The Tasmanian Arboretum

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When first seen by Europeans in the late 1700's, Australian plants amazed botanists such as Banks, Solander and la Billardiare. They collected species new to science. This stimulated an interest in and study of Australian plants that continues to unlock the mysteries of an extremely diverse and specialized flora.

The Australian collection includes several young plantings; rainforest, cypress pines and wattles.

Although called the Australian collection, factors such as rainfall pattern, soil type and temperature restrict our collection to plants from the south of Western Australia, (the karri, marri and jarrah forests), and to the ranges and tablelands of the eastern states.

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The golden wattle (Acacia pycnantha) is Australia's floral emblem. Wattles (Acacia) grow in Australia, South America and Africa. There are more than 1100 species and over 650 occurr in Australia. The next largest group is in southern Africa.

One view of the source for the common name is that the trees were used in wattle and daub construction by early settlers. They are useful in controlling soil erosion and are a colonizer of disturbed land.

Some wattles have bark high in tannins used to cure hides and in dyeing. Many are a source of food for wildlife, a few have edible seeds or store water in their roots and some produce sufficient pollen to be used for honey production.

Wattles are nitrogen fixing plants. Legumes, such as peas, peanuts and wattles, act in concert with nitrogen fixing bacteria on their roots to fix nitrogen from the atmosphere for their own use as a nutrient. Legumes are found on all the continents. In the temperate zones, woody legumes are more common in the southern hemisphere. This reflects the nature of the climate and vegetation. Comparatively, the southern hemisphere is drier with more woodland than forest.

With a wide range of leaf shapes, growth habits, attractive flowers and with species flowering in every month of the year wattles make excellent garden plants. Wattles can be seen opposite the Tasmanian Alpine Arbor.

Remnant Rainforest Refuges

Temperate and tropical rainforests in Australia are remnants from a warmer and wetter period when rainforests were widespread. Rainforests are now restricted to areas where rainfall is usually high and spread over the year, such as north Queensland and the rainforests in the high mountain cloud of the Great Dividing Range.

Australian plants have had ages to adjust to changes in rainfall pattern and the drier climate that have accompanied the drift of the continent.

Lillypillys (right - Syzygium, Acmena, Waterhousia), fleshy fruited relatives of the woody capsuled eucalypts, are related to the plants of the drier areas of Australia. They range naturally as far south as Victoria (Acmena smithii).

The tree lomatia (Lomatia arborescens) is closely related to banksias, and occurs in north eastern NSW and south eastern Queensland, where many other plants closely related to species naturally found in Tasmania occur.

When climate shifted in their favour, species more tolerant of warmer and wetter conditions spread from these refuges.

Many others continued to or can still tolerate cold conditions. Some of these are exhibited in our collections. There are examples of rainforest plants, cypress pines and eucalypts on the western hill.


The Burning Question

Some Australian vegetation has developed a relationship with fire as a result of most of the continent becoming drier and so more susceptible to burning. The question of whether eucalypt dominated vegetation needs fire, or has come to tolerate it over ages of natural selection, intrigues ecologists and botanists.

E sideroxylan

Eucalypts (Eucalyptus) have developed mechanisms similar to other species to allow them to survive fire, such as thick or lighter coloured heat reflective bark, sometimes both on the one tree. If fire also reaches into the canopy of forests, the buds sheltered by and hidden under the same bark allow some eucalypts to produce leaves, quickly dominating the site over any competition encouraged to germinate by fire, such as wattles.

Species like the smaller growing Banksia have woody capsules opening only once a fire has passed. Seeds of other species are stimulated to germinate by chemicals found in the smoke from bushfires and washed into the soil from the ash with the first rains following a fire.

As the climate became drier, rainforest species, less tolerant of fire, were overtaken by vegetation that evolved with fire.