Australian Natural History:

Tropical
Rainforest

‘Rainforest is the single most important biological
resource 
we hold in trust for Australia’s future.’

Professor Michael Archer in Conserving Australia’s Rainforests,
Aila Keto and Keith Scott, 1995

Text Alan Fox – Photography Steve Parish

The World-Heritage-listed Wet Tropics rainforests from Mackay to Cape York are Australia’s richest and most biologically diverse, with around 1160 tree species. All are within 200 kilometres of the ocean. Rainforests to the west and south of this area progressively lose species and become less complex, with as few as 80 flowering species in Tasmania. Some individual rainforest species, such as the figs (Ficus spp.), have tiny, very specialised residual populations that are reminders of wetter times, hidden deep in the semi-arid and arid interior.

The lushest, most magnificent and diverse area of tropical rainforest covers about 7500 square kilometres between Ingham and Cooktown. This is the heart of the 894,000 hectare Wet Tropics World Heritage Area, inscribed in 1988 for its “outstanding natural universal values” and for being an example of “superlative natural phenomena”. This primitive rainforest is largely pristine, undamaged by human interference or natural catastrophe. Its intactness means it operates almost as a huge interdependent organism, parts of which are ancient. One Macintyre’s Boxwood tree is 80 centimetres in diameter and aged at least 3500 years old!

Rainforest Gallery – click below and scroll

 

Wet Tropics rainforests are such uniquely located and productive habitats that some 1164 genera of vascular plants have been recorded, including 13 of the 19 angiosperm families, the most primitive families of flowering plants worldwide. Two of these families are found nowhere else. No less than 50 species in the most primitive families are endemic to the Wet Tropics, but overall at least 700 plant species are unique to this place.

Of the more than 400 Australian fern species, 240 are found here, with about 40 endemic to the region. To this impressive list we can add 90 species of orchid, with 40 of these being endemic. This abundance of flora has meant names such as Daintree, Cape Tribulation, Mossman Gorge, Downey Creek and Tully Gorge are rightfully imbedded in environmental history and these areas are to be protected as wet tropical rainforest wonders of the world.

From the lowlands, almost from sea level, to the top of Mount Bartle Frere there is a considerable range in temperature, humidity and soil type, expressed by various mixes of rainforest plant species. The area experiences 60% of its precipitation in just four months (December to March) with rainfall peaking on Mount Bartle Frere at around 10,000 millimetres. The average is about 2800 millimetres, which is near the optimum level for rainforest. Thus, graduations of habitat occur — the lowlands are very wet; the foothills, wet; the uplands, cloudy and wet; the highlands, moist; the peaks, extremely wet and cloudy; and the western aspects in rain shadow.

The most luxuriant forests are in lowland rainforest. Imagine the forest as a multi-storeyed block of apartments. The penthouses are the tall emergent trees, such as Flooded Gum, Queensland Maple, Candle Nut, Kauri Pines and figs, which lift above the main canopy. These emergents have very large supporting root buttresses to withstand extra wind buffeting above the general canopy. Numerous minor levels in the canopy give these trees a heavy load of fern and flowering epiphytes, as well as a tangle of woody vines and rattan palm. Usually, less than 5% of diffuse sunlight reaches the wet tropical rainforest floor. Consequently, the floor is often quite open, with most plants that have trunks lifting their large, light-seeking leaves far above. Where streams break the darkness or swampy, poorly drained ground makes up the forest floor, palms, such as the elegant Bangalow and Fan Palms may become dominant. Both tree size and leaf size diminish as one ascends higher into the ranges.

Fruits of the Forest

 

Many rainforest trees produce succulent fruits, some of which are borne directly along the trunk and branches, a process known as cauliflory. Often these fruits have brilliantly coloured flesh covering a hard kernel. The green gloom of the rainforest is punctuated by flashes of colour in the stunning purple-blue of the Blue Quandong; the apricot, vile-smelling fruit of the primitive Austrobaileya vine; the cream of Lemon Aspen; the vermilion of Lacewing Vine and Alexandra Palm; and the shining black Variegated Grape. All of the 33 wonderful Syzygium Satinashes add to the rainforest’s palette. These species comprise just a fraction of the “fruits of the forest”, all brilliantly painted in the eponymous book by William T. Cooper.

All of this vibrant colour is not mere decoration, it has a clear purpose. It is a highly effective attractant for animal seed-dispersal agents in this fruity “supermarket”. Agents come in many forms, from forest birds to rats, possums, tree-kangaroos, Musky Rat-kangaroos, fruit bats and Southern Cassowaries.

