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The koala (Phascolarctos cinereus) is a folivore, an animal which feeds primarily, but not exclusively, on the Genus Eucalyptus. Throughout their range in eastern Australia, koalas use a wide variety of eucalypt species. Only a few species of eucalypt will be preferentially used by koalas. Such species, where they occur, are vitally important to the distribution, abundance and well being of koala populations.
A variety of other trees, including many non-eucalypts, are also used by koalas for feeding and shelter, or other behavioural purposes. On their own, however, these trees are not capable of sustaining koalas in the long term. They are used primarily because they are growing in association with or in close proximity to the key tree species. Differing soil landscapes, water availability, nutrient content and other variables are also considered to influence the suitability of several important browse species.
The koala will eat the leaves of a wide range of eucalypts, and occasionally even some non-eucalypt species such as Callistemon (bottle brush), Acacia (wattles), Corymbia, Blood woods, Leptospermum and Melaleuca. Koalas however have firm preferences for particular varieties of eucalypt and these preferences vary from one region to another. |
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Eucalyptus leaves consist of approximately 13% tannins, 2% minerals, 50% water, 18% fiber, 8% fat, 5% carbohydrates and 4% proteins. Sometimes, they also feed on the bark, buds and flowers of the eucalyptus trees. They also contain toxic oils that are extremely poisonous to other animals. Koalas, the greater glider and the ringtail possum are the only three mammals that can survive on a diet of eucalypt leaves.
Not only are they particular about the species of eucalyptus tree leaves that they feed on, they also consume the leaves and buds only after they have reached a particular stage of maturation. It's surprising koalas can survive on such a diet but nature has equipped them with extraordinary mechanisms that ensure their survival. Their digestive system has specialized adaptations that detoxify the toxic oils in the eucalyptus leaves, and this detoxification process is also aided by their liver. |
Koalas also have an additional part in their digestive tract, known as the 'caecum' that breaks down the food further and aids digestion. They also have a very slow metabolic rate that allows them to retain food and energy for a longer period of time.
The species of eucalyptus tree chosen by the koala for feeding also depends on the area of its habitat. Koalas residing in the southern region of Australia, feed on a species of eucalyptus trees, known as the swamp gum and manna gum, while those residing in the northern areas, feed on the species known as blue gum, gray gum and red gum. Other favorite species of eucalyptus trees include swamp mahogany, yellow box, small-leafed peppermint and tallow wood.
Tree species are broken down into primary food trees that offer the highest levels of nutrients and the lowest amounts of phenols and tannins. Primary food trees are usually found on rich, thick soils with a higher nutrient content and greater access to water via regular rainfall. Secondary species are found in areas considered marginal, in that the soils are thin and/or are above rocky substrates with poor rainfall as well as lower levels of nutrients.
Within the South East region of Queensland, the koala food trees most preferred are as follows: |
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This tree can grow to a large spreading tree up to 35 m in height with rough furrowed bark which is mottled grey with yellow and orange shadings underneath. The narrow lanceolate (lance shaped) leaves are a uniform greyish-green in colour. |
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This graceful eucalypt has distinctive red-brown bark which is soft and fibrous, often having horizontal branches. It has small blisters on the bark not seen in other stringy or fibrous barks. It grows to around 40 metres tall and the leaves are thin, can be wave shaped and dark green in colour. |
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This species is mostly seen growing in high rainfall areas. It reaches between 20 and 30 metres tall and is prone to fire. Irregular and mottled bark patches when shed reveals an orange to copper color trunk. The leaf is broad, glossy green above and lighter below. |
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This gum tree most often has a smooth grey trunk. It is also an important pollen source for bees when conditions are favorable. It can grow into a rather large tree of up to 35 metres in height. The glossy, dark green adult leaves are sickle and/or lance shaped. |
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Koalas love this highly desired tree which grows to a height of 20 to 50 metres. The trunk is straight and the bark is shed in irregular sheets resulting in a smooth trunk surface coloured in patches of white, grey and blue. The leaves are narrow, slender and lance shaped. |
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| This medium to tall tree grows to about 40 metres in height usually with a solitary trunk. The bark is smooth, cream,pink to dark grey or bluish and has a spotted or blotched appearance. The leaves are narrow and pendulous (hang down loosely). |
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| This tree is a medium sized to tall forest tree growing to around 45 metres. The bark is rough, fibrous, grey or grey-brown, held in flattish strips rather than like typical stringy bark. Adult leaves are thin, green, glossy and paler on the under side. |
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| The tree grows to a height of about 35 meters. The trunk has deeply furrowed hard (like ‘iron’), dark gray bark and gray or black to gray-brown bark persistent throughout. The foliage crown is somewhat grayish blue. Adult leaves are generally dull, blue-green to gray-green. |
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| This attractive, tall, straight trunked tree grow to over 30 metres. The bark is smooth white to grey in colour. At the base, the bark becomes rough, fibrous and/or flakey, turning grey to grey-brown. The leaves are glossy dark green. |
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| This medium sized tree grows to a height of 30m. The bark is grey, shedding in strips to orange/brown in colour. It's slightly granular and corky to the touch. The leaves are dark green above and paler below. |
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| This is a medium sized to tall tree with rough, persistent bark on the lower trunk, shedding above to leave a smooth whitish or light grey, sometimes shiny surface. The branches are smooth, the bark sheds annually in long strands. The adult leaves are stalked, broad, lance shaped, glossy green with numerous oil glands. |
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| This is a medium-sized to tall forest tree. It is identified by a covering of rough bark, to about half way up the trunk. Above this is white smooth bark. The common name refers to the black base of the tree after fires. The leaves are wide and glossy, green to dark green. |
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| This is a small to medium sized tree grows up to 30 metres tall. The bark is smooth with shedding bark of white, grey or yellow. Scribbles, caused by moth larvae, are often found on the bark and the leaves are grayish green on both sides. When the bark sheds in short ribbons it is white, grey or yellow in colour. |
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| This grows to around 45 metres. The bark is rough, stringy and fibrous. Grey brown to reddish brown in colour with bark persistant up to small branches. The adult leaves are lance shaped, with varying shades of green on either side and marked by dense veins. |
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| This widespread and abundant large tree grows to 50m in height. The bark is smooth, powdery, white or grey, shedding in short ribbons or flakes and sometimes persistent on lower trunk. The adult leaves of the tree are glossy green, lanceolate (lance shaped) to falcate (curved like a sickle, hooked). |
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| This medium sized tree grows to about 30m in height. The bark is smooth, shedding in plates, white or grey brown. The leaves are narrow and dull green. |
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| This ranges in size from a small tree to a tall, graceful tree growing to 35m. The bark is smooth and white-cream in colour except for the lower couple of metres where it is tessellated and dark grey to black. Adult leaves are narrow, lance shaped, green to grey-green and dull. |
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| A medium sized evergreen tree typically developing a single trunk and rounded canopy, This species can attain heights of up to 40m. It has rough brown bark on the lower trunk and smooth pinkish brown bark on the upper trunk and branches. Its leaves are thick, oval shaped, dark green and glossy above and paler beneath. |
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| This is a large tree growing up to 30m, with red-brown, fibrous-papery persistent bark. Its leaves are oval to egg-shaped and broadest in the centre. The leaf tip is blunt or shortly pointed, wedge-shaped, leathery and light green. |
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| This tree is a small to medium-sized tree grows as a spreading tree up to 20 m high, with the trunk covered by a white, beige and grey thick papery bark. The leaves are a leathery dull and grey green in colour. This tree is considered a medical species often eaten when koalas are suffering from digestive ailments. |
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