Australia: The Land Where Time Began

A biography of the Australian continent 

Rainforest - Cape York Peninsula

Tropical rainforests (vine forests) are found on the Cape York Peninsula and from just south of Cooktown to just north of Townsville. The rainforests in the Wet Tropics have more continuous rainfall than those on the Peninsula, that receive less rain during the wet season and have a longer dry season that is drier than the dry season in wet tropics. Rainforest needs heavy rain during the wet season to survive. During the wet season the air in the rainforests is saturated. The Peninsula has about 5 % of its area covered by rainforest, the most luxuriant and extensive being in the area of Iron Range and McIlwraith Range, on the wetter parts of the uplands and the lowlands. Less extensive and patchy rainforests occur in the northern part of the Peninsula, as at Lockerbie Scrub (near Cape York - on the northern tip of the peninsula), on the McHenry Uplands sandstone in the catchment of the Jardine River and on Heathlands Reserve east to the Olive River Dunefields. These northern rainforests are called monsoon rainforests because they are drier than those in the wet tropics, receiving more of the rain in the monsoon season.

South from the Jardine River towards Moreton, and west towards Weipa, there are very small tracts of rainforest, mostly less then 50 Ha, growing in deep red earths derived from laterite and bauxite. To the north and south of Weipa there are also small areas growing on dunes in sheltered areas. In the southeast of the Peninsula there are some patches between Bathurst Heads and the Starke River. They differ in composition fro those of the Wet Tropics to the south and those of Iron Range and McIlwraith to the north. There is a dry corridor around Princess Charlotte Bay area that separates them from those of Iron Range and McIlwraith Range. A number of major river systems, like the Jardine, Archer and Wenlock are fringed with rainforest trees in the wetter parts.

Like other rainforests in Australia, the tropical rainforests of the peninsula are a refuge for relict biota related to Gondwana species. Unlike other rainforests in Australia, the Peninsula rainforests also harbour species from New Guinea, as well as their own suite of endemic species.

Tropical rainforests are more densely populated and biodiversity is much higher than in the less productive vegetation types, and they are even more 3-dimensional than other forest types, whole ecosystems existing in the canopy. The fauna of the tropical forests are usually highly specialised to one of the storeys of the rainforest - the litter layer on the forest floor, the understorey and the canopy. Each level of the rainforest is populated by a different set of plants and animals.

The microclimate of the floor of tropical rainforests is darker, cooler and damper than outside the forest. Rainforests grow on well drained soils that isn't waterlogged, but that has enough available moisture, either from rain or from watercourses, to support luxuriant growth. Saplings from seeds germinating on the forest floor have to struggle to survive, competing with a multitude of other saplings of the same and different species for space, nutrients and light. They put out roots at or near the surface, because that is where most of the nutrients are located. Rainforest soils are often nutrient deficient, most of the nutrients in the system being in the litter and the upper soil layer, as the litter is rapidly recycled by the numerous creatures, fungi and bacteria that keep the nutrients moving from the soil to the trees and back to the soil, aided by the permanently damp conditions in the soil and litter. Nothing is wasted here, tree roots snake across the forest floor making use all available nutrients. Roots grow out from the base of the trees and from the buttresses. Buttresses at least partially keep the tree upright, but their full function is not fully known.

At some places, such as in Lockerbie Scrub and McIlwraith Range, the buttresses of some fig trees are as high as 10 m. The forest floor is littered with leaves, fruit, branches, etc. at various stages of decomposition. This all provides a diverse range of substrates for the many mosses, lichens and liverworts, and fungi, the fruiting bodies of which emerge from the litter is a wide range of colours, shapes and sizes, some luminescing at night.

Also on the litter of the forest floor is a strange leafless flowering plant called Saprophytic Fungus roots (Balanophora fungosa). The white male flowers encircle the stem below the female flowers. Another strange plant is the Giant Climbing Orchid, (Pseudovanilla foliata), that produces large masses of sweetly scented golden yellow flowers. They have a brilliant orange-red labellum (lower petal). The brownish-green stems of this orchid can adhere closely to tree stems by having a flattened lower surface, allowing them to penetrate into the crevices in the bark to obtain nutrients. These orchids are found in the McIlwraith Range.

Fauna

The organisms such as fungi and bacteria break the litter down into smaller pieces that then becomes available to the hordes of detritivores that form the next link in the recycling chain, worms, springtails, amphipods, mites, millipedes and snails, all living in the leaf litter. The breakdown of woody parts such as logs and branches are broken down by termites, cockroaches and some beetles, which increases the speed of the return of the nutrients to the soil, where it can be reused for more tree growth.

Some beetles of the family Passalidae are common around decaying logs. These beetles live in family groups, adults feed on decaying wood, and feeding chewed wood to their cylindrical, whitish-grey larvae. In these larvae the 3 rd pair of legs are short and paw-like, and are used to produce high-pitched sound by rubbing them against their 2 nd pair of legs. They also stridulate in the same way as other insects such as cicadas.

There are also weevils that live gregariously in logs. For example, Baryrhynchus lineicollis, found only in the Iron Range in Australia, though also found in New Guinea and elsewhere in the world. Another species, Ithystenus hollandiae, from the Peninsula, the Wet Tropics and New Guinea. The males of this species have a long rostrum that they use as weapons when fighting over females, trying to push their rostrum under a rival male to turn him over what not affecting the female that can be beneath him.

The colourful predaceous staphylinid beetle. Actinus imperialis, is known only from the areas on Iron Range and McIlwraith Range, where it is attracted to carrion and dung, using its very large jaws to catch flies attracted to the dung.

In the large flightless giant carabid beetle Mecynognathus daemelii the males have a disproportionally large head with massive mandibles that can be up to 18 mm long. Large specimens of this beetle can grow up to 60 mm in length. Adults are mostly active through the wetter months in rainforests and adjacent heath between Lockerbie and Heathlands Reserve. Another flightless carabin, Notobax monteithi, that is restricted to the Iron Range rainforest, a recent find on the Peninsula, is one of the few relatives of the wingless beetle fauna of the Wet Tropics. Another invertebrate common in the rainforests of Iron Range and McIlwraith Range is the long-legged, tail-less whip scorpion Charinus pescotii

Sources & Further reading

Dawn W. Frith & Clifford B. Frith, Cape York Peninsula: A Natural History, Reed, 1995