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OFFICIAL39 In paragraph 3, what is the author's purpose in describing the natural cycle of fires in ponderosa pine forests?

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Forest Fire Suppression
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Forest fires have recently increased in intensity and extent in some forest types throughout the western United States. This recent increase in fires has resulted partly from climate change (the recent trend toward hot, dry summers) and partly from human activities, for complicated reasons that foresters came increasingly to understand about 30 years ago but whose relative importance is still debated. One factor is the direct effect of logging, which often turns a forest into something approximating a huge pile of kindling (wood for burning): the ground in a logged forest may remain covered with branches and treetops, left behind when the valuable trunks are carted away; a dense growth of new vegetation springs up, further increasing the forest's fuel loads; and the trees logged and removed are of course the biggest and most fire-resistant individuals, leaving behind smaller and more flammable trees.

Another factor is that the United States Forest Service in the first decade of the 1900s adopted the policy of fire suppression (attempting to put out forest fires) for the obvious reason that it did not want valuable timber to go up in smoke, or people's homes and lives to be threatened. The Forest Service's announced goal became "Put out every forest fire by 10:00 A. M. on the morning after the day when it is first reported." Firefighters became much more successful at achieving that goal after 1945, thanks to improved firefighting technology. For a few decades the amount of land burnt annually decreased by 80 percent. That happy situation began to change in the 1980s, due to the increasing frequency of large forest fires that were essentially impossible to extinguish unless rain and low winds combined to help. People began to realize that the United States federal government's fire-suppression policy was contributing to those big fires and that natural fires caused by lightning had previously played an important role in maintaining forest structure.

The natural role of fire varies with altitude, tree species, and forest type. To make Montana's low-altitude ponderosa pine forest as an example, historical records, plus counts of annual tree rings and datable fire scars on tree stumps, demonstrated that a ponderosa pine forest experiences a lightning-lit fire about once a decade under natural conditions (i.e.., before fire suppression began around 1910 and became effective after 1945). The mature ponderosa trees have bark two inches thick and are relatively resistant to fire, which instead burns out the understory - the lower layer - of fire-sensitive Douglas fir seedlings that have grown up since the previous fire. But after only a decade's growth until the next fire, those young seedling plants are still too low for fire to spread from them into the crowns of the ponderosa pine trees. Hence the fire remains confined to ground and understory. As a result, many natural ponderosa pine forests have a parklike appearance, with low fuel loads, big trees spaced apart, and a relatively clear understory.

However, loggers concentrated on removing those big, old, valuable, fire-resistant ponderosa pines, while fire suppression for decades let the understory fill up with Douglas fir saplings that would in turn become valuable when full-grown. Tree densities increased from 30 to 200 trees per acre, the forest's fuel load increased by a factor of 6, and the government repeatedly failed to appropriate money to thin out the saplings. When a fire finally does start in a sapling-choked forest, whether due to lightning or human carelessness or (regrettably often) intentional arson, the dense, tall saplings (young trees) may become a ladder that allows the fire to jump into the crowns of the trees. The outcome is sometimes an unstoppable inferno.

Foresters now identify the biggest problem in managing Western forests as what to do with those increased fuel loads that built up during the previous half century of effective fire suppression. In the wetter eastern United States, dead trees rot away more quickly than in the drier West, where more dead trees persist like giant matchsticks. In an ideal world, the Forest Service would manage and restore the forests, thin them out, and remove the dense understory by cutting or by controlled small fires. But no politician or voter wants to spend what it would cost to do that.

8.In paragraph 3, what is the author's purpose in describing the natural cycle of fires in ponderosa pine forests?

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正确答案:C
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【题目翻译】在第3段中,作者描述黄松松林火灾自然循环的目的是什么? A:强调火灾后植苗的重要性。 B:为提高法律对抑制森林火灾的效力而争论。 C:描述在没有人为干预的情况下,火是如何影响一个典型的黄松森林的。 D:解释在控制火势之前,蒙大拿州的黄松森林曾经遭受的长期破坏。 2、【判定题型】:根据题干问法“what is the author's purpose”,题目询问“xxxxxx”(文章引用内容)的修辞目的,可以判断本题为修辞目的题。 【关键词定位】:根据关键词“natural cycle”,定位到第三段的后半段,原句为“But after only a decade's growth until the next fire, those young seedling plants are still too low for fire to spread from them into the crowns of the ponderosa pine trees. @@@@Hence the fire remains confined to ground and understory. @@@@As a result, many natural ponderosa pine forests have a parklike appearance, with low fuel loads, big trees spaced apart, and a relatively clear understory.”。 【引用内容分析】每次新的火起来后,都会因为小树太矮了而烧不到大树的树干,因此火焰被控制在了地面,破坏性也被控制了。作者形容这个过程是为了向我们说明ponderosa树在着火时候的情况,当然也是在无人干预的情况下。 【选项分析】 A.未提及火灾后植苗,故错误。 B.没有要做争论,故错误。 C.符合文意,正确; D.是要说明火和黄松林的关系,不是要说破坏,故错误。

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