The Tree That Changed the World

Two planets diverged in a solar system, and the successful one took a path more wooded.
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Two planets diverged in a solar system, and the successful one took a path more wooded.

The author of A Forest Journey: The Story of Wood and Civilization, begins a series of articles on the world’s first energy crisis: peak wood.

Part I: The Tree That Changed the World
Part II: Wood and Civilization
Part III: Peak Wood and the Bronze Age
Part IV: Peak Wood Brings on the Industrial Revolution and the Age of Fossil Fuels

Astronomers for the longest time have regarded Venus as the planet most resembling Earth. Having almost the exact size as Earth and being almost as close to the sun has led many to call it Earth’s twin.

The clouds always covering the Venusian landscape are another compelling example of Venus’ affinity to Earth. Pioneering astronomer Svante Arrhenius hypothesized great rains pouring from these clouds nurtured lush rain forests below. But when various space probes penetrated the Venusian atmosphere, this belief burst. Astronomers found an inferno rather than a tropical paradise.

Here they discovered the ultimate greenhouse effect: Although the carbon dioxide-laden atmosphere allowed sunlight to pass through, when the solar rays hit the surface of Venus and changed into heat waves, they could not escape the carbon dioxide cover. So the heat had nowhere to go and accumulated at the surface, where temperatures exceed 800 degrees Fahrenheit.

Earth has as much carbon dioxide as Venus. But instead of the gas blanketing the sky as happened on Venus, much of the carbon dioxide on Earth has been locked up inside and on the surface. This has made all the difference in the story of the two planets — one, a heaven bountiful with life, the other a hellish place where nothing animate as we understand it can survive.

Credit much of this carbon dioxide transfer from the atmosphere to the land to the rapid global spread 400 million years ago of the first (or among the first) true trees, Archaeopteris.

Its dense canopy photosynthetically absorbed carbon dioxide. As its fernlike leaves shed, they would have given back the carbon dioxide to the air — had the tree’s deep and powerful root system not broken down rock through which it dug into soil, where chemical reactions eventually locked the carbon dioxide into sediment. Mud buried much of the remaining dead leaves, branches, twigs, trunks and roots.

With the passing of millions of years under great pressure deep in the bowels of the earth, the plant material ended up as rich beds of fossils and coal. Once again, natural forces denied returning to the atmosphere what the trees had devoured.

Archaeopteris prepared the soil for smaller plants to flourish and assist in removing carbon dioxide from the air. Its root system turned rock into rich, soft earth. Their leaves shielded the newly formed soil from erosive rain and wind, and fertilized it as they fell and decomposed. Debris from the growing number of plants filled waterways, promoting plankton, which also feeds on atmospheric carbon dioxide.

Buried by sediments these consumers of carbon dioxide could not release this greenhouse gas to the air. The plunging carbon dioxide levels in the atmosphere caused temperatures on land to drop. The change made it possible for large creatures to amble about the land without overheating. They no longer had to remain immersed in water — which heats more slowly than land surfaces, and which also better conducts heat away from animals than does air — to maintain healthy body temperatures.

At the same time, declining amounts of atmospheric carbon dioxide enlarged the ozone layer above the Earth. Such protection shields land animals from lethal doses of ultraviolet radiation. Previously, creatures of any significant size had to remain underwater for protection from the unfiltered sun’s harmful rays. Of equal importance, the injection of more oxygen into the air by Archaeopteris and smaller plants provided enough of the life-giving gas to make it possible for animals to breathe.

Scientists find charcoal for the first time during the reign of Archaeopteris, suggesting that with the trees’ appearance came sufficient amounts of oxygen to support combustion.

As logs and large branches started to clutter the bottom of shallow waterways, fishlike creatures with limbs could better propel themselves through the plant debris than those with fins. The increasing organic debris finding its way into waterways would rob them of their oxygen as it decomposed. Creatures that could breathe as well as walk could escape sure death by making their ascent to land where a relatively mild climate, sufficient oxygen, protection from ultraviolet radiation, and plenty of food provided by plants made survival possible.

So began the chain of events that has permitted vertebrates to flourish on land so that 400 million years later I can write this, and you can read it.

While Archaeopteris is now extinct, nature kept buried the remains of ancient organic debris of algae, plankton, plants and trees. Their entombment helped keep the carbon dioxide they captured through photosynthesis out of the atmosphere.

But people started to dig up and burn the early trees, ancient plants and plankton first as coal and then as oil and natural gas. The seemingly unlimited availability of long-buried organic material, aptly named fossil fuels, ushered in a new technological era qualitatively separating those living since the middle of the 19th century from the rest of history. This new age of unprecedented growth, the Industrial Revolution, also accelerated the rate of deforestation as growing markets and population require more and more clearing for agriculture, livestock and biofuels, and the consumption of trees for fuel and for timber.

True, deforestation has occurred throughout world history. Plato, for example, saw deforestation turn a fertile piece of Attica into rock. He compared this butchered slice of earth to a carcass stripped of all its meat with only the bones remaining.

“What now remains compared with what then existed is like the skeleton of a sick man, all fat and soft earth having wasted away, and only the bare framework of the land being left,” he wrote in Critias. “… There are some mountains which have nothing but food for bees, but they had trees not very long ago ...”

Since the beginning of the Industrial Revolution, Plato’s compelling description of a particular place in Greece has become universal.

The growing loss of trees has allowed ever increasing amounts of carbon dioxide to return the to atmosphere. So have the engines of commerce and industry by burning fossil fuels. Scientific investigations have proven that since the beginning of the industrial revolution carbon dioxide levels have increased as well as the temperature of the Earth.

Unless drastic changes occur socially and technologically, increasing amounts of carbon dioxide will enter the atmosphere as the burning of fossil fuels continues to accelerate along with deforestation. Deforestation alone accounts for the release of more greenhouse gases than do all the vehicles throughout the world!

Bad forestry practices help hasten the pace of carbon released into the atmosphere. Following a clear-cut, for example, the formerly forested soil releases tremendous amounts of carbon dioxide into the atmosphere.

In North America, for example, 60 percent of all carbon resides within the earth of the forest floor. Replanting does capture carbon dioxide as new organic matter grows. The losses of carbon dioxide to the atmosphere continue to exceed the removal of carbon in the replanted clear-cut for 15 to 25 years depending on the type of tree, climate and soil. Then the trees and the soil underneath start to store more carbon dioxide than released.

Conversely, forests can become a weapon in our arsenal to break global warming if foresters practice enlightened stewardship. Sustainable forestry will need to become the standard on all forest lands globally. Replanting formerly forested land helps if trees are not selectively harvested until the seedlings reach an age where they have taken in more carbon dioxide than has been exhaled. Trees cut down in cycles of 50, 75 and 100 years store only 38 percent, 44 percent and 51 percent, respectively, of the carbon that an old-growth stand retains.

Indeed, trees can play a vital role in reducing atmospheric carbon dioxide. A recent study shows that saving the Amazon can be a cheaper and faster way to mitigate the consequences of global warming than replacing coal-fired power plants with renewable energy.

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