Wet Eucalypt Forest
Evenaged stands of eucalypts over a dense understorey
There are two main types of wet eucalypt forest.
Wet sclerophyll forest has a tall eucalypt overstorey and a dense understorey of ferns, soft broad leaved shrubs such as and musk, blanket bush, dogwood and small trees.
Mixed forest has a tall eucalypt overstorey and a rainforest understorey.
Mixed forest about 100 years after the last fire
Mixed forest about 300 years after the last fire
Wet eucalypt forests occur where the rainfall is between 1000 and 1500 mm per year. Fires occurring on average once every 20 to 100 years maintain wet sclerophyll forest. Mixed forests have fires on average once every 100 to 400 years.
If there are no fires within around 100 years, and there is a source of rainforest seed, the broad-leaf understorey species begin dieing and rainforest species become the dominant understorey. With no fires within 350 to 400 years the eucalypts die out and the mixed forest becomes pure rainforest.
Wet eucalypt forests are relatively simple in terms of structure and diversity of plant species. Moisture-loving ferns, mosses and fungi dominate the groundcover. Like rainforest, its deep, moist litter layer supports many more types of invertebrate creatures than it does vertebrate animals. Eucalypts in these forests often grow to more than 60 metres in height. A swamp gum (Eucalyptus regnans), growing in the southern forests, is the tallest flowering plant in the world with a height of over 96 metres.
Blanket bush
Musk
The eucalypts in a wet eucalypt forest are often all the same age since eucalypt seedlings cannot survive in dense shade. They date back to the last fire that occurred in the area. The fire would have burnt all the litter and plants in the forest exposing bare soil and letting light reach the forest floor. Seeds falling from the eucalypts killed in the fire would all germinate and grow at the same time. Understorey plants begin developing as their seeds are blown into the area, are brought in by birds or on animal fur or develop from seeds present in the ground.
Many plants in the wet sclerophyll forest understorey, like the blanket bush and musk illustrated, have very pale undersides on their leaves. This is a direct result of low light levels beneath the understorey. The plants have nearly all their green pigment (chlorophyll) on the top of their leaves that are exposed to the sunlight filtering through the open eucalypt canopy. (Chlorophyll absorbs light energy at the blue and red ends of the light spectrum and reflects green light.)
As a wet eucalypt forest ages the number of tree stems diminish and the forest takes on a more open and park-like appearance. The dense understorey restricts the entry of light energy. Plants that can grow in the low light levels have little food energy as a result and thus provide little food for ground based animals.