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托福阅读理解真题解析： Alaska and Bark Beetles
Over the twentieth century, global temperatures increased by an average of about 0.7 degrees Celsius, but some places have warmed a lot more than this, and other places have warmed less. These temperature increases have been enough to trigger changes in ecosystems all over the world, especially in places where the warming has been the greatest. In some places, the changes have been subtle, perhaps a slight shift in vegetation that only a careful observer would notice. In other cases, small changes in climate have sparked a chain of larger effects, leading to massive changes.
The biggest climate-caused ecosystem shifts today are happening at the world's most northern latitudes, where the temperature over the last century has been rising about two times faster than the global average. In the northernmost state of the United States, Alaska, for example, warming has paved the way for a spike in the numbers of spruce bark beetles. Bark beetles have been a pest to Alaskan white spruce trees for thousands of years, but their numbers were held in check by the cold climate, which forced the insects to hide in the bark of individual trees for most of the year. As the length of the warm season increased over the 1980s and 1990s, however, bark beetles had more time to fly from one tree to the next, burrow, and lay their eggs between the bark and the wood. The beetles had another thing going for them, too: a multi-year drought had weakened many of the spruce trees, leaving them vulnerable to attack. In the mid-1990s, the bark beetle population exploded, and over the next few years the pests wiped out white spruce forests over an area the size of the U.S. state of Connecticut. In the years since, the combined forces of a longer insect-breeding season and forest management practices that left forests overcrowded gave way to similar epidemics farther south. Large swaths of pine and spruce have been destroyed by insects in several other parts of the United States.
In the late 1990s, the effects of the bark beetle epidemic rippled throughout Alaska's white spruce ecosystem and affected virtually every population of living organisms, but not all of the impacts were negative. Fewer spruce trees meant a sunnier area in the forest below the treetops, which allowed grasses to move in and take hold. The grasses, in turn, changed the soil temperature, making the environment more friendly for some other types of vegetation. Animals that feed on grasses, including moose, elk, and some birds, also benefited. But the beetle infestation was bad news for organisms that rely on white spruce for their habitat, like hawks, owls, red squirrels, and voles. Volesa type of small, mouselike rodentare an especially vital part of the ecosystem because they help spread mycorrhizal fungi, which attach to the roots of plants and help them take in water and nutrients. Voles are also an important food for a number of predators.
Ecosystem changes always hurt some living creatures and help others. [▇] It's hard to say, therefore, whether a change is good or bad overall. [▇] Instead, ecologists (people who study ecosystems) often focus on the impacts on a single species: for instance, us. [▇] In the short term, the Alaskan spruce beetle epidemic supplied a lot of people with firewood, but only by destroying tons of otherwise valuable timber and threatening the livelihoods of loggers. And no one knows for sure what the long-term impacts on the forest will be. Ecosystems tend to return to their previous states after disturbances like pest outbreaks, fires, or major storm events, but if the Alaskan spruce ecosystem is disturbed too often or too much, it might shift to a different type of forest, a woodland, or a grassland instead. [▇]
In extreme cases, major assaults on ecosystems can lead to a total collapse in which the ecosystem doesn't bounce back to the way it was or transition to a new, healthy state. The result is an area with very little life; in the oceans, biologists refer to these areas as dead zones. One such example is the coral reef die-off that happened in the Indian Ocean in the late 1990s.
1.The word “subtle” in the passage is closest in meaning to
A.to limited
B.unimportant
C.not obvious
D.gradual
2.Paragraph 2 suggests that the warming of the Alaskan climate affected bark beetles in which of the following ways
A.By making it possible for a beetle to deposit its eggs in a greater number of trees
B.By making it possible for beetles to survive in the bark of trees for longer lengths of time
C.By making it unnecessary for a beetle to protect its eggs by laying them between the bark and the wood
D.By increasing the number of spruce trees, thereby providing the beetles with far more places to live
3.Which of the following statements most accurately describes the relationship of paragraph 3 to paragraph 2
A.Paragraph 2 explains the causes of the spruce bark beetle epidemic in Alaska, and paragraph 3 discusses the chain of events that occurred as a result of that epidemic.
B.Paragraph 2 shows that warming air temperatures can affect a large number of species, and paragraph 3 shows that warming soil temperatures can have even greater effects.
C.Paragraph 2 discusses one explanation for the disappearance of spruce trees from a part of Alaska, but paragraph 3 shows that an alternative explanation is more likely to be correct.
D.Paragraph 2 describes the negative consequences of climate warming for some species, but paragraph 3 shows that there are also some positive consequences for these same species.
4.According to paragraph 3, which of the following effects did the bark beetle epidemic have on moose, elk, and some birds
A.The epidemic increased the availability of water for these animals.
B.The epidemic increased the availability of food for these animals.
