This column concludes my three part series on "Tree-ology" or, the way trees work and what we can do to help them. And by the way, what we have been discussing works mostly for shrubs and other plants. Trees just have it harder. Because of their height, moving water and nutrients up and down their branches and trunks is a herculean task.
The first discussions focused a lot on plumbing issues. We now will move on to the manufacturing aspects of trees through their leaves. We often think of leaves in terms of providing shade, the oxygen we breathe and the nutrients they provide the soil when they fall and decompose into the soil. But leaves are also amazing food factories, utilizing the sun's energy to convert basic elements into usable food for the tree.
Leaves also give off water in an effort to cool themselves. Yes, leaves try to regulate their temperature by either giving off cooling moisture or by closing their stomates on their undersides to prevent excessive water loss. The process of giving off water is referred to transpiration. This water loss not only cools but also provides the "pull" to draw water and nutrients from the roots up through the xylem.
Photosynthesis is the process whereby leaves utilize sunlight to convert carbon dioxide and water into tree food or sugars and starch. This occurs in the chloroplasts, where chlorophyll, a green pigment, absorbs light to provide the energy for photosynthesis. The stomates on the underside of the leaf take in carbon dioxide as a building block and release oxygen as a byproduct along with water. The stomates open and close using the guard cells surrounding the stoma opening.
Respiration is the second part of the food manufacturing process. The energy of the sun that was captured during the process of photosynthesis is unlocked from the sugars, releasing energy to power the various biological processes within the tree. In a healthy tree, photosynthesis and the production of energy sources such as sugars will exceed the rate of respiration. If not, the tree will fail to grow and prosper.
There you have it. You have just completed a course in plant physiology, though a very short and simple one. So what does this all mean to you? Trees produce oxygen for us to breathe while removing carbon dioxide and impurities from the air. They provide shade that reduces the need to cool our houses, thereby reducing the need to produce more energy that would increase atmospheric carbon dioxide, the evil culprit in the global warming cycle.
The water that leaves release cools the surrounding air and becomes available for precipitation. And of course decomposing leaves shed by deciduous trees provide mulch and then nutrients to the soil to improve soil structure and fertility.
What can you do to help a tree carry out these processes? Make sure you give your trees plenty of space so that they can maximize their ability to capture sunlight. You can prune trees but not excessively or else you will reduce the tree's ability to manufacture food. You can make sure that your tree is not exposed to herbicides and de-icing salts.
That's all there is to it. Enjoy your trees, even in the winter when deciduous trees are bare. Their branch structure can be quite interesting. And don't forget to water them a couple of times this winter. They'll thank you next year with their luxuriant flush of new leaves in the spring.
Jim Leser retired to Cedaredge in 2007 after a career with Texas A&M University Extension in entomology. He is a member of the Cedaredge Tree Board and a Colorado Master Gardener.