Forests in the United States store enough carbon to offset approximately ten percent of the country’s annual greenhouse gas emissions, but scientists are warning that this carbon sink is becoming less effective and may level off by mid-century.
The research team set out to determine the potential carbon sequestration of two different strategies: by planting more trees after wildfires and by allowing forests to take over some marginal croplands. The experts also investigated the ability of restorative topsoils to store carbon.
Luke Nave is an ecologist and biogeochemist at the University of Michigan and the study’s lead author.
“Where reforestation is happening – either through planting of trees or through encroachment – these lands are actively adding carbon to a large pool that will continue to grow for many decades,” said Nave.
“The topsoils of reforesting lands provide a significant long-range solution to the problem of the declining carbon-sink strength of U.S. forests, and they help to mitigate climate change. Even modest increases in the amount of land being reforested would have a multiplicative impact on nationwide carbon sequestration.”
The research team investigated forestlands that have experienced major disturbances such as intense wildfires over the last few decades. They found that only about 7 percent of the forestlands available for restoration have been replanted.
The experts also found that reforestation efforts on marginal croplands have only reached about 10 percent of their potential to expand carbon storage. The study authors said that this discovery highlights “the substantial C-sink capacity of this land-use transition if these lands are allowed to continue returning towards a natural forest condition.”
Furthermore, the study revealed that topsoils used in reforestation projects across the United States are currently storing 13 to 21 million metric tons of carbon each year, which is equivalent to about 10 percent of the country’s total forest carbon sink.
According to Nave, reforesting topsoils will capture a cumulative 1.3 to 2.1 billion metric tons of carbon over the next century, accounting for nearly half of the carbon stored in all of the forest soils across the United States. This amount could be drastically increased by expanding the country’s reforesting acreage, which is currently at around 200,000 square miles.
The study is published in the Proceedings of the National Academy of Sciences.