Methodologies

Many individuals and organizations need information on forest carbon stocks to support planning, reporting, or target setting, but generating these estimates can require specialized technical expertise that is not readily available to all users. Forest inventories can provide highly detailed, site-specific information, but they are also costly and time-intensive to establish and maintain. In cases where highly precise estimates are not required, the cost and effort associated with implementing a dedicated forest inventory may be disproportionate to the intended use.

Recognizing this need, the Default Forest Carbon Tool (herein referred to as the “Default Tool”) enables users with limited site-specific data and knowledge of carbon accounting to produce first-order estimates of forest carbon stocks, changes in carbon stocks within an inventory period, and if desired, potential changes in forest carbon stocks from a set of basic forest management scenarios for a user-defined area within the conterminous United States (CONUS).  The Default Tool is primarily based on the “Level 1” quantification approaches published in the USDA Entity Guidelines Chapter 5: Methods for Managed Forest Systems (Murray et al. 2024) and accompanying Excel-based workbook (Stockmann et al. 2023).  

The information on forest carbon stocks that underlies the Default Tool is based on forest inventory data and estimation methods developed by the USDA Forest Service’s Forest Inventory and Analysis (FIA) Program. The Default Tool matches basic user-supplied stand-level data inputs to forests measured by the FIA matching those user data inputs to reflect generalized patterns of forest carbon stocks and changes for similar stands across ownerships.  

In the Default Tool, changes in carbon stocks represent estimated net change in carbon stored within the defined system(s) (i.e., the forest stand and harvested wood products) over a specified period, expressed as metric tonnes of carbon dioxide equivalent (t CO₂e). The results are presented using an atmosphere-oriented sign convention whereby negative values indicate a removal of carbon dioxide from the atmosphere (i.e., carbon sequestration or carbon removal). Positive values indicate a release of carbon from the ecosystem to the atmosphere and therefore represent emissions. Carbon stocks, in contrast, are presented as positive quantities because they represent the amount of carbon stored in a given pool at a specified point in time, rather than a transfer of carbon to or from the atmosphere. 

The resulting estimates empower users to evaluate the standing forest carbon stocks as well as the potential impact of forest management interventions where site-specific data and analyses are not available.

Ac: Acres (land area measurement)

AFOLU: Agriculture, Forestry, and Other Land Use 

Bf: Board feet (wood volume measurement)

CCF: Hundred cubic feet (wood volume measurement)

CENT: Central States (US Region)

CO₂e: Carbon dioxide equivalent

d.b.h.: Diameter at Breast Height; tree diameter measurement

DFCT: Default Forest Carbon Tool

Dry tons: The oven-dry weight of tree biomass at 0% moisture content, excluding the weight of all water contained in the material. FIA reports this quantity in dry short tons, where one short ton equals 2,000 pounds.

FACT: Forestry Analytics for Carbon Tracking

FIA: Forest Inventory and Analysis (program of USDA Forest Service)

Green tons: The weight of freshly cut tree biomass at its natural moisture content, including the water contained in the wood and bark. FIA reports this quantity in green short tons, where one short ton equals 2,000 pounds.

GP: Great Plains (US Region)

GSV: Growing stock volume

Ha: Hectares (land area measurement)

HWP: Harvested Wood Product(s)

IPCC: Intergovernmental Panel on Climate Change

MBF: Thousand board feet (wood volume measurement)

Metric tonnes: Unit of weight equal to 1,000 kilograms (2,204.6 pounds), or approximately 1.102 short tons (t) 

NFI: Nationwide Forest Inventory of the Forest Inventory and Analysis Program (program of USDA Forest Service)

NC: North Central (US Region)

NE: Northeast (US Region)

NLS: Northern Lake States (US Region)

PNWE: Pacific Northwest, East side (US Region)

PNWW: Pacific Northwest, West side (US Region)

PSW: Pacific Southwest (US Region)

RMN: Rocky Mountain North (US Region)

RMS: Rocky Mountain South (US Region)

SC: South Central (US Region)

SE: Southeast (US Region)

SWDS: Solid Waste Disposal Sites

t CO₂e: Metric tonnes of carbon dioxide equivalent

U.S.: United States of America

USDA: United States Department of Agriculture

The Default Tool is designed to work with standard operational forest inventory data commonly collected by foresters and land managers. It applies USDA Forest Service Forest Inventory and Analysis (FIA) Nationwide Forest Inventory (NFI) data-derived relationships, expansion factors, and published biomass and carbon estimation methods to estimate additional pools where applicable, including non-merchantable live biomass, saplings and understory components, standing dead trees, down dead wood, belowground biomass, and litter and soil carbon.

The Default Tool produces estimates of forest carbon and changes in forest carbon stocks across the Contiguous United States (CONUS) leveraging FIA data, other existing data sources and scientifically credible, broadly applicable methods.  Using coarse, user-supplied information, the Default Tool  leverages a corresponding forest carbon model to present estimates of current carbon stocks and changes over an inventory period.  The carbon model is an empirical mathematical model fitted to FIA observations, rather than a process-based ecosystem model. 

Where a user wishes to explore the carbon impacts from a limited set of generalized forest management scenarios, the Default Tool projects forest carbon stock changes over a period of 50 years.  Where scenarios involve harvest, forest carbon stocks transferred to the Harvested Wood Products (HWP) and Solid Waste Disposal Site (SWDS) pools are estimated, with associated carbon storage and emissions estimates presented for a period of up to 100 years post-harvest.  

3.1 Carbon Pools

The Default Tool evaluates carbon stocks in the five forest carbon pools defined by the Intergovernmental Panel on Climate Change (IPCC):

1. Aboveground live: Carbon in the aboveground portions of live trees and understory vegetation, corresponding to IPCC forest carbon pool 1. The tree component covers live trees at least 1 inch d.b.h., excluding foliage, for both timber and woodland species, and is derived from field measurements through allometric models. The understory component covers seedlings and shrubs and is modeled at the condition level.  
2. Belowground live: Carbon in the belowground portions of live trees and understory vegetation, corresponding to IPCC forest carbon pool 2. The tree component covers the coarse roots of live trees at least 1 inch d.b.h. for both timber and woodland species, and is derived from field measurements through allometric models. The understory component covers seedlings and shrubs and is modeled at the condition level. 
3. Dead wood: Carbon in standing and downed dead woody material, corresponding to IPCC forest carbon pool 3. Standing dead comprises standing dead trees and their coarse roots; down dead comprises woody material greater than 3 inches in diameter lying on the ground, together with stumps and their roots. Both are modeled at the condition level rather than summed from field measurements.   
4. Litter: Carbon in organic material on the forest floor above the mineral soil, corresponding to IPCC forest carbon pool 4. Comprises the litter, fulvic, and humic layers, together with fine woody debris less than 3 inches in diameter. Modeled at the condition level rather than summed from field measurements.  
5. Soil: Carbon in fine organic material below the soil surface to a depth of 1 meter, corresponding to IPCC forest carbon pool 5. Excludes roots, which are assigned to the live and dead tree pools. Modeled at the condition level rather than summed from field measurements. 

These pools are also included in estimates of changes in forest carbon stocks. Soil carbon, however, is assumed to remain constant over time and therefore does not contribute to estimated carbon stock change. This simplifying assumption reflects the substantial uncertainty associated with projecting changes in soil carbon over relatively short time periods, as well as the more limited spatial coverage and sampling frequency of FIA soil carbon measurements compared with other forest carbon pools. 

Where applicable, carbon transferred from the forest into the harvested wood products (HWP) pool (which includes carbon  stored in products in use and in solid waste disposal sites, emissions with energy capture, and emissions without energy capture sub-pools) is included within the forest management scenario projections in the Default Tool that involve harvest. HWP carbon is tracked separately from carbon remaining on the forest site but remains within the AFOLU accounting boundary. 

3.2 System Boundaries

The Default Tool quantifies changes in carbon stocks within forests, including those associated with forest management, within the Agriculture, Forestry, and Other Land Use (AFOLU) sector, as defined by the IPCC. The system boundary includes changes in carbon stored on the forest site and carbon transferred from the site into HWPs. Forest carbon accounting captures changes in relevant ecosystem carbon pools over the assessment period, while the HWP component accounts for the storage and subsequent release of carbon contained in harvested wood products. Carbon removed from the forest and transferred to HWP is treated as a transfer between AFOLU carbon pools rather than an immediate atmospheric emission.

The Default Tool is limited to AFOLU-sector carbon accounting and does not constitute a full life-cycle assessment. Emissions associated with activities outside the AFOLU sector, such as fuel use in harvesting and transportation, wood-product manufacturing, construction, or avoided emissions from substitution of wood for more emissions-intensive materials or fuels, are outside the system boundary.

The Default Tool’s underlying models were constructed using FIA plots classified as forest land at both measurement periods (i.e., forest remaining forest). Accordingly, estimated carbon stock changes reflect changes occurring within existing forest land and do not include carbon stock changes associated with transitions into or out of forest, such as afforestation, reforestation following a nonforest land use, or deforestation. 

3.3 Caveats and Context for Users

The underlying models built using FIA plot data that serve as the basis for the estimates produced by the Default Tool reflect broad regional averages which characterize the range of conditions across U.S. forests. The model outputs are meant to represent what the forest carbon stocks are, on a per-acre basis, for a given forest type and stand origin within a region, at a given age. While this approach offers a uniform, nationally consistent approach, users should recognize that the underlying models do not account for a host of factors that can materially affect forest carbon stocks and growth, such as site productivity, stocking density, edaphic conditions on the site (e.g., slope, soil moisture), active forest management, or disturbance history. Therefore, site-specific conditions can cause substantial departures from what the underlying models predict. 

The Default Tool’s forest management scenario results represent generalized growth trajectories estimated using mathematical growth curves fitted to observed FIA data. The intervention is represented only through scenario framing including the starting age, harvest year (where applicable), and assumed baseline (where applicable) with no explicit process-based modeling of biological response to the treatment itself. Practices known to influence carbon substantially including thinning, site preparation, competing vegetation control, and fertilization are not captured. Therefore, even where two stands under materially different management could return identical estimates in the Default Tool if they share region, forest type group, stand origin, and age class.

