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The Eucalyptus Tree

When foreigners think of Australia, the first image that comes to mind may be the Sydney Opera House, the dry reaches of the Outback, or the majestic red monolith of Ayers Rock. However, a humbler symbol of the continent is much more important, though diminutive. It is the eucalyptus, a tree at the center of much of Australia's forest life.

Eucalyptus trees have dotted the Australian landscape for millions of years, and today they are probably the most common trees on the continent. Eucalyptus, able to survive poor soil, dry spells, and fire, is hardy enough to have spread throughout much of the land and take a central place in the lives of the forest's wildlife.

Eucalyptus grove

Eucalyptus trees are important in Australia.

In THE CALL OF KAKADU, fire sweeps through a eucalyptus forest, destroying the longtime home of a young kookaburra and his parents and leaving behind charred earth. The area appears to be devastated, but the eucalyptus trees there will recover quickly and even thrive. Eucalyptus leaves contain oils that can actually fuel an intense fire, but the tree's thick bark protects its core from damage.

In fact, eucalyptus trees are so well adapted to fire that a conflagration actually causes them to flourish. Soon after a fire dies out, chemical changes triggered by the flames' heat cause new buds to shoot out of the trees. The fire's hot winds can also help distribute eucalyptus seeds, sowing new tree colonies far and wide and eventually providing new homes for kookaburras.

Besides the kookaburras shown on NATURE, many other creatures also depend on the eucalyptus tree. Termites, for example, like to hollow out the trees' trunks and large branches after they have been weakened by fire. The termites turn the wood into a pulp that they both feed upon and use to build nurseries in their homes, the large mounds that dot the landscape. In fact, more than 80 percent of northern Australia's eucalyptus trees are now being hollowed out by termites. Many other insects, such as the larvae and caterpillars of butterflies, feed upon the leaves or other parts of the eucalyptus tree. Those insects themselves are food for prowling spiders, who in turn become dinner for the owls and bats that live in the forest. In addition, dozens of other birds, such as yellow-tailed black cockatoos, thornbills, warblers, tree-creepers, sitellas, parrots, and many other species also probe the eucalyptus trees looking for insect feasts.

The hollows left behind by the munching termites provide homes for a multitude of other creatures, including one-fifth of the birds and fully half of the mammals in northern Australia. Kookaburras, cockatoos, rosellas, and sugar gliders all make their homes in eucalyptus hollows. (Pythons also slither into the hollows looking for food, as filmmaker David Curl discovered one day when he blindly stuck his hand into a nest hollow and found not kookaburra eggs but a very large, very surprised snake.)

Termites are hollowing out more than 80% of Australia's eucalyptus trees.

The trees that manage to survive the termites' hollowing also benefit from this arrangement. The tree's animal tenants, not particularly good housekeepers, all deposit droppings, leftover food, and other organic bits and pieces at the base of the tree, providing it with nutrients.

One of Australia's most famous residents, the sleepy koala, also depends on the eucalyptus. Koalas feed exclusively on eucalyptus leaves, later settling into the tree's crooks and branches for a nap. Even some plants depend on the tree. Fronds of parasitic mistletoe occupy the upper branches, living off the sap of its host. The clinging plant, in turn, provides food for mistletoe birds, which return the favor by spreading mistletoe seeds to other treetops in their droppings.

Humans, not surprisingly, have also learned to take advantage of the versatile eucalyptus. The fragrant oils produced by the tree are used in the mining industry to float detritus away from valuable ore, as a base in many perfumes, and in many cold medications, such as throat lozenges and chest rubs.

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