Methodologies

The Custom Forest Carbon Inventory Tool (herein after referred to as the “Custom Tool”) enables users to translate traditional forest inventory data into a complete forest carbon inventory. Users upload their forest inventory data to the secure platform using the inventory templates provided and the Custom Tool uses those data to produce forest carbon stock and stock change estimates using standard conversion procedures and data from the USDA Forest Inventory and Analysis Program (FIA).

While many corporate forest landowners have extensive forest inventory data, corporate forest inventories are usually focused on the “merchantable” (available for commercial use) portion of the forest. Other forest components (dead wood, soils, forest floor or litter layer) are not typically measured but are important elements of forest carbon estimation. The Custom Tool tool was designed, based on interviews with corporate forest inventory managers, to utilize the data commonly collected through corporate inventories to obtain estimates of all forest carbon stocks and stock changes across all forest carbon pools.

The Custom Tool accomplishes this by matching user-supplied stand-level inventory data to “similar” forests measured through the FIA’s Nationwide Forest Inventory (NFI). This ensures that carbon stock estimates are consistent for similar stands across a variety of ownerships and that users benefit from the scientifically reviewed carbon data and estimation methods used by FIA. Furthermore, to convert traditional tree inventories into carbon estimates, a consistent set of conversion factors are applied to convert tree volumes to weights, and weights to carbon stock estimates. This supports transparency, consistency, and comparability across corporate carbon inventory compilation efforts.

In the Custom Tool, changes in carbon stocks represent estimated net change in carbon stored within the defined system (i.e., the forest stand) 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.

Throughout this document, reference will be made to codes, data, and equation coefficients stored in tables in the Excel workbook “CFIT_User_Documentation_Tables.xlsx” (herein referred to as the CFIT workbook), which is an important part of this documentation. (note: these tables will be uploaded to FACT the week of October 5)

Ac: Acres (land area measurement)

AFOLU: Agriculture, Forestry, and Other Land Use

BF: Board feet (wood volume measurement)

CENT: Central States (US Region)

CO₂e: Carbon dioxide equivalent

Cords: A stacked volume measure of roundwood, most commonly used for pulpwood and fuelwood. (Wood volume measurement)

CCF: Hundred cubic feet (wood volume measurement)

CFIT: Custom Forest Carbon Inventory Tool

DBH: Diameter at Breast Height; tree diameter measurement

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 (program of USDA Forest Service)

FIPS: Federal Information Processing Standard (here, codes for identifying U.S. counties)

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)

IPCC: Intergovernmental Panel on Climate Change

MBF: Thousand board feet (wood volume measurement)

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

NC: North Central (US Region)

NE: Northeast (US Region)

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

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)

Short tonnes: U.S. customary ton; 2,000 pounds (907.2 kg). Equal to 0.907 metric tonnes. 

U.S.: United States of America

USDA: United States Department of Agriculture

The Custom 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 Custom Tool is applicable to forests within the contiguous United States (CONUS) only at this time.

3.1 Carbon Pools

The Custom 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. 

3.2 System Boundaries

The Custom Tool includes sinks and sources within the Agriculture, Forestry, and Other Land Use (AFOLU) sector, as defined by the IPCC, and specifically quantifies changes in forest carbon stocks associated with forest growth and mortality. The system boundary includes changes in carbon stored on the forest site in relevant ecosystem carbon pools for a given inventory. Where two stand inventory datasets representing two dates are provided, the Custom Tool can estimate the changes in forest carbon stocks over that time period. 

The Custom Tool does not quantify carbon transfers from the forest stand to the harvested wood product (HWP) pool. Users who wish to do so may use the FACT Harvested Wood Product Carbon Tool which quantifies carbon storage and release in HWPs using user-entered harvested wood amounts.  

The AFOLU-sector carbon accounting performed by the Custom Tool 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 Custom Tool’s underlying models were constructed using FIA plots classified as forest land at both measurement periods. 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 land, such as afforestation, reforestation following a nonforest land use, or deforestation. 