Where forest management scenarios are explored, users should also recognize that time introduces an additional important source of uncertainty. The tool’s estimates are based on models built using historical FIA data, but the relationships observed in the underlying data will not necessarily continue to be reflected in future forest conditions. Forest growth, mortality, disturbance, and carbon accumulation can change over time in response to shifting climate conditions, altered disturbance regimes, changes in species composition, and evolving management practices. Users should therefore be aware that the scenario projections should be interpreted within the context of increasing uncertainty as projections extend toward the end of the 50-year projection timeline.

Where more precise estimates are needed, users should consider applying appropriate growth and yield models (e.g., the USDA Forest Service Forest Vegetation Simulator) which combine site-specific inventory data with model simulations that accommodate a wide range of even-aged and uneven-aged systems, as well as silvicultural practices including thinning, site preparation, competing vegetation control, and fertilization. Where only estimates of current standing carbon and estimated changes in forest carbon stocks over an inventory period are desired, the FACT Custom Forest Carbon Inventory Tool can convert stand-level inventory data into carbon estimates. Because the Custom Forest Carbon Inventory Tool produces estimates using stand-level inventory data, its outputs offer a significantly higher degree of precision than those produced by the Default Tool.

In summary, Default Tool outputs should be understood as representative estimates rather than precise measurements of conditions on a specific property. Where greater precision is required or desired, a site-specific inventory and more advanced modeled simulations may be necessary to undertake.  

3.4 Sources of Uncertainty

While the Default Tool reduces the technical and financial barriers to estimating forest carbon stocks, the tradeoff is that its outputs carry substantial uncertainty in reflecting the carbon stocks or changes in carbon stocks over time on individual sites. The Default Tool does not offer quantitative assessments of associated uncertainty, and the sources of uncertainty are many. However, major sources can be qualitatively described as follows: 

• The application of coarsely developed models to a specific stand, and the compounding of errors across a diversity of carbon pools, stand structures, species compositions, and site qualities. 
• Sparse plot data for some region–forest type–age class combinations produce high sampling error, resulting in higher uncertainty where those combinations are selected.
• The forest management scenarios represent generalized growth trajectories rather than models of silvicultural practice. Practices known to influence carbon substantially such as thinning, site preparation, competing vegetation control, and fertilization are not captured. Uncertainty in the modeled response likely increases with management intensity and with departure from prevailing regional practice and forest conditions. 
• Where forest management scenarios involving harvest are explored, two significant sources of uncertainty arise:
• • The Default Tool allows users to either enter known harvest amounts or source estimates of harvest volume derived from FIA estimates of growing stock volume (GSV). These are defined by merchantability yet actual harvests routinely remove material that does not meet the FIA’s merchantability definition, particularly in pulpwood, chip, and fuelwood operations. These estimates may therefore underestimate total wood removed from site. See Box 3 for more details. 
  • The underlying methodology for all harvest-oriented scenarios relies on published factors from Smith et al. (2006), which draws data from previous studies. Therefore Default Tool’s underlying methodology integrates assumptions about wood product utilization that are decades old. Utilization efficiency has generally improved since those factors were developed, and they therefore likely overstate logging residues and understate product recovery, rendering the resulting estimates conservative with respect to carbon retained in wood products. Efforts are underway to update these parameters to reflect more contemporary use trajectories of wood products, which will be incorporated in future versions of FACT. 
• Uncertainty in FIA-derived carbon estimates increases where attributes are not directly measured. Aboveground live and standing dead biomass are derived from measured diameter at breast height (d.b.h.) and height via allometric equations, and belowground live biomass as a function of those. Down dead wood, litter, and soil carbon are populated for most conditions by models predicted from live tree carbon density, stand age, forest type, and geographic area. 
• The gain–loss approach to evaluate changes in forest carbon stocks applied by the Default Tool handles transfers between pools by assumption rather than by measurement.

4.1 Overview

The Default Tool can generate two categories of results depending on the level of analysis the user wishes to perform. All analyses begin with completion of the required carbon inventory user inputs. Users may then optionally evaluate future carbon trajectories by selecting from a set of generalized forest management scenarios.

1. Carbon Inventory Results: Current estimated carbon stocks and changes in forest carbon stocks over the previous five-year period for each forest stand evaluated.
2. Forest Management Scenario Projection Results: Projected carbon stocks and changes in carbon stocks for each forest stand evaluated based on the user-selected forest management scenario. These results can include:
3. 1. Forest-level (i.e., “Ecosystem Side) results are projected over a 50-year time period
   2. For scenarios that involve harvest, carbon stocks and emissions associated with harvested wood products (HWP) over a 100-year post-harvest time period. 

4.2 Carbon Inventory User Inputs

Carbon Inventory User Inputs are summarized in Table 1 below. 

Table 1 Carbon Inventory User Data Inputs

Figure 1: Map of broad CONUS regions applied in FACT Forest tools. Adapted from USDA Entity Guidelines, Quantifying greenhouse gas fluxes in agriculture and forestry: Methods for entity-scale inventory, Technical Bulletin 1939, 2nd ed., Chapter 5, Figure 5-4 (2024).  

4.3 Forest Management Scenario Projection User Inputs

Once Carbon Inventory results are generated, the Default Tool allows users to optionally explore how a limited set of broad forest management scenarios could affect stand carbon stocks and changes in forest carbon stocks into the future. Additional user inputs beyond those that were already supplied at the stand-level for the Carbon Inventory are detailed in Table 2 for each forest management scenario included in the Default Tool.

The Default Tool produces two sets of outputs whereby once Carbon Inventory Outputs are rendered, they may opt to explore a set of generalized forest management scenarios. The sections below describe outputs for both the Carbon Inventory and Forest Management Scenario Projections.

5.1 Error checking

During data processing, the Default Tool may need to adapt methodological procedures based on user-supplied data parameters, triggering the platform to produce a “warning” notification intended to support transparent user interpretation of results based on processing adjustments. Examples include when a forest type group is reported in a region in which FIA has few or no records of that forest type group. In these cases, a carbon stock estimate are be computed based on a default such as averages for the forest type group in other regions.

Exact warning message language TBD. 

5.2 Carbon Inventory Outputs

Upon processing of the user-supplied data, several summary metrics and graphical outputs are rendered, as detailed below. 

Summary metrics: 

• Total carbon stock: Modeled total forest carbon stock for the forest stand(s).
• Total carbon change over 5 years: Modeled change in forest carbon stocks for the selected forest stand(s) across the preceding five years. Negative values indicate carbon sequestration, meaning the net removal of carbon dioxide from the atmosphere and storage in forest biomass. Positive values indicate carbon emissions, meaning the release of carbon from forest biomass to the atmosphere as carbon dioxide.
• Annual carbon change: Modeled annual changes in carbon stocks for the selected forest stand(s) across the preceding five years. Negative values indicate carbon sequestration, meaning the net removal of carbon dioxide from the atmosphere and storage in forest biomass. Positive values indicate carbon emissions, meaning the release of carbon from forest biomass to the atmosphere as carbon dioxide.

Graphical outputs:

• Total carbon by pool bar chart (Figure 2) that breaks down the carbon stocks by carbon pool across the 5-year carbon calculation periods. The light blue bars display the carbon stocks by pool at the beginning for the 5-year time interval across which changes in forest carbon stocks are calculated and the dark blue bars display the carbon stocks by pool at the end of the 5-year time interval. 
• Carbon inventory table (Figure 3) that provides a numerical breakdown of carbon stocks by pool at the beginning for the 5-year time interval across which changes in forest carbon stocks are calculated, carbon stocks by pool at the end of the 5-year time interval (i.e., “Current year”), the total calculated change in forest carbon stocks, and annualized changes in forest carbon stocks. Negative values indicate carbon sequestration, meaning the net removal of carbon dioxide from the atmosphere and storage in forest biomass. Positive values indicate carbon emissions, meaning the release of carbon from forest biomass to the atmosphere as carbon dioxide.

Figure 2: Carbon stock in each carbon pool over assessment period bar chart

Figure 3: Carbon Inventory results table

5.3 Forest Management Scenario Outputs

Where users opt to evaluate forest management scenarios, Default Tool produces future projections based on user specifications (as necessary) for the selected scenario. Outputs are presented as summary metrics and graphical outputs. 

5.3.1 Basic Projection Outputs

Summary Metrics:

• Total Net Carbon Change Across the 50-Year Projection: The cumulative net carbon change over 50 years. Negative values indicate carbon sequestration, meaning the net removal of carbon dioxide from the atmosphere and storage in forest biomass. Positive values indicate carbon emissions, meaning the release of carbon from forest biomass to the atmosphere as carbon dioxide.
• Average Annual Carbon Change: Modeled annual changes in carbon stocks across the 50-year projection. Negative values indicate carbon sequestration, meaning the net removal of carbon dioxide from the atmosphere and storage in forest biomass. Positive values indicate carbon emissions, meaning the release of carbon from forest biomass to the atmosphere as carbon dioxide.
• 50-Year Projected Ecosystem Carbon: Modeled change in forest carbon stocks across the 50-year projection. Positive values indicate an increase in stored carbon, while negative values indicate a decrease. The percentage represents the change relative to the initial carbon stock.
• Initial Stock: Modeled carbon stock at the start of the 50-year projection. This number represents stored carbon and therefore is always positive. 
• 50-year projection: Modeled carbon stock at the end of the 50-year projection. This number represents stored carbon and therefore is always positive. 

Graphical Outputs: 

• Carbon stock projection stacked area chart (Figure 4): Presents modeled forest carbon stock by carbon pool over 50 years. The stacked areas show each pool’s contribution to total carbon stock over time. Projections assume no major management change, harvest, or natural disturbance; uncertainty increases over time, particularly beyond 20 years.
• Carbon projection table (Figure 5): Provides a numerical breakdown stand age across the 50-year projection, modeled forest carbon stock, carbon change from forest growth, and average annual carbon change at five-year intervals. Projections assume no major management change, harvest, or natural disturbance. Uncertainty increases over time, particularly beyond 20 years.