C.The epidemic destroyed the habitat of these animals.
D.The epidemic meant that these animals experienced more competition from hawks, owls, red squirrels, and voles.
5.According to paragraph 3, a decline in the vole population in Alaska may have which TWO of the following consequences To receive credit, you must select TWO answer choices.
A.Some predators may have less to eat.
B.Hawk and red squirrel populations may be more successful.
C.Plants may find it more difficult to absorb water and nutrients.
D.Mycorrhizal fungi numbers may increase.
6.Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
A.Ecosystems like the spruce ecosystem in Alaska tend to return to their previous states after disturbances such as pest outbreaks, fires, or major storm events.
B.While ecosystems tend to return to their previous states after disturbances, the Alaskan spruce ecosystem might not if it is disturbed too often or too much.
C.Ecosystems tend to return to their previous states after disturbances, so Alaska might again become covered with woodlands or grasslands.
D.After certain types of disturbances such as pest outbreaks, ecosystems do not always return to their previous states but shift to being woodlands or grasslands instead.
7.In paragraph 5, coral reefs in the Indian Ocean are presented as an example of which of the following
A.Ecosystems that totally collapsed
B.Ecosystems that transitioned to a new, healthy state
C.Ecosystems that bounced back to the way they were
D.Ecosystems that were affected by a nearby dead zone
8.The passage provides an answer to which of the following questions
A.Why has the temperature at northern latitudes been rising faster than the global average
B.Why did corals in the Indian Ocean die off in the late 1990s
C.What types of vegetation benefited from the change in soil temperatures in Alaska
D.What were some of the effects of the bark beetle epidemic for humans
9.Look at the four squares[▇] that indicate where the following sentence could be added to the passage. Where would the sentence best fit?
But even from this limited perspective, the answer is not completely straightforward.
10.Directions:
An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some answer choices do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This questions is worth 2 points.
A.Global warming has led to changes in ecosystems all over the world, with ecosystems at northern latitudes being affected the most.
B.A longer warm season in Alaska caused a sharp increase in the number of bark beetles, leading to the destruction of spruce forests, which in turn seriously affected many other species.
C.Sometimes ecosystems are able to recover from disturbances or to develop into different, but healthy, systems, but in extreme cases, they may collapse completely.
D.The loss of spruce forests caused an epidemic in mycorrhizal fungi, and these fungi damaged the roots of many plants, making them unable to take in water and nutrients.
E.Whereas some types of changes are good for the majority of species in an ecosystem, ecologists believe that most disturbances to ecosystems are bad overall.
F.Coral reefs may die off as a result of the global increase in temperatures, but after a transition period as a dead zone, they are able to return to their original state.
Alaska and Bark Beetles
阿拉斯加和树皮甲虫
文章大意：
在二十世纪，全球温度平均升高了约0.7摄氏度，但有些地方的升温幅度超过此数值，而其他地方的升温幅度较小。这些温度升高足以触发全世界生态系统的变化，尤其是在变暖最大的地方。在某些地方，变化微妙，也许只有细心的观察者才会注意到植被的轻微变化。在其他情况下，气候的微小变化引发了一系列更大的影响，导致了巨大的变化。
