By George Moffat • gmoffattgt@aol.com
Since our carbon dioxide (CO2) level today may be the highest in almost 4 million years, will planting trees help sequester the CO2 driving our catastrophic climate problems? Yes? Maybe? Probably not?
Rapidly changing circumstances make all three answers debatable. Some argue trees will significantly reduce CO2, and some are doubtful.
We should try, anyway, but succeeding in planting trees depends on many factors: growing impacts of local climate change; soil conditions; available water and sunlight; and how fast the tree will grow, its average lifetime, and the total CO2 it can sequester. All plants absorb CO2 through photosynthesis, but trees’ large leaves and canopies make them the most efficient. Choosing a species can be tricky. Many fast-growing trees absorb CO2 quickly, while slow growers can store more over their life spans. For the undecided, the US Forest Service has listed the best temperate zone “carbon sinks”: London plane, Douglas fir, scarlet oak, red oak, Virginia live oak, and bald cypress.
During photosynthesis the tree needs the sun’s energy to absorb water from the air and soil, and CO2 from the atmosphere. The CO2 then breaks down into glucose (simple sugars), which nourishes the tree and is combined with water to create oxygen that is released into the atmosphere. The CO2 remains behind. However, when the tree dies, its decay slowly releases all that stored CO2.
Sequestration Is Not a Forever Thing.
Earth naturally emits about 100 billion tons of CO2 each year from undersea volcanos and hydrothermal vents, while its oceans, forests, and soils absorb an equivalent amount. These processes kept Earth’s CO2 in balance since trees started to appear about 395 million years ago. But as the Industrial Revolution began during the 1700s, we started increasing CO2 emissions, which today amount to an estimated 36 billion tons each year across the globe. If you count other greenhouse gases, such as methane, nitrous oxide, and fluorocarbons, the total goes much higher.
If we plant a tree that will absorb an average of about 22 pounds of CO2 per year, or 2,200 pounds in 100 years, we may feel righteous. However, the average US citizen creates about 22 tons of CO2 a year, equivalent to 2,205 tons in 100 years.
Nevertheless, planting trees will lower our CO2 emissions, if only somewhat. The US Forest Service reported in 2021 that in 2019 forest land, woodlands, and urban trees sequestered enough carbon to offset more than 11% of the total US greenhouse emissions. And it estimated—optimistically—that that by fully restocking federal, state, and private forests that have lost trees, carbon sequestration could be increased by 20%.
However, climate change may make it difficult to fully restock many traditionally forested areas, given heatwaves, droughts, forest fires, and pest destruction. Today, up to 135 US tree species face extinction, including one in six native species. Worldwide, of about 58,500 tree species, one-third are threatened with extinction, while at least 140 species are already extinct.
While trees alone will not offset our additional 36 billion tons of CO2 a year, we should support reforesting “tree sprees.” After all, they sequester some CO2; cool the air; and absorb other greenhouse gases, including ozone, sulfur dioxide, nitrogen dioxide, methane, and carbon monoxide. And don’t forget their photosynthetic bonus—creating our oxygen.
Trees also serve other ecological needs: absorbing rainfall; controlling runoff, erosion, flooding, and water pollution; providing wildlife habitat; moderating temperatures (somewhat); providing cover for other vegetation; plus providing beauty and serenity for our frazzled psyche.
Unfortunately, both old growth trees and saplings are increasingly succumbing to shifting weather patterns, such as droughts and hotter temperatures, forest fires, invasive insects, and declining flora and fauna that sustain their overall ecology.
So, while trees in the United States may sequester just 16% of domestic CO2 each year (955 million tons), compared with the 36 billion tons we create, they have the potential to do a lot more, if we let them.