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A Tree From the Air?
So where does all the food come from that the tree uses to grow?  The answer is simple yet very complex - it comes from the air.  Trees like all plants carry on the process of photosynthesis.  Photosynthesis is the process by which plants utilize the energy from the sun to make sugar from carbon dioxide in the air.  The next time you look at a tree think about the fact that what you see was once nothing but a bunch of carbon dioxide gas.  The general equation for photosynthesis is pretty simple:

CO2(carbon dioxide) + H20 (water) ----------------> C6H12O6 (sugar) + O2(oxygen) 

 

This simple equation reveals much about a plant.  First its obvious they need sunlight to survive.  Different trees are adapted to grow under different levels of light.

There are two forms of light that a tree can receive. The first is direct sunlight. This is where sun is shining directly on the tree leaves. The second is diffuse sunlight. This is indirect sunlight that reaches leaves by reflection or passing through the canopy. An easy way to understand diffuse sunlight is to cover a flashlight with a paper towel and turn it on. The light that goes through the paper towel is similar to indirect sunlight that passes through the canopy to reach smaller trees (by Jared Worley).

American beech
White Oak
Loblolly pine
Some trees such as the American beech can survive in very low light conditions. 
Some trees such as the White Oak can survive in intermediate light conditions
Other trees such as the loblolly pine require large amounts of light. 

 

An interesting experiment you could perform would be to grow several species of tree at different light levels and see which species grows the fastest.

As the pictures illustrate, some trees require certain levels of light. Trees can be classified as follows (click on the category to see examples):

  1. Tolerant - means a tree can survive in low levels of light, or in the shade
  2. Intermediate - means that the tree can survive in low levels and high levels
  3. Intolerant - means that the tree needs high levels of light to survive, no shade

 
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