Figure 4: Basic projection stacked area chart of carbon stocks 

Figure 5: Basic projection results table

5.3.2 Basic Projection with Harvest Outputs (coming soon)

Summary Metrics:

• Total Net Carbon Change Across the 50-Year Projection: Cumulative net carbon flux for the harvest scenario, including forest growth before and after clear-cut harvest, carbon retained in harvest residues and emissions from their decay over 50 years, and carbon storage and emissions from the HWP carbon pool over 100 years after harvest. Negative values indicate carbon sequestration, meaning the net removal of carbon dioxide from the atmosphere and storage in forest biomass. Positive values indicate carbon emissions, meaning the release of carbon from forest biomass to the atmosphere as carbon dioxide.
• Average Annual Carbon Change: Modeled annual changes in forest carbon stocks from forest growth across the 50-year projection. Negative values indicate carbon sequestration, meaning the net removal of carbon dioxide from the atmosphere and storage in forest biomass. Positive values indicate carbon emissions, meaning the release of carbon from forest biomass to the atmosphere as carbon dioxide.
• 50-Year Projected Change in Ecosystem Carbon: Modeled change in forest carbon stock at the end of the 50-year forest projection, including carbon stored in the regrowing stand and carbon remaining in harvest residues. Positive values indicate an increase in stored carbon, while negative values indicate a decrease. The percentage represents the change relative to the initial carbon stock.
• Initial Stock: Modeled forest carbon stock at the start of the 50-year projection. This number represents stored carbon and therefore is always positive. 
• 50-year projection: Modeled carbon stock at the end of the 50-year projection including carbon stored in the regrowing stand and carbon remaining in harvest residues. This number represents stored carbon and therefore is always positive. 

Graphical Outputs: 

• Carbon stock stacked area chart (Figure 6- coming soon): Presents modeled forest carbon stock by carbon pool over 50 years. The stacked areas show each pool’s contribution to total carbon stock over time. Projections assume no major management change, harvest, or natural disturbance; uncertainty increases over time, particularly beyond 20 years.
• Carbon projection table (Figure 7 - coming soon): Provides a numerical breakdown stand age across the 50-year projection, modeled forest carbon stock, carbon change from forest growth, and average annual carbon change at five-year intervals. Projections assume no major management change, harvest, or natural disturbance. Uncertainty increases over time, particularly beyond 20 years.

Figures will be added when available.

5.3.3 Afforestation Outputs

Summary Metrics:

• Total Net Carbon Change Across the 50-Year Projection: The cumulative net carbon change over 50 years. Negative values indicate carbon sequestration, meaning the net removal of carbon dioxide from the atmosphere and storage in forest biomass. Positive values indicate carbon emissions, meaning the release of carbon from forest biomass to the atmosphere as carbon dioxide.
• Average Annual Carbon Change: Modeled annual changes in carbon stocks across the 50-year projection. Negative values indicate carbon sequestration, meaning the net removal of carbon dioxide from the atmosphere and storage in forest biomass. Positive values indicate carbon emissions, meaning the release of carbon from forest biomass to the atmosphere as carbon dioxide.
• 50-Year Projected Ecosystem Carbon: Modeled change in forest carbon stocks across the 50-year projection. Positive values indicate an increase in stored carbon, while negative values indicate a decrease. The percentage represents the change relative to the initial carbon stock.
• Initial Stock: Modeled carbon stock at the start of the 50-year projection. This number represents stored carbon and therefore is always positive. 
• 50-year projection: Modeled carbon stock at the end of the 50-year projection. This number represents stored carbon and therefore is always positive. 

Graphical Outputs: 

• Carbon stock stacked area chart (Figure 8); Presents modeled forest carbon stock by carbon pool over 50 years. The stacked areas show each pool’s contribution to total carbon stock over time. Projections assume no major management change, harvest, or natural disturbance; uncertainty increases over time, particularly beyond 20 years.
• Carbon projection table (Figure 9): Provides a numerical breakdown stand age across the 50-year projection, modeled forest carbon stock, carbon change from forest growth, and average annual carbon change at five-year intervals. Projections assume no major management change, harvest, or natural disturbance. Uncertainty increases over time, particularly beyond 20 years.

Figure 8: Afforestation stacked area chart of carbon stocks 

Figure 9: Afforestation results table

5.3.4 Extended Rotation Outputs (coming soon)

Summary Metrics:

• Net Carbon Change Difference Between Scenarios:  The difference in cumulative net carbon change between the extended-rotation and business-as-usual scenarios. For each scenario, the calculation includes forest growth before and after harvest, carbon retained in harvest residues and emissions from residue decay over 50 years, and carbon storage and emissions from the HWP carbon pool over 100 years after harvest. Negative values indicate that extended rotation results in lower net emissions or greater net sequestration than business as usual. Positive values indicate higher net emissions or less net sequestration. Scenario totals may appear identical because displayed values are rounded.
• • BAU Rotation: Cumulative net carbon change for the business-as-usual harvest rotation length. The calculation includes forest growth before and after harvest, carbon retained in harvest residues and emissions from residue decay over 50 years, and carbon storage and emissions from the HWP carbon pool over 100 years after harvest. 
  • Extended Rotation: Cumulative net carbon change for the extended rotation harvest rotation length. The calculation includes forest growth before and after harvest, carbon retained in harvest residues and emissions from residue decay over 50 years, and carbon storage and emissions from the HWP carbon pool over 100 years after harvest.
• Difference in Total Ecosystem Carbon at Year 50: The difference in total forest carbon stock at year 50, calculated as extended rotation minus business as usual results. It includes carbon stored in the forest stand and harvest residues remaining on site, but excludes the HWP carbon pool . Negative values indicate lower forest carbon under extended rotation, while positive values indicate higher forest carbon. The percentage represents the difference relative to the business-as-usual scenario.
• • BAU Rotation: Modeled carbon stock at the end of the 50-year projection for the business as usual harvest rotation length. This number represents stored carbon and therefore is always positive. 
  • Extended Rotation: Modeled carbon stock at the end of the 50-year projection for the extended rotation harvest rotation length. This number represents stored carbon and therefore is always positive. 
• Difference in HWP carbon pool storage 100-Years Post-Harvest: The difference between scenarios in carbon remaining in the HWP carbon pool 100 years after harvest.  Negative values indicate less carbon storage under extended rotation, while positive values indicate more carbon storage. Scenario values reflect carbon remaining after product use, disposal, and decay.
• • BAU Rotation: Estimated carbon stock remaining in the HWP carbon pool at the end of the 100-year post-harvest projection period for the business as usual harvest rotation length. This number represents stored carbon and therefore is always positive. 
  • Extended Rotation: Estimated carbon stock remaining in the HWP carbon pool at the end of the 100-year post-harvest projection period for the business as usual harvest rotation length. This number represents stored carbon and therefore is always positive. 
• Difference in HWP carbon pool carbon emissions 100-Years Post-Harvest: The difference between scenarios in carbon remissions from the HWP carbon pool 100 years after harvest. 
• • BAU Rotation: Estimated carbon emissions from the HWP carbon pool at the end of the 100-year post-harvest projection period for the business as usual harvest rotation length. This number represents carbon emissions and therefore is always positive. 
  • Extended Rotation: Estimated carbon emissions from the HWP carbon pool at the end of the 100-year post-harvest projection period for the business as usual harvest rotation length. This number represents carbon emissions and therefore is always positive. 

Graphical Outputs: 

• Carbon stock stacked area chart (Figure 10 - coming soon): Presents modeled forest carbon stock by carbon pool over 50 years. The stacked areas show each pool’s contribution to total carbon stock over time.  A toggle allows for the table to switch between the avoided deforestation and the business as usual rotation and extended rotation scenario results. Projections assume no major management change, harvest, or natural disturbance; uncertainty increases over time, particularly beyond 20 years.
• Carbon projection table (Figure 11 - coming soon): Provides a numerical breakdown stand age across the 50-year projection, modeled forest carbon stock, carbon change from forest growth, and average annual carbon change at five-year intervals. A toggle allows for the table to switch between the avoided deforestation and the business as usual rotation and extended rotation scenario results. Projections assume no major management change, harvest, or natural disturbance. Uncertainty increases over time, particularly beyond 20 years.

Figures will be added when available.

5.3.5 Avoided Deforestation Outputs

Summary Metrics:

• Net carbon change difference between scenarios: The difference in cumulative net carbon change between the avoided deforestation and deforestation scenarios, calculated as avoided deforestation minus deforestation. The deforestation scenario assumes that all non-soil forest carbon is emitted and that only soil organic carbon remains stored. Potential carbon storage and emissions from harvested wood products and solid waste disposal sites are not included. The avoided-deforestation scenario reflects continued forest carbon storage and sequestration. Negative values indicate a net carbon benefit from avoided deforestation.
• 50-Year Projected Ecosystem Carbon – Avoided Deforestation: Modeled change in ecosystem carbon stock over 50 years under the avoided-deforestation scenario. This estimate reflects continued forest growth and carbon storage when deforestation does not occur. “Initial stock” is the modeled carbon stock at year 0 of the projection and “+50-year projection stock” is the modeled carbon stock at the end of the projection. 

Positive values indicate an increase in stored carbon, while negative values indicate a decrease. The percentage represents the change relative to the initial carbon stock. HWP carbon pool estimates are not included in this scenario.

• Initial Stock: Modeled carbon stock at the start of the 50-year projection for the avoided deforestation scenario. This number represents stored carbon and therefore is always positive. 
• 50-year projection: Modeled carbon stock at the end of the 50-year projection for the avoided deforestation scenario. This number represents stored carbon and therefore is always positive. 

Graphical Outputs:

• Carbon stock stacked area chart (Figure 12): Presents modeled carbon stock by carbon pool over 50 years for the avoided deforestation scenario. The stacked areas show each pool’s contribution to total carbon stock over time. Projections assume no major management change, harvest, or natural disturbance; uncertainty increases over time, particularly beyond 20 years.
• Carbon stock projection table (Figure 13): Provides a numerical breakdown stand age across the 50-year projection, modeled forest carbon stock, carbon change from forest growth, and average annual carbon change at five-year intervals. A toggle allows for the table to switch between the avoided deforestation and the deforestation (i.e., business as usual) scenario. Projections assume no major management change, harvest, or natural disturbance. Uncertainty increases over time, particularly beyond 20 years.

Figure 12: Avoided deforestation carbon stock stacked area chart

Figure 13: Avoided deforestation carbon stock projection table

5.3.6 Forest Fire Outputs

Summary Metrics:

• Low Severity: Modeled immediate greenhouse gas emissions from forest biomass combustion under a low-severity fire scenario, which assumes less than 20% tree mortality. This scenario may serve as a proxy for prescribed fire. 
• Moderate Severity: Modeled immediate greenhouse gas emissions from forest biomass combustion under moderate-severity fire scenario which assumes 40-60% tree mortality. 
• High Severity: Modeled immediate greenhouse gas emissions from forest biomass combustion under high-severity fire scenario which assumes greater than 90% tree mortality. 

