Forests of the eastern United States are important carbon storehouses. They remove climate-warming emissions from the air, packing them away into leaves, trunks, roots, and soils. Eastern forests are responsible for 85% of all the carbon taken up by US forests. And they support biodiversity, timber products, and other ecosystem services at the same time.
But eastern trees are becoming increasingly stressed by warming temperatures, which can slow their growth and reproduction. How can forest managers maintain the eastern forest carbon sink under these changing conditions?
A recent paper by scientists at Cary Institute of Ecosystem Studies explores how eastern forests are responding to climate change, how disturbances such as harvesting and pests can help or hinder climate adaptation, and what it all means for carbon storage. The study was published in Ecosystems in January.
The team found that responsible harvesting and other small disturbances can help to make eastern forests more resilient to climate change, by paving the way for warm-adapted species to move in, thrive, and continue soaking up carbon.
“It was comforting to learn that eastern forests, which hold the most carbon in the US, are actually doing okay,” said lead author Sara Germain, who completed the research as a Cary postdoctoral associate and is now an assistant professor at University of Wyoming, Laramie. “With moderate, status quo levels of disturbance, eastern forests have the capacity to remain an important carbon sink.”
Cary forest ecologist and co-author Winslow Hansen added that maintaining the carbon sink does come with some tradeoffs, however. “While disturbance plays a critical role for accelerating adaptation of the forest community to species that are better adapted climatically,” he said, “it leads to lower biodiversity, and a temporary drop in biomass accumulation.”
Past, present, and future forests
Much of the research around the potential to leverage forests as a natural climate solution has focused on tropical forests. But study coauthor and Cary Institute forest ecologist Charles Canham recognized that eastern forests — currently rebounding after being cleared for agriculture and logging in previous centuries — are a productive and expanding carbon sink. This new study is part of a broader project Canham is leading to rigorously analyze the carbon storage potential of eastern forests, identify threats to forest carbon stocks, and identify management strategies that maximize forest carbon storage.
The project relies on data from the USDA Forest Inventory and Analysis (FIA) program, which has been surveying forested areas across the US for nearly 100 years to capture trends in forest health, species composition, and use by humans, such as timber harvesting or clearing for agriculture.
FIA data allowed the team to track changes in biomass and forest composition across 22 eastern states from 1995 to 2021, and how those changes are shaped by disturbances. The team particularly focused on changes in seedling and sapling density for 99 tree species, because young trees are the most vulnerable to heat and drought.
Using the current abundance of seedlings, saplings, and adult trees in each plot, the scientists used a model developed by Canham to simulate the forest’s future composition and biomass up to the year 2150. The model simulates trees’ responses to climate, nutrient availability, and competition. It also incorporates natural and human disturbances, including wind, pests and pathogens, and logging, which is the most common disturbance in northeastern forests.
Finding the forest management ‘sweet spot’
Undisturbed forests tended to contain more species adapted to cool climates, the study found, whereas disturbed forests shifted toward more warm-adapted species. Disturbance appears to clear space for warm-tolerant species to migrate northward. “Many species become more abundant in the northern portions of their current ranges, and some show northward expansion,” said Canham.
Birch is one species that’s invading more northern habitats and disappearing from its more southern habitats, said Germain. “There is definitely this movement that's going on across the landscape, and how forests are changing in any one area is going to depend on the species that are already there, the species that are nearby, and how much disturbance they've experienced.”
Because warmer-adapted species are more likely to survive and thrive in a warmer future, the authors conclude that the changes in composition caused by disturbance may support the maintenance of the eastern forest carbon sink over the long term, by increasing climate resilience.
However, climate resilience may come at a cost to biodiversity and productivity. The diversity of the warm-adapted trees that moved in was lower than the diversity of cold-adapted trees that disappeared. And because young trees are small, they don’t store as much carbon, meaning disturbed forests saw dips in biomass. But those dips are likely temporary; “It could still lead to more carbon storage in the future if the altered forests are better able to survive in warmer conditions,” Germain explained.
The authors emphasize that the level of disturbance matters, and that they’re not advocating for clearcutting eastern forests. Severe disturbances can kill off seedlings, reduce carbon storage, and delay forest recovery.
“There was kind of a sweet spot there where low to moderate disturbances initiated the transition to more climate-adapted tree species, but didn't have the huge losses in carbon that we saw under much more severe disturbances,” said Hansen.
“It appears that much of eastern forest management is hitting that sweet spot right now,” Germain added.
Forest managers often must find a balance between competing needs for timber, biodiversity, and carbon storage, and managers at different sites may have different priorities. But overall, Germain said, the results complement a management practice called the triad approach, which divides forestland into a portion managed intensively for timber products, a portion managed for multiple use (including wildlife habitat and recreation), and a portion set aside in reserves.
“People need wood products, and we can't just stop harvesting altogether,” said Germain. “But, especially in the context of our findings, the triad approach is a good way to balance those different objectives of carbon storage, biodiversity, and forest products.”
Another key to maintaining biodiversity will be to protect refugia that are safe from disturbance, where cool-adapted species can continue to thrive and support biodiversity. Mature and old-growth forests provide unique habitat for wildlife while storing vast amounts of carbon.
“The way forests work now is not necessarily the way they're going to work in 20 or 50 years,” said Germain. “Things aren't just getting warmer; they're getting more variable and less predictable. What that means is that having a diversity of forest ages, species compositions, and forest types is going to confer resilience for the entire region.”
Funding
This work was funded by the Environmental Defense Fund and the Three Cairns Group.
Citation
Germain, S.J., Hansen, W.D. & Canham, C.D. Reassembly of Disturbed Forests Portends Climate Resilience but Diversity Loss. Ecosystems 28, 9 (2025). https://doi.org/10.1007/s10021-024-00959-0
