with low diversity of haplotypes could be construed to have been colonized after the glacial period ended, as there wouldn’t have been time enough for a high diversity of haplotypes to develop.

The results of the study showed that Mountain Ashes of the Northeast and Southeast of Tasmania has a high diversity of haplotypes, many of which were unique to the region. This suggests that the Northeast and Southeast of Tasmania harbored refugia that sheltered Mountain Ashes during the glacial period. By contrast, the central parts of Tasmania had a lower diversity of haplotypes. Another way of interpreting this was that there was fixing of haplotypes in that region, suggestive of a more recent colonization of the area following the end of the glacial period.

One consideration that remains to be addressed is the ease with which Eucalypts hybridize. E. regnans for example may hybridize with E. oliqua (Stringybark) and E. delegatensis (Gum-topped Stringybark). Hybridization may result in chloroplast sharing between species and a more comprehensive study will probably be needed to ensure that all these factors are taken into consideration.

For now it seems we are getting closer toward reading the the silent tale of survival that the ancestors of the Mountain Ashes in the Northeast and Southeast have etched in the genes of their descendants.

A single field trip up toward the Central Highlands offers plenty for a plant lover to see and do. One thing that must be done however, is to pay homage to the cider gums (Eucalyptus gunnii) of the highland areas.

This cider gum is a tree of immense significance to Tasmania’s natural history. It is aptly named the cider gum for it’s sap, which has been reported to be used by the aborigines to make a much relished fermented drink (see article). I  was way too late to experience the spring sap that allegedly drips from the tree inviting all to partake of it’s sweetness. What would I give to try that out! It would be one of the most direct means of communion with the cider gum. On this occasion however, my objective was merely to make an acquaintance with the Cider Gum in it’s natural abode.

I drove along the Highland Lakes road north of Miena hoping to catch sight of some cider gums. There are two known subspecies, both of which are endemic to Tasmania. The more common one, E. gunnii subsp. gunnii (simply referred to as the cider gum) is well distributed throughout the highland regions of the southeast, central, and western Tasmania. The other subspecies, E. gunnii subsp. divaricata is known as the Miena Cider Gum, and has a much more restricted distribution to a small area around Miena around the Central Highland lakes. It’s status as a subspecies of the commoner cider gum was only recently elucidated in a publication by Prof. Brad Potts, Dr Wendy Potts and Dr Gintaras Kantvilas in 2001. Previously, the Miena Cider Gum was known as Eucalyptus divaricata.

I practically screeched to a halt when I sighted just by the side of the road, two large and stately trees which I suspected might be the Miena Cider Gum.

I got out and scanned the surrounds. There were quite a number of dead trees in the vicinity but these two trees were different. They exuded a vibe of vitality. I studied them intently, looking out for characters that might give me an opportunity for identification.

A low hanging branch gave me access to photograph a cluster of their leaves and their capsules. The adult leaves also had a slightly pale whitish (glaucous) appearance and there was the persistence of very glaucous, rounded and oppositely arranged juvenile leaves.

Prof Pott’s paper had mentioned that the capsules of the Miena Cider Gum also tend to be more glaucous. The capsules are supposedly a slightly more sub-urned shaped compared to the more consistently bell shaped capsules of the commoner subspecies.

The combination of characters of the Miena Cider Gum seemed to match the specimen I was looking and I am happy to conclude that that was what my specimen was.

More important than the dry an technical act of nailing an subspecific identity to the tree however, was the feeling of communion. Few experiences compare to an acquaintance with trees of such haunting magnificence and presence. There is no words for it, only feelings that linger. Silence would probably make the best conveyance of this.