At maturity wet forest has a tall open canopy of eucalypt trees over a well developed understorey of trees, shrubs or tree-ferns that prevent much light reaching the forest floor. In Tasmania some of the canopy trees in wet forests can reach gigantic heights of up to 100 m, and are the tallest hardwood trees known in the world. The lack of light prevents the regeneration of shade-intolerant species including the dominant eucalypt species. The dominance of eucalypts and their inability to regenerate without a major disturbance distinguishes wet forest from other vegetation types. The understoreys of these forests vary greatly depending on the forest age, fire history and the local environment, especially soil fertility. Wet forests usually occur in high rainfall areas (>1000 mm per year), but in areas where fire is infrequent they may also occur in drier areas with reliable water supplies (river gullies). They are also most typical of moderately fertile to fertile well-drained soils but where fire is infrequent can also occur on low fertility acid soils.
There are several eucalypt species that may dominate wet forest. Most swamp gum (Eucalyptus regnans) and yellow gum (Eucalyptus johnstonii) forests are classified as wet forest. Other eucalypt species that commonly dominate wet forests may also occur over heathy, shrubby, sedgy or grassy understoreys, which are called dry forests because of the open understorey in which eucalypts may regenerate in the absence of major disturbance. Eucalypts that occur in both wet and dry forest include species such as white gum (Eucalyptus viminalis), blue gum (Eucalyptus globulus), stringybark (Eucalyptus obliqua), gum-topped stringybark (Eucalyptus delegatensis), Smithton peppermint (Eucalyptus nitida), alpine yellow gum (Eucalyptus subcrenulata) and snow gum (Eucalyptus coccifera).
Broad-leaved tall shrubs and small trees such as dogwood (Pomaderris apetala), musk (Olearia argophylla) and blanket leaf (Bedfordia salicina) commonly form a prominent layer in wet forest. Wet forest can also have a ground layer in which ferns, excluding bracken, are dominant, or an understorey dominated by temperate rainforest trees, such as myrtle beech (Nothofagus cunninghamii), sassafras (Atherosperma moschatum), and celerytop pine (Phyllocladus aspleniifolius). Forest understoreys dominate by rainforest trees are often called mixed forest and are characterisic in long unburnt and infrequently burnt areas (less than one fire every 100 years or more). More frequently burnt wet forests have understoreys dominated by broad-leafed shrubs or in less fertile or drier situations may include prickly leaved shrubs and sedges.
Where to see wet forest
Wet forest can be seen in all parts of Tasmania. Near Hobart it is found on the middle slopes of Mt Wellington. Near Launceston it is found on the mountains to the east and north west of the city.
Biodiversity values of wet forest
Although some wet forest areas have been converted to plantations they remain extensive in Tasmania and most wet forest types are well reserved. Nevertheless, large areas have been modified by wildfires and logging, so that the extent of oldgrowth forests with rainforest understoreys, and the number of hollow bearing trees has been considerably reduced. The most heavily cleared and modified wet forest communities are swamp gum forest and blue gum forest. The latter community has lost a substantial part of its range in Tasmania and is poorly reserved.
Wet forest contains few threatened plant species but it is an important habitat for hollow-dependent fauna and many rare and threatened fauna. Significant fauna include the little pygmy possum (Cercartetus lepidus), eastern quoll (Dasyurus viverrinus), long-nose potoroo (Potorous tridactylus), and the scrubtit (Sericornis magnus) which is an endemic bird restricted to the ground and leaf litter layer of wet gullies. Several threatened birds including the swift parrot (Lathamus discolor) use hollows in both wet and dry forest for nesting purposes. The wedge-tailed eagle (Aquila audax), and white goshawk (Accipiter novaehollandiae) sometimes choose the canopy of tall eucalypt trees in wet forest to make their nest. Wet forests are also important for invertebrates, including landsnails such as the Tasmaphena lamproides and Helicarion rubicundus which have restricted distributions. Wet forests provide habitat for 15 species of primitive moth in the family Hepialidae, many of which are endemic. Wet forests dominated by blue gum mostly occur on private land. They form important habitat for the vulnerable swift parrot.
Refer to Threatened Species for more information.
Management issues in wet forest
Wet forest needs a fire every few hundred years to enable regeneration of the eucalypts. However, frequent fire will eliminate the ferny and broad-leaved understories, converting them to dry forest. Planned fire in wet forest is extremely dangerous because the fuel levels are high and it can only be burnt in the most extreme weather conditions. Wet forest is of little use to graziers because it has little fodder, although it may be valuable for shelter in some situations. Heavy grazing or logging can open up the understorey and allow the invasion of weeds, especially blackberry (Rubus fruticosus
The critical management recommendations for wet forest are:
- Exclude fire. The only exception to this recommendation is where it may be necessary to burn wet forest after logging in order to promote the regeneration of eucalypts. In this situation the Forestry Code of Practice should be followed. Contact Forestry Tasmania: www.forestrytas.com.au.
- Control weeds. Weeds are not usually a problem in wet forests. However, blackberries can become a problem after logging, fire or grazing.
- Maintain stags, logs, and mature trees with hollows unless they are a particular safety issue, as they provide important habitat for fauna.