Thursday, December 6, 2012

The Giant Sequoia

The world's largest tree by volume is sequoiadendron giganteum, otherwise known as the giant sequoia. Perhaps you've heard of them.

The President, Source

These redwood trees occur naturally only on the western slopes of the Sierra Nevada mountains in California. This highly exclusive environment means that there aren't very many of these trees and that they are uniquely susceptible to climate change. They are, however, amazing creatures. They usually grow between 50 to 85 meters tall (160 to 279 ft) and 6 to 8 meters (20 to 26 ft) in diameter. Some have even been measured up to 94.8 meters (311 ft) tall and 17 meters (56 ft) in diameter. That's huge. These trees are truly staggering, it is hard to conceptualize just how monumentally large they really are.

These trees are huge. Source

Being an evergreen, this tree lives in a very cold climate. Even though it is snow laden most of the year, the leaves of a giant sequoia will never lose their green color. These trees keep their seeds in cones, just as you might expect, but these cones are unique. A giant sequoia can keep its cones closed for up to 20 years or more. The only way for these cones to release their seeds is if they become dried out. This drying usually occurs during low-intensity forest fires where convection currents take heated air up into the canopies of the trees and dry out the cones. For a while, however, giant sequoias weren't reproducing very often. As it turns out, human forest fire prevention and livestock grazing significantly reduced the frequency of low-intensity forest fires. To make matters worse, the lack of fires allowed for white firs to begin to grow which could act as a ladder for high-intensity forest fires, allowing them to reach the vulnerable canopy of the giant sequoias. And the sequoias don't just depend on forest fires to open their seed cones, they also need these fires to clear away undergrowth to allow their seeds to grow. In response to the lack-of-fire crisis, the National Park Service began to set controlled fires back in 1970. So far they have been fairly successful.

Giant sequoias have thick bark to protect them from fires. Source

There used to be a logging problem with these huge trees. Giant sequoias are few in number and take a long time to grow, so logging was seriously damaging their population. As it turned out, however, the wood of these trees was fibrous and brittle, making it of little marketable value. When the public saw that these majestic trees were being cut down and made into toothpicks there was a strong movement to protect them. Now these trees aren't logged, but the mammoth stumps of old logged trees are still a tourist attraction.

The Mark Twain tree. Source

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