Forest Carbon Stocks Based on Land Ownership in the U.S.

The Role of Forests in Carbon Storage

Forests in the United States store over 866 million metric tons of carbon annually, playing a critical role in offsetting greenhouse gas emissions. Estimates from the EPA indicate that are much as 54% of total carbon stored in forests can be found in the soil, yet as of right now, the majority of carbon crediting sources do not account for carbon storage in their estimates (US EPA, 2020). Because of this, the two main pools used in this study are aboveground biomass, which includes trees and shrubs, and belowground biomass, which consists of roots. However, land use changes like deforestation and urbanization can release this stored carbon back into the atmosphere. Sustainable forest management is essential to preserving these carbon stocks.

The county-level data presented in this paper were the result of a capstone project submitted to the Masters of Geographic Information Systems Program in the Department of Geography at Penn State. To access the full report or datasets, contact Melissa Kreye at mxk1244@psu.edu. The full report provides a more in-depth overview of the methodology and sources used for this paper.

Ownership Patterns and Carbon Distribution

The ownership of U.S. forests is diverse, with significant implications for carbon management. Private forest lands in the United States account for between 58–69% of all forested land, with exact ownership numbers fluctuating year to year. The forests are distributed across various ownership categories, including family, corporate, and investment-based entities such as Timber Investment Management Organizations (TIMOs) and Real Estate Investment Trusts (REITs). 31% of the nation’s forest area can be found on Federal lands and is concentrated in the northwestern regions, where dense, old-growth forests store the highest levels of carbon. These protected areas, as defined by the United States Geological Survey (USGS), are lands managed to preserve biodiversity and provide natural, recreational, and cultural benefits (USGS, 2022). While federal lands are considered protected areas, they still have other uses, including some levels of timber harvesting, hunting, and even grazing. These areas include fee-owned lands (outright ownership by public agencies, nonprofits, or private entities), easements (legal agreements restricting land use to protect conservation values), designations (policy-determined protections), proclamations (tribal, military, or congressionally appointed lands), and marine areas (protected water zones).

Carbon Stocks by County

Total forest carbon stocks in the contiguous US vary by region and county. Figure 1 displays the sums of total forest carbon in aboveground and belowground living biomass within specified counties. Highest tonnage of forest carbon (up to 300 million tons) can be found in western counties of the Pacific Northwest. This is partly due to the forest types in this region (i.e., temperate rainforest, dry mixed-conifer forest, subalpine forest, boreal forest, oak woodlands, and pinyon-juniper woodlands) as well as the size of the counties, which are comparatively larger compared to counties in the eastern US. Still, many counties in the eastern US contain around 40 to 90 million tons of forest carbon in aboveground and belowground living biomass. These forest types include eastern deciduous forests, northern hardwood forests, New England-Acadian forests, and eastern temperate forests.

The next figure displays the average tons of carbon per acre in aboveground and belowground living biomass (Figure 2). The counties with the highest averages occur in western counties of the Pacific Northwest and Idaho, and along the Appalachian Mountains, which hold up to 1,500 tons of carbon per acre. These forest types include Pacific temperate rainforests and mixed conifer forests in Idaho. In the Appalachian region, oak-hickory forests, northern hardwoods, and spruce-fir stands are common.

Carbon Stocks by Land Ownership

There are differences in carbon density across ownership types. Federally owned forests in the Pacific Northwest store the most carbon per acre (up to 1,000 tons per acre), benefiting from their ecological richness (Figure 3). However, land use change and increasing wildfires have become important issues in managing these stocks under climate change (Bachelet et al., 2015). For example, from 2005 to 2019, the Southern Rockies lost the most live carbon, declining by 25%, whereas the Pacific Northwest and one Upper Rockies ecoregion increased their live carbon (Hall et al., 2024).

In contrast, eastern forests are largely in private ownership and most stocks are within the Appalachian region. Carbon stocks on family forest lands (up to 821 tons per acre) can be found in Figure 4. The major threats to forests in the Appalachian region include unsustainable logging, mountaintop removal mining, urbanization and fragmentation, invasive species, extreme weather events, forest diseases and insect pests, and land use changes, which can disrupt the natural ecosystem balance and biodiversity of the region (Clark et al., 2001, Drohan et al., 2012, Grable and Harden, 2006).

At the state level, in Pennsylvania, for example, 74% of forest carbon is located on family forest lands, with values ranging from 200 to 700 tons per acre (Figure 5).  Pennsylvania also has a robust forest industry, which provides $21.8 billion in direct annual impact to the Pennsylvania economy and provides jobs to over 600,000 people.

Conclusions

US forests contain a lot of carbon, and sustainable forest management is essential to preserving these carbon stocks. It is worth considering that some of the values presented in this paper could be an underestimation. Past timber harvests have moved a portion of forest carbon (about 4%) into wood products, which means that carbon can remain undisturbed for up to 100 years (Kreye, 2023). Every ton of carbon stored in wood products displaces up to 2 tons of carbon emissions from non-woody materials (e.g., concrete, steel). The climate benefits provided by forests that generate wood products might be 8% higher compared to forests that do not contribute wood products (e.g., some public lands) (Bergman et al., 2014). Recognizing this highlights the possibility of using public-private initiatives to enhance or protect carbon stocks through sustainable timber management and market-based solutions.

These estimates are comparable to estimates calculated through the Forest Carbon Data Visualization project. The website provides sources to explore carbon storage topics further.

If you have any questions or are interested in collaborating with FOCCE, please reach out to Melissa Kreye at mxk1244@psu.edu.

References

Tait, N. (2023) Forest Carbon Ownership and Protection Status in the Contiguous United States. A Capstone project report written for the Masters of Geographic Information Systems Program in the Department of Geography at Penn State.

Bachelet, D., Ferschweiler, K., Sheehan, T. J., Sleeter, B. M., & Zhu, Z. (2015). Projected carbon stocks in the conterminous USA with land use and variable fire regimes. Global change biology, 21(12), 4548-4560.

Hall, J., Sandor, M. E., Harvey, B. J., Parks, S. A., Trugman, A. T., Williams, A. P., & Hansen, W. D. (2024). Forest carbon storage in the western United States: Distribution, drivers, and trends. Earth's Future, 12(7), e2023EF004399.

Kreye, M., & Norman, C. (2023). Forest Carbon Pools: Where are they? Penn State Extension.

Clark, S., Back, J., Tubiolo, A., & Romanaux, E. (2001, October). The Southern Appalachians: A Changing World. In US Geological Survey Appalachian Region Integrated Science Workshop Proceedings, Gatlinburg, Tennessee, October 22-26, 2001 (p. 3).

Drohan, P. J., Brittingham, M., Bishop, J., & Yoder, K. (2012). Early trends in landcover change and forest fragmentation due to shale-gas development in Pennsylvania: a potential outcome for the Northcentral Appalachians. Environmental management, 49, 1061-1075.

Grable, J. L., & Harden, C. P. (2006). Geomorphic response of an Appalachian Valley and Ridge stream to urbanization. Earth Surface Processes and Landforms: The Journal of the British Geomorphological Research Group, 31(13), 1707-1720.

Bergman, R., Puettmann, M., Taylor, A., & Skog, K. E. (2014). The carbon impacts of wood products. US Forest Service Research and Development.

U.S. Geological Survey (USGS) Gap Analysis Project (GAP). (2022). Protected Areas Database of the United States (PAD-US) 3.0: U.S. Geological Survey data release.