Australia: The Land Where Time Began

A biography of the Australian continent 

Cool Temperate Rainforest                                                                                                                Last updated 21/10/2016

In this rainforest type the Antarctic Beech (Nothofagus moorei) is the main or only dominant species, which was present in Australia when it was part of Gondwana 130 million years ago. Cool Temperate Rainforests occur at altitudes between 900 and 1500 m with rainfall between 1750 and 3000 m, and when there is no rain it is often shrouded in mist. They usually have 2 strata, but often only 1, and 2 or 3 species usually making up a uniform canopy. There are no palms, stranglers or plank buttressed trees, though the trunks of the trees can be massive. Small wiry vines and some epiphytes can be present, and there are few if any large vines and epiphytes and possibly orchids. Tree ferns and ground ferns are common, there are many mossy epiphytes and lichens. Large stands occur in the Border Ranges NP and Lamington NP.

Tasmania an Victoria

At the present, this type of rainforest comprises about 25 % of the remaining rainforest cover of  Australia. It is characterised by cool moistness, balanced simplicity in place of the diversity and colour of the tropical rainforests. These southernmost rainforests have been described as 'Tolkein-like', with myrtle trunks covered with moss, tall sassafras with upright branches and smooth mottled bark. Thick brown peat covers the forest floor, with ferns and lichens growing on every surface. There are not many flowers, what colour their is being provided by colourful fungi. The dominant colour of the forest is green, described as 'rich, dark and saturating' (Meier & Figgis, 1985). The forests of Tasmania have been isolated from those of mainland Australia since the Pleistocene ice age when the sea flooded the land bridge to form Bass Strait. These forests are the core area of Australia's temperate rainforests. It is a refuge area, containing a gene pool of species, the ancestors of which were once part of the extensive rainforests of Gondwana. This type of rainforest descended from different ancestral species from those of the warm tropical rainforests and warm temperate rainforests, its composition resulting from being in cooler latitudes than other forest types of Australia.

The present distribution of this forest type is restricted to southeast Australia, the south island of New Zealand and southern South America, indicating they are remnants of the southern part of Gondwana, and fossils of this forests type have been found in Antarctica. The present cool temperate rainforests are the result of periods of expansion and contraction over millions of years, mostly contraction, This forest type covered much of the southern part of the continent at the time Australia broke from Gondwana and began drifting north. Dominated by Nothofagus cunninghamii, this forest was ancestral to the cool temperate rainforests of the present. Cool temperate rainforest was widespread in southeastern Australia 10,000 years ago, reaching the Queensland border in the Great Dividing Range. Its present rang is very limited, being found only in small isolated stands in New South Wales, mostly in the higher ranges and the Barrington Tops. Little remains in Victoria, said to be as little ad 10,000 Ha.

In Victoria there are 4 broad geographical regions of rainforest communities.

The Southern uplands of the Otway and Strzelecki Ranges. Remnants of myrtle beech forests (Nothofagus cunninghamii). The Otway communities are the most westerly occurrence of this forest type in Australia. To the northeast of Melbourne similar forest types occur in the central highlands. One thing these 3 forest communities have in common is major, catastrophic bushfires of 1939 that is suggested to have limited the distribution of the rainforest. Since that time many areas are being re-colonised from unburnt surrounding areas.

East Gippsland. The most diverse and interesting forested area in Victoria, and one of the most intriguing in Australia. This rainforest has been divided into 2 types, the lowland coastal region between Lakes Entrance and Mallacoota, frequently dominated by lilly pilly, (Acmena smithii), now called warm temperate. Rainforest in the coastal region to the north, on the Erinunderra Plateau, is usually thought of as cool temperate.

Tasmania is the only state where there are extensive areas of dominant cool temperate rainforests, mostly in the northwest, large unbroken tracts of pure rainforest occurring in the area of the Savage and Sumac Rivers. There are also rainforest areas in the central southwest, the valley of the Weld River being untouched, a rich mosaic of pure and mixed rainforest. It also occurs in the uplands of the Cradle Mountains-Lake Saint Clair National Park, along the Wild Rivers National Park rivers, and in the northeast, scattered remnants occurring in the highlands, between Mt Maurice and Blue Tier. In protected gullies and on south-facing slopes tiny relict communities exist throughout the lowland east, such as the Douglas River and the Tasman Peninsula.

Tasmania is the most forested state in Australia, about 80 % of the island being covered by forest at the time of first European contact, though this has now been cut to about 40 %, and only about 13 % of this is pure rainforest, about 450,000 Ha, though the number is much higher if forests with an overstorey of eucalypts is included (Meier & Figgis, 1985).

In Tasmania the rainforest areas are restricted to places with an annual rainfall of at least 1200 mm and at least 40 mm/month in summer. Some rainforest can survive in areas with rainfall as low as 800 mm/year and 25 mm/month during summer. Rainforest is not limited to a particular soil type or quality, being found on infertile quartzites to nutrient-rich basalts. Fire is the main limiting factor of rainforests, 300-400 years free of fire being required by pure rainforest to reach full development. In Tasmania, about 47 % of the area that is suitable for rainforest, based on local climate, is button grass plains, the rainforest being prevented from establishing by the frequency of fire (Meier & Figgis, 1985).

