Most of us think we know what a tree is. If you look at a tree in the summer, it appears to be just standing there, not really doing much of anything. Yet, just beneath the surface, there is quite a bit going on that is crucial to everything that lives on earth (including us).
First, let's start by looking at Planet Earth. The earth by itself without the sun would be a dark, very cold (about -250 degrees F), frozen rock in space. Completely dead. So right off, we can see that it is the sun that gives energy and life to the earth. In fact, the sun supplies almost all the energy used by life on this planet. The only exceptions are small microorganisms that live in very deep sea volcanic vents and get their energy from sulfur compounds ... and nuclear energy.
Before we delve into the interesting role that the sun plays in the life of the earth, we should note that there is a real connection between nuclear energy and the sun. The nuclear power plants on earth today are fission reactors. They use the same kind of nuclear energy that was used in the first atomic bombs. In fact, a nuclear power plant is just a controlled atomic bomb. A number of "rods" are moved in and out of the reactor core to control the chain reaction that makes the heat to generate power. An atomic bomb gives up all its heat in an instant, a nuclear power plant tries to let it out gradually.
The sun is a hydrogen bomb (nuclear fusion). Unlike the nuclear power plant the sun's reaction is completely out of control and going full blast all the time. Lucky for us, all this is taking place 93 million miles away or we'd be cooked with radiation. The sun is so far away it takes light 8 minutes to get here. Even at that great distance, many of us have still experienced radiation burns from the sun (sunburn). The sun gives off vast amounts of energy each day, but it will not run out of fuel any time soon. It is so massive it is expected to go on providing the energy for all life on earth for another 4 or 5 billion years.
Now we have the earth heated by the sun. This heat allows ice to melt and water to fill the oceans. Water evaporates in the heat of the sun and rises to the cooler layers of the air and then falls as rain. Air rushes between warm and cold regions creating the winds and the solar powered weather system is born.
Where do trees fit into this whole thing? Interestingly enough, trees and plants are our connection to the sun. Trees are really green solar panels collecting sunlight and converting it into ... sugar. That's what plants and trees do as they stand around appearing to do very little. They are making sugar. Why is that important? Because if plants weren't making sugar from sunlight, none of us would be here. The fact is that people and animals are latecomers to the relationship that plants have with the sun. We make our living taking sunlight from plants in the form of sugar and eating it. We slowly burn the sugar in our bodies to release the energy from the sunlight. This burning of sugar supplies all the energy we need to be alive and is the reason we are warm. We can not get that power directly from the sun or by making sugar from the sunlight ourselves. We are totally dependent on plants to do that for us.
You may be wondering who is eating all this sugar. Plants are quite handy in converting sugar into things like starch, oils, and if you add a little nitrogen, into proteins. Various combinations of this make all the food we eat. Lucky for us or we'd be eating all sugar and nothing else.
We can eat sugar from trees directly (maple sugar), but the really useful thing that trees do is to turn sugar into wood (cellulose). You might wonder why trees do this. Trees make wood so they can reach as high as possible to collect more sunlight than their neighbors. Wood is the preferred method trees use to build tall, strong and flexible supports for their solar collectors. You may have seen their solar panel collectors all aimed at right angles to the sun. You guessed it ... leaves. Sugar is made in the leaves.
So now we have a little better view of trees and plants. They are organic self-replicating collectors of solar energy. Plants create all the food and that means all animals (including people) are just plant parasites. We steal their sugar (in all its delicious forms) because we can't make it ourselves.
Now, if making all the food on the planet was all that trees and plants did that would be quite a lot. However there is more. We burn the sugar we get from plants by combining it with oxygen in our bodies to release the energy we need to live. (Even now, you're using the sun's energy to think about this.) You've heard about burning calories. Calories are a measure of heat. When we say there are 16 calories in a teaspoon of sugar we are saying a teaspoon of sugar will give off 16 calories of heat when burned. (A cube of sugar can actually burn when lit).
Most of us know that without oxygen, nothing will burn. We also know that without oxygen, we will die. Stop burning sugar ... the flame goes out.
We now have it down to a few basics. All energy on this planet for living things (we noted the exceptions) comes from the sun. Trees and plants collect the energy from the sun and convert it into sugar and other tasty foods. We can not eat sunlight but we can eat sugar. We burn sugar with oxygen and release the sun's energy to keep us alive. Once oxygen combines with sugar then the oxygen is no longer free to return to the air. So if animals went around eating and burning sugar all the time and there was no way to get this oxygen back into the air, then we would all run out of oxygen and die.
Here is where trees come in again. Trees and plants have this all worked out. Sugar really is the key to everything that happens on this planet. Here's how it works. Plants make sugar using sunlight. We burn the sugar and release the energy from the sunlight stored in the sugar. Burning sugar in oxygen makes 2 things: water and carbon dioxide. I know it is hard to believe that when you burn sugar you actually make water, but it's true. Water seems like something that is always water, but it's not. Sometimes it's part of sugar. Ok, we still need to find some way that eating all this sugar and burning it up with oxygen is not going to use up all the oxygen. Get ready for this.
Plants make sugar out of 3 things: sunlight (supplies the energy), water and carbon dioxide. When plants make sugar they release back into the air all that oxygen that originally combined with the sugar when it burned. So we have a nifty loop here. Plants make sugar from water, carbon dioxide and sunlight. We combine sugar with oxygen and release the energy from the sunlight and release more water and carbon dioxide back into the air for the plants to make more sugar. Notice that the same materials are recycled over and over and the only thing we really take out of the process is the energy from the sun. That's why we are all solar powered. We use sugar from the plants as a way of getting that solar energy into our bodies. The only thing that actually gets used up is sunlight, everything else is recycled. Now that is an incredibly sustainable system. If we don't mess it up, we can keep going for another 4 or 5 billion years.
By the way, plants also eat a percentage of the sugar they create because they need to burn sugar to live, just like us. The difference is that plants make their own sugar directly from sunlight and we can't. Lucky for us they make a lot more then they need and turn it into lots of interesting forms like food and wood.
Now, finally, back to trees and the woodlot. The heat you feel from your wood stove in the winter is the sunlight that the tree soaked up from all those summers in the forest. Next time you have a fire in your stove, sit back, close your eyes, and feel ... the Sun.