The Eucalyptus Tree in Australia
ANNOUNCER: Part 4. You will hear a student giving a presentation about a type of tree known as the eucalyptus, which is common in Australia. First, you have some time to look at questions 31 to 40. Now listen carefully and answer questions 31 to 40.
SPEAKER: Today, I'm going to talk about the eucalyptus tree, which is also commonly called the gum tree in Australia.
SPEAKER: First, I'll explain why this tree is important, and then I will discuss some of the problems it faces.
SPEAKER: The eucalyptus tree provides shelter for animals such as birds and bats. These and other species also depend on it for food, particularly the nectar from its flowers. In this way, the tree supports biodiversity.
SPEAKER: It is also useful for humans because oil extracted from eucalyptus leaves can be used to make a disinfectant that kills germs.
SPEAKER: Eucalyptus trees grow all across Australia and can live for up to 400 years.
SPEAKER: However, it is worrying that the number of eucalyptus trees is declining because many trees are dying prematurely.
SPEAKER: One possible cause is a disease called Mundulla Yellows, which first appeared in the 1970s.
SPEAKER: In infected trees, the leaves turn yellow and eventually the tree dies.
SPEAKER: In 2004, scientists discovered that the cause was lime (calcium hydroxide), which was used in road construction.
SPEAKER: Rain washed the lime into the soil, affecting the roots of nearby eucalyptus trees.
SPEAKER: This chemical prevented the trees from absorbing iron, which is necessary for healthy growth.
SPEAKER: When iron was injected back into the trees, they recovered quickly.
SPEAKER: However, this problem only affected a small number of trees.
SPEAKER: Another major problem is a disease called Bell-miner Associated Die-back, which has affected many trees along Australia’s East Coast.
SPEAKER: The disease is linked with the bell-miner bird.
SPEAKER: Insects attack the leaves and feed on them, producing a sugary liquid.
SPEAKER: Bell-miner birds like this liquid and drive away other species so they can keep access to it.
SPEAKER: As a result, insects and bell-miners thrive, causing serious damage to the leaves, and eventually the tree dies.
SPEAKER: However, scientists noticed that some trees appear unhealthy even before this disease appears.
SPEAKER: One possible explanation involves bushfires.
SPEAKER: Ecologist William Jackson suggested over 40 years ago that the frequency of bushfires affects which types of vegetation grow.
SPEAKER: If fires occur very frequently, grass tends to grow. If fires are less frequent, eucalyptus forests develop.
SPEAKER: Bushfires help eucalyptus trees because they stop other plants from competing for water and soil nutrients.
SPEAKER: Therefore, some bushfires are actually necessary for eucalyptus survival, as long as they are not too frequent.
SPEAKER: Australia's Indigenous people used controlled burning of bushland for thousands of years.
SPEAKER: However, since the arrival of Europeans, bushfires have been strictly controlled.
SPEAKER: Scientists now believe this reduction in fires has led to the development of dry rainforest.
SPEAKER: This ecosystem has dense vegetation but low species diversity.
SPEAKER: The dense shade provides ideal conditions for the bell-miner bird, which builds nests there.
SPEAKER: Unfortunately, this situation is not beneficial for the eucalyptus tree.
ANNOUNCER: That is the end of part 4. You now have one minute to check your answers to part 4.