Wet tropical rainforest habitat has more layers than eucalypt forest. There is a dense, interlinked upper canopy of extreme species diversity and productivity, particularly in flowers, fruits and leaves. Some very tall species, such as figs, break right through to become immense emergents. Tying many of the individuals together and connecting them to the ground are networks of vines or lianes. Larger trees carry huge loads of epiphytes and are “gardens of life”, where climbers such as ants, other invertebrates, reptiles, frogs and birds can nest — this is a very special micro-habitat within the larger system. Light and wind conditions below the canopy are subdued and control what may grow beneath. Below this primary canopy, palms form a storey and usually outpace the young trees,which are impaired by the lack of light. Below the palms and young trees are numerous smaller climbers, such as rattans, Lawyer Vine, peppers, Walking-stick Palms and shrubs.

 

Tree ferns may overtop this ground layer. Most of the lower-layer plants are awaiting a storm to open up the light. All the while, collecting on the floor is a considerable depth of the combined litter fall from plants and animals. The moist, warm conditions maintain a high rate of fermentation — a feature used by the Brush-turkey in building its incubator nest. There is also a constant release of nutrients from this mulch. Moisture and nutrients are in abundance, so only shallow roots are needed; instead, trees grow huge plank buttresses and props to assist their standing. If we think of all of the rainforest nutrient as a bank account, we find that more than half the capital is in the living forest itself. Human use of rainforest tends to destroy that 60% of infrastructure in one attack!

Each tree leans on its surrounding neighbours, providing access for fruit-eating and predatory climbers — lizards, invertebrates, small mammals, possums, frogs and even tree-kangaroos — to reach from the ground to all parts of the canopy.

Classic birds:

 

There are at least 137 species of closed forest-dependent (rainforest and mangrove) in the Wet Tropics.  Some of the more classic species are the Orange-footed Scrubfowl; Brush-turkey; Satin, Golden and Tooth-billed Bowerbirds; Rose-crowned, Topknot and Pied Imperial-Pigeons; Figbird; Noisy Pitta; Victoria’s Riflebird; Spotted Catbird; Australian King-Parrot; Red-cheeked Parrot; Palm Cockatoo; Double-eyed Fig-Parrot; Eclectus Parrot; boobook; Rufous Owl; Northern Logrunner; Spectacled Monarch; Rufous Fantail; Golden Whistler; Grey-headed Robin; Pale-yellow Robin; Lovely Fairy-wren; Chowchilla; Bower’s Shrike-thrush; Macleay’s Honeyeater; Bridled Honeyeater; Yellow-bellied Sunbird; Eastern Whipbird; Grey Goshawk; Buff-breasted Paradise-Kingfisher.
Above and clockwise: Cassowary with chicks; Paradise Riflebird and Golden Bowerbird male enticing a female to its bower.

Classic mammals:

 

Musky Rat-kangaroo; Lumholtz’s Tree-kangaroo; Red-legged Pademelon; Herbert River Ringtail Possum; Lemuroid Ringtail Possum; Green Ringtail Possum; Striped Possum; Fawn-footed Melomys; Giant White-tailed Rat; Yellow-footed Antechinus; Spotted-tailed Quoll; Tube-nosed Bat; Diadem Bat; Ghost Bat; Spectacled Flying-fox; Little Red Flying-fox; Black Flying-fox; Blossom Bat.
Above: The unique Musky Rat-kangaroo, Australia’s smallest macropod.
Below:  Lumholtz Tree Kangaroo

Classic frogs and reptiles:

 

Green-eyed Tree-frog; Red Tree-frog; Northern Barred Frog; Lesueur’s Frog; Robust Frog; Dwarf Tree-frog; Orange-eyed Tree-frog; Dainty Tree-frog and White-lipped Tree-frog; Red-throated Rainbow Skink; Spiny Skink; Pink-tongued Skink; Chameleon Gecko; Red-sided Skink; Lace Monitor; Boyd’s Forest Dragon; Brown and Green Tree Snakes; Carpet Python; Scrub Python; Green Python
Above, top to bottom: Orange-eyed Tree Frog; Boyds Rainforest Dragon and Green Python.

Classic spiders and insects

 

Cairns Birdwing, Ulysses, Orchard, White Nymph, Australian Rustic Red Lacewing, Green Spotted Triangle, Union Jack and Cruiser Butterflies; Hercules, Yellow Emperor and Blue-banded Moths; Stag, Mueller’s Stag, Rhinoceros, Green Leaf, Jewel and Pink-spotted Longicorn Beetles; King Cricket; Spiny Long-horned Grasshopper; White-kneed Weta; mantids; stick insects; katydids; the world’s largest dragonfly (Petaleura ingentissima); numerous bugs; Jumping Spider; Golden Orb-weaver; Spined Spider; Cataxia and Homogona trapdoor spiders.
Above: Cairns Birdwing Butterflys

Photographing Australia promotion
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