What is Permafrost?
Permafrost is permanently frozen ground located in polar regions and the most frigid parts of the world. According to the U.S. National Park Service, the ground must be frozen for at least two years straight to qualify as permafrost---many permafrost areas have been frozen for over 10,000 years. The thickness of the permafrost also varies by location, with some areas reaching only a foot thick and others almost 5,000 feet thick. Everything in permafrost is frozen, including water, soil, rock and other minerals. At places where trees grow in permafrost areas, such as the Wrangell-St. Elias National Park and Preserve in southern Alaska, there is an active soil zone on top of the permafrost layer that thaws some during the warmer months. The depth of this area affects trees and other plant-life that grow in permafrost.
Can Trees Survive?
Survival is more difficult for trees that grow above permafrost, though several species have adapted to the conditions. In ground where the permafrost layer begins closer to the surface, only black spruce trees can survive, though white spruce, poplar and aspen trees can develop in areas where permafrost layers begin further underground. Trees that grow above permafrost are less able to receive nutrients because the extreme cold and thawing cycles damage their roots and limit their ability to absorb scarce available nutrients. Their roots are also not as developed as those of other trees and often grow laterally across the upper parts of the soil because they cannot burrow down into the dirt. Therefore, trees growing in these areas are smaller and less robust. Trees in these regions also grow, produce nutrients and regenerate more slowly than trees that grow in less harsh environments.
Drunken Forests
Because trees above permafrost cannot grow deep root systems due to the frozen layer below them, they do not have a solid foundation and are more susceptible to changes in the upper soil layer. A lot of water build up can occur on top of permafrost ground because the water cannot be absorbed by the frozen ground underneath. When this occurs, roots that are close to the surface can be warped or the soil that holds up the tree can over-saturate and shift, causing the plant to lose its bearings and slightly tip in one direction. Forests affected like this are called drunken forests because of the wobbly, crooked appearance of the trees.
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