Tundra is the name given to the low, marshy plains of Europe, Siberia, and North America that border on the Arctic Ocean. In Alaska, the vast, cold region known as the "Northern Slope" is part of the tundra. Nature sets harsh terms for survival in this land. Only those plants and animals that are adapted to the hostile environment can survive in it.
Long periods of darkness and bitter cold are the major threats to life on the tundra. At the Arctic Circle, the sun cannot be seen above the horizon in December. North of the Circle, the darkness lasts even longer. Over the northern reaches of the tundra, no sunlight can be seen at all for several months of the year.
The darkness is balanced, to some degree, by continuous daylight during the summer months. But even in the warmest month, the temperature only averages about 50 degree F (10 degrees C). During the dark winter months the average temperature falls to -16 degrees F ( -27 degrees C), and sometimes to -40 degrees (C and F) and below.
Because of the intense cold, the subsoil of the tundra remains permanently frozen to a great depth. During the brief summer, a few feet (about a meter) of soil thaw at the surface. It is this thin layer of active soil that supports all living things on the tundra.
For nine months of the year, the tundra is a dark, seemingly lifeless wild land. Then in June, as if by magic, a never-setting summer sun gives birth to hundreds of species of arctic plants to cover the ground.
A plant that grows more than three feet (about a meter) is unusual on the tundra. There are no tall trees. The frozen subsoil prevents roots from growing deep enough to support them. By the end of August the breath of winter returns, and by mid-September the tundra is white again.
The animal life on the tundra is unusually rich for an environment that seems so harsh. Herds of arctic deer move from place to place in search of food. [此处开始无录音]Bands of wolves follow them and hunt for the weak or sick ones.
Few birds actually live on the tundra. However, a variety of birds migrate to nest and feed during the summer. The wet, marshy land produces a large number of insects that provide food for the smaller birds that, in turn, provide food for the arctic fox and the wolf.[无录音结束]
The balance of nature is so delicate on the tundra that even minor disturbances may produce major changes in the environment. Any increase or decrease in the population of one species may affect all other species on the tundra. For example, if the number of wolves and foxes decrease, the food chain is upset. Without wolves, the number of grazing animals - like the deer - would increase. This increase would result in a food shortage, which would cause death to many smaller animals. A decrease in the number of these smaller animals would in turn decrease the food supply for the arctic fox and the wolf. In this way, the entire food chain might be affected by a change in the number of a single species.
Until recently, the changing seasons on the tundra were seen only by a few Eskimo hunters and explorers. What would draw men and women to live in such a hostile land? The answer is oil.
In 1968, oil was discovered beneath the frozen soil on Alaska's Northern Slope. Now an 800-mile (about 1300 kilometers) pipeline has been built from Prudhoe Bay on the Arctic Ocean to Valdes, a port on the south coast of Alaska. The pipeline carries the oil from the Northern Slope, across the tundra, to the port. From there, it is shipped to the rest of the United States.
Thousands of men and women were needed to build and maintain the pipeline. For the first time, large numbers of people were brought into contract with the tundra. Their presence and the presence of the pipeline they built represented a major change in the environment. How will the life cycles of the tundra be affected?
The survival of the United States depends on the ability to find new sources of energy. Oil from beneath the tundra is very important to the nations' development. But the survival of the tundra depends on how carefully people maintain the delicate balance of nature in this environment.
欧洲、西伯利亚和北美洲接近北冰洋的低洼沼泽平原名之为冻土带。在美国阿拉斯加洲，那块广阔寒冷通称为"北边坡地"的地区就是冻土带的一部分。大自然为这片土地设置的自下而上条件十分恶劣。只有那些能适应在逆境中生存的植物和动物才能在这种环境中生存下来。
长期的黑暗和刺骨的严寒对在冻土带上生活是两大最主要的威胁。北极圈在12月份，在地平地线之上是看不到太阳的。从北极圈往北黑暗的时间通常会持续得更长些。在冻土带北部边缘的上空，一年中有好几个月根本见不到阳光。
持续的黑暗，在某种意义上来说，同夏季几个月连续不断的的白昼达到了平衡。但即使是在最暖和的月份里，平均温度刚刚能达到华氏约50度。在冬季那几个黑暗的月份里，平均气温降到华氏负16度，有时达零下40甚至更低。
由于酷寒，冻土带的下层封都冻得很深。在短暂的夏季仅三英尺的表层土壤能解冻。正是这被太阳晒暖了苏醒过来的薄薄的一层土壤养活着冻土带上的一切生物。
每年长达9个月，冻土带都是一块看上去毫无生机的荒凉的土地。然后到3-6月份，好像是施了魔法一样，一轮永不落的夏天的太阳生出了数百种北极的植物覆盖着大地。
一种植物若能长得超过了三英尺，这在冻土带上就是很不平常的了。冻土带上根本就不要有高大的树木。深层的永冻土使植物的根不能常常地扎下去来支撑高大的树木。到8月底，冬天的气息又返回来了，到了9月中旬这冻土带又是冬天了。
在这种非常恶劣的环境中，冻土带上动物的生活却非常充实。一群一群的北极鹿到处迁徙以便寻找食物。一帮一帮的北极狼跟踪着北极鹿群以便猎吃鹿群中的老弱残病者。
实际上几乎没有鸟类生活在冻土带上。但是各种各样的候鸟到了夏季会到这里来筑巢繁衍生息。这湿润的沼泽地能生出大量的昆虫，这就给小鸟提供了食物。接下来这些小鸟又充作了北极狐和北极狼的食物。
自然界的平衡在冻土带上是非常灵敏的，那怕只要稍微有一点破坏平衡的现象出现就可能产生环境上的一些重大变化。任何一个物种在数量上的增加或减少都会影响到冻土带上所有的其他物种。例如，如果北极狼和北极狐的的数量减少，那食物链就会遭到破坏就会脱节。倘若没有了北极狼，那些食草兽--像驯鹿之类--就会增加，这一增加就会导致很多小动物的死亡。倘若这些波动的数量减少了，接下来就会减少了供应给北极狐和北极狼的食物。这样下来，由于某一物种的数量的改变，就有可能影响到整个食物链的脱节。
不久前，也只有极少数的爱斯基摩的猎手和探险家才能深究到冻土带上的寒来暑往冬去春来。那么，是什么东西把男男女女都吸引到这块环境十分恶劣的土地上来的呢？答案就是：石油。
1968年在阿拉斯加北边坡地的冻土下面发现了石油。现在已经把一条800英里长的输油管从北冰洋上的普拉德霍贝架设到了阿拉斯加北边坡地的冻土下面发现了石油。现在的普拉德霍贝架设到了阿拉斯加南岸的港口城市瓦尔迪兹。这条输油管把石油从北部坡地，越过冻土带，输送到瓦尔迪兹港口，又从那里把石油装船运送到美国其他地方。
为了和维护保养这条输油管，需要有成千上万的男男女女参与工作。这是破天荒第一次，把一大批又一大批的人送到这里来与冻土带打交道。这些人的到来以及他们所修建的输油管的出现标志着冻土带的环境的重大改变。那么，冻土带的生活周期会受到什么影响呢？
美国能否继续生存下去，依赖于是否有能力找到新的能源。来自冻土带下面的石油对美国的发展至关重要。但是，这块冻土带上的一切是否能继续维持下去，这依赖于人们是否能细心地维护在这种环境下大自然里各个物种之间的平衡。
