Today we have a post on Australian trees, the eucalypts, contributed by Reader Rodney Graetz. This is part 1 of a two-part series. Rodney’s captions are indented, and you can enlarge the photos by clicking on them.
The Trees that identify Australia
Australia is one of many countries that include plants as part of their identity. The national floral emblem is the Golden Wattle (Acacia pycnantha), one of more than 1000 Acacia species found on the continent. The two colours of the plant represent the essence of the continent. The golden flowers represent its beaches, mineral wealth, grain, and wool harvests. The green of the (leathery) leaves imitates the continent’s forests and productive landscapes.
Internationally, when Australian sporting teams compete, here Cricket, their uniforms are always in the national floral emblem colours: the Green and the Gold.
What trees identify Australia by being visually dominant in the country’s diverse landscapes? Only one tree group emphatically says Australia, and that is the Eucalypts, aka ‘Gum Trees’. Though diverse in size, form, and colouring, this is a typical specimen. They are all substantial evergreen hardwood trees, with tough, leathery, long-lived leaves, and the annually renewed bark can be rough or smooth, and multi-coloured. Though widely called ‘Gum Trees’, only a few species produce a solidifying liquid ‘gum’ from surface wounds. In contrast, all Eucalypt leaves contain aromatic ‘oils’ which render them highly flammable and fragrant, when green, and especially so, when dried.
From an estimated 900+ species total, a small sample of the variation in appearance of the adult trees is this collage of the bark of just eleven different Eucalypts.
Initially named as just one genus, Eucalyptus, it now includes Corymbia and Angophora. Together they are still called ‘Eucalypts’, because of their common flower structure with sepals and petals fused to a cap (calyptra) and the showy insect-attracting role played by numerous stamens. There is significant species variation in flower size and colour.’
In a 55 million-year evolutionary history, Eucalypts have evolved characteristics to repel leaf-eating animals. Rapidly evolving insects remain the most successful, while vertebrate folivores are largely excluded by sclerophylly, the leaves are woody, and by the production of toxic chemicals. The only vertebrate dependent on Eucalypt leaves is the marsupial Koala (Phascolarctos cinereus), which spends far more time (10-15 hours) digesting than harvesting leaves.
Australia is justifiably called “A Burning Continent”, with Africa being called “The Burning Continent”. Eucalypts are a noticeable component of all Australian landscapes, with the exception of the sandplain deserts, and the (>2000m) high country. Wherever Eucalypts are found, wildfire is possible, only the frequency varies. The two principal adaptations of Eucalypts to frequent fire are increased bark thickness, and the capacity to produce new (epicormic) shoots anywhere along a burnt stem or branch.
Tall forests, such as this, occur only in the two wettest, temperate regions of the continent, where one species (Eucalyptus regnans) has been recorded as the Earth’s tallest flowering plant at 100 metres (330 feet). The species here is Karri (Eucalyptus diversicolor).
The sub-tropical, Eucalypt-dominated, savannas are always impressive in the early dawn light with the blackened record of their frequent (1-3 years) fires is visible in their bark.
Growing at the low temperature limit of Eucalypts, the Snow Gums (Eucalyptus pauciflora), are more shaped by the blizzard winds than by the brief snowfalls.
Part 2 to come.
Many thanks for this. For anyone used to European and North American forests, one of the most impressively beautiful things in Australia is the variety of the Eucalyptus trees, especially the bark.
Thanks for the great photos! I live in the Pacific NW of the U.S., and it’s fascinating to see how different the flora and fauna are in other parts of the world.
..lThere is a very interesting Australian novel called Eucalyptus, which involves the capacity to identify the numerous rare eucalyptus trees grown by one of the characters. The variety of eucalyptus trees is central to the plot. It’s quite a unique novel, and one could do well to look at the wonderful photos we have been given, before beginning the novel.
That is a unique novel, for sure. I picked it up solely due to my love of eucalypts, having no idea what I was getting into. I found it odly charming.
Today’s series is beautiful. Look forward to the next one.
Nice post, thanks!
Beautiful pictures—and exotic to those of us who live among the fauna and flora of North America. Australia separated from Gondwanaland some 100 million years ago (depending on what counts as separation). That’s a long time to evolve a unique and fascinating biota.
Some lovely pictures, and an informative narration as well. Many thanks!
I am ashamed to say that the first couple of pictures reminded me of the little rhyme in Monty Python:
“This here’s the wattle,
Symbol of our land.
You can stick it in a bottle;
You can hold it in your hand”.
Sorry!
I grew up in Northern California, and the coast always had many Eucalyptus. Their smell reminds me of my youth and the ocean. They planted them many years ago for wind breaks, since they are so fast growing . I don’t know the specific species, but they don’t live very long (100-200 years?) and now many are falling hazards.
Anyway, thanks for this fascinating post. The photos are very beautiful.