小站论坛_托福论坛

[机经题库答案] 托福阅读生物类真题Forest Succession原文+题目汇总

5040
5

Rank: 19Rank: 19Rank: 19

排名9

小站金币
42046
跳转到指定楼层
1#
发表于 2017-5-15 14:52 |只看该作者 |倒序浏览
类别:生物类
真题110108CN-P3
Title:Forest Succession
Succession  is a continuous change in the species composition, structure, and function of  a forest through time following disturbance. Each stage of succession is  referred to as a successional sere. The final stage of succession, which is  generally self-replacing, is referred to as the climax sere. There are two  major types of succession: primary and secondary. Primary succession is the  establishment of vegetation on bare rocks or radically disturbed soil.  Secondary succession is the reestablishment of vegetation following a  disturbance that killed or removed the vegetation but did not greatly affect  the soil. Volcanic eruptions, retreating glaciers, and bare sand dunes are  examples of sites subject to primary succession, while clear-cutting of  forests, wild fires, and hurricanes are examples of sites subject to  secondary succession. Hundreds to thousands of years are required for primary  succession to reach the climax sere, compared to decades to hundreds of years  for it to occur in secondary succession. A longer time is needed to reach the  climax sere for primary than secondary succession because soil development  must first take place in primary succession. The rate of succession is  dependent upon the extent of the disturbance and the availability of appropriate  seeds for recolonization.
What  morphological (structural) and ecophysiological characteristics determine the  species composition and abundance in succession? In general, nitrogen fixing  plants (plants that can make use of atmospheric nitrogen) are important early  succession species in primary succession because nitrogen is not derived from  the weathering of rock and little or no organic matter is present in the  soil.
Weedy  plants are common early successional species because of their rapid growth  and high reproductive rates, while stress-tolerant species are common late  successional species.
The  structure of a forest changes as well in secondary succession. Depending on  the type and the severity of the disturbance, a moderate to large amount of  dead organic matter from the previous forest remains on the site immediately  from the disturbance. The leaf area of the forest is at a minimum and slowly  increases as new vegetation occupies the site. Following a disturbance, such  as a fire, the new canopy (the uppermost spreading and branching layer of a  forest) is largely composed of similar-aged, or even-aged, trees. Light,  nutrient, and water availability are highest during the early successional  sere because the vegetation has not completely occupied the site. Canopy  closure, or maximum leaf area, can occur within several years after  disturbance in some tropical forests, but may take three to fifty years in  evergreen forests.
In the  second stage of forest development there is tree mortality caused by competition  for light, nutrients and water. The intense intraspecies (within a species)  and interspecies (between species) competition for light, nutrients and water  induces the mortality of plants that are shaded or have one or more life-history  characteristics that are not well adapted to the changing environment. The  third stage of forest development is characterized by openings in the  overstory canopy, caused by tree mortality, and the renewed growth of  understory in response to increased light reaching the forest floor.  Consequently, the forest canopy becomes more complex, or multilayered. The  final stage of forest development, the climax or old growth stage, is  characterized by a species composition that in theory can continue to replace  itself unless a catastrophic disturbance occurs. Unique characteristics of  old growth forests include large accumulation of standing and fallen dead trees--referred  to as coarse woody debris. Also, the annual input of forest litter is  dominated by coarse woody debris compared to the earlier stages of forest  development, when leaf and fine root debris were the dominant sources of  nutrients and organic matter input into the soil.
Some  ecosystems may never reach the latter stages of succession if natural  disturbances (fire, flooding, hurricanes, etc) are frequent. A pyric climax  refers to an ecosystem that never reaches the potential climax vegetation  defined by climate because of frequent fires. The ecotone, a boundary,  between grassland and forest is a pyric climax, and only with fire  suppression have woodlands and forests began to advance into these regions.
  
Paragraph 1  
Succession  is a continuous change in the species composition, structure, and function of  a forest through time following disturbance. Each stage of succession is  referred to as a successional sere. The final stage of succession, which is  generally self-replacing, is referred to as the climax sere. There are two  major types of succession: primary and secondary. Primary succession is the  establishment of vegetation on bare rocks or radically disturbed soil.  Secondary succession is the reestablishment of vegetation following a  disturbance that killed or removed the vegetation but did not greatly affect  the soil. Volcanic eruptions, retreating glaciers, and bare sand dunes are  examples of sites subject to primary succession, while clear-cutting of  forests, wild fires, and hurricanes are examples of sites subject to  secondary succession. Hundreds to thousands of years are required for primary  succession to reach the climax sere, compared to decades to hundreds of years  for it to occur in secondary succession. A longer time is needed to reach the  climax sere for primary than secondary succession because soil development  must first take place in primary succession. The rate of succession is  dependent upon the extent of the disturbance and the availability of  appropriate seeds for recolonization.
  
