We are inextricably linked to trees
By Rick Reynolds
All school kids learn that trees “breathe” in carbon dioxide, and “exhale” oxygen, which is fortunate for them because, as students, they’ve also learned that they breathe in that oxygen and exhale carbon dioxide. While this is a gross oversimplification, it’s easy to remember.
This carbon/oxygen cycle holds true for most other plants as well, but it’s unpleasant to climb a cactus, as one example, so we come of age climbing trees and, thereafter, they continue to hold a special place in our hearts.
From the trees’ perspective, forests host a diversity of life that fertilizes and loosens the very soil in which they are serving life imprisonment. While early humans were nomadic in their search of nourishment, root bound trees have always needed to synthesize their own food. Unlike school kids, trees need to be self-sufficient out of the gate.
In a process known as photosynthesis, trees combine sunlight, carbon dioxide, and water to make sugars. The tree’s own chlorophyll absorbs the energy from sunlight. The staple of the tree diet is sugar. Xylem sap consists primarily of water, along with hormones, minerals, and nutrients. Phloem sap consists primarily of water, in addition to the sugar, hormones, and mineral elements dissolved within it.
Through respiration, trees convert the sugars created by photosynthesis back into energy. Here the sugars combine with oxygen in a process that is the reverse of photosynthesis. Oxygen taken up by the stomata of the leaves (or needles) and the roots leads to the oxidation that burns the carbohydrate fuel. In this regard, respiration is the burning of sugars to supply the energy for growth and to maintain the internal processes of living.
So how does water move uphill from the earth to the leaves or needles? Working in concert, osmosis, transpiration, and capillary action are responsible for this gravity-defying feat.
Ground water (and dissolved nutrients) enter the roots through osmosis*, and then are partially drawn up through the tree by the loss of water vapor escaping through the stomata (or pores) in a process called “transpiration.” In the resulting vacuum, the liquid is drawn up the cellulose tubes in the xylem.
Aiding osmosis and transpiration is a process called “capillary action,” which itself is the sum of two gravity-defying properties of water: “cohesion” and “adhesion.”
Cohesion, better known as surface tension, is the magnetic bond water molecules have to each other. This phenomenon explains why water climbs slightly up the insides of a straw placed in a glass of water. This raised water is called the “meniscus.” When the tube is so narrow that the meniscus of one side can touch the meniscus on the other, capillary action occurs, continuously drawing the water up the tree.
Adhesion, describes the forces attracting water molecules to other surfaces, in this case, the interior of the tree’s water vessel, the xylem.
By combining these properties, water molecules seemingly draw themselves up by their bootstraps, all the more impressive considering that trees process massive amounts of water. A fully grown tree may lose several hundred gallons of water a day, displacing much of it into the atmosphere. 90 percent of the tree’s water is just passing through, while the remaining 10 percent is used in photosynthesis and cell growth.
As such, trees create microclimates, perspiring water, like humans, to dissipate heat. This evaporation from trees, in turn, cools the air and draws off the heat produced when the carbon in atmospheric carbon dioxide is combined with sunlight through photosynthesis and transferred to the lignin of the trees’ fiber.
The heat, in turn, raises the tree’s water vapor through the cooled microclimate of its own creation and up into the atmosphere, where it eventually condenses into droplets that fall as rain. The rain is then redistributed by the tree’s radial fractals** to efficiently re-hydrate their roots (and all their hosts).
Finally, to help facilitate the process, thermals created by the heat from biological and solar sources create wind that, like the birds and the bees, also brings in pollen for fertilizing seeds designed to be eaten and carried off, expanding the forest and completing the cycle.
And, to create fertilizer and fertility (so they can age in place), trees summon other organisms for home visitation. Like in-home pizza delivery, it has its advantages and disadvantages.
To do all this, trees, since time immemorial, have created beauty, refuge, and sustenance for flora and fauna alike, including the birds and the bees and the pre-humans in the trees. In return, trees receive the nitrogen rich nutrients (and pollen) needed to serve out their sentences and facilitate connubial visits, respectively. The bad news; like a cheese-stuffed gourmand planted on the sofa, a tree can’t easily pull up its roots and flee from danger (or towards procreation).
But all-in-all, it’s not a bad system. To help mitigate climate change, sustainably harvested trees can be used to build beautiful wooden houses that sequester carbon over their lifetimes. For us, the biophilic qualities of wood affect our health and well-being in ways that are just beginning to be understood. The warmth, the familiarity, the majesty, the strength, and that certain je ne sais quoi wood brings to homes, embrace us in ways no other building material can match.
Indeed, wood has been ingrained in us since our tree-climbing years and never leaves us as we seem to grow younger in its presence.
* Osmosis: The tendency of molecules of a solvent to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one, thereby equalizing the concentrations on each side of the membrane. Parenthetically, maple phloem sap reduced through osmosis complements our pancakes, waffles, and snow cones.