Trees have been on Earth much longer than people. Their solid trunks reach up to the sky attempting to capture more sunlight than any other nearby vegetation. This Darwinian urge to dominate gives rise to a plant that grows straight and tall for tens of metres. With people’s fertile imaginations, trees have come to hold a critical place in our civilization.
In a simple life style, living trees provide shade and perhaps a support for lofty houses. Specialists shave their limbs and trunk into spoons and arrows. Or, great limbs join together to become the mast of a ship or wall of a house. Most important though is the chemical reaction we unleash when burning wood. Fire will release the sun’s stored energy and spread the energy about as heat. This great contributor kept cold winter nights at bay and made some questionable food much safer to eat to the benefit of many human lives.
A tree’s utility varies based upon its intended role. Assume we have a maple tree to be cut for lumber. If it’s 28 inches diameter at the smallest end and has a trunk height of 80 feet then, according to Doyle’s formula, we could get about 240 cubic feet of cut wood. Or, we can assume that this tree has a diameter at chest height of about 36 inches and a total height of 100 feet. From this, the total tree weight is about 42000 pounds or about 890 cubic feet of material. Both these calculations have gross assumptions but we can effectively see that in this instance much less than a third of the tree goes to a useful finished product.
Assume a tree, roots and all, did weigh 42000 pounds. Let the ratio of dry wood to wet wood be 0.6 and the energy content of dry wood be 15e6J per kg. Then, this tree’s total energy content nears 1.7e11J.
True, finding a maple tree a hundred feet tall may be nigh on impossible. But, if one were to exist it would have this huge amount of energy after living for 300 years. That’s 5.7e8 J per year captured from the sun’s rays. This is sustainable energy production, as long as we allow the trees the time and space to grow.
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