We emphasize the fact that trees are living and complex organisms. Many property owners, however, take trees for granted. Because trees cannot communicate verbally, some people fail to realize that these large plants are truly alive even though they watched them grow from seedlings to giants.
Trees have no mouths, so how do they eat? They have no lungs, so how do they breathe? They have no blood...wait: that's where you are wrong. Three words are essential to understanding how trees live: osmosis, assimilation, and photosynthesis.
Osmosis is the interchange of two fluids through a permeable partition by virtue of their concentration.
Assimilation is the absorption of nutritive elements and their transformation into body elements.
Photosynthesis is the process that makes assimilation occur with the assistance of sunlight.
The action of osmosis happens because cells are composed of fluid: protoplasm. The differences in concentration between the water-containing nutrients and the protoplasm permit the cells to take in water by osmosis. This nutrient-laden water is transported up the trees in the xylem, and other fluids come down the trees in the phloem. These are the trees' blood vessels. This movement takes place in the cambium layers, living tissue just behind the bark. Each year the layers are replaced by duplications, adding growth rings to the trees.
Leaves act as solar collectors, using sunlight acting on chlorophyll to activate the assimilation process. This converts nitrogen, lime, phosphorous, and potash into starch, sugar, protein, fat, and fiber. That is why trees grow toward the sun and its light: for optimum photosynthesis.
In forests, trees are planted closely adjacent so they will grow upward seeking sunlight, leaving little room for any branch extension. Thus the trees grow tall and straight, ideal for lumber.
Another term used by botanists is respiration. The trees use the carbon dioxide we exhale and give back the oxygen we need to breathe. It is somewhat more complex than this summary, but people benefit by an abundance of oxygen where trees are plentiful.
Fresh oxygen is delightful. Joseph Pilsudski, a former president of Poland, once built an air duct from a pine forest to his country villa and, via fans, transported the pine scent to his rooms.