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.

Double-Trunk Chestnut Oak

The chestnut oak is a tough tree. It grows on land where more fussy trees fail. Click to enlarge.

Tree Life, Sickness, and Death—Part 4

As I wrote earlier, trees coordinate their production of seeds. They literally plan a year ahead, so they all reproduce at the same time, in order for them to mix genes. Because of this, same species of trees are far more genetically variable than animals.

Each tree in a forest grows unequally—due to the luck of location. Every individual receives different amounts of water, light, and nutrients. Unable to move to a more advantageous location, a tree does its best where its seed happened to fall. Because of the inequality of location as well as robustness of trees, they cooperate with one another, and strive to equalize their differences. They literally protect each other.

A tree's roots are like its brain. Its experiences and memories are stored in its roots. Roots transmit chemical and electrical signals to the above-ground tree body—very much brain-like. As roots wend their way through the soil, they alter their course—depending on what they encounter; whether it be obstacles like rocks and other plants’ roots, or rich, moist soil. Is this behavior not a type of intelligence?

For a few hundred miles inland from the ocean, moisture is supplied by the ocean's water vapor. Farther inland, however, another mechanism takes over—one provided by trees. The first deserts tend to occur at this distance from the shore, unless trees pull moisture from the ground, transpire it into the air, and create clouds and rain. This is exactly the mechanism of the rain forest. That's why, when large tracts of tropical trees are cut, the area will dry out—leading to savannas and even deserts.

Our skin provides us many crucial functions: it (1) holds in fluids, (2) keeps our organs inside, (3) blocks pathogens, (4) provides tactile sensations, (5) allows us to grow, and (6) sheds. Bark is a tree's skin—it provides the same functions. As a tree ages, its bark grows increasingly wrinkled, as does our skin. Older trees experience a thinning of their crown—just as our hair thins. Their growth slows and they become more spread out; the tree’s bark cracks and allows disease and damaging fungus to invade. It's on its way to death.

A sick tree may put out suckers at its base, while a healthy tree grows primarily at the top. Low leaves on suckers cannot get enough light, and so produce less sugar and nutrients. Saplings from recent seedlings will try to outcompete the older tree’s suckers.

Many other threats imperil trees. Besides the processes of aging bark splitting and allowing various invasions, many alternative kinds of bark damage may occur—from fire, lightning, and due to various animals. The bark assaults open the way for insects, harmful fungi, bacteria, and viruses to invade—just as what happens when we get a cut in our skin. Storms fell many trees. Last and worst: human logging and pollution are major existential threats. It is a testament to the hardiness and resilience of trees, that more death doesn't occur.

A Mighty White Oak

Healthy Tree Growth and Symbiosis with Others—Part 3

Over most of the world, parents—especially mothers—spawn babies and then watch over them, until they can fend for themselves. For some species—primarily those who create thousands of babies, such as fish—the mother deposits eggs and is gone when the offspring hatch. They’re on their own. For others, there may be a lengthy development phase, during which babies mature and learn how to survive. Human newborns require a decade or two before they are able to fend for themselves. Climax trees in a forest require even longer; a baby's dependency phase on its parents may last for several decades.

A mother tree may have numerous offspring sheltered on the forest floor beneath her, although she will hog some 97% of the sunlight, leaving a measly 3% to filter down to them. Under these low light conditions, they grow very slowly—but that's part of Nature's strategy, as they gradually prepare for full maturity. A baby tree's leaves are much larger than mom's, in order to capture as much of that wee bit of light as possible. Their trunks grow extremely slowly; creating bark that is tough and smooth, to ward off disease and insects.

Baby trees photosynthesize lots of sugar to foster their growth, but this also makes them scrumptious to herbivores. In Yellowstone National Park, elk became plentiful during the first part of the 20^th century, as wolves were killed off. Aspen and other species of trees suffered, as their saplings were mostly consumed. The reintroduction of wolves in the 1960s saw a reduction in the elk herds—allowing aspen and other tree babies a better chance to mature. The Yellowstone forest and streams are much healthier now.

When mother trees die and fall, the saplings—having waited all those years—are prepared and ready to quickly respond. A race for the sun ensues. The healthiest and fastest saplings succeed, while their less-robust siblings die. As they shoot for the sky, the straightest trees do best. They are balanced and can withstand winds better. Curved trees are less strong and resilient. Trees with forked trunks are weak and may split and then be susceptible to disease. These are Nature's ways of building healthy and vigorous forests.

Another aspect of a healthy forest is the symbiosis that occurs between trees and massive underground structures of different species of fungi. The fungus can be huge—up to several thousand years old and extending over thousands of acres. They are the largest living organisms in the world. Their relationship with trees is usually a case of mutual cooperation. Fungi provide water and nutrients to trees, ward off bacteria, and filter out harmful heavy metals. In response, trees feed sugar and various other carbohydrates to the fungi.

But the exchange is not always fully equal, as the fungi may emit hormones that induce a tree's growth to their advantage. Selfish fungi may even consume up to one-third of a tree's production of sugar from photosynthesis. That said, tree-fungi interdependence is just one example of Nature's web that maintains a flourishing forest.

Tree Hugger

I am hugging the white oak in the previous post--with a little help from my cat.

Trees Interact with Their Environment—Part 2

Trees are like any other living entity, in that they interact with their environment in many ways. A tree must deal with threats and respond to advantageous events, as well as cooperate with other trees—all in a process of contributing to a healthy ecosystem. All of this in an attempt to strive to prosper, at least until it successfully procreates; which is the goal of all life on Earth—all possess a drive to perpetuate their species.

Trees intimately connect with each other—both through their root systems, and by pheromones and other chemicals that they release into the air. Their root connections form vast underground structures that are equal in size and mass to what we see above ground. Collectively, a grove of trees form a kind of interdependent superorganism—much like an ant or termite colony, in which every member plays a cooperative role in the wider ecosystem.

The complex interconnections between trees—both through their roots and by exchanging airborne chemicals—allow them to cooperate in resisting invasions of herbivores; both insect and mammal. When attacked, a tree will quickly send chemicals coursing through its trunk and limbs, that spoil the taste of its leaves. It will also emit chemicals into the air that float to neighboring trees—warning them to similarly defend themselves. Sometimes a tree will excrete pheromones into the air, to attract beneficial insects to prey on its invaders. Human-cultivated plants do not possess these defenses, so farmers often turn to insecticides.

Trees signal surrounding members of their same species to coordinate the simultaneous release of seeds. If they all set free their seeds at the same time, the abundance ensures that some seeds will survive hungry mouths. I have written before of the masting process of oaks, wherein all of them drop an extraordinarily massive crop of acorns every few years, in a cooperative manner. Acorn lovers such as squirrels and deer cannot possibly eat them all, thus securing a good crop of oak seedlings the following year.

Trees grow a trunk only as strong as needed—saving energy to put into foliage. In a forest, trees depend on each other for mutual support, to withstand winds. If a few trees in a stand are logged, the others will suffer because they may not have strong enough trunks; or due to the new access to sunlight, which can upset a tree's balance between its trunk and its foliage. A healthy forest depends on a healthy balance between all of its members—forming a vast, interconnected web of life.