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The role of trees is to ______.
A．loose soil
B．keep soil in position
C．harden soil
D．Both A and B
答案
更多“The role of trees is to ______.A．loose soilB．keep soil in positionC．harden soilD．Both A an”相关的问题
第1题
The role of trees is to______.
A．loose soil
B．keep soil in position
C．harden soil
D．Both A and B
第2题
The role of trees is to __________.
A．loose soil
B．keep soil in position
C．harden soil
D．Both A and B
第3题
Which of the following is the main idea of the whole passage？
A．There are three ways in which trees are important to human beings.
B．Providing man with shelter is the most important role the trees play.
C．Supplying man the wood and warship is the most important way the trees have.
D．Assisting in stopping drought and floods is the most important role the trees play.
第4题
Tree cover from city to city has been measured by any number of studies, so direct comparisons of figures are hard, but across the country, things are trending downward. In the past few decades, Washington has lost half its tree cover; San Diego's is off about a quarter; the cover in cities in Michigan, North Carolina and Florida has fallen to about 27% of what it once was; Chicago and Philadelphia are just 16%. "Urban deforestation," says Ed Macie, an urban specialist with the U.S. Forest Service in Atlanta, "compares with what's going on in the world's rain forests."
As with so many other environmental problems, there are a lot of things causing the tree trouble. In the mid to late 20th century, Dutch elm disease wiped out millions of city trees, and now bark beetles, gypsy moths and emerald ash borers are chomping through millions more, thanks in part to climate change that makes cities more hospitable to the pests. The fact that so many trees exist in cities to be eaten in the first place is a tribute to our greener impulses. Many municipalities planted their now towering canopies right after World War II, but age is taking a toll as a lot of those trees simply reach the end of their life span.
Development too much is a problem. In and around cities, single-family homes that once covered only a portion of their lot are being replaced by McMansions that don't leave enough yard space to support large-canopied trees. Sprawl is causing the footprints of cities themselves to increase, with what was once relatively lush land being bulldozed and paved over.
Urban fiscal woes have had a hand as well. Cities unable to keep up with the maintenance of large roadside trees swap them for pygmy-statured hawthorns and crape myrtles. Newly designed parks are replacing trees with no-fuss tennis courts and playgrounds. "Budgets are tight, and no one is giving extra money to plant larger trees," says Greg McPherson, director of the U.S. Forest Service Center for Urban Forest Research..
All this hits the environment hard, starting with air quality. But it's the thermometer that most noticeably reflects the loss of trees. A high canopy prevents sunlight and heat from ever reaching the ground; by contrast, unshaded asphalt soaks up thermal energy and radiates it back, creating what is known as heat islands.
Local governments are finally responding to the problem. More than 2,000 big and small cities have launched long-term planting and preservation programs. For now, the most immediate answer is less the planting strategy than the preservation one, something that can best be achieved by curbing sprawl and downsizing our taste for too-big homes. For people who plan cities as well as those who live there, it's important to remember that most of the time, sidewalks and sycamores are equally important.
Which of the following best summarizes the author's understanding of urban trees？
A．The decline of urban trees poses a big threat to human life.
B．The falling of trees causes big trouble in cities.
C．They play no real role in the global ecosystem.
D．There's no need to worry about their decline.
第5题
A．Tree leaves are green all the time in the monsoon forest.
B．There is a dry season in the cloud forest on tropical mountains.
C．Clouds help the plants in the rain forest near the deserts to grow.
D．The formation of climate in the rain forest has little to do with the trees.
第6题
Fossil charcoals tell us that wildfires have been part of life on the earth for as long as there have been plants on land. Fire was here long before such plants as grasses; it predated the first flowers. And without wanting to get mystical about it, fire is ,in many respects , a kind of animal, albeit an ethereal one .Like any animal, it consumes oxygen .Like a sheep, it eats plants. Sometimes, it merely nibbles a few leaves; sometimes it kills grown trees. Sometimes it is more deadly and destructive than a swarm of locusts.
The shape-shifting nature of fire makes it hard to study. Some fires are infernally hot; others, relatively cool. Some stay at ground level; others climb trees. Moreover, fire is much more likely to appear in some parts of the world than in others. Satellite images of the earth show that wildfires are rare in, say, Northern Europe, and common in parts of Central Africa and Australia.
