Trees can tell us so much about life, yet many species are gradually disappearing from our landscapes before we even know their full story. Take for example the humble Scribbly Gum.
WORDS AND IMAGES | GAIL BRUCE
Iconic Australian gums like Scribbly Gums, unfortunately labelled ‘widow makers’ for their propensity to drop large limbs, are often the first to be removed from development sites. With their smooth white/cream trunks and distinctive markings, Scribblies form a defining part of our Australian identity with the bush. Those strange zigzagging patterns often noticed on them were first illustrated in 1918 by author May Gibbs in her much loved classic Snugglepot and Cuddlepie. Great Australian poet Judith Wright wrote about the mysterious
“Scribbly Gums naturally grow in an open forest with an understorey of native grasses and wildflowers.”
scribbles underneath the splitting bark in her 1955 poem“Scribbly-Gum”. But it was only in recent years that the biology behind the tree’s complex scribbles was further unravelled. A group of retired scientists contributed to an in-depth CSIRO study of Scribbly Gum Moths (Ogmograptis species) (Horan et al. 2012). It was determined that Ogmograptis is linked to the Australian Tritymba genus belonging to the Bucculatricidae family, and eleven new species of the moth were found and described. The study demonstrates some of the difficulties involved in classifying insects with shared Gondwanan ancestry.
“I would like to see more arborists encouraging tree owners to manage trees long term instead of removing them at will.”
Only a small group of smooth-barked eucalypts (mostly in Queensland and New South Wales) attracts Scribbly Gum Moths including E. haemastoma, E. racemosa, E. rossii or/and E. sclerophylla. Several other eucalypt species not considered to be “Scribbly Gums” can also have scribbles on their upper branches eg Blackbutt (E. pilularis), Sydney Blue Gum (E. salignus) and Snow Gum (E. pauciflora).
orest with an understorey of native grasses and wildflowers. These forests would have been traditionally burnt every decade but modern fire management practices require more frequent burning of remnant bushland. Such controls threaten the longterm survival of the habitat and the species that have come to rely on them. More pressing than fire management is the ongoing removal of large and veteran trees from the ever increasing urban landscape. The few that do survive the onslaught of development or infilling will suffer from accumulated effects as many local government arborists can attest. Redland City Council arborist, Ken Folkes, believes the trend to fill blocks with the house envelope, leaving little room for yard and garden, has contributed to the loss of natural environments. He said people are adapting to living indoors for the most part and many now rely on public parks for their weekend “green fix”.
“My experience is that people have basically turned from being risk tolerant to risk averse. This perception and fear of big trees only exacerbates the demise of large trees surviving in urban areas. It is not uncommon for the new owner to deem a remaining tree to be dangerous and request its removal. These trees can be pruned and I would like to see more arborists encouraging tree owners to manage trees long term instead of removing them at will.
“It is the loss and fragmentation of veteran eucalypts like Scribblies that worries me the most. I would like to be able to save as many as possible on development sites and larger properties. Some of these trees can be well over 200 years old and extremely valuable in terms of habitat and species preservation.
“We have to remember, these trees have been here before the white man and have adapted to climatic changes and the microchanges to their environment caused by extensive logging in the past and alteration of natural overland water flow. The value of seed from veteran trees is priceless – once they’re gone, they’re gone.”
Ken is particularly passionate about protecting Scribbly Gums due to the presence of crucial hollow bearing limbs, which many arboreal creatures are so desperately in need of. “These trees are being trashed at a phenomenal rate and cannot be replaced simply by hanging wooden boxes. I am a strong advocate for education by way of assisting the public to better understand the importance of preserving giant remnant eucalypts.
One of the veteran trees Ken’s team managed to have retained is a 200 yearold eucalypt with extensive large diameter hollows – homes to cockatoo, galah, parakeet, goanna, possum, and many other arboreal critters that all rely on the shelter and subsequent food chain this tree provides. A sign at its base enlightens the public as to why the now dead tree is being preserved.
Horak, M., Day, M.F., Barlow, C., B, Edwards, E.D., Su, Y.N., and Cameron S.L. (2012). Systematics and biology of the iconic Australian scribbly gum moths Ogmograptis Meyrick (Lepidoptera: Bucculatricidae) and their unique insect–plant interaction Invertebrate Systematics Vol:26, 357-398. Horak, M. (2012) Unravelling the mystery of eucalypt scribbles https:// theconversation.com/unravelling-themystery-of-eucalypt-scribbles-11023, retrieved 12 November 2017.
Biology Behind The Scribbles
According to Dr Marianne Horak (2012), this is how it all happens: in late autumn, the tiny grey Scribbly Gum Moth lays its eggs on the surface of the eucalypt bark. Once hatched, the larvae bore through the undersurface of the egg into the bark and then make elaborate trails, first burrowing in long irregular loops and later in a more regular zigzag, which is doubled up after a narrow turning loop. When the cork cambium starts to produce cork to shed the outer bark, it produces scar tissue in response to the feeding of the caterpillar, filling the double part of the larval tunnel with highly nutritious, thin-walled cells. These replacement cells are ideal food for the caterpillar, which moults into the final larval stage with legs, turns around and eats its way back along the way it has come. It then grows rapidly to maturity, bores its way out of the trunk, drops to the ground and spins a flat, ribbed silken cocoon on a hidden spot attached to a stone or fallen bark. By late summer or autumn, pupation has taken place and the moth leaves to begin another life cycle. Not long after, the bark cracks off, exposing the iconic scribbles beneath. Adult moths are rarely seen, despite the evidence left behind. AA