Why Trees Don't Grow On Mountaintops
Have you ever seen a mountain and noticed that all the trees stop growing at a certain altitude? Why is that?
The tree line is the elevation at which trees stop growing-either because of the low temperatures, or lack of pressure and moisture. Tree lines are pretty consistent between the latitudes of 30°N and 20°S. But the farther away, the lower the tree line gets. Within latitudes, however, the tree line can differ significantly. The tree line in the U.S. is pretty different from east to west: New Hampshire's White Mountains are at 44°, and Wyoming's Teton Range is 43°. The tree line in the White Mountains is at 4,500 feet (1,371 meters) while in the Tetons, it's all the way up at 10,000 feet (3,048 meters). So what accounts for the big difference?
Researchers have noted that tree lines follow the permanent snow line of mountains. This would seem that temperature is a major factor in determining them, which would make sense since temperatures can limit how seeds sprout and how trees grow. Tree cells have a hard time multiplying in temperatures below 44° F (7° C). In addition to temperature, other factors affect where a tree line falls: the amount of sun and wind the surface of a mountain gets can affect where trees end up growing. Another factor: Climate change. Scientists have been keeping their eyes on changing tree lines as another way to measure the long-term effects of the changing climate.
Global Treeline Position (Nature)
"High-elevation treelines are a global phenomenon, but the large-scale ecological and physiological mechanisms that define their existence still elude ecologists."
Why Is the Treeline at a Higher Elevation in the Tetons than in the White Mountains ( Northern Woodlands)
"Trees grow where they can. And they are surpassingly capable, making do in an impressive array of conditions around the globe, including many harsh places."