1.     According to paragraph 1 each of the following can create a site that  is likely to be subject to secondary succession EXCEPT  
¡  large scale forest clearances  
¡  volcanic eruptions  
¡  hurricanes  
¡  major forest  fires  
  
2.     Paragraph 1 supports which  of the following statements about disturbances  
¡  They occur in a series of stages.  
¡  They can result from natural causes or human activities.  
¡  They may contribute to increased volcanic eruptions.  
¡  They have no impact on the speed with which  succession occurs.  
  
3.     According  to paragraph 1 the main factor that explains why it takes so long for a primary succession to reach  climax is the time it takes for  
¡  glaciers to  retreat  
¡  dead vegetation to decay  
¡  soil to form  
¡  seeds to mature after recolonization  
  
Paragraph 2  
What morphological (structural) and ecophysiological characteristics determine the species  composition and abundance in succession? In  general, nitrogen-fixing plants (plants that can make use of  atmospheric nitrogen) are important early succession species in  primary succession because nitrogen is not derived from the weathering of the  rock and little or no organic matter is present in the soil. Weedy plants are  common early successional species  because of their rapid growth  and high reproductive rates, while stress-tolerant species are common late  successional species.  
  
4.     Paragraph  2 supports the idea that nitrogen-fixing plant species are heavily represented in the early stages of a primary succession because they  
¡  do not require soil that contains nitrogen.  
¡  generally grow more rapidly than other plants.  
¡  tend to be more stress tolerant than other plants.  
¡  tend to be less weedy than other plants.  
  
Paragraph 3
The structure of a forest  changes as well  in secondary succession. Depending on the type and the severity of the disturbance, a moderate to large amount of dead  organic matter from the previous forest remains on the site immediately from the disturbance. The leaf area of the forest is at a  minimum and slowly increases as new vegetation occupies the site.  Following a disturbance, such as a fire, the  new canopy (the  uppermost spreading and  branching layer of a forest) is largely composed of similar-aged,  or even-aged, trees. Light, nutrient, and water availability are highest during the  early successional sere because the vegetation has not completely occupied the  site. Canopy closure, or maximum leaf area, can occur within several years after  disturbance in some tropical  forests, but may take three to fifty years in evergreen forests.  
  
5.     The word "severity" in the passage is closest in  meaning to  
¡  suddenness  
¡  seriousness  
¡  location  
¡  timing  
  
6.     According  to paragraph 3 the earliest stage of a secondary succession is characterized  by each of the following EXCEPT  
¡  an incomplete covering of vegetation  
¡  a canopy made up of trees that vary widely in age  
¡  relatively ample nutrients available in the soil  
¡  relatively plentiful light reaching growing plants  
  
Paragraph 4  
In the second stage of forest development there  is tree mortality caused by competition for light, nutrients and  water. The intense intraspecies (within a species)  and interspecies (between species) competition for  light, nutrients and water  induces the mortality of plants that  are shaded or have one or more  life-history characteristics that are not well adapted to the changing environment. The third stage of forest development is  characterized by openings in the overstory canopy, caused  by tree mortality, and the renewed growth of understory in response to  increased light reaching the forest floor. Consequently,  the forest canopy becomes more complex, or multilayered. The final  stage of forest development, the climax or old growth stage, is characterized  by a species composition that in theory can continue to replace itself unless a catastrophic disturbance  occurs. Unique characteristics of old  growth forests include large accumulation of standing and fallen dead trees--referred to as coarse  woody debris. Also,  the annual input  of forest litter is  dominated by coarse woody debris compared to the earlier stages of forest  development, when leaf and fine root debris were the dominant sources of nutrients  and organic matter input into the soil.  
  
