Oxygen in, carbon dioxide out. All day, everyday, our human bodies cycle these gases through our lungs. Our bodies die if this cycle breaks down. If a heart can no longer pump the blood that carries the oxygen, our organs die from the lack. If our lungs cannot efficiently release built-up carbon dioxide, we suffocate. We don’t think about breathing unless or until it becomes difficult due to illness or injury. As with most human physiology, we are blithely unaware of its intricate rhythms.
Turn an image of the lungs upside down, and it looks remarkably like a tree. The trachea becomes the trunk, dividing into two main branches/bronchi, then smaller and smaller branches/bronchioles until they reach the leaves/air sacs, where the work of gas exchange occurs.
Oxygen in, carbon dioxide out, but where does this vital oxygen come from? It’s just in the air. But it’s more complicated than that. Oxygen is constantly being pumped into our atmosphere by plants. Taking carbon dioxide from the air, combining it with water, and using energy from the sun, plants create sugars on which to nourish themselves, releasing oxygen as a by-product. This is photosynthesis—carbon dioxide in, oxygen out.
Here is the great reciprocity between the animal world and the plant world. Both rely on the other’s waste gas for their own livelihood. Animals cannot live without oxygen given off by plants, and plants cannot live without the carbon dioxide given off by animals. We are dependent on each other.
When I was hiking in redwood forests of California, I wondered how much oxygen was released by just one of these magnificent trees. Lots of digging led me to a few facts, but nothing reliable about the coast redwood specifically. I read that one mature unspecified tree produces enough oxygen for one to ten adult humans in a year. This wide range is because of variables such as a tree’s size, age, or total leaf surface area. The maple, birch, fir, and spruce produce the most oxygen, but over half of our atmospheric oxygen comes from oceanic plankton and other aquatic plants.
The greater gift that the coast redwood contributes is its ability to capture and sequester carbon dioxide in its massive trunk and exceptionally thick layer of bark. These giants remove and store more carbon per acre than any other forest on earth. They are vital to the health of our planet, especially as we face an uncertain future because of rising levels of carbon dioxide and climate change.
So not only do we owe trees our gratitude for providing oxygen to us, and to the entire animal kingdom, but the whole of the earth is dependent on them to soak up the byproducts of our existence. They are the lungs of the earth.
Thank you, trees.