Total emissions are reported as CO_₂e and include carbon dioxide, methane, and nitrous oxide. Post-fire decomposition, regrowth, and other subsequent carbon fluxes are not included. See Section 5.2.3, Wildfire and Prescribed Fire, in Chapter 5, Quantifying Greenhouse Gas Sources and Sinks in Managed Forest Systems, of the USDA guidelines for more information on fire emissions modeling and underlying assumptions.

Graphical outputs:

• Emissions by fire serenity scenario stacked bar chart (Figure 14): Presents modeled immediate greenhouse gas emissions from forest biomass combustion under low-, moderate-, and high-severity fire scenarios. Each bar shows the contribution to total emissions by gas, including carbon dioxide, methane, and nitrous oxide, reported as CO_₂e. Post-fire decomposition, regrowth, and other subsequent carbon fluxes are not included.
• Emissions from immediate combustion of forest biomass by fire severity scenario table (Figure 15): Presents modeled immediate emissions of carbon dioxide, methane, and nitrous oxide from forest biomass combustion under each fire-severity scenario. Total emissions are reported as CO_₂e. Post-fire decomposition, regrowth, and other subsequent carbon fluxes are not included.

Figure 14: Stacked bar chart of emissions by fire severity scenario and the relative contribution of each greenhouse gas 

Figure 15: Emissions from immediate combustion of forest biomass by fire severity scenario

5.4 Summary report 

Summary-level information is also provided to the user in reports/tables that can be generated and saved via the user interface.

6.1 Forest Carbon Stocks

Extensive compilation and analysis of FIA data was conducted to build sets of equations and lookup tables that provide the carbon stock estimates used in FACT’s Custom Forest Carbon Inventory Tool and the Default Tool.  Data were retrieved from the FIA database using the FIA EVALIDator tool (USDA 2026) through its application programming interface (API). Queries were conducted using the two most recent non-overlapping FIA evaluation groups available for each state or region to maximize temporal coverage while avoiding duplicate plot measurements across evaluation periods. Analyses were limited to FIA plots classified as unreserved forest land, representing forest land generally available for management and timber production activities. 

EVALIDator outputs were extracted at the plot level, including grouping-variable attributes and the associated estimate of interest (e.g., aboveground live tree carbon) for each plot. For stand-age modeling, plot-level results were matched with recorded stand ages for individual FIA plots rather than the broader stand-age classes available directly through EVALIDator. The resulting datasets were then used to develop stand-level and tree-level models.

Stand-level estimates were developed for carbon density (t CO₂e acre⁻¹) across all modeled carbon pools as a function of stand age. Models were stratified according to the grouping variables used to match user-supplied forest conditions to comparable FIA plots, including FIA region, broad forest type group, FIA forest type group, and stand origin (natural or artificial regeneration). In theory, the combination of 11 FIA regions, 32 FIA forest type groups, and two stand-origin classes yields up to 704 unique model combinations; however, model development was constrained by data availability, and some combinations were not represented in the FIA dataset. For each valid grouping combination, carbon density by stand age was modeled using the Hugershoff growth function (Prodan 1968), expressed as:

For stand-level modeling of carbon density by age, the Hugershoff model (Prodan 1968) was used:

y = y₀x^be^-kx

where y is the carbon density, y₀, b, and k are coefficients, and x is the stand age. 

After all modeling was conducted, tables were prepared for each modeling step with all of the relevant grouping variables and the three modeling coefficients (y₀, b, and k for Hugershoff models; y₀, k, and c for negative exponential models). These tables of model coefficients, combined with the tables developed without modeling, represent the synthesized information that allows the Default Tool and Custom Forest Carbon Inventory Tool to perform all of the necessary calculations to develop carbon stock estimates from user inventory data at the stand level. These tables are available in the Custom Forest Carbon Inventory Tool User Documentation Tables file.  

For more detailed information, see the Custom Forest Carbon Inventory Tool User Methodology. 

6.2 Growing Stock Volume Carbon Ratios

FIA-based lookup tables and statistical models were developed to estimate forest carbon stocks and harvest-related metrics across a range of forest conditions in CONUS. Building on the framework described for developing modeling coefficients that described relationships between stand-age and carbon density to stand age for across forest carbon pools, additional analyses were conducted to support the Default Tool to support modeling of harvest-oriented forest management scenarios where users do not possess stand-level forest inventory or merchantable volume data. 

Domain-specific growing stock volume-carbon (GSVC) ratios were developed expressing the relationship between growing-stock volume and live aboveground carbon. Growing-stock volume was defined according to FIA standards as net merchantable bole volume of live growing-stock trees (TREECLCD = 2) at least 5 inches d.b.h. on unreserved forest land. Ratios were developed using weighted FIA estimates and stratified according to region, forest type group, stand origin, and stand-age class, subject to data availability and statistical reasonableness constraints. Where sample sizes were insufficient to support fully stratified estimates, a hierarchical aggregation approach was applied consistent with existing Platform procedures to derive more generalized fallback estimates. These resulting GSVC lookup tables support estimation of merchantable growing-stock volume from modeled live aboveground carbon estimates within the Default Tool, thereby improving consistency between modeled forest carbon stocks and downstream HWP calculations.

The GSVC ratios are provided in the accompanying “Growing Stock Volume-to-Carbon Ratios” Excel document.

6.3  Fire Lookup Tables

To offer estimates of potential emissions from fire scenarios (naturally occurring and prescribed), a lookup table containing emission factors by region, forest type group, and fire-severity class has been prepared and is included in Annex III of this document.

The emission factors applied in the Default Tool are the same as those developed for quantifying immediate emissions from fire in forests under the “Level 1” approach documented within the 2024 Entity Guidelines (Murray et al. 2024). Users are directed to Section 5.2.3, Wildfire and Prescribed Fire, of that report for additional information regarding the derivation of the underlying emission factors.

The original emission factors were reported in units of megagrams per hectare (Mg CO₂e ha⁻¹). For compatibility with the Default Tool and other estimates reported throughout this methodology, emission factors were converted to metric tons per acre (t CO₂e ac⁻¹) using the standard hectare-to-acre conversion factor (1 ha = 2.471 acres).

7.1 Carbon Inventory

The Default Tool produces carbon estimates in metric tons of carbon dioxide equivalent (t CO₂e) for the current inventory year as well as an estimated annual changes in carbon stocks over the preceding 5 years. Positive changes in forest carbon stocks indicate a CO₂ emission (i.e., release of biomass carbon to the atmosphere), whereas negative numbers represent a removal of CO₂ from the atmosphere.

7.1.1 Source appropriate estimates of carbon stocks for the current inventory year and five years prior to the current inventory year. 

Based on user inputs for region (r), forest type (t), stand origin (p), and current stand age (a), t CO₂e per acre estimates are sourced by referencing the appropriate growth models (see section 6.1).  This data retrieval renders estimates carbon stocks across all carbon pools. 

7.1.2 Compute forest carbon stocks for the stand 

To generate estimates of total carbon stocks in the stand, per acre estimates must be extrapolated to match the user-defined stand area by multiplying the stand-level carbon by the user-supplied area, as described in the following equation: 

Where:

C_r,t,p,a = Total stand-level C stocks for corresponding user-selected region (r), forest type (t), stand origin (p), and age (a) (t CO₂e)

CD_r,t,p,a= Carbon density (t CO₂e acre⁻¹) for corresponding user-selected region (r), forest type (t), stand origin (p), and age (a). 

A = Area (acres). Where users entered data into the “area” user entry field as hectares, convert hectares to acres by multiplying the area by 2.471.

7.1.3 Estimate Changes in Carbon Stocks over 5 years 

The difference in Total Inventory Carbon Stocks between the user-defined stand age and the preceding five-year timestep is calculated to determine total carbon change over that period. This value is then divided by five to produce an estimate of the average annual change in carbon stocks for the timestep, as shown in Equation DFCT-2 below. 

7.2 Forest Management Scenario Projections

These scenarios offer a first-order estimate of projected forest carbon stocks at 5-year timesteps, up to 50 years into the future, for the user-selected combination of U.S. region, forest type, age class, stand origin, and rotation length (where applicable). 

7.2.1 Basic projection 

This projection offers an estimate of the carbon stocks and changes in carbon stocks from the forest stand up to 50 years into the future, quantified and reported as total carbon change in living and dead carbon pools (t CO₂e) over that period.  This projection essentially follows the same steps as documented in section 7.1 section of this document but repeats the calculation at 5-year timesteps across the 50-year projection.  

Projection timesteps are indexed as:

i = 0, 1, …, 10

where i denotes the current inventory year and each subsequent five-year interval across the 50-year projection period.

Stand age is denoted a throughout, with a subscript identifying the timestep at which it is evaluated. Stand age at each timestep is calculated as:

aᵢ = a_₀ + 5i

where a_₀ is the user-defined stand age in the current inventory year and aᵢ is the stand age at timestep i. Carbon stocks are estimated at each aᵢ using the growth models described in Section 7.1.1.

7.2.1.1 Calculate total change in carbon stocks over the projection period

Total changes in carbon stocks across the 50-year projection is calculated as the difference between carbon stocks at the start year of the projection and those at the end of the projection, as described in the equation below: 

7.2.1.2 Calculate average annual change in carbon stocks over the projection period

The average annual change in carbon stocks across the 50-year projection is calculated as described in the equation below: 

Basic Projection - Final Results Summarization

7.2.2 Basic projection with harvest (coming soon)

This projection estimates the carbon stocks and sequestration up to a user-specified planned harvest time and then re-grows the forest post-harvest. Projected forest carbon changes from growth, bark emissions, and harvest residues are combined with estimates carbon storage and emissions from harvest to offer total forest biogenic (AFOLU sector) carbon stock change (t CO₂e). 

The current modeling framework assumes stand-replacing harvest conditions (i.e., clearcut) for purposes of post-harvest carbon accounting. This simplifying assumption was incorporated to support generalized scenario modeling while avoiding the additional complexity and uncertainty associated with modeling residual stand structure and carbon dynamics under partial harvest systems (See Box 2).

Under this framework, biomass estimated to become delivered forest products is routed to the FACT Harvested Wood Products Carbon Tool, carbon contained within the bark is emitted immediately following harvest, while remaining non-soil, non-bark biomass is assigned to a post-harvest logging residue pool. This may include tops and limbs, non-merchantable material, unutilized biomass, harvest losses, and other organic material remaining onsite following harvest activity.

