Friday, August 29, 2008

The Arctic Treeline

My next post has little to do with my chosen topic of Geology, although it has everything to do with Geography. I am going to write about the Arctic Treeline.

A Treeline/Timberline is a line on a map past which trees are unable to grow because of the environmental conditions. There are several types of treeline:
Alpine Treeline - A line past which trees cannot grow because the land is too high up. The air pressure, temperature or terrain is unsuitable. Alpine treelines are found circling mountains, etc.
Desert Treeline - A line around a piece of dry land, which cannot support trees because of a lack of rainfall, or water from other sources.
Exposure Treeline - Strong winds or other forces found near the edge of islands, can create an area of land unsuitable for trees near coasts.
Others - Other factors such as unsuitable soil near volcanoes or high altitudes where condensation is incapable of occurring can lead to treelines. The specific treelines I'm going to talk about are the Arctic and Antarctic treelines.

Beyond these lines trees cannot grow because not enough light reaches the land, and the growing season (if it exists at all) is too short. The Antarctic treeline is actually only theoretical, as no trees grow on the Antarctic continent anyway, and the land to the north (South America, Australia, etc) has no treeline, so the 'Antarctic Treeline' doesn't exist.

The Arctic Treeline however is very real and exists in Greenland, Canada, Alaska, Russia, Finland, Norway, and Sweden. It is an approximately mile wide line in most locations, completely circling the North Pole, with a radius of around 2,600km. Although the transition between forests and tundra is gradual and subtle within this mile-wide line, from a small distance away the line is well defined. Beyond the line the trees cannot grow for the following reasons:
- Not enough light reaches the trees, therefore photosynthesis (and growth) cannot occur.
- The extremely cold temperatures freeze the sap inside the trees, killing them.
- The thin soil on top of the constantly frozen 'permafrost' cannot support trees.
- Strong winds can carry small shards of ice that can cut and kill trees. In this way, arctic winds have shaped the treelines in Russia and Canada.
- The required temperatures of at least 10°C during the growing seasons are not present.
- The trees above this line can become completely coated with snow, reflecting all light.
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The Arctic has not always been incapable of supporting tree life. At a different time, with a different climate, huge forests covered the North pole. These 40m tall trees have been found, perfectly preserved in the ice, less than 700 miles from the Pole.

So why am I interested in this strange topic, well I believe it is fascinating to think that it would be possible to fly a helicopter high over this greatly defined line, and see on one side a sprawling green woods, stretching for thousands of miles, with a barren Arctic tundra on the other. I have included several pictures and a map of the treeline.


























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