Flowering in the Rainforest

Skyrail Nature Diary: November 2012

November is the time of the year when we usually start noticing the heat, although the heat sometimes turns up as early as late September. The flowering in the rainforest is on the ebb, the trees are getting ready to put out fruits for the onset of the rainy season. Black Bean is finishing its flowering and will soon be fruiting. The flowers are borne on the branches, a phenomenon known as ramiflory. The flowers are large red and yellow pea flowers. The wooden pea pods are borne on the branches and contain 2 to 5 large seeds with a seam on one of the flat sides. The seeds are mildly toxic and were eaten by the Djabugandjii after extensive leaching in running water. Research has come up with an unusual use for the toxins in the form of a treatment for certain types of cancer. The leaves are compound (several leaflets on each leaf) and smell strongly of cucumber when crushed.  Black Bean was commercially harvested for its beautiful dark timber. Red Tulip Oak is just in the process of finishing its fruiting. The fruits are large round seeds with a formidable papery wing attached on one end. This gives the seeds a rotating movement towards the ground like a crooked helicopter. There are often large numbers of seedlings on the ground the first couple of years or so after a fruiting episode. The vast majority of seedlings will perish. The timber is dark red and quite hard and was harvested as cabinet timber. The Djabugandjii used the large buttresses as shields. The leaves are trifoliate (each leaf consists of three leaflets) and have a layer of shiny brown hairs on the underside.

This month we will also be looking at life on the forest floor. In a rainforest there are generally three main vertical layers; the canopy, the sub-canopy and the forest floor. Depending on the complexity of the rainforest in question there may often be even more layers. Most of the activity in the rainforest is in the canopy, the topmost layer. In the canopy there will be things like orchids, ferns, countless insects, spiders and most of the mammals and birds in the rainforest. As you move downwards from the canopy, light diminishes drastically. Whilst there is 100% light in the canopy, this drops to approximately 10% just a few metres under the canopy. The light drops to as little as 1% on the forest floor. Unlike what people often think, the rainforest floor is not an impenetrable mass of vines and bushes. There is simply not enough light for that. If, however, the forest has been disturbed such as in times after a major cyclone or logging, more light hits the ground and vines and pioneer trees start cluttering up the forest floor. Surprisingly there are some plants that manage to live off very low light levels on the forest floor. The best adapted are various ferns and mosses. These plants require high levels of moisture and the forest floor is generally a very damp area with a much lower evaporation rate than the canopy. At Red Peak the Robber Fern and the Native Wishbone Fern are the most obvious of the low light tolerant ferns in the area. There are also some small tree species that do well on the forest floor. At Red Peak there are Native Mangosteens, Cherry Beeches, Native Nutmegs and the primitive Bubbias and Lethedons. All of these trees grow very slowly in the low light conditions and generally don’t like full sun, which causes their leaves to bleach and even shrivel. As for animal life on the forest floor the level of food available dictates what is around. The Barron Gorge has low quality soils which means that the trees are often laced with a variety of toxins to keep animals away. This is why there are no possums or tree kangaroos in the Barron Gorge.

The Cassowary is possibly the best known animal in the rainforest. Cassowaries are large flightless birds with very tiny wings and long quill shaped feathers. The name means “helmet head” and refers to the distinct casque on top of the small head. The casque is made up of thin bony struts and lots of blood vessels coated with a layer of keratin on the outside. The casque is believed to have two main functions. The most obvious is for marking an individual’s social status. Female cassowaries always have the biggest casques. A less obvious function is to provide communication over large distances. Research shows that cassowaries have a low frequency rumble that has the same frequency as the surrounding trees’ natural vibration. This means that the rumble will pass unhindered through the trees and drift impressive distances to mark territory or call for a mate. On the throat they have two red wattles. The powerful feet look like dinosaur feet and have a large sharp claw used in defense and territorial fights. Male cassowaries look after the striped chicks. Cassowaries are important seed dispersers in the rainforest. A lot of large fruits are simply too heavy to spread much on their own and have inhibiting chemicals in the seed coat that prevent germination until a cassowary eats them and digests the inhibiting chemicals. Cassowaries also eat dead animals, mushrooms and fish. Cassowary droppings are ideal for revegetation as they germinate quite readily without any assistance.

The Musky Rat Kangaroo is one of only two daytime mammals in Australia. The other is the almost extinct Numbat in Western Australia. Musky Rat Kangaroos are unusual “kangaroos” in that they have a big toe on their hind feet and very little fusing of the toes. This characteristic causes them to bound rather than hop. These beautiful dark furred creatures have a slightly ratty like appearance and eat mostly fruits on the forest floor. Insects and fungi are alternative food sources when fruits are scarce. Fruits are often hoarded which helps in dispersing them away from the mother tree. Musky Rat Kangaroos usually give birth to two joeys, occasionally three, and they are kept in the nesting site as they have no pouch.

Red-legged Pademelons are small “wallabies” with reddish legs and are quite shy. They are perfectly adapted to life in the rainforest although they also venture into wet sclerophyll forests. Their diet consists of leaves, fruits and grasses that grow on the rainforest edges. Their hop is unusual in that it is more horizontal than usual in kangaroos and wallabies to make it easier to move quickly through dense vegetation. Pademelons are active throughout the day but tend to rest between midday and early afternoon. These beautiful mammals are solitary.

By Tore Lien Linde