As opposed to forests, grasslands receive markedly less precipitation. ■ This is one of the reasons why trees, which usually require a significant amount of moisture, are spaced relatively sparsely in grasslands. ■ Due to the facts that most grasslands are situated in the center of continental landmasses, and that costal mountain ranges can block west-to-east winds as is the case with the Great Plains in North America, air masses from the north and south are highly influential on grasslands. ■ The Great Plains receive cold Arctic air in winter and hot tropical air in summer. ■ A typical grassland climate includes hot summers with long periods of desiccation and cold winters with erratic snow cover. Consequently, plants in these grassland areas experience low soil moisture and, additionally, are exposed to fixll sun, strong dry winds, and extreme summer heat and winter cold. Grassland plants must adapt to these conditions.
To support research on various types of ecosystems, during the 1970s, The National Science Foundation started what is known as the Long-Term Ecological Research (LTER) program. With the LTER program, scientists working at far-away sites can share data and collaborate to identify and understand large scale ecological patterns. At one LTER site in the Flint Hills of Northeastern Kansas, scientists made an important discovery about the influence of precipitation on plant productivity, the fuel on which ecosystems run. It was found that grasslands respond more strongly to pulses in rainfall than any other ecosystem. Dramatic bursts of plant growth and significant increases in primary productivity result from intermittent rainfall in grasslands. This pattern indicates that grasslands have a high underlying growth potential that surfaces when enough water is suddenly available. Because of these findings, LTER scientists have proposed that grassland annual primary productivity can be a useful indicator of global climate change. Similar to the canaries that miners used to carry into mines to warn of poisonous gases, grasslands may be able to serve as a warning of climate change and how it is affecting plants and humans. •
When maintaining grasslands, fire plays an essential role. In the summer, dry grasses and their dead remains which have accumulated over previous years on the upper layer of soil (known as mulch) make a highly combustible fuel for fires started by people or lightning. When there is an absence of rain, dry lightning is a common occurrence in grassland areas, as is the accidental escape of campfires or other human-related fires. These fires in grasslands can bum for many kilometers before being stopped by rain or wet areas. Studying charcoal buried in soil layers have suggested that under natural (pre-European settlement) conditions, at least a hectare of North American prairie may have burned once every 5 to 30 years.
Plants in the grasslands are adapted to survive fire in many ways, but, just as importantly, fire is an essential component of grassland ecosystems. The invasion of both fire-sensitive plants and most trees are prevented by fire, and fire clears away dead plant material, thereby releasing necessary nutrients that facilitate new growth. Since the development of new grass was favored by Native Americans’ horses and was also attractive to the buffalo they hunted, they often set grassland fires to stimulate it. These fires on grasslands was also helpful in increasing productivity of the Native Americans’ wild food plants, improving visibility (which brings security), and helping control pests such as ticks. Nowadays, people use fire as an important tool in restoring and preserving grasslands.eaters create a disturbance to which grassland plants are adapted in many ways. In grasslands, grazing is more significant than in other types of ecological communities. Up to 60 percent of energy and grassland materials flows through primary and other consumers. In other terrestrial ecosystems, on the other hand, less than 5 percent of the ecosystem’s material and energy usually flows through consumer food webs. This difference coordinates with the relatively large herbivore populations that grasslands support.
Benefits brought about from grazing include helping lower-growing plants by preventing shading by tall species, and providing a rich source of nutrients from grazer excrement. Grazing and fire both prevent just a few plants from dominating grasslands and help maintain the high natural plant diversity. Researchers at the University of Minnesota have found that high plant diversity has been pivotal in establishing and maintaining the high fertility in natural grassland soils.