今天，由气候引起的最大的生态系统变化发生在世界最北部的纬度地区，上个世纪的温度上升速度是全球平均水平的两倍左右。例如，在美国最北端的阿拉斯加，变暖为云杉树皮甲虫数量激增铺平了道路。几千年来，树皮甲虫一直是阿拉斯加白云杉树的害虫，但由于寒冷的气候，树皮甲虫的数量一直受到控制，这迫使昆虫在一年中的大部分时间都藏在个别树的树皮中。然而，随着1980年代和1990年代温暖季节的延长，树皮甲虫有更多的时间从一棵树飞到另一棵树，挖穴，并在树皮和木头之间产卵。甲虫也有另一件事：多年的干旱削弱了许多云杉树木，使它们容易受到攻击。在1990年代中期，树皮甲虫数量激增，在接下来的几年中，虫害席卷了美国康涅狄格州大小的白云杉林。此后的几年中，更长的昆虫繁殖季节和森林管理实践共同导致了森林过度拥挤的局面，被更南端的类似流行病所取代。在美国其他几个地方，大片的松树和云杉被昆虫破坏了。漫长的昆虫繁殖季节和森林管理实践的共同作用，使森林拥挤不堪，而更南端的类似流行病也让位于。在美国其他几个地方，大片的松树和云杉被昆虫破坏了。漫长的昆虫繁殖季节和森林管理实践的共同作用，使森林拥挤不堪，而更南端的类似流行病也让位于。在美国其他几个地方，大片的松树和云杉被昆虫破坏了。
在1
990年代后期，树皮甲虫流行的影响波及整个阿拉斯加的白云杉生态系统，并几乎影响了所有活生物体，但并非所有影响都是负面的。较少的云杉树木意味着在树梢下方的森林中有一个阳光充足的区域，这使草可以进入并占据。反过来，草改变了土壤温度，使环境对某些其他类型的植被更加友好。以草为食的动物，包括驼鹿，麋鹿和一些鸟类，也从中受益。但是对于以白云杉为生的生物来说，甲虫的侵害是个坏消息，例如鹰，猫头鹰，红松鼠和田鼠。软体动物类的小型鼠类啮齿动物是生态系统中至关重要的部分，因为它们有助于传播菌根真菌，附着在植物的根部并帮助它们吸收水分和养分。田鼠也是许多捕食者的重要食物。
生态系统变化总是伤害某些生物并帮助其他生物。因此，很难说变化总体上是好是坏。取而代之的是，生态学家（研究生态系统的人们）通常关注于对单个物种的影响：例如我们。在短期内，阿拉斯加云杉甲虫流行为许多人提供了柴火，但仅仅是摧毁了许多原本有价值的木材，并威胁了伐木工人的生计。而且没有人能确定对森林的长期影响。在虫害爆发，火灾或重大风暴事件等干扰之后，生态系统趋于恢复到以前的状态，但是如果阿拉斯加云杉生态系统受到过多或过多干扰，则可能会转移到其他类型的森林，林地或森林中。草原代替。
在极端情况下，对生态系统的重大攻击可能会导致彻底崩溃，从而使生态系统无法恢复原状或过渡到新的健康状态。结果是一个几乎没有生命的区域。在海洋中，生物学家将这些区域称为死区。一个这样的例子就是1990年代后期在印度洋发生的珊瑚礁死亡。
刘凯老师解析：
1.答题解析：答案:C；Subtle：微妙的。所以选C。
2.答题解析：答案:A；此段讲气候的影响讲了两点：（1）As the length of the warm season increased over the 1980s and 1990s, however, bark beetles had more time to fly from one tree to the next, burrow, and lay their eggs between the bark and the wood.有更长的时间在树木之间来回穿梭并产卵。（2）The beetles had another thing going for them, too: a multi-year drought had weakened many of the spruce trees, leaving
them vulnerable to attack.使更多的数容易被攻击和理由，综合两点来看，deposit its eggs in a greater number of trees是可能实现的，A对。BCD均无支持。
3.答题解析：答案:A；第二段讲了spruce bark beetle epidemic in Alaska发生的过程，第三段讲了是the effects of the bark beetle epidemic，有好有坏，BUT之前讲的好的，BUT之后讲的坏的，D肯定不对，因为BUT之后为意思中心讲的是坏处。A讲后续events，即为the effects of the bark beetle epidemic意思
4.答题解析：答案:B；The grasses, in turn, changed the soil temperature, making the environment more friendly for some other types of vegetation. Animals that feed on grasses, including moose, elk, and some birds, also benefited.显然是B。
5.答题解析：答案是A和C；解析：Voles a type of small, mouselike rodent are an especially vital part of the ecosystem because they help spread mycorrhizal fungi, which attach to the roots of plants and help them take in water and nutrients.而现在Voles数量减少了，故C对D错。Voles are also an important food for a number of predators.，现在Voles数量减少了，A对，B无体现。
6.答题解析：答案:B。转折句，虽然ecosystem有恢复力，但是如果ALSKAN的生态系统被disturb太多，就可能恢复不了，而是变成另外一种生态系统。A只有“虽然”后的意思，没有“但是”后所强调的重要信息，C的Alaska might again become covered with woodlands or grasslands与原文“但是”后的信息相反，D的信息有错，原文说的是Alaskan spruce ecosystem是否能恢复，并非讨论一般的ecosystems。B的话是对原句的转述。
7.答题解析：答案:A；讲One such example is the coral reef die-off that happened in the Indian Ocean in the late 1990s.【其中一个例子就是上世纪90年代末发生在印度洋的珊瑚礁灭绝。】是为了印证前面的In extreme cases, major assaults on ecosystems can lead to a total collapse in which the ecosystem doesn’t bounce back to the way it was or transition to a new, healthy state. The result is an area with very little life; in the oceans, biologists refer to these areas as dead zones.，【在极端情况下，对生态系统的重大攻击可能导致生态系统的全面崩溃，无法恢复到原来的状态或过渡到一个新的、健康的状态。结果是一个几乎没有生命的区域;在海洋中，生物学家称这些区域为死亡区。】显然为A。D错在affected by a nearby dead zone
8.答题解析：答案:D；
ABC均无法回答，而第四段的In the short term, the Alaskan spruce beetle epidemic supplied a lot of people with firewood, but only by destroying tons of otherwise valuable timber and threatening the livelihoods of loggers. And no one knows for sure what the long-term impacts on the forest will be.【在短期内，阿拉斯加云杉甲虫的流行为人们提供了大量的柴火，但它摧毁了数吨原本很有价值的木材，并威胁到伐木工的生计。没有人确切知道对森林的长期影响会是什么。】长期effects不知，但一些短期effects，如有更多的木柴，所以D对，这里说的是some of the effects，不一定要知道total effects.
