Midsummer on the tundra and the sun does not set. At these latitudes the sun's rays are glancing and not enough of their energy reaches the ground to enable trees to grow. You need to travel 500 miles south from here before that is possible. These stunted shrubs mark the tree line, the beginning of the boreal forest, the taiga. The needle-shaped leaves of the conifers are virtually inedible so this forest supports very little animal life. It's a silent place where the snow is unmarked by footprints. In the Arctic winter snow forms a continuous blanket across the land. But as spring creeps up from the south the taiga is unveiled. This vast forest circling the globe contains 1/3 of all the trees on Earth and produces so much oxygen it changes the composition of the atmosphere. As we travel south so the sun's influence grows stronger and at 50 degrees of latitude a radical transformation begins.


现在是冻土带的仲夏季节，太阳24小时挂在天空。在这一纬度地区，太阳的光是斜射的，地上所获得的能量不足以让树木生长。再往南800公里才可能有树木。这些低矮的灌木丛是林木线的开始，往南就是针叶林。动物无法吃针叶树的针形叶子，所以这片森林无法维持动物生存。这里一片静寂，雪地上没有任何脚印。北极的冬天，雪像一张巨大的毯子覆盖着大地。春天从南方悄然来到之后，针叶林也揭开了自己的面纱。这种广阔的森林带环绕地球一圈，占地球树木总量的1/3，它为地球提供了大量氧气，甚至改变了大气的构成。继续往南走，太阳的热力越来越大，在北纬50度地区，会出现完全不同的景象。