英語聽力：從南極到北極 6

Midsummer on the tundra and the sun does not set. At these altitudes, the sun’s rays are glancing and not enough of their energy reaches the ground to enable trees to grow. You’ll need to travel five hundred 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 a third of all the trees on earth and produces so much oxygen, it changes the composition of the atmosphere.