【BBC地球脉动】辽阔草原 05

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They trim the grass down to its roots leaving little in their wake but within days the plant will recover and continue to sustain the biggest herds on earth. Grass is not confined to the tropics. It manages to grow even in the bitter conditions of the Arctic. Beyond the limits of the last tree the planet is barren and ice locked. The frozen no man's land at the end of the earth. But, for a short time each year, the long dark winter releases its grip. Temperatures rise, and grass that has lain dormant and frozen throughout the winter sprouts once more. Green returns to the Arctic. The receding ice reveals an immense flat plain, the size of Australia. This is the Arctic tundra.它们一直啃到接近草的根部，吃得几乎不留痕迹，但几天之后草又会很快长出来，继续供养着地球上最大的动物群体。草不只生长在热带，甚至在北极那样恶劣的条件下也能生长。这是地球极地冰封的无人区，树木无法生长的地方，地表冰雪覆盖，一片荒凉，但每年会有一段短暂时光。漫长的冬夜露出了曙光，气温逐渐升高，冬天里处于冬眠和封冻状态的草慢慢地生长了出来。绿色重返北极，解冻的冰层露出了面积相当于澳大利亚的一大片平原。这就是北极冻原。