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.