Rainforest Answers

by Deb on October 14, 2011


Do you know about rainforests? If you’d like to try the quiz, close your eyes and click back.

1.     Rainforests are millions of years old. They developed before the last ice age when the world was much warmer and covered much of the tropics and sub-tropics. What we have left today are the remnants. They look exuberant but they are part of a cycle. If that is disrupted it is almost impossible for them to reclaim their former glory. Rainforests obviously need a lot of rain, they also need nutrients to support all that growth. But they don’t get it from the soil.

The first plants that began the rainforest used the soil nutrients and stored them in themselves. Now, the nutrients are all locked up in the incredible biomass of the rainforest. This is why there are so many parasitic plants in rainforests, they are living on the nutrients in the trees rather than the soil. Rainforest soil tends to be very shallow and nutrient poor, in the hot, humid, dark conditions decomposers work so quickly that fallen leaves or dead plants don’t have the chance to enrich them.

In traditional slash and burn agriculture some of the trees would be felled and burnt in place and others left for shelter. The ash would be dug in to return some nutrients to the soil but the garden could still only be used for a year or two before a new one was needed. The gardens were relatively small because all the work was done by hand and still surrounded by rainforest. Even then, it would take many years to become fertile again. It’s thought that some of the grasslands on New Guinea were created by slash and burn agriculture.

Today large areas are cleared and the nutrients locked in the trees are removed because they are used as timber. When large numbers of trees are removed the canopy is opened up and the full strength of the rain reaches the ground. In a healthy rainforest the canopy catches and diverts the rain, it is broken up, bounced off trunks and branches or runs down them rather than hitting the ground directly. A full power storm suddenly hitting the thin topsoil quickly erodes it away, so even those poor nutrients are lost.

The loss of the shelter also makes it difficult for young plants, as there is nothing for their roots to anchor in, they are flattened by storms and exposed to bright sun they aren’t adapted for. Most rainforest saplings are designed to germinate in gloom and humidity, the light disrupts them and the sun dries them out.

Even if rainforest clearing stopped today, they would not regenerate by themselves and it would probably be impossible to recreate them. Once these remnants are gone, that’s it.

2.     Rainforests are not just tropical! There are temperate rainforests too, and most Australian Rainforests are temperate.Eastern Australian Rainforests

Around the NSW/Queensland border is an area known as the Gondwana Rainforests, because it appears that when Australia was part of Gondwana it was covered in this type of temperate rainforest. These are remnants of a forest that was around with the dinosaurs.

Temperate rainforest mapTasmania has a large proportion of the world’s remaining temperate rainforest.

World Tropical Rainforest Map

There are patches of tropical rainforest throughout the NT and Kimberley, but most of them are very small and occur along rivers.

3.     What’s black and blue and wears a helmet? A cassowary of course! They are ratites, large flightless birds closely related to emus, ostriches and kiwis. They live in the deep forest in Australia and New Guinea and feed on fallen fruit, their shaggy black feathers make them almost invisible in the gloom. The bright blue appears to be like a peacock’s head, to show off to other cassowaries. Unlike peacocks females are more colourful, probably because they have something of a role reversal with the males staying and minding the nest and chicks.

Double Wattled Cassowary

Image thanks to Phyzome

The helmet is something of an unknown, with several possible explanations. It may be a protection when they are running through bushes or feeding under trees – it is the right shape and composition to protect their head from heavy seeds the size of golfballs falling on them.

It could also have an acoustic function, to amplify very deep sounds. It’s been discovered that some species of Cassowary make very low frequency ‘booms,’ right at the edge of human hearing ability. It could be a way of communicating with each other in dense, dark forest. The video below has recordings of some of their sounds.

4.     The food of the gods is quite literally chocolate. The main chemical in cacao beans is called theobromine, and the scientific name of the cacao tree is Theobroma cacao. It was named by Linnaeus himself when he developed our system of naming living things, and is derived from the Greek roots ‘theo’ or gods and ‘brosi’ or food. It is closely related chemically to caffeine.


Fresh beans inside a cacao pod.


Images thanks to Jodi Rowley of the Australian Museum.

5. The picture at the top is a vampire flying frog. They have recently been discovered in rainforests in Vietnam. You can see the extended webbing between their toes that lets them leap and glide through the canopy. They rarely if ever come down to the ground, laying their eggs in water trapped in hollow trees.

Their tadpoles are the vampires – most tadpoles have mouths like beaks, but the flying vampire frogs have two little black fangs. It isn’t known what they are for. One possibility is that they are to slice open eggs, as frogs who lay eggs in tiny pools are known to lay unfertilised eggs with them as food for their babies.

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