Carbon associated with harvest residues is modeled over time using literature-informed decay assumptions, including decay rates adopted from the Forest and Agricultural Sector Optimization Model with Greenhouse Gases (FASOM-GHG; Beach et al. 2010), to represent gradual decomposition and associated emissions following harvest. For purposes of generalized scenario modeling, a common decay framework is applied across post-harvest residue pools despite likely differences in decay dynamics among biomass components. 

Because post-harvest residue dynamics vary substantially based on harvest practices, utilization rates, site conditions, slash treatment, disturbance, and decomposition environment, modeled residue trajectories should be interpreted as generalized representations rather than stand-specific forecasts of post-harvest carbon behavior.

7.2.2.1 Calculate Projected Forest Carbon Changes-Pre-Harvest

The calculation procedures for this step are the same as described in section 7.2.2 Basic Projection of this document, except the projection end time (i.e., the value for “x” in Equation DFCT-3) is modified to reflect the user-specified harvest year. 

7.2.2.2 Calculate Projected Forest Carbon Changes-Post-Harvest

Once harvest occurs, carbon changes associated with post-harvest regrowth are estimated. Regrowth is projected through the remainder of the 50-year period using Equation DFCT-3, with the following modifications:

• Stand age resets at harvest. C_{r,t,p,a₀} reflects the carbon stocks of nonstocked stands for the selected region, representing a stand regenerating on land that remains forest land.
• Following establishment, C_{r,t,p,a₁…aₙ} reflects the selected region, forest type group, and stand origin, with stand age accumulating from zero (aᵢ = 5i).
• Regrowth is projected to the end of the 50-year period. Harvest years are restricted to 5-year increments, with the earliest allowable harvest at year 5. The number of post-harvest regrowth timesteps is n = 10 − h/5, where h is the harvest year. For example, a harvest in year 10 leaves 40 years of regrowth, so n = 8.

7.2.2.3 Calculate Wood Harvested

The Default Tool offers two options for estimating the carbon storage and emissions associated with HWP under the Basic Projection with Harvest forest management scenario.  User selection between the two options is based on whether the user knows the amount of wood harvested.

Option 1: Where harvest amounts are known: The user enters the estimates of harvest amounts into the Default Tool interface. These values represent the amount of merchantable wood harvested that will be transported to the mill for processing. FACT follows the IPCC production approach to estimate carbon storage and emissions associated with HWP, including the portion of discarded products deposited in solid waste disposal sites.  This approach relies on underbark wood harvest estimates, meaning the quantity of wood excluding bark. Therefore all harvest amount inputs must be entered on an underbark basis, and where only an overbark estimate of harvest is available, users must reduce the volumes or weights to only reflect underbark values. Link to guidance when available.

The harvest amounts (weights or volumes) are then converted to t CO₂e following procedures documented in the FACT Unit Conversion Methodology.  This estimate is then compared to the total carbon stocks within the live aboveground biomass pool for the user-selected region, forest type, stand origin and age. This procedure is necessary due to potential for harvest amounts to exceed what the Default Tool’s carbon model predicts is available for harvest on the stand. 

A 70 percent threshold was adopted as a conservative screening criterion for evaluating the reasonableness of reported harvest quantities relative to modeled live aboveground biomass in the Default Tool. The threshold is informed by the expected allocation of aboveground tree biomass between merchantable and nonmerchantable components, including tops, limbs, bark, and foliage. While this value does not represent a fixed biological limit or an IPCC default value, it was introduced to identify cases in which reported harvest quantities may be inconsistent with the regional-average biomass conditions represented by the model. Where the estimated carbon (t CO₂e) contained within the harvest amount exceeds 70 percent of the stand’s total live aboveground carbon pool, it is assumed that the Default Tool’s underlying carbon model outputs cannot reliably predict the carbon stocks on the forest stand and the Default Tool produces an error message as follows: 

"The harvest amount you entered converts to more than 70% of the modeled aboveground live carbon on your stand. This may indicate that your stand is more productive than the regional averages applied by the Default Tool carbon model, or that harvest amount, units, or stand characteristics should be reviewed. Because the modeled carbon stock may not reliably represent conditions on this stand, please verify the information entered and try again. If you wish to evaluate just the carbon stored in your wood products, navigate to the Harvested Wood Product Carbon Tool.”

Where this threshold is not met, estimates of harvest t CO₂e and applied to equations documented in Step 8: Calculate emissions from harvest residues section below to estimate harvest residue pool emissions.

Tool outputs, converted from the entered amounts into units of CCF (hundred cubic feet) following procedures documented in The FACT Unit Conversion Methodology are then sent to the FACT Harvested Wood Product Carbon Tool which will return estimates for: 

• Total wood carbon (t CO₂e) remaining in the HWP and SWD pool, across the post-harvest projection. See documentation contained within the Harvested Wood Product Carbon Tool User Methodology (coming December 2026) for details on how those estimates are produced.
• HWP emissions (with energy capture and without energy capture). See documentation contained within the Harvested Wood Product Carbon Tool User Methodology (coming December 2026) for details on how those estimates are produced.

Option 2: Where harvest volumes/mass are not known: This option applies FIA-derived default estimates of growing-stock volume to estimate the portion of the live tree carbon pool represented by merchantable growing-stock trees and therefore potentially available for harvest.

Figure 16: Illustrative process flow diagram for methodological procedures for the Default Forest Carbon Tool where harvest amounts are not known. Box sizes are illustrative; actual proportions vary by region and forest type group.

The following steps capture how the amount of harvest is calculated (CCF) using Option 2, which are then ported into the Harvested Wood Carbon Tool for deriving a final estimate of carbon stored in harvested wood products over a 100-year post-harvest timeline in t CO₂e.  Figure 16 provides a process flow diagram and Figure 17 provides a methodological decision tree that illustrates the steps that send the estimated CCF removed at harvest to the Harvested Wood Product Carbon Tool. 

Step 1: Source growing stock volume estimate (CCF/acre)

Lookup tables for deriving the growing stock volume estimates are provided within the accompanying “Growing Stock Volume-to-Carbon Ratios” Excel document. The tab “stdageclass5yr_main” provides GSVC ratio to modeled live aboveground carbon estimates, grouped by 5-year stand-age class intervals.  This ratio represents the relationship between merchantable growing-stock volume and live aboveground carbon and is expressed as cubic feet per short ton C (ft³ short ton C⁻¹).  Specifically, the numerator reflects net merchantable bole wood volume of growing-stock trees (≥5 inches d.b.h. “FIA class 2” trees) on forest land, measured in cubic feet, while the denominator reflects FIA forest carbon pool 1 (live aboveground carbon) expressed in short tons C per acre.

Figure 17: Methodological decision tree for the Default Forest Carbon Tool where harvest amounts are not known

Because the GSVC ratio is defined relative to the FIA live aboveground carbon pool, live aboveground carbon estimates are first calculated separately using the applicable model coefficients (see Custom Forest Inventory Tool documentation). The resulting live aboveground carbon estimates (t C acre⁻¹) are then converted to short tons C acre⁻¹ to align with the denominator units of the GSVC ratio (ft³ short ton C⁻¹). The converted carbon estimates are then multiplied by the GSVC ratio to estimate growing stock volume in cubic feet acre⁻¹ and subsequently divided by 100 to convert estimates to hundred cubic feet per acre (CCF acre⁻¹), as expressed in the formula below:

If no matching record is found in the “stdageclass5yr_main” table, alternate values from the “GSVC stdageclass5yr_exceptions” table are used as a fallback. These fallback values represent generalized GSVC estimates aggregated across forest types, stand origins, and age classes. In contrast to the primary lookup table, the exception table does not stratify GSVC estimates by region and instead provides region-agnostic average values.

Step 2: Partition the growing stock into wood types

Based on the user data entry, users will either select “hardwood”, “softwood”, or “unknown” as their wood type. Where users know the wood type (i.e., “hardwood” or “softwood” are selected), there is no need to partition into wood types and this step can be skipped because only the CCF for that selected wood type will be estimated. 

Where users select “hardwood” or “softwood” the value WT_f in the Equation DFCT-6 below is therefore “1”.

Where users do not know the wood type (i.e., “unknown” is selected), refer to Smith et al. Table 4 (Table 5 in Annex II, column highlighted in blue) to select the appropriate fraction of GSV that is softwood that matches the user-selected region and forest type group. The remaining fraction (i.e., 1 minus softwood fraction) is assumed to be hardwood. 

Step 3: Assign fraction of growing stock volume that is sawtimber size for hardwood and softwood harvested 

Based on the user data entry, users will either select “sawlogs”, “pulpwood”, “fuelwood”, or “unknown” as their log type. 

Where users select "sawlogs" or "pulpwood," there is no need to partition into log types and this step can be skipped, because only the CCF for that selected log type will be estimated. The value LTfrac in Equation DFCT-6 is therefore "1." Where users select "fuelwood," Equation DFCT-8 applies and no log type fraction is used.

Where users do not know the log type, refer to Smith et al. Table 4 (Table 5 in Annex II, column highlighted in blue, columns highlighted in orange) to select the appropriate fraction of wood that is sawtimber size for the hardwood and softwood categories that matches the user-selected region and forest type group. 

Step 4: Determine the amount of growing stock volume that is removed as roundwood by log type based on region, for each of the wood and log types identified 

Referring to Smith et al. Table 5 (Table 6 in Annex II), apply the ratio of total roundwood to the growing stock volume removed as roundwood, for the selected wood and log types matching the user-selected region and forest type group. Values exceed 1 where roundwood is also drawn from non-growing-stock sources such as tops, limbs, and cull trees.

Step 5: Determine the amount of growing stock roundwood by log type that is removed (this step discounts logging residue, breakage etc.)

Referring to Smith et al. Table 5 (Table 6 in Annex II), apply the fraction of growing stock volume removed as roundwood (the share not left on site as logging residue) for the selected wood and log types matching the user-selected region and forest type group. Steps 4 and 5 are multiplicative; together they convert growing stock volume to total roundwood volume. 

