Photo: Australian National Botanic Gardens


                                                                                                                                                                                                         Photo: Ian Clark

Eucalypts are at the center of many Australian ecosystems, and numerous organisms have lifestyles that include some type of interaction with these plants.  The first organism that comes to mind for many is Phascolarctos cinereus, the koala, which feeds exclusively on eucalyptus leaves, preferring the leaves of the red, grey, manna, and swamp gums.  However, many more complex webs of life are anchored to these trees.

As the eucalypts adapted to become the dominant vegetation of the Australian bush and forest landscapes, an open, spacious type of arboreal environment emerged.  This is an ideal place for the yellow-bellied glider, Petauris australis, to swoop from tree to tree, feeding on sap and dwelling in hollow stumps.  The trees are primary producers, and their leaves provide Nutrition to many herbivorous insects, which in turn are an energy source for insectivores such as owls, bats, and spiders.  A common parasite in these forests, mistletoe, grows near the tops of the trees and extends its roots into the tree’s branches and saps nutrients.  Interestingly, the mistletoe is a favorite nursery for some species of blue butterflies.

The leaves of eucalypts are rich in oil, with E. dives being one that is commercially exploited, and within these oils are special toxins designed to reduce predation.  However, certain herbivorous mammals, like the koala and the common brushtail possum Trichosurus vulpecula, have livers adapted to protect them from these toxins. 

Photo (left): David Cook Wildlife Photography


Some species of insects lay eggs on the eucalyptus leaves, and when the insect larvae hatch and begin feeding on the leaves, they form protective body casings called lerps.  These lerps are composed of leaf material that the larvae could not digest, and bell miner birds (Manorina melanophrys) find them irresistible.  Groups of bell miners have even been seen vigorously defending lerp territory.

                                                                                                                                         Photo: Michael Dawes

Human Impact

Eucalyptus as a genus has enormous economic and physiological significance to humans.  The fast-growing trees, particularly the giant E. regnans, have been an important source of timber for over a century in Australia.  Eucalyptus diversicolor was especially prized as a ship-building hardwood because it has a natural resistance to termites and teredo, or “shipworms” (a species of clam).  The timber trees are also a renewable source of firewood, and the flowering E. globulus is a preferred foraging tree for bees.

Photo: Australian National Botanic Gardens. Macdonald, C.

In addition, eucalyptus leaves are a source of eucalyptus oil, with E. dives being a tree commercially cultivated for this product.  The relative chemical compositions of the oils vary by species, but E. dives is rich in a compound called eucalyptol (or cineole).  This biological compound has numerous medicinal properties.  It can be used as an anesthetic and antitussive, making it a good ingredient for cough drops, and as a decongestant and expectorant, eucalyptol may appear in many over-the-counter cold medicines.  Some mouthwash formulas list eucalyptol as an ingredient because, as an antihalitosic, it fights bad breath.  Interestingly, eucalyptol has also been used as an antiseptic (a chemical that prevents microbial growth), as an antihelmintic (used in treating parasitic worms), and as a hypotensive agent (for lowering blood pressure).  The aboriginal peoples native to Australia have also used the leaves from the broad-leaf peppermint to make a tea to treat fevers.  The oil from E. dives also contains a-terpineol, an aromatic alcohol, making it popular on the fragrant essential oil market.        

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