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Montane Forests
Yellowstone is clothed in forests, covering roughly 80 percent of the park. Miles and miles of lodgepole pine forest characterize the park, especially within the confines of the Yellowstone caldera. Also present in the park are extensive areas of forest dominated by subalpine fir and Engelmann spruce, especially in areas underlain by andesites such as the Absaroka Range. These species can also be common in the understory where the canopy is entirely composed of lodgepole pine. Through time, in the absence of fire, the subalpine fir and Engelmann spuce will replace the lodgepole pine, leading to a canopy dominated by these species. At higher elevations, such as the Absaroka Mountains and the Washburn Range, whitebark pine becomes a significant component of the forest. In the upper subalpine zone, whitebark pine, Engelmann spruce, and subalpine fir often grow in small areas separated by subalpine meadows. Severe conditions near treeline, wind and dessication, cause distorted forms known as krumholtz where most of the 'tree' is protected below the winter snow.
Douglas-fir Forests
Douglas-fir forests occur at lower elevations, especially in the northern portion of the park. The thick bark of Douglas-fir trees allows them to tolerate low intensity fire. Some of the trees in the forest are several hundred years old and show fire scars from a succession of low intensity ground fires. In contrast, lodgepole pine trees have very thin bark and can be killed by ground fires.
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