Step 6: Calculate the final harvest amount to send to the Harvested Wood Product Calculator

The final calculations for the pulpwood and sawlogs log types are the same (DFCT-6) and differ from the final calculations for fuelwood (DFCT-7 and DFCT-8).  The final estimate of wood volume to send to the Harvested Wood Product Calculator is calculated by applying Eq. DFCT-9 which is the sum of the relevant results from DFCT-6, DFCT-7, and/or DFCT-8. Table 3 below provides a guide for which equations to apply based on the user data entry wood type and log type options: 

Where the user does not know the wood type or log type, the formula is applied separately for each category in the unspecified dimension (i.e., softwood and hardwood, sawlogs and pulpwood, or both) and the results are summed in Equation DFCT-9.

Note: Where the user selects fuelwood as the log type, see Equation DFCT-8. Where the user does not select fuelwood but opts to generate default fuelwood values as a byproduct of harvest, see Equation DFCT-7.

Where the user does not know the wood type or log type, the formula is applied separately for each category in the unspecified dimension — softwood and hardwood, sawlog and pulpwood, or both — and the results are summed.

Where the user selects fuelwood as the log type, all growing stock volume removed as roundwood is allocated to fuelwood. No log type apportionment is applied, so neither LTfrac nor the fuelwood ratio enters this equation — the fuelwood ratio applies only where fuelwood is generated as a byproduct of a sawlog or pulpwood harvest (see Equation DFCT-7).

Where the user does not know the wood type, the formula is applied separately for softwood and hardwood, and the results are summed.

Where the user selects fuelwood as the log type, all growing stock volume removed as roundwood is allocated to fuelwood. No log type apportionment is applied, so neither LTfrac nor the fuelwood ratio enters this equation — the fuelwood ratio applies only where fuelwood is generated as a byproduct of a sawlog or pulpwood harvest (see Equation DFCT-7).

Where the user does not know the wood type, the formula is applied separately for softwood and hardwood, and the results are summed.

Step 7: Convert final harvest amount from volume (CCF) to t CO₂e

Refer to procedures documented in the FACT Unit Conversion Methodology.  

Output: HWP_tot  (t CO₂e)

Step 8: Calculate emissions from harvest residues 

To estimate carbon in harvest residues which reflects the biomass left on site (i.e., coarse root biomass, stumps, branches, leaves), it is necessary to estimate the amount of harvest residue first and then apply harvest residue/coarse woody debris decay rates to determine the emissions from the harvest residues over time. 

Step 8.a Estimate harvest residues

Harvest residues are estimated by first estimating the harvest residue immediately post-harvest and then applying a decay factor. This is because harvest residues do not decay as a fixed amount each year and decomposition occurs at a rate that is proportional to the amount of material remaining. 

The initial post-harvest residue is estimated by subtracting the wood volume removed from harvest in t CO₂e (Step 7 above) from the original carbon stocks at the harvested site (not including soil carbon stocks), as described in Equation DFCT-10.  While residues generated by harvest would typically be treated as additions to the deadwood and litter pools, for accounting completeness and transparency, they are tracked as a separate post-harvest decay pool in the Default Tool.

Harvest is assumed to be stand-replacing. All carbon not removed as harvested wood products or bark is treated as residue remaining on site.

After the harvest year, the onsite residue pool decays each year by the annual decay rate (DR), provided in Table 4 below. 

The remaining residue carbon stock at each 5-year point is estimated by applying continuous exponential decay over the number of years since harvest.

Step 8.b Estimate post-harvest emissions from bark and harvest residues

Emissions during each 5-year timestep are equal to the decrease in the remaining residue stock over that timestep, though the first five-year timestep also includes bark emissions. Equation DFCT-12 described below describes the quantification procedure. 

Basic Projection with Harvest - Final Results Summarization

7.2.3 Extended rotation (coming soon)

This projection estimates the carbon benefit from deferring harvest in even-aged stands, including estimates of carbon change from harvest, to estimate total biogenic carbon stock change (t CO₂eq). The results reflect the difference between projected carbon stocks under the business-as-usual (BAU) planned harvest date and the extended rotation harvest date. Thus the calculation procedures for this scenario are the same as the "Basic projection with harvest" scenario as described in Section 7.2.2. above, except the calculation is performed twice, reflecting two harvest dates. The analysis does not allow for custom harvest user data inputs and rather only relies on default values on growing stock volumes to estimate postharvest carbon change.

Extended Rotation - Final Results Summarization

Business-as-usual (BAU) planned harvest date

Extended rotation planned harvest date

7.2.4 Afforestation 

Two afforestation options are offered: (1) natural; and (2) planted. Results show the projected total amount of carbon sequestered over 50 years. 

The methodological procedures for this scenario are the same as those included under Section 7.2.1 from the “Basic projection” scenario described above, except: 

• Cr,t,p,a₀will reflect the stand carbon stocks for carbon stocks at age 0 of the model, which only reflects soil carbon stocks. This assumes the stand is just established at year 0, and the selection of the model outputs is based on the user-selected region, forest type, and stand origin (stand origin is automatically determined based on user inputs. 

Afforestation - Final Results Summarization

7.2.5 Avoided Deforestation 

For this forest management projection, the Default Tool compares the difference in cumulative net change in carbon stocks between the avoided deforestation and deforestation scenarios. The deforestation scenario assumes that all non-soil forest carbon is emitted and that only soil organic carbon remains stored. Potential carbon storage and emissions from harvested wood products and solid waste disposal sites are not included. The avoided-deforestation scenario reflects continued forest carbon storage and sequestration. The avoided deforestation scenario reflects the ecosystem carbon that remains stored by avoiding deforestation, as well as projected change in carbon stocks (i.e., carbon accumulation) over 50 years into the future. 

The methodological procedures for this scenario are the same as those included under Section 7.2.1 from the “Basic projection” scenario described above, except: 

Avoided Deforestation - Final Results Summarization

Deforestation

Avoided Deforestation

7.2.6 Forest Fire (prescribed or natural) 

Under this scenario, greenhouse gas emissions are quantified for three fire-severity classes, defined based on tree mortality (see Figure 18). Estimates reflect immediate emissions from combustion of forest biomass, including carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). The estimates do not include longer-term post-fire carbon fluxes, such as changes in forest regeneration, decomposition, or subsequent carbon accumulation following the fire event. Users are directed to refer to section 5.2.3 Wildfire and Prescribed Fire within the 2024 Entity Guidelines (Murray et al. 2024) for more information on how these emission factors were devised.

Figure 18: Diagram of the Three Fire Severity Levels (Source: USDA Entity Guidelines, Quantifying greenhouse gas fluxes in agriculture and forestry: Methods for entity-scale inventory, Technical Bulletin 1939, 2nd ed., Chapter 5, Figure 5-6.

The per-acre emissions magnitude for carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) by fire severity scenario (high, moderate, low) have been pre-calculated and converted into metric tonnes of carbon dioxide equivalents (t CO2e) for each forest type group and region.  This scenario projection only uses forest type and region user data entries to estimate immediate emissions from the combustion of forest biomass, so no future projection is included. Therefore, the calculation procedures for this scenario are relatively straightforward, as described in equation DFCT-13 below. 

The low-severity fire scenario may be interpreted as a general proxy for prescribed burning.  

Forest Fire - Final Results Summarization

Emission estimates for certain combinations of region, forest type, and fire severity scenario may be unavailable. This occurs where available data are insufficient to support a reliable emission factor, either because this severity class is uncommon for the forest type’s typical fire regime or because the region and forest type combination is not well represented in the underlying data.

Because fire severity classes are based on simulated tree mortality rather than on the total amount of biomass consumed, fire emissions outputs do not always increase with the modeled severity class. For example, the “high severity” class describes the effect of the fire on the trees, assuming greater than 90% tree mortality. A high-severity fire can kill most trees through intense heat and crown scorch while leaving much of the litter, duff, and downed wood only partially consumed. Conversely, a moderate-severity fire, defined based on a tree mortality rate between 40-60 percent, may kill fewer trees but burn slowly through dry surface fuels, consuming a larger share of litter, duff, and woody debris. 

• Murray, L.T., C. Woodall, A. Lister, K. Stockmann, H. Gu, S. Urbanski, K. Riley, E. Greenfield, et al. 2024. Chapter 5: Quantifying greenhouse gas sources and sinks in managed forest systems. In Hanson, W.L., C. Itle, K. Edquist. (eds.). Quantifying greenhouse gas fluxes in agriculture and forestry: Methods for entity‐scale inventory. Technical Bulletin Number 1939, 2nd edition. Washington, DC: U.S. Department of Agriculture, Office of the Chief Economist. Available at: https://www.usda.gov/oce/entity-scale-ghg-methods/chapter-5
• Prodan, M. 1968. Forest Biometrics. Pergamon Press, Ltd.
• Smith, J.E., Heath, L.S., Skog, K.E., and Birdsey, R.A. 2006. Methods for calculating forest ecosystem and harvested carbon with standard estimates for forest types of the United States. General Technical Report NE-343. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northeastern Research Station. 216 p
• USDA Forest Service, Forest Inventory and Analysis Program, Tue, 07 Apr 2026 13:28:19 GMT. Forest Inventory EVALIDator web-application Version 2.1.2. St. Paul, MN: U.S. Department of Agriculture, Forest Service, Northern Research Station. [Available only on internet: https://apps.fs.usda.gov/fiadb-api/evalidator]

Terms specific to this methodology are defined below. See the main FACT Glossary for general terms and for the sources from which definitions are adapted.  

Aboveground live carbon pool: Carbon in the aboveground portions of live trees and understory vegetation, corresponding to IPCC forest carbon pool 1. The tree component covers live trees at least 1 inch d.b.h., excluding foliage, for both timber and woodland species, and is derived from field measurements through allometric models. (Adapted from FIA EVALIDator and FIADB Database Description)

Annualized Carbon Stock Change: The average annual net change in the mass of carbon within a defined carbon pool over a specified time period. It is calculated by dividing the total carbon stock change by the number of years across that period  and is expressed in metric tons of carbon dioxide equivalents per year (t CO₂e/yr^-1).  

BAU (Business as usual): A scenario in which current management continues unchanged, used as a point of comparison against scenarios involving a change in practice. 

Belowground live carbon pool: Carbon in the belowground portions of live trees and understory vegetation, corresponding to IPCC forest carbon pool 2. The tree component covers the coarse roots of live trees at least 1 inch d.b.h. for both timber and woodland species, and is derived from field measurements through allometric models. (Adapted from FIA EVALIDator and FIADB Database Description)

Biomass: The mass of organic material in trees, including stems, bark and branches, typically expressed as oven-dry or green weight. Biomass may refer to live or dead components and can be converted to carbon using standard conversion factors.

