What causes a timber line?
There must be a reason why forests grow so far and no farther up the slopes of a high mountain. There must be a reason why the northern trees halt at the doorstep of the Arctic tundra. These rigid demarcations are called timber lines and they are set by rigid rules of nature. A tall mountain peak may be anywhere from 2 1/2 to 5 1/2 miles above the level of the sea. The weather, the atmosphere and other conditions change with every step up in the altitude. And every set of conditions favors its own plant and animal communities. As we ,journey from the base of the mountain to its summit, we traverse across three, four or even five very different ecology zones. On an African safari, we may begin our climb through a stretch of grassy savanna to reach rolling foothills clothed in dense, green rain forests. Above the jungle zone, we may hack a trail through a tangle of giant bamboo. Above this is a high, dry zone of prairie grasses and clusters of small trees. At 12,000 feet also, we reach t
