野火

主题:磷火可控燃烧 页数:5(1781字) 发布时间:2011年4月20日
甲野火是在草原,刷,或林地不受控制的燃烧的任何实例。野火破坏财产和宝贵的自然资源,并可能威胁到人与动物的生命。野火可以发生在任何一年的时间,但炎热,干燥的天气通常发生。野火通常被浓烟可能弥漫方圆几英里信号。美国国家气象局,美国森林服务,以及国家林业机构共同发出野火概率的预测。当地电台和电视台播出的当地消防条件的信息和警告。野火会对住宅美国日益严重的威胁。1987年5.3万个火消耗超过两百万英亩。到1988年10月,将近70000大火夺去了超过四百万英亩。在火灾的增加是在农村社区和野生的土地和城市界面人口增长的结果。 Fire is a powerful, natural phenomenon (www.nps.gov/pub_aff/issues/fire.html, pg.3). Fire has great impact on the people and environment of North America as one saw when in 1988 wildfires broke out all over Yellowstone National Park burning 793,880 acres. For hundreds of years man has suppressed wildfires. The federal government controls fires on federal forestland, and state government controls state forestland. It was believed that by suppressing the fires man ensured a healthy future for the forest. But, as scientists have gathered more information on the effects of fire on forest ecosystems, they have learned that fire exclusion might not have been the best practice for land management. A new technique known as prescribed fire has been used in the last twenty years to reintroduce the natural process of fire back into the forests. While not all the effects of prescribed fire are seen right now, we do know the effects of fire exclusion, and we do know some of the benefits of prescribed fire. Over the past couple of decades, forest management teams have noticed that fire suppression has caused many problems in the forest ecosystem. Today it is known that fire exclusion causes thick vegetation and large amounts of dead fallen materials. The heavy vegetation and dead material increase the fuel quantity on the forest floor and may cause fires to ignite more easily. When a fire begins on the thickly covered floor, the blaze burns at a much higher intensity causing more damage to the forest ecosystem. Not only does fire exclusion cause an accumulation of thick vegetation on the forest floor, but also causes and increased density of smaller trees. When fire does occur, these small trees guide the raging fire from the forest floor to the crown of the older trees causing a crown fire (www.fs.fed.us/fire/.com , article 2). Another observed result from fire suppression is vegetation modification. Forests that have not had a fire in decades may become the home to a plant species that is not adapted or dependent on fire. Plants that are adapted for wildfire usually have a thick layer of bark to protect its living tissue from the heat. Also, many trees are dependent on the heat of fire in order to open up their seed cones for regeneration. Vegetation modification also affects the ecosystem’s insects and diseases, wildlife populations, soil structure, and nutrient recycling. Thick vegetation, excessive dead material, and vegetation modification all caused by fire suppression, have caused forest managers to turn to a technique known as prescribed fire. A prescribed fire is a fire that is started by man or by nature and is monitored very carefully. Such items that forest managers consider when starting a prescribed fire are wind conditions, seasons, weather, humidity, the amount of moisture in dead vegetation, and the fullness of the forest floor vegetation. If all of these conditions prove favorable for a fire then the forest manager will plot an area for the burn. Boundaries are usually set using...
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