首页
登录
职称英语
NORTH AMERICAN GRASSLANDS1 In North America, native grasslan
NORTH AMERICAN GRASSLANDS1 In North America, native grasslan
游客
2025-02-08
37
管理
问题
NORTH AMERICAN GRASSLANDS
1 In North America, native grasslands occur primarily in the Great Plains in the middle of the continent. The North American prairie biome is one of the most extensive grasslands in the world, extending from the edge of the Rocky Mountains in the west to the deciduous forest in the east, and from northern Mexico in the south to Canada in the north. Average annual rainfall ranges from about 40 cm (16 inches) in the west to 80 cm (31 inches) in the east. Average annual temperatures range between 10 degrees and 20 degrees Celsius (50 to 68 degrees Fahrenheit). In the moist regions of the North American grasslands, especially in the northern Great Plains, rainfall is distinctly seasonal, and temperatures can vary widely from very hot in summer to bitter cold in winter.
2 One hundred years ago, the Great Plains grasslands were one vast, unbroken prairie. Much of the prairie is now farmland, the most productive agricultural region in the world, dominated by monocultures of cereal grains. Wheat, barley, soybeans, corn, and sunflowers occupy the land that was once prairie. In areas given over to grazing lands for cattle and sheep, virtually all the major native grasses have been replaced by
alien
species.
3 An important feature of the northern Great Plains grasslands is the presence of millions of glacial depressions that are now small ponds known as prairie potholes. They were formed during the most recent Ice Age, when streams flowed in tunnels beneath glacially formed sandy ridges. When the Ice Age ended around 12,000 years ago, the retreating glaciers created about 25 million depressions across a 300,000-square-mile landscape—about 83 potholes per square mile. As the ice blocks melted, much of the water was left behind, forming wetlands ranging in size from a tenth of an acre to several acres. The wetlands were soon surrounded by fluttering waves of grasses: shortgrass, mixed grass, and tallgrass.
4
Today these small wetlands still cover the prairies, although much of the landscape— including both native grasses and potholes—has been transformed to cropland and grassland for grazing.
What does remain of the wetlands, however, still serves as an important breeding area for more than 300 bird species, including large numbers of migrating shorebirds and waterfowl. The potholes fill up with water during spring rains and usually dry out by late summer. Every spring, birds arrive in great numbers—northern pintails, mallards, coots, and pied-billed grebes—4 to 6 million strong, to mate in the seasonal wetlands that dot portions of Minnesota, Iowa, North and South Dakota, Montana, Alberta, Saskatchewan, and Manitoba. Prairie pothole country produces half of North America’s 35 to 40 million ducks and is renowned worldwide as a "
duck factory
."
5 Recently biologists have discovered that the prairie pothole region is potentially a vast carbon sink: a natural sponge that absorbs carbon dioxide emissions from cars, factories, and power plants. Carbon dioxide is the most common of all the pollutants acting as greenhouse gases that heat up the atmosphere. Fortunately, however, carbon dioxide is captured naturally and stored in trees, soil, and plants. Scientists have termed
this
"carbon sequestration." They have determined that prairie potholes hold an average of 2.5 tons of carbon per acre per year when not being farmed. This means that if the entire pothole region in the United States and Canada were to stop being farmed, the region would store about 400 million tons of carbon over 10 years—the equivalent of taking almost 4 million cars off the road. Thus, preserving the potholes could be a way to
offset
greenhouse gas emissions that are warming the planet.
Glossary:
biome: one of the world’s major natural communities, classified by predominant vegetation
monoculture: cultivation of large land areas with a single plant variety [br] The word alien in paragraph 2 is closest in meaning to
选项
A、healthy
B、simple
C、cheaper
D、imported
答案
D
解析
Alien means imported in this context. Clues: ... virtually all the major native grasses have been replaced by alien species. Imported grasses have replaced the original, native grasses. (1.4)
转载请注明原文地址:https://tihaiku.com/zcyy/3947995.html
相关试题推荐
In(theearly)nineteenthcentury,theCherokeenationofAmericanIndians(was
TheSpanish(claiming)titleto(allof)NorthAmericaandestablishedthe(olde
ThemigrationofAfricanAmericansfromtheruralSouthtothe(industrial)Nort
(Addressing)themesthatwere(unique)American,thepoetWaltWhitman(celebrat
Ofalltheart-relatedreferenceandresearch(library)inNorthAmerica,(that
ThetuliptreeisnativetotheeasternUnitedStates,______thetallestandla
IntheNorthAmericancolonies,redware,asimplepotteryfiredatlow
Ineighteenth-centurycolonialAmerica,flowersandfruitweretypicallyt
InwesternNorthAmerica______formtheGreatDivide,whichseparatestheareas
WhataspectofNorthAmericadoesthepassagemainlydiscuss?[br]Thepassages
随机试题
Readthetextbelowaboutsalaryraise.Inmostofthelines(41-52),the
Technology,entrepreneurship(创业能力)andinnovationsarekeywordsthatsumup
WhichstatementaboutVesaliusismostprobablyFALSE?[br]WhywasVesaliuscri
某住宅工程,建筑面积12300㎡,地上六层,地下两层,筏形基础,框架剪力墙结构。
纳税人的下列行为中,应同时征收增值税和消费税的有()。A.将自产高档香水精用于
()是指除了信用评级不同外,其余条件全部相同(包括但不限于期限、嵌入条款等)两种
建设项目的经济类信息不包括( )。A:施工信息收集 B:资金使用计划 C:
2014年,全国资助学前教育(幼儿)、义务教育、中职学校、普通高中和普通高校学生
所有电气装置都必须具备防止电气伤害的直接接触防护和间接接触防护。下列防护措施中,
劳动卫生学是研究劳动条件对健康影响的学科,健康受影响的是A.劳动者 B.体力劳
最新回复
(
0
)