Rainforest is dominated by a dense canopy of non-eucalypt tree species over an understory of climbers (which often climb well into the canopy and become part of it), broad-leafed shrubs, tree-ferns, epiphytic ferns, ground ferns and small soft-leafed herbs. It is found on deep loamy soils of sheltered gullies at altitudes ranging from about 200 to 1200 m above sea level and rainfalls between 800 and 1500 mm a year. About 85% the area once supporting Rainforest in Victoria falls on public land while a little over one third is represented in conservation parks and reserves. All Victorian rainforest is protected from clearing and timber harvesting.
There are two basic types of Rainforest in Victoria; Cool Temperate Rainforest (CTR) and Warm Temperate Rainforest (WTR) both of which are listed as threatened under the Flora and Fauna Guarantee Act (FFG).
CTR is found in sheltered hills at higher altitudes (700-1200 m) with higher rainfall (1100-1500 mm) cooler temperatures (average maximum and minimum temperatures around 2°C less than WTR) in gullies surrounded by Wet Sclerophyll Forest (WetSF). Its principal tree species is Nothofagus cunninghamii (Myrtle Beech) in central and western Victoria and Elaeocarpus holopetalus (Black Oliveberry) in the east, with Atherosperma moschatum (Southern Sassafras) and Acacia melanoxylon (Blackwood) commonly co-dominants in all areas. Eucalyptus regnans (Mountain Ash) is often present as an emergent, tall tree along the margins.
WTR is found in eastern Victoria along steep creeklines at lower
altitudes (200-1000 m) with lower rainfall (700-1100 mm) warmer
temperatures (average maximum and minimum temperatures around 2°C more
than CTR) in gullies
surrounded by Damp
Sclerophyll Forest (DampSF). Its principal tree
species is the broad-leafed Syzygium smithii (Lilly Pilly) with
Acacia melanoxylon as a common co-dominant.
The two types of Rainforest share a significant proportion of understory species, with ferns (often more than half the species), epiphytes and fleshy-fruited plants being the major kinds. The dominance of tree-ferns in a secondary layer beneath the trees creates a humid and more or less stable microclimate within which epiphytic plants such a ferns, fork-ferns, filmy ferns, orchids and Fieldia australis (the only epiphytic dicotyledon in Victoria) can develop. The trunks of tree-ferns, Dicksonia antarctica (Soft Tree-fern) in particular, are the most heavily utilised substrates for these species although fallen logs and large tree bases are also common surfaces for colonisation.
Apart from the dominant tree species the most noticeable difference between CTR and WTR is the greater number of climbers (lianas) in the latter and its generally higher number of species. There are typically nearly twice the number of plant species in a stand of WTR as CTR and a significant part of this increased diversity is climbers; there are normally ten or more species in a hectare of WTR compared with two or three in CTR. In addition the climbers in WTR often form a significant part of the canopy, sometimes almost completely covering the Lilly Pilly and Blackwood they are climbing on. Unlike the climbers of CTR many of those in WTR have fleshy fruit (sometimes quite large; Jungle Grape, Red Passionflower) which provide the local frugivorous and omnivorous fauna with a wider variety of food. Consequently the numbers of Satin Bowerbird and Olive-backed Oriole are greater in WTR while nomadic species such as Topknot Pigeon, Brown Cuckoo-dove, White-headed Pigeon and Grey-headed Flying-fox are only found in WTR.
WTR is often more weedy and shows greater signs of disturbance that CTR principally because there are sometimes stands of WTR which have had the surrounding forest removed or altered. In many circumstances the composition of the flora remains largely intact but around the edges non-native climbers, brambles, thistles, broad-leafed shrubs and grasses may be so dense that the rainforest itself is hidden. While CTR is usually less obviously disturbed, the development of a disease called Myrtle Wilt, caused by infection by the native fungus Chalara australis, has become a serious problem in parts of the Otway Ranges, about 150 km south-west of Melbourne, and other areas to the east. The fungus invades Nothofagus cunninghamii either via wounds in the branches or via root contact with infected plants. A healthy tree may be killed within a year or two after infection.
The key concerns with Rainforest conservation in Victoria centre around two apparently unrelated factors. One, is that Rainforest occupies only small areas which are usually very narrow (a characteristic it shares with Riparian Forest) so any disturbance to the surrounding forest can expose it to invasive weeds and dehydration. Any roads or bridges that cross it will effectively fragment it more and its association with rivers and other drainage lines means that it is a sink for damaging runoff from land-use upstream. The other, is that Rainforest definition has always been a rather fluid and controversial one so, despite the legal protections offered by the FFG, Rainforests can still suffer damage while those involved can argue that the vegetation in question doesn't fulfil their concept of what it is.
From a scientific and plant geographical perspective Victoria has had rainforest since the term was originally coined by the German botanist, Andreas Schimper, in his 1898 opus on plant geography. Schimper recognised both tropical and temperate rainforests and specifically mentioned the presence of the latter in Australia, based on descriptions of Nothofagus-dominated forests (largely Tasmanian), in 1878, by the Catholic priest and naturalist Julian Tenison-Woods. Despite the presence of similar forests in Victoria, this recognition had little effect on Victorian botanical literature and, until the late 1900s, CTR was known as Fern Gully vegetation while WTR was simply called Jungle.
During the 1970s, Victorian botanists began to refer to both vegetation communities as rainforest and in the early 1980s the first scientific reports and vegetation maps were published which defined and mapped their distribution. This change in nomenclature coincided with an upsurge in the systematic survey of native vegetation and its formal classification into recognisable communities, and with the worldwide concern for the conservation of rainforests. Rainforest studies intensified in Victoria and an unambiguous definition was developed as a guideline for management and protection. This definition underwent controversial changes in subsequent years amid heated and sometimes vitriolic debate, a debate that was never satisfactorily resolved.
Today each form of CTR and WTR is defined, loosely, in the DSE Ecological Vegetation Class (EVC) benchmarks and maps of their extent are available on the Department's website. Nevertheless, the mapped units are frequently regarded as guidelines rather than definitive boundaries. and formal definitions, in the form of FFG Action Statements, are yet to be published.
© Paul Gullan, Viridans Biological Databases