Carbon (C): The mass of carbon contained within a defined pool (e.g., biomass, dead organic matter or harvested wood products), typically expressed in units of mass (e.g., metric tons of carbon, t C) and derived from biomass using established conversion factors.

Carbon density: The amount of carbon stored per unit of land area, typically expressed as mass per area. 

Carbon dioxide equivalents (CO₂e ): A common unit that allows the climate effects of different greenhouse gases to be compared and summed. The quantity of a greenhouse gas is multiplied by its global warming potential (GWP), which expresses its warming effect timbrelative to carbon dioxide over a specified time horizon, conventionally 100 years. The result is reported as the mass of CO₂e that would produce an equivalent climate effect. (Adapted from ISO 14067)

Carbon Pools: Discrete, mutually exclusive reservoirs in which carbon is stored, defined so that stocks can be summed without double counting and transfers between pools can be tracked. FACT follows the five ecosystem pools used in IPCC greenhouse gas reporting and implemented by FIA: aboveground live, belowground live, dead wood, litter and soil organic carbon.

Where applicable, carbon removed from the forest at harvest is accounted for separately in the harvested wood products pool, which tracks carbon stored in products in use and in solid waste disposal sites subpools, along with emissions released as those products are burned or decay over time in two subpools, emitted with energy capture and emitted without energy capture.

Carbon stock: The total mass of carbon contained within a defined pool, expressed as t CO_₂e in FACT. Stocks are always reported as positive values because they represent carbon held in a pool, not movement of carbon to or from the atmosphere. 

Change in carbon stocks: The estimated net change in carbon stored within the defined system over a specified period, expressed as t CO₂e. Values are reported from the atmosphere's perspective: negative when carbon moves from the atmosphere into forest or harvested wood product pools (sequestration), positive when it moves from those pools into the atmosphere (emission). 

Conterminous United States (CONUS): The 48 states within the contiguous United States, excluding Alaska and Hawaii. 

Cull/Cull tree: Live trees that do not meet growing stock specifications, classified by FIA as either rough trees (those lacking a saw log primarily because of poor form, splits or cracks, along with all trees of noncommercial species) or rotten trees (those lacking a saw log primarily because of rot). Cull trees are excluded from growing stock volume. (Adapted from the FIA Glossary and the FIADB Database Description and User Guide)

Dead wood carbon pool: Carbon in standing and downed dead woody material, corresponding to IPCC forest carbon pool 3. Standing dead comprises standing dead trees and their coarse roots; down dead comprises woody material greater than 3 inches in diameter lying on the ground, together with stumps and their roots. (Adapted from FIA EVALIDator and FIADB Database Description)

Diameter at breast height (d.b.h.): The diameter of a tree stem, outside bark, measured at 4.5 feet above the ground on the uphill side of the tree. For multi-stemmed woodland species, diameter is instead measured at the root collar (d.r.c.). Diameter at breast height is the primary field measurement from which tree volume, biomass, and carbon are estimated.

Emissions: The total mass of greenhouse gases released to the atmosphere over a specified period. Emissions may occur immediately or over time. For example, a wildfire may cause immediate emissions through combustion of live and dead fuels, followed by additional emissions as fire-killed biomass decomposes. 

Emissions with energy capture: An harvested wood product (HWP) emissions component representing Carbon released to the atmosphere through combustion in which the energy produced is recovered and used. This category includes fuelwood and may also include wood residues or discarded products burned for useful energy.

Emissions without energy capture: An harvested wood product (HWP) emissions component representing carbon released to the atmosphere without useful recovery of the energy contained in the wood. This includes wood burned without energy recovery and carbon released through other product-related losses or decay rather than remaining stored in products in use or solid waste disposal sites.

EVALIDator: A USDA Forest Service Forest Inventory and Analysis (FIA) web application (https://apps.fs.usda.gov/fiadb-api) that allows users to generate population-level estimates and associated sampling errors from the Forest Inventory and Analysis Database (FIADB). Users can select geographic areas, forest attributes, ownerships, forest types, and other parameters to estimate metrics such as forest area, tree volume, biomass, growth, removals, and mortality.

Forest Inventory and Analysis Program (FIA): A national program of the U.S. Forest Service that conducts continuous, standardized inventories of forest resources across the United States and provides authoritative information on forest extent, composition, structure, growth, removals, and mortality. FIA conducts a variety of inventories, surveys, and reporting activities, including the Nationwide Forest Inventory (NFI), National Resource Use Monitoring (NRUM), National Woodland Owner Survey (NWOS), and Urban Forest Inventory and Analysis (Urban FIA).   

Forest Inventory and Analysis Database (FIADB): The publicly available database maintained by the U.S. Forest Service that stores and distributes data collected through FIA, including plot- and tree-level measurements, population estimates and derived forest metrics.

Forest land: FACT applies the so-called “FIA” definition of forest: Forest land has at least 10 percent canopy cover of trees of any size or has had at least 10-percent canopy cover of trees in the past, based on the presence of stumps, snags, or other evidence, and that will be naturally or artificially regenerated. Additionally, the land is not subject to nonforest use(s) that prevent normal tree regeneration and succession, such as regular mowing, intensive grazing or recreation activities. Forest land includes transition zones, such as areas between heavily forested and nonforested lands that are at least 10 percent canopy cover with trees and forest areas adjacent to urban and built-up lands. Also included are pinyon-juniper and other western hardwood areas and afforested areas. The minimum area for classification of forest land is 1 acre (0.4 ha) in size and 120 feet (36.6 m) wide measured stem-to-stem from the outermost edge. Unimproved roads and trails, streams and clearings in forest areas are classified as forest if less than 120 feet wide. For more information, see Forest Definitions Applied in Reporting.

FACT adopts “unreserved forest” as the domain of interest. See Unreserved forest glossary term.  

Forest type: A classification of forest land based upon and named for the tree species that forms the plurality of live-tree stocking. A forest-type classification for a field location indicates the predominant live-tree species cover for the field location; hardwoods and softwoods are first grouped to determine predominant group, and forest type is selected from the predominant group. (Adapted from FIA Glossary: Standard Terminology)

Forest Type Group: A classification used by FIA that aggregates individual forest types into broader categories based on dominant tree species and ecological similarity, enabling consistent summarization and reporting of forest attributes across regions. See Forest Type Group metadata: https://data.fs.usda.gov/geodata/rastergateway/forest_type. (Adapted from FIA Glossary: Standard Terminology) 

Fuelwood: Roundwood harvested for use as an energy source, such as heat, steam or electricity. This category does not include residues or coproducts generated during the processing of sawlogs or pulpwood and subsequently used as fuel; those materials are accounted for as mill coproducts. Fuelwood is classified separately from industrial roundwood.

Greenhouse gases (GHGs): A gaseous constituent of the atmosphere, both natural and anthropogenic, that absorbs and emits radiation at specific wavelengths within the spectrum of infrared radiation emitted by the Earth's surface, the atmosphere, and clouds, thereby trapping heat in the atmosphere. The greenhouse gases relevant to forest management are carbon dioxide (CO_₂), methane (CH_₄) and nitrous oxide (N_₂O). (Adapted from ISO 14050:2020, 3.9.1) 

Growing-stock tree: All live trees of commercial species 5.0 inches d.b.h. and larger that meet minimum merchantability standards. In general, these trees have at least one solid 8-foot section, are reasonably free of form defects on the merchantable bole and at least 34 percent or more of the volume is merchantable. Excludes rough and rotten cull trees. (Adapted from the FIA Glossary: Standard Terminology) 

Growing stock removals/harvest removals: The growing stock volume removed from poletimber and sawtimber trees. Includes volume removed for roundwood products, logging residues and other removals. (Adapted from FIA Glossary: Standard Terminology) 

Growing stock volume (GSV): The cubic-foot volume of sound wood in growing stock trees with 5.0 inches d.b.h. or larger, measured from a 1-foot stump to a minimum 4.0-inch top diameter of the central stem (outside bark). (Adapted from FIA Glossary: Standard Terminology) 

Hardwood: Wood produced by angiosperm trees, generally characterized by the presence of vessels or pores. Hardwood species are typically broad-leaved and may be deciduous or evergreen. See Wood type glossary term.

Harvest: A timber harvest is the process of cutting and removing trees from a forest for commercial, ecological or management purposes. Timber harvesting is a central activity in forestry that goes beyond simply cutting trees to transport them for use as roundwood.

Harvest removals: The growing stock volume removed from poletimber and sawtimber trees. Includes volume removed for roundwood products, logging residues and other removals. (Adapted from FIA Glossary: Standard Terminology) 

Harvested Wood Product (HWP): Wood removed from the forest ecosystem and entering the HWP accounting system as roundwood, including both industrial roundwood and fuelwood. Logging residues (slash) left on-site after harvesting are excluded.  Under the production approach, HWP calculations are based on underbark volume; therefore bark removed during harvest is not explicitly included in HWP carbon estimates. See harvested wood product carbon pool glossary term. .

Harvested wood products (HWP) carbon pool: Carbon in wood removed from the forest and either used directly as fuelwood or processed into wood and paper products. Harvested wood product (HWP) accounting is organized into four components representing the storage and disposition of harvested carbon: products in use, solid waste disposal sites, emissions with energy capture and emissions without energy capture. Logging residues and other material left at the harvest site are not included

Intergovernmental Panel on Climate Change (IPCC): The United Nations body for assessing the science related to climate change. Its guidance for national greenhouse gas inventories provides the international standard for carbon accounting methods, including the carbon pool definitions and accounting approaches.

Litter carbon pool: Carbon in organic material on the forest floor above the mineral soil, corresponding to IPCC forest carbon pool 4. Comprises the litter, fulvic, and humic layers, together with fine woody debris less than 3 inches in diameter. (Adapted from FIA EVALIDator and FIADB Database Description)

Logging residues:  Biomass remaining on-site following logging operations, including non-merchantable material (e.g., tree tops, limbs, stumps, belowground biomass, deadwood, and litter) and any merchantable wood that is cut but not removed. Under the Default Forest Inventory Tool, whose harvest scenarios assume clearcut harvest, logging residues comprise all live and dead biomass not removed from the site post-harvest, excluding bark and soil organic carbon.

Logging residues: Biomass remaining on-site following logging operations, including non-merchantable material (e.g., treetops, limbs, stumps, belowground biomass, deadwood and litter) and any merchantable wood that is cut but not removed. 

