Forests across the United States have absorbed carbon at an unusually high rate over the past two decades, turning them into one of the country’s most significant natural allies in slowing climate change. A new scientific analysis shows that this surge is the result of a complex interaction between climate trends and human decisions about how forests are managed and conserved.
Researchers from Ohio State University analysed national forest inventory data to separate carbon gains driven by natural factors from those influenced by land use and forest management. The findings suggest that U.S. forests are currently holding more carbon than at any point in recent history, but scientists caution that this trend may not continue indefinitely.
Climate Conditions and Forest Growth Have Boosted Carbon Storage
Forests play a critical role in climate regulation by storing carbon in trees and soil, preventing carbon dioxide from accumulating in the atmosphere. In temperate regions like the United States, this role is shaped by both environmental conditions and human activity.
The study found that changes in temperature and precipitation patterns between 2005 and 2022 increased forest carbon storage by around 66 million metric tonnes per year. Rising levels of atmospheric carbon dioxide also contributed, as higher CO₂ concentrations can stimulate plant growth under certain conditions.
Scientists noted that unmanaged forests, in particular, are acting as effective ecosystem buffers. Allowing forests to grow naturally has helped them accumulate carbon, especially where trees are in their most productive growth phases. However, researchers warned that as global warming intensifies, the ability of forests to continue absorbing carbon may weaken.
Forest Age Structure Emerges as the Biggest Driver
One of the most significant findings of the study was the role of forest age. As large areas of U.S. forests have matured into peak growth stages, changes in age structure accounted for an estimated 89 million metric tonnes of additional carbon stored each year more than any other single factor.
While tree planting and reforestation added roughly 23 million metric tonnes of carbon annually, deforestation and land conversion reduced forest carbon by about 31 million metric tonnes per year, partially offsetting these gains. The results highlight that simply allowing forests to age, when conditions are favourable, can be one of the most powerful tools for carbon storage.
The researchers stressed, however, that forest growth patterns vary widely across regions. Some forests may benefit from warmer temperatures and longer growing seasons, while others could face slower growth, drought stress, pest outbreaks, and increased wildfire risk.
Implications for Climate Policy and Forest Management
The study underscores the importance of accurate carbon accounting in shaping climate policy. Carbon gains resulting from climate-driven growth differ from those achieved through deliberate forest management and conservation policies, and each carries different risks and levels of control.
Researchers argue that understanding these distinctions is essential for designing effective carbon markets, conservation strategies, and land-use policies. They also emphasised the need for more detailed, local-level tracking of forest carbon trends, as national averages can mask regional declines or emerging threats.
As forests age and climate pressures intensify, scientists say adaptive management will be crucial to ensure that forests continue to function as a brake on climate change rather than becoming a source of emissions.