Tree Species Identification in Tropical Rain Forests

Paragraph 1：Identifying tree species in tropical rain forests may be harder than you think. Plant species identification can be difficult for all kinds of reasons, even identification of trees, which are big and conspicuous. For example, for some willow trees, both leaves and flowers may be needed for identification, but the two may not be present at the same time. Yet whatever problems may confront us in temperate climates, we can be sure that the tropics will pose far worse difficulties.

 

 

1. In paragraph 1, why does the author discuss willow trees? 

 

A. To provide an example of a tree that is unusually large  

 

B. To explain the process of tree species identification  

 

C. To support the idea that tropical trees can be more difficult to identify than temperate trees  

 

D. To demonstrate one reason why it can be problematic to determine what species a tree belongs to

 

 

 

 

 

Paragraph 2：In tropical rain forests, the flowers of a given tree species are typically not in bloom and so cannot be observed. In seasonal rain forests (with a distinct wet season and a distinct dry season), many trees adjust their flowering to the rains, so flowering is to some extent predictable. But much rain forest (as in much of the Amazon region) is nonseasonal, and trees may flower at any time. To be sure, different trees of the same species generally flower simultaneously, for if they did not, they could not pollinate each other. So they must be responding to signals from the environment at large, or else (or in addition) they must be communicating with one another. But what those signals are is unknown, at least to us. To the human observer, the flowering seems random. In any case, in a tropical forest (at least in a secondary forest, which is forest that is regrowing after previous harvesting or clearance), the trees grow very close together, and most are remarkably thin, like poles, and grow straight up and disappear into the gloom, twenty meters overhead. Even if there are flowers, you would not necessarily see them . 

 

 

 

2. Paragraph 2 implies which of the following about tree flowering in seasonal rainforests? 

 

A. It is less predictable than tree flowering in tropical rain forests  

 

B. It results from an unknown means of communication between the individual trees of each species.  

 

C. It is more useful to researchers trying to identify tree species than is the tree flowering in tropical rain forests. 

 

D. It follows the same pattern that tree flowering follows in a tropical secondary forest. 

 

 

 

3. In paragraph 2, why does the author discuss pollination? 

 

A. To provide evidence that in many tropical tree species flowering is at least somewhat predictable  

 

B. To help explain why flowers on trees in tropical rainforests can be absent most of the time  

 

C. To help explain why different trees of the same species bloom at the same time 

 

D. To suggest one reason why trees might benefit from adjusting their flowering to the rains 

 

 

 

4. According to paragraph 2, what is true about much of the Amazon region? 

 

A. It has tree species that adjust their pollination to rainfall.  

 

B. It has not yet been harvested or cleared.  

 

C. It has trees that typically flower during periods of rain.  

 

D. It does not have separate wet and dry seasons.

 

 

 

 

 

Paragraph 3：The leaves may not be accommodating either, at least when viewed from the ground. Rain-forest trees all face the same kinds of conditions and have adapted in the same general kinds of way. Rain forests are wet by definition. But in some there is a dry season, and even when there is not, it doesn’t rain all the time. Thus the forest floor may be moist, but the topmost leaves of the canopy are far above it and are exposed to the fiercest sun. So the uppermost leaves must resist desiccation (drying out). Yet from time to time, and in due season every day, they must also endure tremendous downpours. Leaves that can cope with such contrasts tend to be thick and leathery (to resist drought), oval in shape, and have a protection at the end known as a drip tip to let surplus rain run off the leaf. Many hundreds of trees from dozens of only distantly related families have leaves of this general type. But even if you can distinguish individual leaves, it is hard to be certain if they belong to the tree you are interested in or to the one next to it or to some epiphyte (a plant that grows on other plants) or liana (vine) slung over its branches. Often, in short, researchers must base their identification of a tree on the bark of its trunk. The trunks of tropical trees are sometimes highly characteristic, being deeply furrowed or twisted, but in most species the bark is simply smooth and gray, dappled with lichen and moss. 

 

 

5. Paragraph 3, researchers provide an explanation for each of the following characteristics of rain-forest tree leaves EXCEPT  

 

A. their having a drip-tip at the end  

 

B. their thickness  

 

C. their leathery texture  

 

D. their oval shape

 

 

 

6. According to paragraph 3, what is one reason that looking at leaves may not be very useful when trying to determine the species of a rain-forest tree?  

