The Subalpine Ecosystem occupies elevations
approximately between 9,000 and 11,000 feet. A typical subalpine
forest may consist mostly of subalpine fir and Engelmann spruce.
However, previously-burned areas may contain varying amounts,
or even almost pure stands, of lodgepole pine. Lodgepole seedlings
do well in sunlight, often abundant after fire, but once the
forest is established, plant succession may result in increasing
amounts of spruce and subalpine fir. Ground cover in a previously-burned
forest area often includes two species of huckleberry. Limber
pine, with flexible twigs and needles in groups of five, may
also be a part of subalpine forests. In high, windblown areas,
limber pines often grow into grotesque shapes. Engelmann spruce
and subalpine fir, which grow straight and tall in the lower
subalpine forests, become shorter and deformed nearer treeline.
Even as the trunk grows upward, strong, cold, dry winds may
destroy new growth on the windward side, leaving permanent
growth only on the lee side of the trunk. Trees with branches
on only one side are often called banner trees or flag trees.
At treeline, tree seedlings may germinate
on the lee side of rocks and grow only as high as the rock
provides wind protection. Further growth is more horizontal
than vertical, and additional rooting may occur where branches
contact the soil. The resulting low growth of dense trees
is called krummholz. Snow cover may protect krummholz trees
during the winter, but branches higher than wind-shelters
or snow cover are usually destroyed. Well-established krummholz
trees may be several hundred to a thousand years old.