Snow Gums Sublime

Periodically I've dedicated a post here to my favourite trees - the latest was here, and you can track back from there if you so desire. The last three, including this one, have been dedicated to eucalypts and maybe it's time to diversify, but not today. 

As winds and cold rain batter the mountains above Canberra, most animal species are either moving to lower elevations (or lower latitudes), or going into one form or other of torpor. Many plants are also closing down, surviving winter as underground roots or tubers, or as seeds. Not the trees however - and at the highest altitudes this means just one species, the wonderful Snow Gum Eucalyptus pauciflora. (In Tasmania Snow Gum refers to other species, but today I'm just talking about the mainland.)

Snow Gums, Kosciuszko National Park.
Growing seasons up here are short and harsh, and the brutal conditions of their youth
inevitably show in their gnarled later years.

Up at the tree line in Kosciuszko (here at 1800-1900 metres) the Snow Gums are
more stunted and permanently wind-bent.

There are many wonderful things to say about Snow Gums, but one of the greatest mysteries is down to us - why the name? Pauciflora means 'sparsely flowering', and while I unfortunately can't show you here, the flowering can be quite profuse and regular. It was bestowed by the early 19th Century German botanist Kurt Sprengel, from material supplied by Czech-born collector Franz Sieber (his tragic life is worth exploring further another day). Presumably it was either atypically sparse in buds or flowers, or was damaged in transit; the type specimen would tell us, but I don't have access to that...

Snow Gums, as we'd expect, have some pretty nifty adaptations to short growing conditions, with snow on the ground for weeks or months of the year and frosts all year round.

Winter Snow Gum, Namadgi National Park.

One neat trick is to change its optimal temperature for photosynthesis as the season progresses, so that whatever temperature it is, is the best temperature for growing! (ie it photosynthesises better at lower temperatures earlier and later in summer, and higher in mid-summer.)

These old-timers at Charlotte Pass, high in Kosciuszko National Park, grow among
and sprawl over the granites. They probably have only a few weeks a year in which to grow.
These high altitude Snow Gums are sometimes given their own species, E. niphophila ('snow-loving'),
though most botanists recognise them only as a sub-species.

 

Further, at lower altitudes the optimal photosynthetic temperature is also higher. For Snow Gums at the tree line the preferred temperature is 18 degrees; at the same time the most efficient temperature for their colleagues at 900 metres is 28 degrees.

These lower altitude trees are associated with frost hollows; less cold-tolerant trees grow above them,  logically but counter-intuitively. The Canberra airport was built in a Snow Gum-encircled frost hollow, hence it is often closed in winter by heavy fogs, as any ecologist could have told them!

Low altitude Snow Gums north of Canberra (800-900 metres); at these altitudes
they form a distinct sub-category of the grassy woodlands, one of our most threatened habitats.
Where E. niphophila is recognised, these low-down Snow Gums remain E. pauciflora.

In the devastating fires of 2003, vast areas of mountain Snow Gum woodlands burnt. Numerous ancient trees were burnt to the ground, though there is vigorous resprouting from subterranean shoots.

Ten years later. Views through the regenerating Snow Gums, from the ridge line
of Namadgi National Park, above Canberra.

 

One characteristic of Snow Gums is the 'scribbled' bark, legacy of the larvae of a tiny moth, which chew along within the nutritious cambial layer; when it's time to pupate they drop into the litter at the base of the tree. Until recently they were know as Ogmograptis scribula (the 'wavy-writing scribe') from the highest Snow Gums to the sea, and west into the slopes country. Then a wonderful collaboration between a Canberra school girl and some retired scientists - botanists and entomologists - revealed the existence of at least a dozen related scribbly moth species. The story, told in detail here, is well worth your while reading.

One of the many fascinating things about this little caterpillar is the
fact that it nearly always turns around and tunnels back parallel to its existing track.
Perhaps it is taking advantage of the tree's response, growing new tissue to
replace the damaged material - like a burglar returning after the insurance company has replaced his loot!

As we start to put our warming strategies into action down here in wet cold Canberra, high above us the Snow Gums endure, as they always have and always will long after I'm forgotten.

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