Forest Air Quality—Part 5

Most of us know that all green vegetation absorbs sunlight and carbon dioxide in its photosynthetic process, and emits oxygen as it manufactures various sugars and carbohydrates. All animal life on Earth gets its energy this way. Without photosynthesis, without plants, there would be no animals.

The carbon dioxide that trees inhale gets turned into carbon—creating the structure of a tree. A mature tree can store up to 22 tons of CO₂ in its trunk. That's why there is so much attention put to planting trees: to counter all the CO₂ that we humans are discharging. Unfortunately, modern forest management sequesters far less CO₂ than a natural forest, because soil disruption has prevented the necessary role of tiny soil critters. Additionally, only recently was it demonstrated that old trees grow fastest and thus absorb the most CO₂.

Due to trees’ exchange of CO₂ for oxygen, forest air is fresh; but not just because trees exhale oxygen. Leaves filter out small particles like soot, pollen, dust, acids, and toxic hydrocarbohydrates and nitrogen compounds. In addition to oxygen, trees emit phytonicides, which possess antibiotic properties. This makes me feel good about living in an area surrounded by hundreds of acres of forest. These benefits do not occur in human-planted forests, however, because many of those trees are not planted in the appropriate locations that Nature selects, so they are not as robust as in a natural forest stand.

The benefits of people living in a forested area have been measured. Human blood pressure is lower in a stand of trees than in open grassland. Older people's lung capacity and elasticity of their arteries improve, when they enter a forest. Yet forest air is not always rich in oxygen. During the day—when photosynthesis is active—a stand of trees will release up to 3 tons of oxygen per square mile; enough for 10,000 people. But at night the oxygen level drops significantly, as photosynthesis pauses.

Quaking aspen trees are unique, in that they can photosynthesize on both sides of their leaves, rather than just the top surface, as is the case for other deciduous trees. Think about that, the next time you observe an aspen's leaves fluttering and flapping in the wind—exposing top and bottom to the sun.

Because of this double-sided photosynthesis, aspens are an excellent pioneer species—they move into new areas and grow quickly. The downside is that herbivores enjoy the taste of sugary aspen leaves. (Remember the comeback of aspens in Yellowstone National Park, when wolves were reintroduced and reduced the elk population.) Aspen trees respond to overgrazing by expanding their root system, so a single tree may come to extend over a wide area. In Utah's Fishlake National Forest, a single aspen tree spans across 100 acres (40 hectares). It has grown some 40,000 individual trunks over a time span of thousands of years!

This completes a five-part series of fascinating facts about trees and their beneficial effects on us... from the book The Hidden Life of Trees: What They Feel, How they Communicate (2015), by Peter Wohlleben, who worked for many years as a forester in Germany.

Treasuring Trees—Part 1

I am fortunate enough to live in a rural environment that is heavily populated by trees—of all varieties and ages. Part of my land was once farmed, about 100 years ago, and then abandoned to Mother Nature's succession process, wherein the first wild growth—weeds—gets replaced by short-lived saplings, followed eventually by long-lived, majestic towering trees. Thus, in my immediate environs, I can enjoy the dynamics of the forest's initial rebuilding cycles, as well as the grand, soaring trees of a climax forest.

Immediately surrounding our small, domesticated clearing—which required only the removal of several interim short-lived pine trees—are towering trees that shade us and inspire respect. They possess a natural beauty that I liken to the spires of cathedrals. They bend and sway in the wind, reminding me of green-clad monks, as they bow in blessing.

I have become acutely aware of the blessings that they provide for us, besides their loveliness, which evokes wonder: they expire life-giving oxygen, as they inspire and capture our carbon dioxide, transforming it into trunks, branches, and leaves. When they die and tumble to the ground, trees offer one last gift of firewood that will provide us a cozy experience on winter nights.

I love to watch and listen to the wind blow through the trees. I can hear distant waves of wind approach and flow by, as I observe branches swinging to and fro in response. Sometimes an individual limb or leaf will flutter in isolation, as the remainder of the tree stands still—as if that leaf alone has been excited by the passing breeze and is waving to it, as it blows through.

I sometimes ponder how similar I am to my brother trees, despite our obvious differences—and how our existence complements each other. Besides our exchange of atmospheric oxygen and carbon dioxide, I appreciate how trees refresh the air in so many ways, and how their photosynthesis transforms the sun's energy into food that most all life on Earth depends upon.

We each are composed of many of the same organic molecules. The water and blood surging through my body is similar to the sap flowing through the tree's capillaries. My bones provide the same function of support as does a tree's strong trunk. We both—along with all lifeforms—are a component of the cycle of life, as we die, to become part of follow-on lifeforms. We come into being, exist for a while (although a tree dwarfs my lifespan), and finally become sustenance for the life that follows. These thoughts help me to comprehend the deep connectivity between all life forms.

Over the next four posts I will describe some of the fascinating facts about the lives of trees, mostly taken from the book The Hidden Life of Trees: What They Feel, How they Communicate (2015), by Peter Wohlleben, who worked for many years as a forester in Germany.

Covert Critters

We critters who live on the surface of planet Earth can become quite provincial about our kind—by being quite unaware of the many life forms that live underground. For example, people see other people as the most important critters on the planet. That's probably true for other surface species. We see each other, interact with each other, and conclude that's about all there is to it.

But there's a vast biosphere that is hidden from us, just below our feet. It might as well be covert. All of us surface critters live in an extremely thin layer on the surface of the planet. The atmosphere and the exposed land are like the thin skin of an apple—there's so much more below the skin. For example, subsurface fresh water—existing down to many miles—has a volume of about 100 times that of surface fresh water. Subsurface life has a mass of some 20 times all that lives in the ocean and makes up about one-third of all the planet's biomass. That's pretty impressive!

Never experiencing the sun, subsurface life cannot depend on photosynthesis, as must all surface life. Photosynthesis in plants enables them to manufacture sugars for themselves, as well as all other critters of the light, who eat plants or other plant-eating creatures. How do the covert critters survive without light and its resultant photosynthetic sugars? They feed on dissolved minerals in the water, as well as raw hydrogen. Thus they are reliant on biochemical reactions, which are much less efficient than photosynthesis. As a result, subsurface life exists in the slow lane. Underground microbes (and most life down there is in the form of microbes) may divide once every thousand years or so. Contrast that to surface E.coli, which divide every 20 minutes! This is a pace of life some 30 million times faster!

Moreover, underground life-forms are much tougher than their surface cousins. In 2003 the space shuttle Columbia broke up during reentry into the atmosphere. Aboard Columbia was a biological experiment on nematodes—very hardy, underground tiny worms. They survived the fiery explosion and they survived the 25 mile plunge to the ground where, a few weeks later—when they were subsequently located—they were reproducing!

Earth's subsurface life-forms are closer in character and metabolism to the earliest kinds of life on the planet, thus recent discoveries of these covert critters are helping scientists to understand how those deep ancestral creatures survived and thrived. Our expanding comprehension of the limits of metabolism of life on Earth is preparing us to better understand what kinds of life (if any) we'll find on Mars, or Jupiter's moon Europa, or Saturn's moon Enceladus—most all of which is likely to be subsurface, if it exists.

These findings make us wonder about what other kinds of critters we'll yet find on (or under) Earth. With each passing year we expand the limits of what we know to be life.