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形式有点象鸭子里的文章，了解一下应该有用处。 INDEPTH: FORCES OF NATUREForest FiresCBC News Online | July 6, 2006Canada's forest fire season usually starts as early as April, with grass fires that scorch the landscape. Then the season moves into high gear with the first round of forest fires in May and June, with more to come in the dry summer months. By the time it's all over in September, an average of 25,000 square kilometres ? an area the size of Lake Erie ? will have burned in roughly 10,000 fires across the country. Fighting fires During those six months, an entire industry comes alive. Provincial governments and Parks Canada hire and train hundreds of firefighters who spend the summer doing the annual battle with fire. Many are college and university students who need a job. Others are highly trained firefighters who have gone to school to learn the intricacies of fire behaviour and suppression. They may spend weeks living in fire camps and spend long, hard hours fighting stubborn blazes that will only get worse because of high winds. They will be transported to other provinces to reinforce firefighters worn down by a blaze that won't be controlled. Many will be on the ground, using hand tools, chainsaws and water pumps to control fires. But Canadians have also become experts in battling blazes from the air with helicopters, rappelling and parachuting crews, water tankers and even satellite monitoring systems. Applicants for the more dangerous jobs ? Rapattack crews, which rappel from helicopters to reach remote fires, and Parattack crews, which parachute into fire zones from airplanes ? must go through rigorous fitness and endurance tests even after completing basic firefighting courses and training in rappelling or parachuting. From towers to satellites Although fire lookout towers, first introduced in the '20s, are still used in high-risk zones, more sophisticated methods have been introduced. Computerized monitoring systems log all lightning strikes, and the federal government's Canada Centre for Remote Sensing can detect locations of fires across the country using satellites. Using the Canadian Forest Fire Danger Rating System, fire managers can determine the moisture levels within the forest, how fast the trees will burn, how much of the forest will be consumed, and in which direction the blaze will spread. Once a fire has been brought under control, infrared scanners are used to detect remaining heat sources. Most fires are caused by humans: 58 per cent of the wildfires that consume our forests and grasslands every year are caused by carelessness and could have been prevented. The rest, 42 per cent, are caused by lightning. This breakdown in the numbers was first discovered in Canada during aerial patrols of lumber yards and parks in the 1930s, and soon the first fire prevention campaigns were launched, posting warnings in schools and along highways. Fire's ecological benefits Since those early days, millions of dollars have been spent on campaigns to prevent forest fires. But researchers now know that fire is not necessarily bad. It can be a natural part of a healthy grassland or forest ecosystem. Fire reduces the build-up of dead and decaying leaves, logs and needles that accumulate on the forest floor. It reduces or eliminates the overhead forest canopy, increasing the sunlight that stimulates new growth from seeds and roots. Many plants and animals have adapted to fire. Both lodgepole pine and jack pine have resin-sealed cones that stay on trees for many years. The heat of fire melts the resin and the cones pop open. Thousands of seeds then scatter to the ground and grow into new stands of pine. Woodpeckers feast on bark beetles and other insects that colonize in newly burned trees. And so, 20 years ago, Parks Canada decided that it wouldn't interfere in natural processes such as fire, insects and disease unless it had to ? that is, unless people or neighbouring lands were threatened. Playing with fire? More recently, forest managers across North America have introduced programs of deliberately lit "prescribed fires" to clear out forest debris and restore ecosystems that are dependent on fire to thrive. Trained specialists decide when and where, and for how long, to permit such fires to burn. They consider weather, vegetation type, fire behaviour and terrain in order for the fires to burn safely. Although prescribed fires have become common in the United States and Canada, they are also controversial. In Canada, prescribed burns have been strongly opposed by landowners and outdoors-related businesses. Timber is a valuable resource and it's hard to convince anyone that burning down trees, even on a small scale, makes sense. In 1988, the U.S. Forest Service was heavily criticized when parts of Yellowstone National Park were allowed to burn after being struck by lightning. The fires spread quickly and, in the end, men and resources were moved in to douse the flames. It was the costliest firefighting effort in U.S. history, at $120 million US. And in 2000, a prescribed fire in New Mexico got out of control and destroyed 200 homes in Los Alamos. Fires, weather and climate When a fire gets as big as the Okanagan Valley fire in B.C. in the summer of 2003, they can create their own weather systems. And fires that big usually create weather conditions that can lead to more fires. It happens because of an effect called "thermal buoyancy" ? air around a very intense fire heats and rises, the fire pulls in more surrounding air, and a wind pattern emerges from the cycle. Smoke from the fire contributes to natural cloud cover and enhances lightning conditions. The wind pattern creates hot and dry conditions that can be felt several kilometres from the fire. Although these effects on the local weather are clear, scientists are not sure how large swaths of burnt land affect the global climate. A healthy forest is considered a carbon "sink" or "reservoir." Carbon emissions are absorbed by healthy trees and reduced in the atmosphere. But, when a forest burns, carbon is released back into the atmosphere ? often in the form of carbon dioxide, a known greenhouse gas. When high volumes of greenhouse gases are released into the atmosphere, they may aggravate patterns of global warming. What may result is called a "positive feedback loop." Global warming enhances conditions that feed forest fires, while a large increase in fires releases more greenhouse gases into the environment. Greenhouse gas emission contributes to global warming ? a cycle that constantly feeds itself. Some scientists point to a recent increase in the amount of forest burned every year as evidence that the loop has already started. Others say the increase could be part of natural variation. Scientists have only been collecting forest fire data for the past 40 years, a short time from which to draw long-term predictions.

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沙发!

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超赞 赏 反馈:珊瑚鱼 和 真榕 annieyu 0$(VIP 0) 4,1472006-07-28#3 Thanks for this piece of article ,it is good for us to widen horizon meanwhile we can learn some things about Canada.I add scores of credit for you although it is no use .

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happytom 说:沙发!点击展开... 呵，这沙发可不用抢。我最近还为自己发的这个帖子是零观众而郁闷呢，谢谢！

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annieyu 说:Thanks for this piece of article ,it is good for us to widen horizon meanwhile we can learn some things about Canada.I add scores of credit for you although it is no use .点击展开... Thank you so much, your scores is the greatest encouragement to me.

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超赞 赏 反馈:annieyu harvey66 0$(VIP 0) 1,4422006-08-03#7 Yes, It can be a IELTS article itself.

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2005.5.13 FNHKVO:TCWwaiting for MEone slang per day 超赞 赏 珊瑚鱼 0$(VIP 0) 8162006-09-07#8 useful for reading!Thanks with SW!

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perfect, thanks.

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reading is better

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