Chapter 4: Trees Pump CO2 From the Atmosphere & Sequester it Within Life

Carbon is a remarkable element. Carbon forms the foundational building blocks for all life on Earth, including proteins, carbohydrates, lipids, and nucleic acids. We can think of these as being LEGO bricks with the ability to form intricate life forms.

Recall that when trees perform photosynthesis, they use energy from the Sun to convert CO₂ and water into oxygen and sugar. The sugar is loaded with carbon that has been pulled from the atmosphere and is now sequestered within the plant. When the trees feed herbivores with their leaves and soil with their roots, they pass sequestered carbon from the plant to the consumer. Similarly, when consumers are eaten by predators, carbon moves between life forms. In this way, trees pump carbon from the atmosphere into terrestrial life and ecosystems as a whole.

Soil is a big recipient of sequestered carbon. Some estimate that it holds 80% of all carbon present within terrestrial ecosystems. We know that trees release carbon-loaded sugar from their roots to feed bacteria and fungi. Populations of bacteria and fungi grow and help feed below-ground predators such as protozoa and nematodes, who in turn feed springtails, who feed other predators, and so forth. Some do not hunt and instead eat organic matter. After consumption comes pooping, which also contains carbon, and serves as food for other members within the soil. Some die natural deaths and become organic matter. On and on this goes with dizzying complexity.

Above ground we find the same progression but with new species. Caterpillars and other insects consume leaves. Birds eat the insects and hawks eat the birds. Mice feed on acorns and coyotes hunt mice. Zebras munch on grass and lions munch on zebras. They all poop. Some reproduce. Some are never eaten and instead die natural deaths.

At every exchange below and above ground—whether from reproduction, predation, eating organic matter, pooping, or dying a natural death—carbon is passed between life to form growing populations. The net result is an accumulation of sequestered carbon from the atmosphere into the terrestrial ecosystem.

It is worth noting that the soil line does not serve as a barrier—ecosystems blend. For example, earthworms eat nematodes and birds eat earthworms. The bird poops and eventually dies. Both the poop and dead bird provide organic matter that bacteria below ground consume.

Terrestrial ecosystems are loaded with carbon. These are the original, vast storehouses of CO₂ from the atmosphere. If we go back in time to the early Carboniferous Period (millions of years before the dinosaurs), there were an estimated 1,500 parts per million (ppm) of CO₂ in the atmosphere, which is close to four times more than there is now. As the Carboniferous Period advanced, there was an explosion of life. CO₂ in the atmosphere began decreasing dramatically as forests pulled carbon from the sky and sequestered it into soil and other life. These plants did this in great quantities, creating thick beds of stable carbon in the ground (these formed the fossil fuels we rely on today). As a result of this transfer, CO₂ in the atmosphere plummeted, dropping as low as 200 ppm and ushering in an age of cold that lasted millions of years.

The pump driving the movement of carbon from the atmosphere to a sequestered state within life is photosynthesis. We can strengthen the pump and expand stores of sequestered carbon by increasing native plants, soil, fresh water availability, and the diversity of life. Or we can do the opposite, which has unfortunately been the norm.