Once a fire gets started, many factors contribute to how it will behave. The weather obviously has a huge effect: winds can fan flames, rains can quench them. The lie of the land matters, too: fire runs uphill more readily than it goes down. But another crucial factor is what type of plants the fire has to eat.
It’s common knowledge that plants regularly exposed to fire tend to have features that help them cope with it, such as thick bark, or seeds that only grow after being exposed to intense heat or smoke.
第7题
Change
As relentlessly bad as the news about global warming seems to be, with ice at the poles melting faster than scientists had predicted and world temperatures rising higher than expected, there was at least a reservoir of hope stored here in Canada's vast forests.
The country's 1.2 million square miles of trees have been called the "lungs of the planet" by ecologists because they account for more than 7 percent of Earth's total forest lands. They could always be depended upon to suck in vast quantities of carbon dioxide, naturally cleansing the world of much of the harmful heat-trapping gas.
But not anymore. In an alarming yet little-noticed series of recent studies, scientists have concluded that Canada's precious forests, stressed from damage caused by global warming, insects and persistent fires, have crossed an ominous (危险的) line and are now pumping out more climate-changing carbon dioxide than they are sinking. Worse yet, the experts predict that Canada's forests will remain net carbon sources, as opposed to carbon storage "sinks", until at least 2022, and possibly much longer.
"We are seeing a significant distortion of the natural trend," said Werner Kurz, senior research scientist at the Canadian Forest Service and the leading expert on carbon cycles in the nation's forests. "Since 1999, and especially in the past five years, the forests have shifted from being a carbon sink to a carbon source."
Translation: Earth's lungs have come down with emphysema(肺气肿). Canada's forests are no longer our friends.
So serious is the problem that Canada's federal government effectively wrote off the nation's forests in 2007 as officials submitted their plans to abide by the international Kyoto Protocol, which obligates participating governments to reduce their greenhouse gas emissions.
Under the Kyoto agreement, governments are permitted to count forest lands as credits, when calculating their national carbon emissions. But Canadian officials, aware of the scientific studies showing that their forests actually are emitting excess carbon, quietly omitted the forest lands from their Kyoto compliance calculations.
"The forecast analysis prepared for the government ... indicates there is a probability that forests would constitute a net source of greenhouse gas emissions," a Canadian Environment Ministry spokesman told the Montreal Gazette.
Canadian officials say global warming is causing the crisis in their forests. Inexorably rising temperatures are slowly drying out forest lands, leaving trees more susceptible to fires, which release huge amounts of carbon into the atmosphere.
Higher temperatures also are accelerating the spread of a deadly pest known as the mountain pine beetle, which has destroyed pine forests across British Columbia and is threatening vital wood in the neighboring province of Alberta. More than 50,000 square miles of British Columbia's pine forest have been stricken so far with the markers of death: needles turn bright red before falling off the tree.
Bitter cold Canadian winters used to kill off much of the pine beetle population each year, naturally keeping it in check. But the milder winters of recent years have allowed the insect to grow rapidly. "That's what's causing some of our forests to switch from a carbon sink position to a source position," said Jim Snetsinger, British Columbia's chief forester. "Once those infested trees axe killed by the pine beetle, they are no longer taking in carbon -- they are giving it off. "
Snetsiuger noted that eventually, over the course of a generation, some of the dying forests will begin to regenerate and once again begin storing more carbon than they release. But for the foreseeable future, experts say, their models show that Canada's forests will stay stuck in a bad global-warming c
A．they balance the world temperatures
B．they are abundant to cleanse the earth's atmosphere and play an important role in cleansing the earth's atmosphere
C．they could always suck in vast quantities of carbon dioxide
D．they naturally cleanse much of the harmful heat-trapping gas
第8题
______of the land in that district ______ covered with trees and grass.
A．Two-fifth; is
B．Two-fifth; are
C．Two-fifths; is
D．Two-fifths; are
第9题
City landscapers will be______the trees throughout the city this weekend.
A．trimming
B．climbing
C．reducing
D．bordering
第10题
(24)
A．The trees are being cut down.
B．The trees are blocking my view.
C．The trees grow better around the office.
D．The trees help cool my office.
