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I've been a Canberran since moving here from Adelaide on the first day of 1980. I now live in suburban Duffy with my partner Louise Maher, ABC 666 radio and on-line journalist. Among my early memories is following Sleepy Lizards (Shinglebacks) around the paddocks north of Adelaide, guarded by the faithful bull terrier. I have always been passionate about the natural world, trying to understand how it works, how the nature of Australia came to be, and sharing those understandings. My especial passions are birds, orchids and mammals. For much of my life I have been a full-time naturalist, running bush tours, writing books etc, doing consultancies, presenting a regular radio slot on local ABC, chairing a government environment advisory committee and running adult education classes. Recently I have eased back somewhat, but am still writing, teaching, doing some radio work and running overseas tours - as part of my fascination with our Gondwanan origins I've been running tours to South America for the past decade. I was awarded the Australian Plants Society Award in 2001 and the Australian Natural History Medallion in 2006, both for services to education and conservation.

Monday, 21 January 2013

Bark Codes; or Barking Up the Right Tree

The oozing of sap from the trunk is not the first - or probably 10th - thing I'd think of when asked to characterise eucalypts, but early Europeans certainly did. Abel Tasman back in 1642 in van Diemen's Land (later to be renamed Tasmania for him) was intrigued by it, and collected samples. This may have been a hint as to the nature of their interest; he probably had hopes of economic applications. Forty-six years later the English pirate-naturalist William Dampier reported that "the Gum distils out of the knots or cracks that are in the bodies of  the trees". Governor Arthur Phillip, who commanded the first British colony on what is now Sydney Harbour, first used the term 'gum-tree' in 1770; he too collected this gum, and send samples back home.

Now, most people probably use Phillip's term for all eucalypts (ie in excess of 700 of them) but in an attempt to make such a huge number of species manageable, and in part because such characteristics do largely reflect relationships within the genus, we divide eucalypts up according to their bark characteristics and use descriptive terms to reflect it. In this classification 'gums' are actually smooth-barked eucalypts.
Salmon Gums E. salubris, Wilmington South Australia.
These were planted in a town park, but the species is native to inland southern Western Australia.
All eucalypts shed their bark - the question as to why they do does not have a generally agreed answer, but perhaps it makes life harder for bark-burrowing insects. However, gums shed it all at once, leaving a clear smooth surface. At least, that's the theory, but nature being nature the rule is immediately broken. For instance in many gums patches of bark remain on the tree, giving darker or differently-coloured patches.
Spotted Gum E. maculata, Nowra, New South Wales. (Above and below.)

Yet other gums retain the shed bark, still attached to the branches.
E. sheatheana, Wongan Hills, Western Australia.
Most eucalypts however retain their dead bark, which comes off in bits over time, giving a rough surface to trunk and often branches too. We classify these rough-barks too according to the surface type. Boxes - nothing to do with containers, but named for the European Buxus, which also produces hard wood used for instance in making mallet heads - have bark which tends to be in plates or narrow blocks. 
Coastal Grey Box E. boistoana, near Candelo, southern New South Wales.

Apple Box E. bridgesiana, Canberra.
Peppermints have short-fibred, crumbly bark; they also have chemicals called pipiterones in the foliage which have a strong peppermint aroma and have been used to make menthol. Eucalypt - including peppermint - oil extraction has been a major industry in Australia; in South Africa it still is!
Narrow-leaved Peppermint E. radiata, Brindabellas near Canberra.
By contrast, some eucalypts have very long-fibred bark, which when dead can be pulled off in long strips.
Red Stringybark E. macrorhyncha, Canberra.
The bark can also be cut away in sheets and was used for shelters by both indigenous and early
European Australians.
Ironbarks can look superficially similar, but the bark is deeply fissured, generally impregnated with tannin-bearing kino, beads of which can be seen in the bark, and which help to make the bark literally iron-hard; you can easily bounce an axe off it.
Grey Ironbark E. paniculata, Narooma, New South Wales.
Bloodwoods have tessellated bark, often quite soft, which 'bleed' non-viscous kino from damage to the trunk. Some mammals, especially Sugar Gliders Petaurus brevipes, exploit this by chewing the bark and harvesting the flow.
Red Bloodwood E. gummifera, south coast New South Wales.
Below, 'bleeding'.

As I suggested above, it's never straight-forward; members of the ash group (again named for the resemblance of the timber, this time to Northern Hemisphere Fraxinus) have a rough stocking on the lower trunk, but bare upper limbs.
Alpine Ash, E. delegatensis, Namadgi National Park, near Canberra.
Such classifications are ultimately just human constructs but when dealing with so many species, any help is worth trying! Anyway, any excuse for talking about the wonderful eucalypts is worth seizing on.

BACK THURSDAY


8 comments:

Susan said...

Our recent trip to Australia reinforced for me how much I love Eucalypts.

There is a European tree that sloughs its bark much like Eucalypts do, and is very popular because of it. London Plane Plantanus x acerifolia is a naturally occuring hybrid that appeared spontaneously in Spanish gardens in the late 17thC when American Sycamore P. occidentalis was introduced and met the Eurasian species P.orientalis. It became highly valued as a tree in urban situations once the industrial revolution kicked in, as pollution doesn't stick to it.

I've just been reading various reports about the fire in the Warrumbungles -- gloom...

Ian Fraser said...

Gloom about the Warrumbungles indeed. It will be some years, from the sound of it, before at least the vegetation cycles around again to what we know and love. Needless to say, the fabulous volcanic landscape is oblivious to such fleeting episodes.

Plane Trees, hmm. A sore point. In my previous abode (where I abided for 27 years) the nature strip trees were thus. I would have perjured myself for eucs; round the corner were Chinese Elms, which left me unmoved, but at least provided compostable leaves! The planes' were non-biodegradable. A layer in the compost was still there two years later. They also drop fruit with fuzzy material which sparked my latent asthma when I mowed. They blew into and smothered my garden so I had to bag and take them to the recycling depot (maybe they had industrial-scale processes!); one year I weighed 120kg of them.

Sorry Susan, not your fault! Just touched a nerve. And I'm glad to hear of your love of eucs.

Susan said...

The fuzzy stuff is ghastly. My office in London overlooked St James's Park and going out at lunchtime at certain times of the year was almost insupportable on a windy day because of the plane trees along Birdcage Walk.

Flabmeister said...

Not only does the gum not make my top 10 attributes of Eucalypts, but most of the gummy things I see in the bush are emanating from Acacias. Of course, this could be a comment on my plant ID skills!

WRT to the leaves of plane trees, and how to deal with them should it be necessary in future, I suggest breaking them up into small bits before putting them in the compost. I usually do this for things like tomato vines and corn stalks by piling them up and parking a running lawn mower on top. Adding some horse poop (my memory is that there is plenty of that available near St James Park, if not Duffy) with them also helps break them down.

Martin

Rebecca Gee said...

Thanks Ian, this is a wonderful explanation of the different gums. I'll definitely be using this as a reference point in the future

Ian Fraser said...

Hi Rebecca; good to hear from you, and I'm delighted it was of use to you. Hope all's well.

Anne said...

Hi there Ian, I actually am wondering if you could recommend to me a store that sells landscape bark mulches?

Ian Fraser said...

Hi Anne. I'm not sure which Anne I'm talking to, and I don't really want to do commercial recommendations here, so can you send me an email? I can certainly recommend if you're in Canberra.