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Thursday, 26 October 2006

Giant Sequoias: Earth's Oldest Living Things

Written by Dr. Ronald Francis
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treeA lot of us like walking in the forest for the sheer simplicity and beauty of it; the peacefulness of the air, the smell of the wood and flowers, the colors and shapes of the various fungi. Yet we also yearn for something unusual in our lives – something removed from the mundane of our favorite forest trolls.

In ‘Giant Forest’ at Sequoia National Park, you can have your cake and eat it too.  On one hand – you are visiting one of the oldest national parks with views of the Western edge of the Sierra Nevada Mountains and the rivers streaming down from the same, but you are also literally walking among the giants,.  And it is spooky, as well, so the kids will love it.

What’s the largest living thing on the earth?  It’s the Giant Sequoia (Sequoiadendron giganteum) and is also called Big Tree, or Sierra Redwood.   The giant sequoia trees dwarf everything around them.  People, other trees, roads and the like all seem miniature compared to the tree.   Remember, you are talking about a tree twice the height of the Statue of Liberty.  tree

The wide diameter trunks (30 to 40 feet) make you feel like you are in a film where the trees are about to start running around tossing houses to a fro.

The raw specifications of the Giant Sequoias are staggering:  the Giant Forest features trees that have the largest volumes in the world.   The combination of the diameter of the tree (about two school busses long) plus enormous height (a bit less than a football field in length) certainly get your attention.   Because the trees are stump-like (shaped like a baseball bat or club, and not like a broom handle), I was able to calculate the total volume in cubic feet.  It’s a little less than 1,000,000 cubic feet.

treeHow much is a million cubic feet?   Let’s compare it to the volume in the cabin of a typical 757 with an average of 6 seats wide.   It turns out to be about 25 airplane cabins worth of volume!

Some interesting physics ideas that present themselves are capillary action and center of mass.  First: capillary action.  It has been calculated that water rises in a thin tube (due to forces of adhesion between the water and the tube) such that the tallest trees can never go past 130 meters or about 30 percent higher than the Giant Sequoias.

Capillary action works because the xylem cells in trees have diameters on the order of 25 microns or .025 mm – about one fourth the size of a piece of paper.   The extreme thinness helps the water climb up so that thousands of gallons can be lifted up into the heights of a tree.  (Note that the strongest manmade pumps can’t get water that high!)

treeWater is indeed a special molecule whose particular polar nature allows it to be an excellent solvent (necessary for life) and very adhesive to other polar substances.

Second is Center of Mass.   We’ll talk about center of mass by asking if these trees ever fall over.   Factors would include the wind forces during hurricanes compared the mass of the tree.  Wind forces are proportional to the diameter of the tree, whereas the mass would be proportional to the square of the diameter.  (Both wind speed and mass are proportional to length of the tree).  Therefore one might think that it would be much more difficult for the wind to knock down a sequoia compared to an average tree.

But it turns out that these trees do get knocked down; the reason is that they don’t have deep root systems (3 to 6 feet only!) so there is nothing to prevent them from falling.  So the trees do fall down now and then – but obviously at a rate that allows the Giant Forest to survive over thousands of years.

Center of mass comes into this discussion because it is critical for balance: Giant Sequoias are able to withstand only because they grow so straight!   I have calculated that if the trees grew at an angle of 5 to 10 degrees off from the vertical then they would fall over because their center of mass would lie over a point which is not on the base of a tree and thus the tree would be forced to fall.   This is an interesting combination of Darwin’s survival of the fittest ideas and physics:  These trees outlived other trees because they have a unique ability to grow very straight.

treeThese trees have other interesting survival-related facts: fires help them survive (clearing forest for sun which helps seedlings, preparing the soil for seedling growth, burning other trees since the bark with tannin – 20 to 30 inches thick – protects the giant sequoia from fire, and providing heat to open the seedlings.

Insects can’t really hurt them because the bark is too thick and strangely enough the brittle nature of the wood has made the trees somewhat unattractive for lumberjacks. Lightning doesn’t affect the trees much because the bark is a poor conductor of electricity.  Given these fun facts, no wonder the trees are the oldest living things on the planet!

Get to Sequoia National Park by taking route 99 up from Southern California or down from San Francisco.

© Dr. Ronald Francis


Last modified on Sunday, 16 December 2012

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