PART 4

Today I’m going to talk about the eucalyptus tree.

今天我要讲的是桉树。

This is a very common tree here in Australia, where it’s also sometimes called the gum tree.

这种树在澳大利亚很常见，当地人称它作胶树。

First I’m going to talk about why it’s important, then I’m going to describe some problems it faces at present.

首先，我要讲一下它的重要性，接着我会陈述目前这种植物遇到的问题。

Right, well the eucalyptus tree is an important tree for lots of reasons.

好的，桉树的重要性体现在很多方面。

For example, it gives shelter to creatures like birds and bats, and these and other species also depend on it for food, particularly the nectar from its flowers.

比如，它为鸟类和蝙蝠提供庇护所，这些动物和其他物种都以它为食，尤其是桉树花朵中的花蜜。

So it supports biodiversity.

所以，桉树维持了物种的多样性。

It’s useful to us humans too, because we can kill germs with a disinfectant made from oil extracted from eucalyptus leaves.

桉树对人类也有帮助，因为我们需要用桉树叶中提取的油来制作杀死细菌的消毒剂。

The eucalyptus grows all over Australia and the trees can live for up to four hundred years.

桉树遍布澳洲，最长可以存活400年。

So it’s alarming that all across the country, numbers of eucalyptus are falling because the trees are dying off prematurely.

因此让人担忧的是，全澳洲的桉树数量在下降，因为这些树木正在过早地死亡。

So what are the reasons for this?

那么是什么原因呢？

One possible reason is disease.

疾病可能是一个原因。

As far back as the 1970s the trees started getting a disease called Mundulla Yellows.

早在20世纪70年代，桉树就开始得了杜蒙拉黄叶病。

The trees’ leaves would gradually turn yellow, then the tree would die.

桉树的树叶逐渐变黄，最终死亡。

It wasn’t until 2004 that they found the cause of the problem was lime, or calcium hydroxide to give it its proper chemical name, which was being used in the construction of roads.

直到2004年，专家才发现修路时用到的建筑材料石灰——化学学名为氢氧化钙，是致病的原因。

The lime was being washed away into the ground and affecting the roots of the eucalyptus trees nearby.

石灰经雨水冲刷进入地下，影响了附近桉树的树根。

What it was doing was preventing the trees from sucking up the iron they needed for healthy growth.

石灰阻碍桉树树根吸收对它的健康成长很重要的铁元素。

When this was injected back into the affected trees, they immediately recovered.

当铁元素被注入受影响的树的时候，这些桉树马上恢复了。

But this problem only affected a relatively small number of trees.

但是石灰只影响到了相当小的一部分桉树。

By 2000, huge numbers of eucalyptus were dying along Australia’s East Coast, of a disease known as Bell-miner Associated Die-back.

截止2000年，澳洲东海岸的桉树大量死亡，病因是矿吸蜜鸟关联性枯萎病。

The bell-miner is a bird, and the disease seems to be common where there are high populations of bell-miners.

这种病在矿吸蜜鸟数量庞大的地区似乎尤其普遍。

Again it’s the leaves of the trees that are affected.

同样，受影响的是树叶。

What happens is that insects settle on the leaves and eat their way round them, destroying them as they go, and at the same time they secrete a solution which has sugar in it.

桉树树叶上的昆虫会把它周围的树叶啃光，边移动边破坏树叶，同时还会分泌一种含糖的液体。

The bellminer birds really like this solution, and in order to get as much as possible, they keep away other creatures that might try to get it.

矿吸蜜鸟十分喜食这种溶液。为了尽可能多得获得食物，它们会驱散其他可能尝试觅食的物种。

So these birds and insects flourish at the expense of other species, and eventually so much damage is done to the leaves that the tree dies.

所以矿吸蜜鸟和昆虫在影响其它物种的生存的情况下疯狂繁殖，最终严重破坏了树叶，导致桉树死亡。

But experts say that trees can start looking sick before any sign of Bell-miner Associated Dieback.

然而专家认为在出现矿吸蜜鸟关联枯萎病的迹象之前，桉树早已开始呈现病态。

So it looks as if the problem might have another explanation.

因此，看起来这个问题也许有其它的解释。

One possibility is that it’s to do with the huge bushfires that we have in Australia.

另一个可能的原因与澳大利亚的巨大丛林山火有关。

A theory proposed over 40 years ago by ecologist William Jackson is that the frequency of bushfires in a particular region affects the type of vegetation that grows there.

生态学家威廉·杰克逊于40年前提出了这样的理论，说明特定地区的频繁丛林山火影响了当地的植被种类。

If there are very frequent bushfires in a region, this encourages grass to grow afterwards, while if the bushfires are rather less frequent, this results in the growth of eucalyptus forests.

如果某个地区山火非常频繁，丛林山火结束后草会得到养料，迅速生长。但是如果山火频率降低，桉树会迅速生长。

So why is this? Why do fairly frequent bushfires actually support the growth of eucalyptus?

为什么呢？为什么相对频繁的丛林山火会促进桉树的生长呢？

Well, one reason is that the fire stops the growth of other species which would consume water needed by eucalyptus trees.

一个原因是丛林山火阻止了其他与桉树争抢水源的物种的增加。

And there’s another reason.

还有一个原因。

If these other quick-growing species of bushes and plants are allowed to proliferate, they harm the eucalyptus in another way, by affecting the composition of the soil, and removing nutrients from it.

如果其他生长期短的灌木和植物大量生长，会从另一个角度影响桉树——它们会吸收土壤养分，破坏土壤成分。

So some bushfires are actually essential for the eucalyptus to survive as long as they are not too frequent.

事实上，只要发生频率不是特别高，丛林山火其实可以保护桉树的生存。

In fact there’s evidence that Australia’s indigenous people practised regular burning of bush land for thousands of years before the arrival of the Europeans.

实际上，有证据显示澳大利亚土著居民在欧洲人到达前的数千年中经常有规律地烧荒。

But since Europeans arrived on the continent, the number of bushfires has been strictly controlled.

但是自从欧洲人到达澳洲，山火的数量明显被控制了。

Now scientists believe that this reduced frequency of bushfires to low levels has led to what’s known as ‘dry rainforest’, which seems an odd name as usually we associate tropical rainforest with wet conditions.

现在科学家们认为丛林山火频率降低形成了所谓的“干燥雨林”，这个名词听起来古怪是因为我们经常把热带雨林和它的潮湿气候联系起来。

And what’s special about this type of rainforest?

那么这类雨林有什么特别之处呢？

Well, unlike tropical rainforest which is a rich ecosystem, this type of ecosystem is usually a simple one.

和拥有复杂生态系统的热带雨林不同，这类干燥雨林只有一个简单的生态系统。

It has very thick, dense vegetation, but not much variety of species.

在这里植物茂盛繁密，但是生物物种却不多。

The vegetation provides lots of shade, so one species that does find it ideal is the bell-miner bird, which builds its nests in the undergrowth there.

植被提供了树荫，所以有一种找到了理想住所的物种，那就是矿吸蜜鸟。它们把巢搭在生长在大树之下的灌木之中。

But again that’s not helpful for the eucalyptus tree.

但是这对桉树也没有帮助。