树木死亡和气候
【时事聚焦】 近一个世纪，世界上森林覆盖面积大幅度锐减，除了人为因素的大量砍伐，也有相当数量的树木由于自然气候死亡。自然气候的改变带来的炎热和干旱导致了世界上越来越多的树木奄奄一息。下面我们就来看一则建立在几十篇科学文献基础上，有关此话题的最新报道。
TreeDeaths Linked To Climate Change
Hot and dry conditions triggeredby climate change are killing the world's trees, according to a new reportwhich examines dozens of scientific articles on the subject.
Stanford Universitygraduate student William Anderegg has seen this forest die-off firsthand.
His doctoral thesisdocuments the impact of drought on trembling aspen, the most common tree inNorth America.
“These are completehillsides of trembling aspens that are dying off," Anderegg says."And when the main tree in a forest goes, you tend to see a lot of theother species, especially the grasses and the wild flowers, tend to disappearas well. But you lose a lot of those species from those forests.”
Changing ecology
With colleagues fromStanford and North Arizona State University, Anderegg co-authored the newreport which presents a picture of accelerating worldwide tree deaths thatappear to be linked to changes in the global climate.
Anderegg says thesechanges, triggered by rising levels of heat-trapping gases in the atmosphere,are stressing the world’s forests.
“One of the ways thatwe expect climate change to increasingly play out in forests is through thesewidespread tree mortality events where you stress the trees enough that youessentially push a whole region of them off the edge and in fact what happensafterwards, after a forest dies from drought is every bit as important and insome sense matters more to humans who rely on forests.”
Trees provide a rangeof ecological services. They hold soil in place, help purify water and shelterspecies. They are valued for timber and tourism. When trees die, the ecologyand hydrology of a forest change, which in turn promotes insect infestation andfire.
This can result inlong-term shifts in the area’s dominant species and may even trigger atransition to a different ecosystem, such as grass land.
Devastating consequence
Anderegg says themost devastating consequence may be that the changing forests, in turn, willstart affecting the global climate.
“Because forests do alot to stabilize the climate and to store carbon and when they start to dieoff, you can actually have forest die-off accelerate climate change," hesays. "You get into a vicious cycle.”
This is especiallytroubling for Anderegg because trees, which cover 30 percent of the earth’ssurface, absorb 25 percent of the climate-changing gases emitted into theatmosphere from cars, buildings and factories.
Forest monitoring
While scientists aregetting better at tracking the effects of climate change on forests, data isstill sparse. Anderegg says his study urges governments and specialists frommany disciplines to support wide-scale forest monitoring.
“It is not justecologists, but we also need people working with satellites. We need people ingovernment agencies. We need people on the ground to do this as well. It’sunfortunately not something that just the scientific research community canpull off on their own.”
Anderegg, whoseresearch is published in Nature Climate Change, says a better understanding ofhow climate change is killing off the world’s forests can help shape betterforest management, business decisions and policies.【热点话题】 根据以上的这则研究报道，我们发现树木死亡的话题和雅思阅读考试有十分紧密的联系，雅思阅读话题中有很多都涉及到环保，生态，这在2012年1月-9月的考试中可见一斑。平时对这类话题的背景知识累积有助于考生更好地理解新文章。因为吸热气体在大气层中的不断增加，所以不仅是森林里的树木，野花和草类也逐渐消失。这样的后果会造成该地区生态系统的改变，转而再次影响全球气候。
【难句词汇】 雅思考生的阅读难点之一就是对词汇量和句型的掌握程度不同，如果学生的词汇量不足，那么文章将看不懂，我们从上文中就可以学到很多的句型和词汇。
› Hot and dry conditions triggered by climate changeare killing the world's trees, according to a new report which examines dozensof scientific articles on the subject.
定语后置修饰(过去分词短语作后置定语)
l trigger v. 导致，引发
l dozens of 几十个
› These are complete hillsides of trembling aspensthat are dying off, the most common tree in North America.
定语从句和同位语
l trembling adj. 颤抖的
l aspen n. 白杨
l die off 死亡，消失
› And when the main tree in a forest goes, you tendto see a lot of the other species, especially the grasses and the wild flowers,tend to disappear as well.
条件状语从句，插入语
l species n. 种类
l wild adj. 野生的
› One of the ways that we expect climate change toincreasingly play out in forests is through these widespread tree mortalityevents where you stress the trees enough that you essentially push a wholeregion of them off the edge and in fact what happens afterwards, after a forestdies from drought is every bit as important and in some sense matters more tohumans who rely on forests.
定语从句，地点状语从句，主语从句
l mortality n. 死亡
l drought n. 干旱
l in some sense 在某种意义上
l edge n. 边缘
› When trees die, the ecology and hydrology of aforest change, which in turn promotes insect infestation and fire.
时间状语从句、非限制型定语从句
l ecology n. 生态
l hydrology n. 水文学
l infestation n. (害虫)出没，横行
› Because forests do a lot to stabilize the climateand to store carbon and when they start to die off, you can actually haveforest die-off accelerate climate change," he says. "You get into avicious cycle.
原因状语从句，时间状语从句
l stabilize v. 使…稳定
l accelerate v. 增加，加速
l vicious adj. 凶猛的，恶劣的
从以上这些内容中我们学到了很多的表达方式和句型，这样一来对于雅思阅读的理解力和速度的提高有很大的帮助。从文章结构上来看，本文是很明显的现象—解释原因—后果—预测——建议的行文模式。这和很多剑桥系列里的文章相似。文章中同时也涉及了许多生态，环保类的雅思高频词，比如 stabilize,infest, mortality等等。
分析发现，在剑桥雅思真题中也有相关类型的文章供考生阅读理解和训练：剑四Rainforest; 剑七Deforestation; 剑七The Little Ice Age, 以上三篇文章都是当下热点的环保类文章，考生可以精读加考题训练。
【真题预测】 根据刚才关于树木死亡和气候的原版文章，我们来练习一下雅思阅读的常考题型之——是非无判断题：
Do the following statements agree with the views of the writer in thispassage?
TRUE / FALSE / NOT GIVEN
1. If a kind of speciesdie off, the ecology of this region is likely changed also.
2. Forests only serveas the role of storing carbon.
3. The government isnow carrying out specific programs to address this deteriorating phenomenon.
