Australia: The Land Where Time Began

A biography of the Australian continent 

Southern Warm Temperate Rainforests

This type of rainforest occurs in south-eastern New South Wales in foothills and coastal ranges, in localities where there are deep, moist, sheltered gullies. They grow on soils that are granite-derived, or sedimentary substrates, of moderately fertile soil types. They occur in the 1000-1300 mm per year annual rainfall zone, though is some well sheltered sites that can be found in areas where the annual rainfall is less than 900 mm. They grow from sea level to about 800 m. The canopy, up to 15-20 m, is relatively uniform, and there are up to 3 dominant species. There are scattered shrubs and occasionally vines. The understorey is dominated by ferns.

At some places in southern New South Wales they merge with Cool Temperate Rainforests. The transitional zones all occur at elevations of 500-800 m. The Robertson Plateau had rainforests in large areas of the transitional zone. Before clearing, there were large areas of intermediate communities, the remnants are restricted to a series of fragments. Based on these fragments, some of the major ecosystems have been reconstructed.

This type of rainforest usually occurs within wet sclerophyll forest, which is in turn within areas of dry sclerophyll forest that is fire prone, the patches not usually larger than 50-100 ha. The rainforests don't usually burn under mild conditions, but in extreme bushfires small patches may burn. Lilly pilly (Acmena smithii) is the dominant tree in Southern Warm Temperate Rainforests. It and some other species can survive the occasional fire by coppicing.

When the canopy cover is broken by trees falling, fires or logging, flast-growing shrubs flourish when the light reaches the forest floor. Among the first plants to respond to the increased light are rose-leaf bramble (Rubus rosifolius) and stinging nettle (Urtica incisa) and vines such as giant water-vine (Cissus hypoglauca), that soon envelop the reduced tree crowns. When this occurs, the vines may dominate the canopy for decades, smothering the recovering tree crowns, preventing a burnt forest from recovering for many years. If fires occur too often, trees that have been unable to recover, die, and if the canopy remains open for long enough, the rainforest can be invaded by flammable eucalypts from the surrounding sclerophyll forests. Fires are a major factor in the Southern Warm Temperate Rainforests from becoming more continuous, maintaining the patchwork of rainforest. Rainforest expansion can occur if fire is excluded, but this occurs where soil fertility and water are less limiting more often in northerly areas.

Although they have a patchy nature, this type of forest is found over large areas from Shoalhaven Bay to the Victorian border, and along the Gippsland coastal foothills. In New South Wales, the cumulative area covered by the rainforests is as much as 200 square kilometres. These forests have suffered less than other types of rainforest because of the steep nature of their habitat, and the infertility of the soils they grow on. Bell Bird Creek Nature Reserve, a few km north of Eden, is a good example.

Sources & Further reading