7.     The word "induces" in the passage is closest in  meaning to  
¡  explains  
¡  increases  
¡  disappears  with  
¡  brings about  

  
8.     The word "consequently" in the passage is  closest in meaning to  
¡  in other words  
¡  nevertheless  
¡  as a result  
¡  basically  
  
9.     The word "catastrophic" in the passage is  closest in meaning to  
¡  extremely harmful  
¡  very complex  
¡  different  
¡  long-lasting  
  
10.     According  to paragraph 4 which of the following is a characteristic of old growth forests  
¡  improved ability to withstand major disturbances  
¡  increasing amounts of woody debris  
¡  a decline in the mortality rate of tree species  
¡  increasing reliance on leaf and fine root  deatritus as a source of nutrients  
  
11.     According  to paragraph 4 one difference between the second and the third  stage in forest development is that in the third stage  
¡  there is more intraspecific competition than  interspecific competition.  
¡  the growth of understory and suppressed  substory trees slows down.  
¡  sudden changes in the environment are less frequent.  
¡  the canopy becomes more complex.  
  
Paragraph 5  
Some ecosystems may never reach the latter  stages of succession if natural disturbances (fire, flooding, hurricanes, etc) are frequent. A pyric climax  refers to an ecosystem that  never reaches the potential climax vegetation defined by climate because  of frequent fires.  The ecotone, a boundary, between grassland and forest  is a pyric climax, and only with fire suppression have woodlands and forests began to advance into these regions.  
  
12.     Why does the author discuss  pyric climax in the passage?  
¡  To help explain the idea that a forest may  not necessarily reach the old  growth stage.  
¡  To suggest that fire is a natural disturbance  least likely to prevent an ecosystem from reaching its potential  climax stage.  
¡  To acknowledge that the pattern of succession  following a disturbance is a very different in ecosystems such as  grasslands than it is in forests.  
¡  To help explain  how the boundary areas of an ecosystem affect  the way its  structure changes during succession.  
  
Paragraph 1:  
Succession is a continuous change in the  species composition, structure, and function  of a forest through time following disturbance. Each stage  of succession is referred to as a successional sere. The  final stage of succession, which is generally self-replacing, is referred to  as the climax sere. There are two major types of succession: primary and  secondary. Primary succession is the establishment of vegetation on bare rocks  or radically disturbed soil. Secondary succession is the reestablishment of  vegetation following a disturbance that killed or removed the vegetation but did  not greatly affect the soil. Volcanic  eruptions, retreating glaciers, and bare sand dunes are examples of sites subject to primary succession,  while clear-cutting of forests, wild fires,  and hurricanes are examples of sites subject to secondary succession.  ■ Hundreds to thousands of years are required for primary succession to  reach the climax sere, compared to decades to hundreds of  years for it to occur in secondary  succession. ■ A longer time  is needed to reach the climax sere  for primary than secondary succession because soil development must first take  place in primary  succession. ■ The rate of succession is dependent upon the extent of the disturbance  and the availability of appropriate seeds for recolonization. ■  
  
13.     Look at the four  squares [■] that  indicate where the following sentence can be added to the passage.  

  Tree species  that have small,  light seeds that  are dispersed by wind or transported  by animals recolonize a disturbed area more quickly than species with large seeds.  
Where would  the sentence best fit?  
  
14.     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  question is worth  2 points.
  
  Succession  is a continuous change in the species composition, structure, and function of a forest  through time following disturbances.  
Answer Choices
1.     Primary  succession occurs at sites where soil must be developed and thus takes  a far longer to complete than secondary succession, which occurs where relatively undisturbed soil already exists.  
2.     The  second stage of forest development is much shorter in boreal forests  than it is in tropical forests.  
3.     Old  growth forest differs from earlier succession stages in that most soil nutrients come from leaves  and fine root  debris rather than  from dead trees  and other coarse woody debris.  
4.     Early  in secondary succession resources are relatively abundant and vegetation increases until canopy closure, after which competition for resources brings about increased plant mortality.  
5.     With  a rising tree mortality, openings in the canopy develop, leading to layered  plant growth beneath the overstory canopy, and eventually a climax  stage is reached.  
6.     The  effective suppression of grassland wild fires has provided opportunities for the ecotone to proceed  into a forest.
最新 托福机经 雅思机经 免费下载
回复

使用道具 举报

领取福利

我们将以您绑定的 (****)
作为接收批改短信的默认手机号码

订阅小站最新精品课程信息

领取福利

输入您的手机号码,批改动态随时掌握!

订阅小站最新精品课程信息

您可以在设置—密码安全—绑定手机中随时修改您的手机号码

领取福利

还差最后一步了!只要填写完邮箱即可同时获得批改短信提醒小站精品课程信息两大福利了!

领取福利

网站地图 | 最新帖子 | 联系我们 | 站点统计 | 版权声明 | 免责及隐私声明 © 2011-2018 ZHAN.com All Rights Reserved. 沪ICP备15003744号-3
  沪公网安备 31010602002658号