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Tree planting as a carbon sequestration plan

A bright and shiny new object recently appeared on the climate-change stage, tree planting. Policymakers have finally discovered the relationship between greenhouse gas emissions and carbon sequestration. Words about the TTP (Trillion Tree Plan) recently echoed through the halls of congress. However, the current set of policymakers in Washington DC are not known for their science and math skills, so perhaps we should take a look at the numbers.

For starters, planting trees is good. Trees capture carbon from the atmosphere, primarily as CO2, and use photosynthesis to turn that carbon into biomass. Also, excess carbon, beyond what the trees need, can be exuded into the soils where microbes fix the carbon as humus. This process is good for sequestration, and the humus enriches the soils.  In an era of rising greenhouse gas emissions, the forests play a significant role in sequestering carbon and thus reducing the rate of global temperature rise.

Trees and forests are part of the solution to controlling fossil fuel emissions in a changing environment. But the real question is, how much of a role can tree planting reasonably play?

Trees, forest, and available land

The U.S. Forest Service calculates that forests comprise 33 percent of the total U.S. land area or about 750 million acres. The U.S forests sequester about 15 percent of the 6.4 billion metric tons of greenhouse gasses emitted in the USA each year. So, forests sequester roughly one-sixth of the total fossil fuel emissions. 

So, as a total solution, we would need to plant enough trees to increase current forest carbon capture by a factor of six. This solution presents a very straight forward calculation showing that we need a total of 4.5 billion acres of forest to take care of the emissions problem completely. Now we come to our first clash with reality. The total amount of land available in the USA is 2.3 billion acres. We need twice as much land as we have. 

A look at actual tree numbers, however, shows that the TTP does not mitigate all emissions through sequestration. The estimate of total trees in the USA is 300 billion (trees greater than one inch in diameter). So complete sequestration of atmospheric carbon by the forest would require about two trillion trees. The current plan for one trillion new trees presents a 50-percent solution to the carbon emissions problem. Still, a trillion new trees represent an admirable goal.

Now, 300 billion trees spread over 750 million acres averages out at 400 trees per acre. Hence there is a need for 2.5 billion acres of new trees to reach the one trillion mark. The new forest land needed is just about the total size of the USA. As nice a fit as this is, planting the entire surface area of the USA with trees seems to stretch the bounds of realism.

 Implementation worries

Thus far, the tree planting solution seems constrained by the actual space available, making it more of a political symbol than a real plan. But ignoring that observation, the devil still is in the details, and planting a trillion trees requires that someone actually put them in the ground. 

At the end of 2019, the National Forest Foundation was pleased to announce they had planted five million trees during the year, representing almost a 100 percent increase over 2018. This tree planting program was an impressive effort. But planting at a rate of five million trees per year requires 200,000 years of work to reach the one-trillion-tree goal. 

Other more optimistic groups have asserted that Americans plant 1.6 billion trees each year. Planting at this more optimistic rate decreases the amount of time needed, and the last of the trillion trees will be planted in the year 2645. 

Reality

The reality is that planting trees is good and that carbon sequestration in our forests is an important process. The truth also is that the one trillion tree goal is not a real plan. Instead, it is a political talking point to avoid making actual policy dealing with climate change. Carbon sequestration is part of a solution, not the whole answer. 

Better policymaking starts at the ballot box.


ArcheanWeb:

Forests as a pathway for terrestrial carbon sequestration (Source: ArcheanWeb) – https://archeanweb.com/2020/02/06/forests-as-a-pathway-for-terrestrial-carbon-sequestration/ Also:

Sources:

Inventory of U.S. Greenhouse Gas Emissions and Sinks (EPA) – https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissions-and-sinks Also:

US Forest Facts and Historical trends (US Forest Service) – https://www.fia.fs.fed.us/library/brochures/docs/2012/ForestFacts_1952-2012_English.pdf Also:

Our Impact in 2019: 5 million trees, 18,000 acres, and so much more (National Forest Foundation) – https://www.nationalforests.org/blog/our-impact-in-2019 Also:

The world’s 3 trillion trees, mapped (By Chris Mooney; Washington Post) – https://www.washingtonpost.com/news/energy-environment/wp/2015/09/16/the-countries-of-the-world-ranked-by-their-tree-wealth/ Also:

U.S. Forest Facts on Forestland (By Steve Nix; ThoughtCo.) – https://www.thoughtco.com/us-forest-facts-on-forestland-1343034 Also:

Feature Image: Redwood Forest (By William House)

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.