9.答题解析：答案:C；
前文应该提到this limited perspective，根据语境知指对人类的effects，即只看对人类的影响不看对整个生态的影响。后面要具体阐述为什么not completely straightforward。对应C，C前面说focus on the impacts on a single species: for instance, us.，C之后说短期可能有益，长期对人类影响未知，有坏有好，长短期effects不一样，故显得not completely straightforward.
10.答题解析：答案:A B C；
D错在epidemic in mycorrhizal fungi，原文讲的是Voles数量变少，影响到mycorrhizal fungi的扩散，并非造成了mycorrhizal fungi因传染病而亡。E的话，第四段说Ecosystem changes always hurt some living creatures and help others. It’s hard to say, therefore, whether a change is good or bad overall.。F的but after a transition period as a dead zone, they are able to return to their original state.没有体现。A注意到第二段论点The biggest climate-caused ecosystem shifts today are happening at the world’s most northern latitudes, where the temperature over the last century has been rising about two times faster than the global average.B为第二段和第三段的概括，C为第四段和第五段的概括。
刘凯老师介绍
刘凯，男，蒙古族，黑龙江省齐齐哈尔人。本科为哈尔滨师范大学英语系，硕士为北京理工大学。2010年赴美国宾夕法尼亚大学交流学习；2013年美国亚利桑那大学访问学者；2015年澳大利亚新南威尔士大学ESL研修；2018年加州理工学院语言学双学位获得者；2019年赴澳大利亚麦考瑞大学交流习；GRE托福考试全球高分获得者；荣获长江商学院EMBA。
北京市优秀青年教师，北京市级重点高中示范校骨干教师，多年高中一线执教经验，高三年级把关教师，多次参与东城区模拟试题命题工作，教学理念先进，教学成果突出，多篇教学论文获市区级奖项。多篇文章发表在《中国教育报》《中国考试》《北京教育》等报刊上。多次参加高考阅卷工作，参与人民教育出版社、北京教育出版社、外研社等各类高考教学用书的编写工作，有丰富的备考经验，国际核心期刊发表多篇论文。
教育部课题研究员，参与国家十二五课题计划，并作出突出贡献，参与初中、高中各年级区级试题的命制，多次承担区级和市级研究课任务。北京市科技英语优秀指导教师，所带学生在各级英语口语、作文竞赛中多次获奖；将扎实的英语基本功和严谨的学术思想作为教学的基础，课堂上善于寓教于乐，信息量大，内容丰富，使学生在和谐的课堂气氛下欣赏英语、享受英语、掌握英语、运用英语。
2009-2012年期间，多次受邀在北京广播电台主持英语高考大纲解析及英语新课程改革节目，学术功底深厚，兼具偶像派与实力派特点，教风亲切洒脱，诙谐幽默，思维开阔，屡有奇思妙想，善于引导学生学以致用，对高考动向把握极其准确，深受学生和家长欢迎。尤其擅长英语语法和单词记忆法。
海外生活学习十年，社科人文类学科偏爱者；10年雅思教龄，知名教师培训师；指导上万考生快速冲刺雅思写作、阅读，平均分数7.5分；独创“段落清空”、极简化“针对检索式”阅读法等众多高效技法；每年雅思考试均在10次以上；均分8+；真题回忆准确度97%以上；贴近西式思路和语言指导学生写作；善于帮助学生突破学术写作思维瓶颈。讲授科目有长难句、翻译、四六级考试、阅读和写作；在2014、2015、2017、2019四年考研中，接受其培训的所有考生中有近万名考生取得高分。带给学生的不只是考分的提高，更多的是对英语领悟和感知的突破。纯正的英音、独到的见解、睿智的思维和轻松幽默的语言，为其赢得了广大学生的认同和喜爱。
资深考研培训讲师；
英语四六级考试天团高级讲师；
雅思阅读、雅思写作培训主讲名师；
六级考试阅卷组成员；
深谙命题规律和解题套路，对英语的学习规律和方法见解独特。
呼吁国人学习英语的态度：
重复是记忆之母。
用听，用看，用心去触摸每个单词，你便会有好的记忆。
中国人要学好英语就要有一点点变态。
上课特点：课堂从不需点名，却无人缺席
教学理念：英语教师很幸运也有责任与学生一同叩响世界之门
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