With carbon offsets in vogue, trees are getting an outsized amount of attention for their ability to sequester carbon, but they’re just one piece of the climate restoration puzzle.
Trees, like all photosynthesizing plants, sequester carbon. Plants convert sunlight, carbon dioxide, and water into sugars from which they build their cells. In every living being, some amount of carbon is sequestered. Trees are powerful carbon sinks because they can sequester a large amount of carbon, especially in their primary growing years, and then hold that carbon for a long time. As long as the tree is alive, the carbon is sequestered. Because of the carbon sequestration potential of trees, extensive efforts of reforestation have popped up to offset emissions and curb climate change.
Trees in the Climate Limelight
Planting trees is popular because it is easy, cheap and relatively apolitical. Perpetuating the narrative that planting a tree can save the planet can obscure the need to reduce reliance on fossil fuels. Planting a tree is also relatively inexpensive. Along with reusing shopping bags and buying a hybrid vehicle, planting a tree is synonymous with being eco-friendly. Tree planting is non-controversial because it doesn’t directly question the systems that perpetuate climate change. It’s also popular because it is a natural solution to carbon emissions, which some people favor over more technologically intensive solutions. Regarding reforestation and afforestation, it is simple to understand why trees are good for the environment.
Forests are excellent carbon sinks, but they’re also valuable for other reasons. For example, forests provide habitat and food for other wildlife, prevent erosion, and maintain healthy waterways.
Caveats to Reforestation
Trees sequester carbon, but the amount varies based on tree type, where they grow and longevity, which is shortened due to wildfires and disease. Endowed with an abundance of rain and sunshine, tropical rainforests can sequester much more carbon than a pine forest in northern Canada or Russia. In addition, certain species tend to sequester more carbon. For example, hardwood oaks sequester more than pine trees in the temperate forests of the U.S. Strategic reforestation can provide multiple benefits by creating new habitats and cleaning waterways. Forests should not only be protected because of their carbon sequestration potential but also for their overall ecological values.
The main limiting factor to using trees for carbon sequestration is space. A substantial amount of space is needed to plant enough trees to sequester significant amounts of carbon. Land value is often seen as too high for people to prioritize forests over farmland or human settlements. There is conflict between industry and reforestation efforts in most countries.
All of the earth’s land can’t simply be covered in forests. Studies show this would not be beneficial as it would reduce the diversity of ecosystems. Experts have found that it’s best to plant trees in the tropics, where the warm and humid climates allow trees to grow the fastest, however, this is a view with controversial geopolitical implications.
Planting trees on every inch of soil that could sustain them would not be a cost-efficient solution. That land could be better used for agriculture or high-density human settlements. Meanwhile, other carbon sequestration methods can sequester carbon while taking up less space. A 2017 study led by Bronson Griscom found that natural climate solutions could sequester about 37% of annual carbon dioxide emissions. However, that 30% includes many solutions in addition to tree planting.
Some studies suggest that afforestation can increase rainfall in dry, tropical regions, allowing for more plant growth and more carbon storage. However, planting trees may harm local ecosystems in other areas, especially if they are monocultures. Replacing natural forests with monoculture forests, or forests with only one species of tree is incredibly detrimental to the health of the surrounding regions and reduces the biodiversity of other organisms.
Forests in the Time of Climate Change
The climate is changing right now and has been for decades. Ecosystems and weather patterns are shifting, which affect forest productivity. We can calculate possible carbon sequestration from today’s forests, but we do not know how those forests will fare in the future. Under climate change, trees may not be as productive carbon sinks as they are currently. As the Earth changes, forests change with it.
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Climate change can move forests, killing off valuable tree species. As the climate warms, forests slowly shift towards their preferred temperature zone, a decades-long process known as forest migration. Some tree species may survive forest migration, but other tree species may not adapt to the fast rate of change.
Meredith Martin, a professor of forestry at North Carolina State University, states how high-altitude trees in Mexico, like the Pinus hartwegii (pine tree) and Quercus crassifolia (oak tree), may not survive climate change because they require specific conditions that can disappear. Therefore, when thinking about protecting forests, thought must be given to the future and how climate change will affect the growth and health of forests.
Planting Policy
Climate policy heavily relies on offsetting carbon emissions, and those offsets are often through reforestation efforts. Companies can pay to plant trees in another country to cancel out their emissions. Carbon offsets are popular because they are easy to sell as a free-market solution to climate change and because they don’t require massive cuts to emissions.
U.S. President Joe Biden has included carbon sinks as a part of his plans to reduce carbon emissions by 2035. In Ghana, a country with some of the highest rates of forest loss, the government is handing out seedlings to its people to reforest their nation. Tree planting programs and policies are common and an essential part of many countries’ climate strategies.
Countries are banking on reforestation to keep emissions down. These efforts, though valuable, are not a definitive solution to climate change. It’s not sufficient given the current atmospheric burden of carbon dioxide. It's not feasible nor realistic to plant enough trees to offset all the carbon that the continues to be emitted. Reforestation should be an integral part of the climate solutions portfolio, and forests must be protected for their ecological value, but reducing carbon emissions and removing existing CO2 from the air are also necessary measures.
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