 

A. Leaves of rainforest trees often look very different when they are wet than when they are dry.  

 

B. Leaves that are exposed to the hot tropical sun dry out and lose their distinguishing characteristics.  

 

C. It can be hard to determine whether a leaf has a drip tip or not.  

 

D. It can be hard to determine whether a leaf belongs to a tree or to another plant growing on the tree.

 

 

 

7. According to paragraph 3, one reason that researchers in tropical forests must often rely on a tree’s bark for species identification is that  

 

A. distinct species of tree often have similar kinds of lichens and moss growing on their trunks  

 

B. the leaves of many different tropical tree species are very similar to each other in appearance 

 

C. many rainforest trees have neither epiphytes nor lianas  

 

D. the bark of the trees is less affected by changes in light and moisture than leaves are 

 

 

 

 

 

Paragraph 4：In a temperate forest you can be fairly sure that any one tree is the same species as the one next to it or, at least, it will be one of a list that is unlikely to exceed more than half a dozen (oak with ash in much of Britain; lodgepole pine with aspen in the northernmost reaches of North America; aldercotch pine, and spruce in the Baltic; and so on). But in the Amazon in particular, you can be fairly sure that any one tree is not the same species as the one next to it. Often there is a third of a mile between any two trees of the same species, and there can be up to 120 different species of trees in any one acre. So the task, often, is to identify an individual tree that may be not much thicker than your arm from the appearance of its bark, out of a total list of several hundred (or thousand) possibilities, which may well include some that have not been described before, so that there is nothing to refer back to. 

 

 

 

8. 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. Different temperate forests contain different combinations of tree species but in all such forests, all the trees of any one species are likely to be found close together.  

 

B. Temperate forests rarely contain more than about six species of tree, and trees growing next to each other tend to be of the same species. 

 

C. You can easily make a list of all the tree species that are likely to be found in temperate forests, and if one tree is not on that list，you can be confident that the tree next to it will be. 

 

D. Forests in Britain, in North America, and in the Baltic generally contain no more than half a dozen tree species, and all these species can be found on lists.

 

 

 

Paragraph 3：The leaves may not be accommodating either, at least when viewed from the ground. Rain-forest trees all face the same kinds of conditions and have adapted in the same general kinds of way. ■Rain forests are wet by definition. But in some there is a dry season, and even when there is not, it doesn’t rain all the time. Thus the forest floor may be moist, but the topmost leaves of the canopy are far above it and are exposed to the fiercest sun. ■So the uppermost leaves must resist desiccation (drying out). ■Yet from time to time, and in due season every day, they must also endure tremendous downpours. ■Leaves that can cope with such contrasts tend to be thick and leathery (to resist drought), oval in shape, and have a protection at the end known as a drip tip to let surplus rain run off the leaf. Many hundreds of trees from dozens of only distantly related families have leaves of this general type. But even if you can distinguish individual leaves, it is hard to be certain if they belong to the tree you are interested in or to the one next to it or to some epiphyte (a plant that grows on other plants) or liana (vine) slung over its branches. Often, in short, researchers must base their identification of a tree on the bark of its trunk. The trunks of tropical trees are sometimes highly characteristic, being deeply furrowed or twisted, but in most species the bark is simply smooth and gray, dappled with lichen and moss. 

 

 

 

9. Look at the four squares that indicate where the following sentence could be added to the passage.  

 

As a result, the topmost level of a rainforest can be desert-like. 

 

Where would the sentence best fit Click on a square to add the sentence to the passage. 

 

 

 

 

 

10. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selected THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points. Drag your choices to the spaces where they belong. To review the passage，click on View Text  

 

 

 

Answer Choices 

 

A. In tropical forests different trees of the same species flower at different times so they are not able to pollinate one another.  

 

B. Flowering in tropical trees is often unpredictable and when it occurs, the flowers themselves tend to be too high up to be clearly visible. 

 

C. Many tropical tree species have leaves that look very similar from the ground, and because the trees often grow close together, correctly matching a leaf with a particular tree can be difficult. 

 

D. The leaves and bark of a single rainforest tree are often very different at different heights due to the need to adapt to different conditions, which adds to the difficulty of species identification.  

 

E. Because trees in rain forests are spaced closely together, it is easy to tell whether neighboring plants are the same species, but that is not much help in determining which species they are.  

 

F. Often, a rain-forest tree has to be identified by its bark, but trees of like species are widely scattered, the list of possible species is very long, and many have similar-looking bark.

 

 

答案请付费后查阅：