Log type: A classification of harvested roundwood based on its intended use or processing pathway. FACT distinguishes sawlogs, pulpwood, and fuelwood log types. The classification is based on the roundwood categories and harvested wood product accounting methods described in Smith et al. (2006).

Merchantable volume: The volume of sound wood in the portion of a tree meeting merchantability criteria, measured on the central stem from a 1-foot stump to a specified top diameter, and expressed in cubic units. (Adapted from FIA Glossary: Standard Terminology) 

Mortality: The average annual volume of sound wood in growing-stock trees 5.0 inches d.b.h. (or diameter at root collar for woodland species) and larger that died from natural causes, including insects, disease, competition, drought and weather, during the remeasurement period. Trees removed through harvest are accounted separately as removals. (Adapted from FIA Glossary: Standard Terminology)

Nationwide Forest Inventory (NFI): The ongoing inventory of U.S. forest resources conducted by the USDA Forest Service Forest Inventory and Analysis (FIA) Program. The inventory provides consistent estimates of forest area, condition, composition, growth, removals and mortality across ownerships and forest lands in the United States. It is based on a network of permanent field plots distributed at approximately one plot per 6,000 acres, with additional measurements of attributes such as down woody material, soils and understory vegetation collected on a subset of plots. FIA measurements, together with models, are also used by the Forest Service to estimate forest carbon stocks and changes over time and form the primary data foundation for U.S. forest carbon reporting, including the national greenhouse gas inventory. 

Nongrowing stock: Tree volume that does not meet FIA growing-stock definitions, including portions of growing-stock trees outside the growing-stock section and volume from trees that do not qualify as growing-stock trees.

Nongrowing-stock sources: Sources of harvested volume from nongrowing stock, including stumps, tops, limbs, cull sections of the central stem and material from rough, rotten, sapling, dead, or nonforest trees.

Nonstocked stand: Forest land with less than 10 percent live-tree stocking that does not meet the minimum stocking threshold for a stocked stand-size class. See Stand Size Class glossary term.

Overbark: A scaling approach that includes bark in the estimate of the amount of harvested wood.  

Products in use carbon pool: An harvested wood product (HWP) carbon storage component representing carbon stored in harvested wood products while they remain in use. Products remain in this pool for the duration of their service life. At the end of service, carbon may remain in products through reuse or recycling, be transferred to solid waste disposal sites, or be released to the atmosphere through combustion with or without energy capture.

Pulpwood: Roundwood intended for processing into pulp, paper, paperboard, or other fiber-or-composite-based wood products. Specifications may vary by region, market and whether dimensions or volumes are expressed on an underbark or overbark basis. 

Region: A spatial unit defined by administrative or analytical boundaries that groups states, or portions of states, for the purpose of summarizing and comparing forest attributes. In FACT, regions may be delineated in more than one way depending on how a given dataset is organized, including U.S. Forest Service administrative regions or aggregations of states. In general, regions reflect the finest spatial resolution at which the underlying data in FACT can support reliable estimates. 

Removals: The term “removals” is associated with two separate concepts.  

• In the context of carbon sequestration, it refers to a removal of carbon from the atmosphere. In keeping with the atmospheric perspective of carbon accounting adopted within FACT, carbon removals or sequestration is expressed as a negative number. 
• In the context of conventional forest management operations, and in the FIADB (Burrill et al. 2021), “removal” is used to describe trees that are removed from a site through harvesting operations. 

In FACT, harvesting removals (cutting trees and transporting them) are referred to as “harvest removals.”

Sapling: A live tree of small diameter, typically defined as having a diameter at breast height (d.b.h.) between 1.0 and 4.9 inches (2.5–12.7 cm). (Adapted from FIA Glossary: Standard Terminology) 

Sapling-size trees: Live trees at least 1.0 inch but less than 5.0 inches d.b.h. See Stand size class glossary term.

Sawlog: A log meeting applicable regional or market specifications for diameter, length, and soundness, and where relevant, bark basis, for manufacture into lumber or other solid wood products. Sawlogs are cut from the sawlog portion of sawtimber-size trees.

Sawtimber-size trees: Softwoods at least 9.0 inches d.b.h. and hardwoods at least 11.0 inches d.b.h. Also referred to as large-diameter trees. See Stand size class glossary term.

Sawtimber volume: Growing stock volume in the sawlog portion of sawtimber-sized trees in board feet (international ¼-inch rule). (Adapted from Murray et al. 2024, Box 5-8) 

Sequestration: The process by which greenhouse gases are taken up from the atmosphere and stored in a carbon pool. In forests this occurs primarily through photosynthesis, which converts atmospheric CO₂ into carbon stored in plant biomass. Used interchangeably with removals in greenhouse gas accounting. 

Soil carbon pool: Carbon in fine organic material below the soil surface to a depth of 1 meter, corresponding to IPCC forest carbon pool 5. Excludes roots, which are assigned to the live and dead tree pools. Modeled at the condition level rather than summed from field measurements. (Adapted from FIA EVALIDator and FIADB Database Description)

Softwood: Wood produced by gymnosperm trees, primarily conifers and generally lacking the vessels or pores characteristic of hardwoods.  (Adapted from the FIA Glossary: Standard Terminology) 

Stand: A community of trees that can be distinguished from adjacent communities due to similarities and uniformity in tree and site characteristics, such as age-class distribution, species composition, spatial arrangement, and structure. 

Stand age (as defined by FIA): The average total age of representative overstory trees in the predominant stand-size class. FIA generally estimates stand age using increment cores from selected trees on the plot, adjusted to approximate total tree age from establishment. (Adapted from FIA Glossary: Standard Terminology) 

Stand age (as a data input for FACT): The approximate number of years since the current forest stand was established or regenerated. For even-aged stands, this generally corresponds to the time since planting, harvest or another stand-replacing disturbance. For uneven-aged or mixed-age stands, enter the approximate age of the predominant overstory cohort. 

Stand origin: A classification used by FIA that indicates the regeneration origin of a forest stand, distinguishing between stands established through natural regeneration and those established through artificial means (e.g., planting or seeding).  (Adapted from FIA Glossary: Standard Terminology) 

Stand size class: A classification of forest land based on the predominant diameter size of live trees presently forming the plurality of live-tree stocking. Classes are defined as follows: 

• Sawtimber stand (large diameter): A stand at least 10 percent stocked with live trees, in which half or more of the total stocking is from live trees 5.0 inches or larger in diameter, and with sawtimber stocking equal to or greater than poletimber stocking.
• Poletimber stand (medium diameter): A stand at least 10 percent stocked with live trees, in which half or more of the total stocking is from live trees 5.0 inches or larger in diameter, and with poletimber stocking exceeding sawtimber stocking.
• Sapling/seedling stand (small diameter): A stand at least 10 percent stocked with live trees, in which half or more of the total stocking is from live trees less than 5.0 inches in diameter.
• Nonstocked stand: Forest land that does not currently meet the minimum stocking threshold for a stocked stand-size class. A nonstocked stand has less than 10 percent stocking with live trees but was formerly stocked and has the potential to become at least 10 percent stocked again, such as following harvest, fire or windthrow.

(Adapted from FIA Glossary: Standard Terminology) 

Stratum/Strata: A relatively homogeneous subset of a population, defined by selected attributes, within which sampling and estimation are conducted to reduce variance and improve the precision of statistical estimates.

Standing dead tree: A dead tree that remains upright and sufficiently intact to be classified in the standing dead wood carbon pool rather than as down woody material. Under FIA protocols, standing dead trees generally must meet minimum diameter and intact-bole requirements and lean less than 45 degrees from vertical. Portions that become severed or no longer meet standing-dead criteria are assigned to the down woody material pool when applicable.  (Adapted from FIA Glossary: Standard Terminology)

Solid Waste Disposal Sites (SWDS): Disposal locations (e.g., landfills and dumps) where discarded harvested wood products are deposited. Unlike dumps where total decay is assumed, landfills have decomposition ratios reflecting permanent storage. Decay rates for the portions subject to decay are also lower than they are in dumps  resulting in prolonged carbon storage.

Solid Waste Disposal Sites (SWDS) carbon pool: An harvested wood product (HWP) carbon storage component representing carbon in discarded harvested wood products placed in solid waste disposal sites, including landfills and, for historical periods, dumps. Some of this carbon remains stored for long periods, while some decays over time and is released to the atmosphere.

System boundary: The set of criteria determining what is included in, and excluded from, an assessment.

In greenhouse gas inventory accounting, the system boundary specifies which activities, greenhouse gases and carbon pools are included. It operates alongside spatial boundaries, which delimit the geographic area assessed; sector boundaries, which determine where emissions and removals are reported; and temporal boundaries, which establish the accounting period. (Adapted from Murray et al. 2024)

For harvested wood products, FACT applies the IPCC production approach, under which HWP carbon is attributed to the location of harvest regardless of where the wood is subsequently processed or used. 

Tops: The portion of a tree above the defined merchantable limit (e.g., minimum top diameter), consisting of smaller stem sections and branches that are not considered merchantable under specified utilization standards but contribute to total tree biomass and carbon accounting. 

Tree Diameter Class: A grouping of tree diameters (d.b.h. or d.r.c.) into classes of a specified range. Diameter classes are commonly in 2-inch (5 cm) increments, beginning with 2 inches (5 cm). Each class provides a range of values with the class name being the approximate mid-point. For example, the 6-inch class (15-cm class) includes trees 5.0 through 6.9 inches (12.7 cm through 17.5 cm) in diameter, inclusive. (Adapted from FIA Glossary: Standard Terminology) 

Uncertainty: Lack of knowledge of the true value of a variable that can be described as a probability density function characterizing the range and likelihood of possible values. Uncertainty depends on the analyst’s state of knowledge, which in turn depends on the quality and quantity of applicable data as well as knowledge of underlying processes and inference methods. 

Underbark: A log scaling approach in which the amount of harvested wood measured or estimated excluding the bark, representing the amount of wood inside the bark as stipulated in the IPCC Production Approach. See Overbark glossary term.

United States Department of Agriculture (USDA):  A federal executive department of the United States responsible for developing and implementing policies related to agriculture, forestry, rural development and food systems, including oversight of Forest Service programs such as FIA. 

Unreserved forest land: Forest land not withdrawn from management by statute or administrative designation, and therefore generally available for multiple uses, including timber production.  (Adapted from FIA Glossary: Standard Terminology) 

Wood type: Broad classification of tree species as either hardwood or softwood.