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. [此處開始無錄音]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.[無錄音結束]

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.

歐洲、西伯利亞和北美洲接近北冰洋的低洼沼澤平原名之為凍土帶。在美國阿拉斯加洲，那塊廣闊寒冷通稱為"北邊坡地"的地區就是凍土帶的一部分。大自然為這片土地設置的自下而上條件十分惡劣。只有那些能適應在逆境中生存的植物和動物才能在這種環境中生存下來。

長期的黑暗和刺骨的嚴寒對在凍土帶上生活是兩大最主要的威脅。北極圈在12月份，在地平地線之上是看不到太陽的。從北極圈往北黑暗的時間通常會持續得更長些。在凍土帶北部邊緣的上空，一年中有好幾個月根本見不到陽光。

持續的黑暗，在某種意義上來說，同夏季幾個月連續不斷的的白晝達到了平衡。但即使是在最暖和的月份里，平均溫度剛剛能達到華氏約50度。在冬季那幾個黑暗的月份里，平均氣溫降到華氏負16度，有時達零下40甚至更低。

由于酷寒，凍土帶的下層封都凍得很深。在短暫的夏季僅三英尺的表層土壤能解凍。正是這被太陽曬暖了蘇醒過來的薄薄的一層土壤養活著凍土帶上的一切生物。

每年長達9個月，凍土帶都是一塊看上去毫無生機的荒涼的土地。然后到3-6月份，好像是施了魔法一樣，一輪永不落的夏天的太陽生出了數百種北極的植物覆蓋著大地。

一種植物若能長得超過了三英尺，這在凍土帶上就是很不平常的了。凍土帶上根本就不要有高大的樹木。深層的永凍土使植物的根不能常常地扎下去來支撐高大的樹木。到8月底，冬天的氣息又返回來了，到了9月中旬這凍土帶又是冬天了。

在這種非常惡劣的環境中，凍土帶上動物的生活卻非常充實。一群一群的北極鹿到處遷徙以便尋找食物。一幫一幫的北極狼跟蹤著北極鹿群以便獵吃鹿群中的老弱殘病者。

實際上幾乎沒有鳥類生活在凍土帶上。但是各種各樣的候鳥到了夏季會到這里來筑巢繁衍生息。這濕潤的沼澤地能生出大量的昆蟲，這就給小鳥提供了食物。接下來這些小鳥又充作了北極狐和北極狼的食物。

自然界的平衡在凍土帶上是非常靈敏的，那怕只要稍微有一點破壞平衡的現象出現就可能產生環境上的一些重大變化。任何一個物種在數量上的增加或減少都會影響到凍土帶上所有的其他物種。例如，如果北極狼和北極狐的的數量減少，那食物鏈就會遭到破壞就會脫節。倘若沒有了北極狼，那些食草獸--像馴鹿之類--就會增加，這一增加就會導致很多小動物的死亡。倘若這些波動的數量減少了，接下來就會減少了供應給北極狐和北極狼的食物。這樣下來，由于某一物種的數量的改變，就有可能影響到整個食物鏈的脫節。

不久前，也只有極少數的愛斯基摩的獵手和探險家才能深究到凍土帶上的寒來暑往冬去春來。那么，是什么東西把男男女女都吸引到這塊環境十分惡劣的土地上來的呢？答案就是：石油。

1968年在阿拉斯加北邊坡地的凍土下面發現了石油。現在已經把一條800英里長的輸油管從北冰洋上的普拉德霍貝架設到了阿拉斯加北邊坡地的凍土下面發現了石油。現在的普拉德霍貝架設到了阿拉斯加南岸的港口城市瓦爾迪茲。這條輸油管把石油從北部坡地，越過凍土帶，輸送到瓦爾迪茲港口，又從那里把石油裝船運送到美國其他地方。

為了和維護保養這條輸油管，需要有成千上萬的男男女女參與工作。這是破天荒第一次，把一大批又一大批的人送到這里來與凍土帶打交道。這些人的到來以及他們所修建的輸油管的出現標志著凍土帶的環境的重大改變。那么，凍土帶的生活周期會受到什么影響呢？

美國能否繼續生存下去，依賴于是否有能力找到新的能源。來自凍土帶下面的石油對美國的發展至關重要。但是，這塊凍土帶上的一切是否能繼續維持下去，這依賴于人們是否能細心地維護在這種環境下大自然里各個物種之間的平衡。