Australia: The Land Where Time Began

A biography of the Australian continent 

Northern Warm Temperate Rainforest

These are simpler in structure and species composition than Subtropical Rainforests. The canopy is very even, few if any emergents, comprised of 3-5 species, though it can occasionally be up to 15 tree species. The size of leaves, up to 12.5 cm, are usually smaller than those in Subtropical Rainforests, there are few if any buttresses. There are not many epiphytes and palms, if they are present it is only 1 or 2 species. Vines reaching into the canopy are less common than in Subtropical Rainforest. There is usually an understorey of scattered saplings and shrubs, while herbs and ferns form a variable groundcover. 

This type of rainforest is usually found on certain rock types, granites, rhyolites, syenites, or sedimentary substrates yielding acid soils with moderate nutrient levels. Northern Warm Temperate Rainforest occurs on soils that would not support most other rainforest types. One environmental effect on the ecology of the Northern Warm Temperate Rainforests resulting from the rock types they grow on is that they include many trees that accumulate aluminium in their leaves, such as coachwood (Ceratopetalum apetalum) and other Cunoniaceae species and Prickly Ash (Orites excelsa). This accumulation of aluminium in the leaves eventually accumulates on the floor of the forest, and eventually into the topsoil, and this aluminium tends to exclude species less tolerant of aluminium - allelopathy.

The Cunoniaceae, a major part of Northern Warm Temperate Rainforest, originated in Gondwana. There are about 300 species of this family in the forests of eastern Australia, and outside Australia, they are scattered across the Southern Hemisphere in the South Pacific, South America, and South Africa, all the continents and fragments that were once part of Gondwana.

Many fossil Cunoniaceae appear different from the extant species, but they can confidently be assigned to this family. Several 30-15 million year old extinct species of Ceratopetalum have been found in northern New South Wales. In the rainforests of the same region today there is only a single species, Ceratopetalum apetalum. The genus Weinmannia has been found as fossils in Australia, but there is no known surviving members of this genus in present-day Australia. Barring a discovery like that of the Wollemi Pine, the genus is apparently extinct in Australia, and has been for at least a few million years, but survives in other places that were previously part of Gondwana, some Pacific Islands, New Zealand, central and South America.

Northern Warm Temperate Rainforests rarely occur on coastal lowlands, usually occurring on the hilly and steep sections of the coastal ranges and Plateaux. They merge into the Cool Temperate Rainforests above 800 m on the Great Dividing Range. The Cool Temperate Rainforests are usually situated on more fertile soils.

Some pockets of NWT Rainforests occur in Queensland north of the Lamington Plateau, but the main area of this forest type occurs from the Lamington Plateau south to Batemans Bay along the New South Wales coast. The forest type gradually changes from Northern to Southern Warm Temperate Rainforest between the Shoalhaven River and Batemans Bay. Species diversity declines noticeably with increasing latitude.

To the north of Glen Innes, the Washpool area is where the most extensive NWT Rainforest occurs, other large areas being New England NP, Werrikimbe NP and Blue Mountains NP, and on the Illawarra Escarpment.

In places with large areas of acid soils, such as the Washpool and Blue Mountains, they are the predominant forest type. A mosaic of soil types, such as occurs in the Dorrigo, Werrikimbe, Illawarra and Tweed areas, leads to an associated mosaic of forest types, resulting in juxtaposition of Subtropical and Northern Warm Temperate Rainforest.

The difficult terrain and acid soils of the areas covered by the NWT Rainforests has largely saved them from being cleared for agriculture. Timber has been extracted from many stands, but because they weren't often cleared, there are still places of intact forest.

Sources & Further reading