Permafrost & Forests
Visitors often wonder why the forests in and around the park don't all look the same. Some trees are tall and straight. Others look weak and spindly. The absence and presence of permafrost profoundly influences tree growth in park forests.
Permafrost, or permanently frozen ground, develops when soils remain below freezing for two or more years. Permafrost occurs in many areas of the park, but does not occur beneath large lakes, major streams, and south-facing bluffs.
Permafrost may occur one to ten feet below the surface soil and be 100 to 200 feet thick! In summer, some thawing occurs in the active zone-the upper layer of soil that seasonally thaws. The thickness of this active zone affects the size and survival rate of trees and other plants.
Where permafrost is near the surface, soils are cold, saturated with surface water that cannot drain through the permafrost, and are low in nutrients. The black spruce forests that survive here are slow growing and stunted.
Where permafrost is deep or not present at all, the soils are well drained and deep. They are rich in nutrients and support a rapidly growing mixed-species forest of white spruce, birch, poplar, and quaking aspen.
Did You Know?
The Alaska Pipeline, built during the 1970’s, stretches 802 miles from the oilfields of Prudhoe Bay to the tanker loading facility at Valdez.