原文已被隐藏，你可用 快捷键 - 或点击 显示原文 按钮来查看原文
第一段
1 .Today I’m going to talk about the eucalyptus tree, this is a very common tree here in Australia, where it’s also sometimes called the gum tree.
今天我要与大家讲讲桉树。这是澳洲非常常见的一种树木，在这里有时还会把桉树称作gum tree。
2 .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，我将会谈到桉树为什么重要，然后将会描述这种树木当前面临的一些问题。
3 .Right. Well, the eucalyptus tree is an important tree for lots of reasons.
那么，由于很多原因，桉树是一种非常重要的树木。
4 .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.So, it supports biodiversity.
比如，它给了很多像鸟或蝙蝠一类的生物一个庇护所，然后这些生物和其它物种也会依赖桉树来获得食物，尤其是桉树花朵中的花蜜。所以，它维护了生物的多样性。
5 .It’s useful to us humans too, because we can kill germs with a disinfectant made from oil extracted from eucalyptus leaves.The eucalyptus grows all over Australia and the trees can live for up to 400 years.
它对于人类也同样有用，因为我们可以使用一种由桉树叶中所提取的精油来制作消毒剂来杀死细菌。桉树遍布澳洲生长，以及它可以存活长达400年。
6 .So, it’s alarming that all across the country numbers of eucalyptus are falling because the trees are dying off prematurely.So, what are the reasons for this?
因此，由于当前桉树提早地相继死亡，全国范围内的桉树数量下降这件事是令人恐慌的。那么，这件事情的原因是什么呢？
7 .One possible reason is disease.As far back as the 1970s, the trees started getting a disease called Mundulla Yellows, the trees leaves would gradually turn yellow, then the tree would die.
一个可能的原因是疾病。追溯回1970年代，树木开始得了一种叫做Mundulla Yellows的疾病，树叶随即逐渐变黄，然后树木就死去了。
8 .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，他们终于找到了这个问题的根源是石灰，或者叫一个专有化学名词，氢氧化钙，是一直被用来建设公路的物质。
9 .The lime was being washed away into the ground and affecting the roots of the eucalyptus trees nearby.What it was doing was preventing the trees from sucking up the iron they needed for healthy growth.When this was injected back into the affected trees, they immediately recovered.
石灰被冲进土地里，影响到了附近的桉树根。这种石灰会阻止树木吸收它们健康成长所需的铁质。当铁质被注入回受影响的树木时，它们很快就恢复了。
10 .But this problem only affected a relatively small number of trees.By 2000, huge numbers of eucalyptus would dying along Australia’s east coast of a disease known as "Bell-miner Associated Die-back".
但这个问题只影响了相对少数的树木。到2000年，大量的桉树在澳大利亚东海岸死于一种叫做“Bell-miner Associated Die-back（矿吸蜜鸟相关树病）”的疾病。
11 .The Bell-miner is a bird and the disease seems to be common where there are high populations of Bell-miners.Again, it’s the leaves of the trees that are affected.
矿吸蜜鸟是一种鸟类，树木的死亡在有众多这种鸟类出没的地方非常常见。再一次，是树叶被影响了。
12 .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.
事情是这样发生的，昆虫会停留在树叶上，然后沿着边吃掉，边爬边破坏。同时，他们会分泌一种含有糖分的溶液。
13 .The bell-miner 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.
矿吸蜜鸟很喜欢这种溶液，为了尽多得获取这种溶液，他们会远离其它也想获得这种溶液的生物。
14 .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.
所以这种鸟类和昆虫的繁荣生长是以其它物种为代价的，最终由于对树叶有了太大的破坏以至于树死亡了。
15 .But experts say that trees can start looking sick before any sign of "Bell-miner Associated Die-back".
但是，专家说在树有任何“Bell-miner Associated Die-back（矿吸蜜鸟相关树病）”的症状之前，它会先看起来很虚弱。
16 .So it looks as if the problem might have another explanation.
所以，看起来这个问题可能还会有其它的解释。
17 .One possibility is that it’s to do with the huge bushfires that we have in Australia.
一个可能性是说这个可能与在澳洲的巨大森林火灾有关。
18 .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.
40年前由生态学家William Jackson所提出的一个理论是某一区域的火灾发生频率会影响到那里生长的植被。
19 .If there are very frequent bushfires in a region, this encourages grass to grow afterwards.While, if the bushfires a rather less frequent, this results in the growth of eucalyptus forests.
如果在一个区域经常发生森林大火，就会促进那里的草的生长。但是，如果森林火灾不那么频繁，那么桉树林则会生长。
20 .So why is this?Why do fairly frequent bushfires actually support the growth of eucalyptus.
所以这是为什么?为什么一定程度的火灾会促进桉树的成长呢？
21 .Well, one reason is that the fire stops the growth of other species which would consume water needed by eucalyptus trees.
其实，一个原因是大火阻止了其它物种的生长，这些物种原本会消耗掉桉树所需要的水分。
22 .And there’s another reason, 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.
还有另一个原因，如果这些快速生长的灌木和植物得以激增，它们会以另一种方式伤害桉树，通过影响土壤的构成，移除掉其中的养分。
23 .So some bushfires are actually essential for the eucalyptus to survive as long as they are not too frequent.
所以，一些森林大火对于桉树的存活其实是有意义的，只要火灾不要那么频繁。
24 .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.
事实上，有证据表明，在欧洲人到达之前，澳大利亚土著已经实施了常规的灌木林燃烧长达千年。
25 .But since Europeans arrived on the continent, the number of bushfires has been strictly controlled.
但是自从欧洲人到达大陆之后，森林大火的数量被严格控制。
26 .Now scientists believe that this reduced frequency of bushfires to low levels has led to what is known as dry rainforest, which seems an odd name as usually we associate tropical rainforest with wet conditions.
现在科学家相信，这种森林大火的频率降低导致了干雨林，这好像是一个奇怪的名字，因为我们经常将热带雨林和潮湿的条件联系在一起。
27 .And what special about this type of rainforest?
这种雨林有什么特点呢？
28 .Well, unlike tropical rainforest, which is a rich ecosystem, this type of ecosystem is usually a simple one.It has very thick, dense vegetation, but not much variety of species.
呃，它不像富饶的热带雨林系统，这种生态系统往往是简单的。它有着非常厚重密集的植被，但物种并不是很多。
29 .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.But again, that’s not helpful for the eucalyptus tree.
植被提供了大量的阴凉，所以有一类物种会认为这种条件很理想，那就是将鸟巢建在林下灌丛的矿吸蜜鸟。但这对于桉树来说并不有利。