Forest structure

Cool temperate rainforests are not multilayered as are tropical rainforests. A single canopy layer, that is often very dense, is the usual structure, myrtle (Nothofagus cunninghamii) being the dominant species, also known as myrtle beech in Victoria.

In Australia it is traditional to define rainforests based on structural characters, mainly by the degree to which the canopy is 'closed', covered by a protective canopy. One of the disadvantages of this method of defining rainforest, when dealing with cool temperate rainforests, is that it excludes rainforest types that are more open, such as occurs in subalpine regions.

Another disadvantage is that it doesn't distinguish between closed forest that are essentially rainforests, but with some eucalypts. An alternative definition of cool temperate rainforest based on species composition and regeneration processes would avoid these problems. In Tasmania, the definition used by biologists for such communities in which trees are more than 8 m tall and are dominated by myrtle or deciduous beech (Nothofagus), sassafras (Atherosperma), leatherwood (Eucryphia), pencil or King Billy pine (Athrotaxis), Huon pine (Lagerstrobus), celery-top pine (Phyllocladus) or Diselma. It's also defined as being capable of regenerating in the absence of catastrophic disturbance, such as fire (Meier & Figgis, 1985).

The definition of rainforest type in Tasmania used by the Forestry Commission, rainforest with less than 5 % eucalypt canopy cover, an arbitrary figure, is not based on ecological data. This is the definition on which management practices and logging are based, and is oriented towards timber production rather than the ecological considerations of the forest. Australian ecologists have reached a consensus on the definition of rainforest explicitly including transitional communities with eucalypt emergents, as long as their composition is similar to pure rainforest. The Forestry commission defines rainforest as mixed forest, not mixed rainforest, even in forests in which the rainforest species comprise up to 95 % of the total forest species. This definition allows the rainforests to be managed as if they had no rainforest component. As a result there has been a major loss of rainforest in Tasmania, that goes unnoticed by anyone unaware of the significance of the unrealistic and arbitrary nature of the definition of mixed forest. The rainforests of Victoria have the same problem, where timber production takes precedence over preservation of the very diminished rainforest, the definitions being used to maximise logging.

The cool temperate rainforests of Tasmania have been divided into 4 broad subgroups - Callidendrous, Thamnic, implicate and open montane rainforests.

Callidendrous rainforest

Callidendrous rainforest is the type usually associated with cool temperate rainforest. A tall, protective canopy is formed by myrtle, beneath which conditions are cool and moist. The forest floor is covered with old accumulations of leaves and twigs, with many tree ferns, and there are scalloped trunks of the myrtles. There are often long strands of moss and lichen hanging from the branches of tall sassafras in groves.

Thamnic rainforests

Thamnic rainforests grow to heights that are intermediate between the tall Callidendrous and the low tangled implicate communities. The tree species are highly diverse. As well as the usual myrtle, there can be Huon, celery-top or King Billy pine, leatherwood and sassafras. Shrubs, such as the broad-leaved native laurel are common, and there are Pandani. There are many leech ferns. The pink climbing heath that flowers in summer, the pink and red flowers hanging in masses of pendulous red and pink bells.

Implicate rainforest - tangled or woven

The definition of this rainforest type refers to 'the dense network of stems in the understorey which makes upright movement through these forests almost impossible ... The understorey is continuous with the canopy' (Jarman et al., 1984). This is believed to have been the forest type encountered by the explorer Osbourne Greeves in 1881on his journey to the headwaters of the Old River in southwest Tasmania. ' ... grass trees from knee high to 30 feet, mingled with horizontal scrub and occasional cutting grass ... [we] took an hour to clear a place big enough to pitch a tent, and another to collect firewood and bedding. Long before we had firewood it began, as I had suspected, to rain ... started off after breakfast ... heavy black clouds overhead ... so dark I could scarcely read the points of the compass with my spectacles ...'. Jarman had stated that 'detailed definition of individual plant communities within implicate rainforest has proved difficult ...'!

Open montane rainforest

This rainforest type is restricted to high altitudes, mainly amongst outcropping rocks or boulder fields, or along streams. These are the pencil pine forests found in the central and southwestern highlands. There is an understorey that is always distinct, and sometimes thick. According to Meier & Figgis 'often the very beautiful association with the deciduous beech occurs.'

Rainforests evolved in environments with very low fire frequency. As a result, all rainforest species are fire-sensitive. Pure rainforest doesn't burn easily because of the cool, moist microclimate beneath the closed canopy, fires often die out when they reach the edge of rainforest. This can change when there is disturbance to the canopy, when the threat is higher as the understorey can dry out and promote the invasion of flammable species such as eucalypts. Rainforest can burn very fiercely when it does burn, and when this happens recovery is very slow as rainforests have a relatively low growth rate. Once a forest is burnt it becomes very susceptible to future fires. Rainforest species that are killed before they can reach seed-bearing age can be completely eliminated by repeated fires.

Mixed forest usually replaces pure rainforest once it has been burnt. In these forests rainforest species grow beneath eucalypt emergents, though the rainforest understorey species shade out further replacement by the eucalypts, as the eucalypts require full sunlight to grow. If fire doesn't return within the 350 years lifespan of the eucalypts of the overstorey, pure rainforest can eventually grow again in the area when this occurs.

Sources & Further reading

  1. Meier, Leo & Figgis, Penny, 1985, Rainforests of Australia, Kevin Weldon

Author: M. H. Monroe Email:  admin@austhrutime.com

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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading