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Fuel reduction burn at Risdon Vale

16/04/2014

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Tasmania's Cool Temperate Rainforest

Introduction

Myrtle tree growing in its natural forest habitat

Our rainforests are dominated
by myrtle-beeches

Tasmania contains Australia's largest tracts of cool temperate rainforest, covering around 10% of the State. Cool temperate rainforest is very different from rainforest found in warmer climates. Unlike tropical and warm temperate rainforests, there are no root buttresses or palms, and climbing plants are rare.

Cool temperate rainforest is characterised by an open and verdant, cathedral-like quality; a silent, cool, dark and damp place where both the trunks of trees and the forest floor are festooned with a luxuriant carpet of mosses and lichens. In autumn and early winter in particular, the rainforest floor is dappled with an array of brightly coloured fungi.

What is a cool temperate rainforest?

Defining Tasmania's cool temperate rainforest is difficult, partly because it can grow in so many different habitats. However, there are generally three things to look out for:

  • Most rainforest grows in areas receiving over 1 200 mm of rain a year, but some isolated patches occur in much drier areas;
  • It is dominated by particular trees, such as myrtle, leatherwood, celery-top pine, sassafras, Huon pine, pencil pine, King Billy pine or deciduous beech maybe important in some areas; and
  • Species living in rainforest don't require disturbance, such as fire, to reproduce, and are generally disadvantaged by disturbance, which allows in light-dependant, short-lived competitors.

Tasmanian rainforest evolved way before Australia's eucalypts

Tasmanian rainforest contains some of the most ancient species of Australia's flora. Many of their ancestors once grew in Antarctica, Africa, South America and New Zealand, when these continents were joined together as a landmass called Gondwana. So our rainforest dates back over 60 million years, well before what we now call "sclerophyll vegetation" evolved (like eucalypts and acacias). Particularly ancient genera with fossil and pollen evidence to support their presence and evolution within Tasmania include Agastachys, Athrotaxis, Anopterus, Archeria, Bellendena, Cenarrhenes, Dicksonia, Eucryphia, Phyllocladus, Microcachrys, Microstrobos, Nothofagus, Orites, Lomatia, Tasmannia, and Telopea.

Different types of Tasmanian rainforest

Tasmanian rainforest grows in many different places and in many different ways. There are four main types: callidendrous (tall trees with an open, park-like understorey); thamnic (shrubby understorey); implicate (short, tangled vegetation); and, montane (woodlands and forests at high altitude). Each has different groups of species growing in different ways. The variation is largely due to differences in soil, rainfall, aspect and altitude. One intermediate forest type between rainforest and eucalypt forest is mixed forest, where rainforest species live beneath tall eucalypts.

The definition of rainforest is arbitrary, and is taken as rainforest species with 5% cover of eucalypts. More eucalypts than this means it is defined as mixed forest.

Where are all the rainforest animals?

Tasmanian rainforest is such a quiet place that sometimes it seems that there are no animals. Of course there are many, but generally there is a smaller variety of vertebrate animals and they are fewer in number (compared with other forests). Mammals include the Tasmanian long-tailed mouse, ringtail possum,pademelon, spotted-tailed quoll and dusky antechinus. Twenty-one species of native birds regularly visit rainforest, including the black currawong, green rosella, olive whistler and grey goshawk. Of the reptiles, the Tasmanian tree frog, tiger snake and brown skink are relatively common. Tasmanian rainforest contains some of the most ancient and primitive representatives of invertebrates. Some of these include the large land snail, Macleay's swallowtail butterfly, freshwater crayfish and the peripatus, or velvet worm.

Threats to rainforest

The greatest threats to rainforest are from human activities. Fire poses the biggest problem in Tasmania where most fires result from either deliberate or accidental burning. In the last century over seven per cent of Tasmanian rainforest has been burnt.

Following fire, vegetation generally passes through a number of stages and if undisturbed culminates in the return of mature rainforest after several hundred years. If fires are cool and the vegetation long unburnt then some rainforest trees may survive and most species will regenerate successfully from soil stored seed and seed dispersed from nearby areas. However some very fire sensitive rainforest species, such as the conifers, King Billy pine and pencil pine, may be eliminated by a single fire event and have no means of recovering.

The land that rainforest grows on is often wanted for other uses, such as for agriculture, forest plantations, dams and mining. Another threat is from pests and diseases. Myrtle wilt is a serious fungal disease which kills myrtles, especially where there has been some form of disturbance. Phytophthora root rot, Phytophthora cinnamomi, can also be a problem in rainforest, especially on recently burnt sites, at the edge of rainforest or along roads.

Our use of rainforest

There is a lot of competition for the use of Tasmanian rainforest and the land it grows upon. Many of its trees are highly valued by the craftwood industry for their utility and aesthetic appearance; Huon pine, myrtle, celery-top pine and sassafras are best known. However, because rainforest trees grow slowly, it is not economical at present to grow them in plantations, and their future long-term supply is uncertain. At present, there are export embargos on Huon and King Billy pine. The salvage from hydro-electric impoundments of long-dead Huon pine logs satisfies much of the current demand, but this resource is not renewable.

Rainforest is also used by bee keepers to produce leatherwood honey, and of course, rainforest is very popular with tourists. All of these uses must be carefully managed if we are to maintain rainforest for future generations.

Where does Tasmania's rainforest grow?

The most extensive areas of callidendrous rainforests occur in Tasmania's north-west, though it is also found throughout the western half of the State, and in patches in the north-east highlands. Much of the rainforest of the north-west lies outside reserves. Tiny patches of rainforest also survive in some east coast gullies where extra moisture from clouds or streams make up for the low rainfall. About 41% of rainforests are in the Tasmanian Wilderness World Heritage Area (TWWHA). The best examples of implicate and thamnic rainforests which are richer in endemic species occur in the TWWHA. Another 25% of rainforests occur in other reserves around the state.

Where can I see rainforest?

There are a number of excellent trails that will give you more understanding (and a real rather than virtual experience!) of our cool temperate rainforest. The Creepy Crawly Trail in the Southwest National Park is worth a visit, as is the Franklin River Nature Trail in the Wild Rivers National Park.

There are also excellent walks through rainforest at Cradle Mountain and Lake St Clair, as well as at Liffey Falls at the northern edge of the Tasmanian Wilderness World Heritage Area.

Forestry Tasmania also have some excellent, interpretive walks through rainforest, such as those at Weldborough Pass in the north-east, Sandspit and Tahune in the south-east and the Julius River Rainforest Walk in the north-west.