Species of the Rainforest
Tasmania contains Australia's largest tracts of cool temperate rainforest, covering around 10% of the State. Most rainforest occurs in areas receiving over 1 200 mm of rain a year, and on average at least 50 mm of rain in the driest month, but some isolated patches occur in damp gullies in drier areas.
Cool temperate rainforest is a verdant, cool, dark and damp place where both the trunks of trees and the forest floor are usually 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?
Tasmania's rainforest can be recognised from other vegetation by the dominance in the canopy of any of the following tree species:
Where these rainforest tree species are common beneath a eucalypt canopy the vegetation is defined as mixed forest, a form of wet eucalypt forest. If the canopy eucalypts form less than 5% cover then the vegetation is classified as rainforest.
Species living in rainforest don't require catastrophic disturbance, such as fire, to reproduce, and are generally disadvantaged by disturbance, which allows in light-dependent, short-lived competitors. Nevertheless, although relatively shade-tolerant many species still require the additional light available in canopy gaps for their seedlings to be able to grow to maturity. Canopy gaps may be generated when the mature trees fall over or die from old age or disease.
Cool temperate rainforest is very different from rainforest found in warmer climates. Unlike tropical and warm temperate rainforests, the trees do not have large buttresses, there are no palms, and climbing plants are relatively uncommon in Tasmania's rainforest. In common with their warmer counter-parts, epiphytic ferns (ferns growing on tree ferns, tree trunks and logs) are common in cool temperate rainforests.
Tasmanian rainforest contain some species with an ancestry dating back to the super continent of Gondwana, and have been present in Tasmania for more than 60 million years. They evolved well before the species that dominate what we call "sclerophyll vegetation" (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, Pherosphaera, Nothofagus, Orites, Lomatia, Tasmannia
Different types of Tasmanian rainforest
There are four main rainforest types: callidendrous (tall park-like rainforest with an open understorey); thamnic (rainforest with a shrubby understorey); implicate (short tangled vegetation); and, montane (woodlands and forest at high altitude). The distribution of these various types is largely controlled by soil fertility and temperature. Callidendrous rainforests occur on the most fertile soils while implicate forests are those on the least fertile sites and the thamnic forests occur on soils with an intermediate fertility. Montane communities develop in cool highland areas in relatively fertile situations.
Mixed forests, which are wet eucalypt forests with a well developed rainforest understorey, although not classified as rainforest, provide an important habitat for many rainforest plant and animal species.
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
. 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 and fire. The land that rainforest grows on is often wanted for other uses, such as for agriculture, forest plantations, dams and mining.
Rainforests only become flammable after 30 days in which rainfall total is less than 50 mm, so in general rainforests occur in areas where they are rarely able to carry fire. However, even within high rainfall areas rainforests are more likely to be confined to places in the landscape which are naturally protected from fire. Nevertheless, in the last century over seven per cent of Tasmanian rainforest was burnt. If fires are cool and the vegetation long unburnt then some rainforest plants will resprout and recover quickly following fire. Others will successfully germinate from seed dispersed from nearby areas, and less commonly from seed stored in the soil. However fast growing disturbance loving plants are able to establish dominance of sites following fire and it commonly takes several decades and sometimes as long as a century before the slower growing rainforest trees can reestablish canopy dominance. 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.
Another threat to rainforest is from pests and diseases. Myrtle wilt is a serious but natural fungal disease which kills mature myrtles, especially where there has been some form of disturbance such as logging or road development nearby.
Phytophthora root rot (Phytophthora cinnamomi), can also be a problem at the edge of rainforest, along roads or following fire. Normally rainforest soils are too cool to support this pathogen but where the canopy is opened by disturbance soils temperatures can be warm enough to allow this pathogen to disease susceptible rainforest species.
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?
Rainforest occurs in areas of high rainfall or where there is a consistent source of moisture and where fires have rarely occurred. The most extensive areas of callidendrous rainforests occur in Tasmania's north-west, though it is also found in more fertile areas 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
Franklin River Nature Trail
in the Wild Rivers National Park and Philosopher's Falls track in north-west provide examples of Tasmania's rainforest. There are also excellent walks through rainforest at
Lake St Clair
, as well as at Liffey Falls at the northern edge of the Tasmanian Wilderness World Heritage Area. Visit the Parks and Wildlife Service web site at
to find out more about these walks.
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.
The Tahune airwalk in Tasmania's Southern Forests provides an experience of walking above the rainforest canopy within a mixed forest.
Tasmanian Rainforest - Notesheet