1. According to paragraph 1, grassland regions have extreme summer heat and winter cold as a result of those areas being
(A) affected primarily by air masses that move from east to west
(B) surrounded by mountains on all sides
(C) in the middle area from both the tropics and the Arctic
(D) isolated from west-to-east air movements
2. The word collaborate in the passage is closest in meaning to
(A) work together
(B) make an attempt ,
(C) compare outcomes
(D) acquire evidence
3. Why does the author use the phrase the fuel on which ecosystems run?
(A) To explain why grasslands are a difficult ecological pattern to study
(B) To illustrate what discovery scientists made at the LTER site in the Flint Hills of northeastern Kansas
(C) To point out that research run by the LTER program can lead to practical results
(D) To emphasize the fundamental importance of precipitation on ecosystems
4. The word intermittent in the passage is closest in meaning to
5. According to paragraph 2, what indicates the strong growth potential underlying in grasslands?
(A) The frequency with which they occur geographically
(B) The average rate in which they reproduce
(C) The way they respond to rainfall
(D) The speed with which they respond to global climate changes
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) Dead and dry grasses that form on the soil surface in grasslands are called mulch.
(B) In summer, people use dry grasses and their dead remains to fuel fires in grasslands.
(C) In grasslands, summer fires started either by lightning or by people are fueled by dry grasses and their dead remains at the soil surface.
(D) It is always easy to find fuel to use for fires in grasslands because dry grasses and mulch accumulate at the soil surface during summers
7. According to paragraph 3, which of the following is true about lightning in grasslands?
(A) Only in the dry months of summer do storms with lightnings occur in grasslands.
(B) Only during the most dry months of summer do storms with lightning occur.
(C) Almost all the severe storms that have happened in grasslands involve a great deal of lightning.
(D) Lightning at the absence of rain is a common phenomenon in grasslands.
8. The word essential in the passage is closest in meanirig to
9. According to paragraphs 3 and 4，what is one way in which fire helps maintain the character of grasslands?
(A) It prevents trees from becoming permanently established.
(B) It helps new plants grow.
(C) It causes charcoal to deposit in layers on grassland soils.
(D) It kicks out the wild grazing animals that can quickly consume too many of the grassland plants.
10. According to paragraph 4，each of the following is a benefit that Native Americans gained from grassland fires EXCEPT
(A) increased height of new plants in which to hide
(B) decrease of insect pest populations
(C) enhanced productivity of wild food plants
(D) raised availability of the food their horses preferred
11. According to paragraph 5，what indicates that grazing is more essential in grasslands than in other ecological communities?
(A) The animals that graze on grasslands include more natural herbivores than livestock, which is usually not true of other ecological communities.
(B) Adaptation to the disturbance of grazing causes grassland plants to grow more slowly than plants in other ecological communities.
(C) In grasslands herbivores consume a higher percentage of the plant material than they do in other ecological communities.
(D) Grazing is a harmful disturbance in grasslands but not in other ecological communities.
12. According to paragraph 6，one way grazing contributes to maintaining high natural plant diversity of grasslands is by
(A) controlling how fast nutrients leave the soil
(B) guaranteeing that enough sunlight is given to low-growing plants
(C) allowing tall plant species to compete for space
(D) improving the distribution of the plants with the highest productivity throughout grassland areas
13. Look at the four squares [■] that indicate where the following sentence could be added to the passage.
A typical grassland area averages only 25 to 100 centimeters per year.
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 sentences 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.
Grassland plants must be able to cope with low moisture levels and extreme climates. Answer Choice
(A) Before being stopped by wet areas or rain, fires started by humans have resulted in grasslands，being burned over many square kilometers.
(B) Grassland plants are not only well adapted to survive grazing, but grazing actually helps maintain high plant diversity.
(C) Recurring grassland fire serves an essential part in maintaining grasslands，characteristic vegetation.
(D) Grassland ecosystems have been preserved with the help of Native Americans hunting herbivores such as buffalo and horses.
(E) Despite grasslands having hot dry summers, plant growth dramatically increases in response to some rainfall.
(F) Grassland summers are dry, so grassland plant productivity relies largely on the amount of snowfall that accumulates throughout winter.