I HAVE ALWAYS loved the North American alpine ecosystem, areas above the limit of tree growth, which extends from the northern sea-level tundra of Canada and Alaska, at 11,000 feet (3350 m) and above on the peaks in Colorado and the southern Sierra Nevada, to the southern mountains of Mexico, and west from the coastal volcanic Cascades to the top of Mt. Washington in the east. While many regard these vast ecosystems as largely conserved because they are beyond the reach of man-made disturbance, they are extremely susceptible to change, and climatic change is happening on a global scale.