3.3 Caveats and Context for Users

The Custom Tool accommodates two general categories of forest inventory information, each representing distinct levels of detail on the forest stand(s). These are described in detail in Section 4 below, but as a general principle, where more precise and detailed stand information is supplied to the Custom Tool via the “Stand Detail” template, Custom Tool outputs can be expected to more accurately represent the stand conditions. Where the less detailed “Stand Description” template is used to supply the Custom Tool with information, the tool relies more heavily on underlying models built using FIA plot data. 

These models reflect broad regional averages which characterize the range of conditions across U.S. forests. Model outputs are meant to represent what the forest carbon stocks are, by carbon pool, 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. Site-specific conditions can cause substantial departures from what the underlying models predict, and therefore outputs should be understood as representative estimates rather than precise measurements of conditions on a specific property. 

The Custom Tool requires users to  supply data for a specified point in time. However, forest inventories are rarely conducted on an annual basis; some portions of the forest may be measured and the rest “grown” or projected (using growth models) to a specific point in time. This projection of inventory data is done by the user using the models available to them, so there may be variability between users as a result of the models they choose.

Forest inventories may include tree volume (or weight) measurements in a variety of units (board feet, cords, cubic feet, etc.). The Custom Tool therefore accepts a variety of units and converts the data into green tons, then dry tons, then carbon. Therefore, conversion factors used by individual users may differ from the FIA-based standard conversion factors applied in the Custom Tool.

The Custom Tool does not offer future projections of forest carbon stocks and changes in forest carbon stocks. Where future simulations are desired, users may consider applying appropriate growth and yield models 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.

3.4 Sources of Uncertainty

Sources of uncertainty for Custom Tool outputs range from the data entered into the templates to the underlying models and coefficients built into the tool.  The Custom Tool does not offer quantitative assessments of associated uncertainty, but these can be qualitatively described as follows: 

• Where stand information is supplied in the more comprehensive “Stand Detail” template, uncertainty may arise and compound where information on the stands contains errors. These errors may include sample representativeness, measurement error, expansion of plot-level values to stand-level estimates, and where field measurements are translated into volume estimates. 
• Where stand information is supplied in the less comprehensive “Stand Description” template, uncertainty may arise due to the greater reliance on 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 (as discussed above). Furthermore, sparse plot data for some region–forest type–age class combinations produce high sampling error, resulting in higher uncertainty for those combinations.
• Regardless of the selection of data input template, the Custom Tool applies standard FIA-based models and coefficients to estimate carbon pools not typically measured in commercial forest inventories, including non-merchantable live biomass, saplings and understory components, standing dead trees, down dead wood, belowground biomass, and litter and soil carbon. This introduces sources structural uncertainty across the tool, including:
• • Converting biomass to carbon via generalized coefficients including wood specific gravity by species and region, and a carbon fraction.
  • In general, measurement-derived carbon estimates carry lower uncertainty than those derived from predictive models. Aboveground live and standing dead biomass estimates 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. In contrast, 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. 
• Where information on changes in forest carbon stocks is sought by uploading inventory data representing two dates, the gain–loss approach applied by the Custom Tool handles transfers between pools by assumption rather than measurement.

4.1 Overview

The Custom Tool results are produced based on user-supplied inventory data, which must be submitted using the templates provided in the Platform. These data serve as the basis for estimates of carbon stocks, as well as changes in those carbon stocks if more than one year of inventory data are provided. 

Users have the option to choose one or both of the templates/inventory file types provided by the Platform, depending on the level of detail contained in their existing forest inventory data, described in Table 1 below. 

Table 1: Description of Custom Forest Carbon Inventory Tool Stand Inventory File Types/Templates

If a user supplies the Custom Tool with a single set of inventory data that represents a single point in time, the Custom Tool provides carbon stock estimates for that point in time. Users may also upload two sets of inventory data for the same set of stands reflecting two points in time, enabling the Custom Tool to estimate carbon stocks for each point in time and calculate the annual carbon stock change between them.

Because the Custom Tool is based on FIA data, FIA coding systems for forest types, tree species, etc. are applied. Users will find valuable additional information on FIA coding standards and data in the FIA Database User Manual (Burrill, et al. 2024).

4.2 Inventory date(s)

The Custom Tool requires that users enter an inventory date for each set of inventory data uploaded. Most forest inventories represent a specific point in time, reflecting when the entire ownership is inventoried, as may be done before a purchase or sale of a forest. However, it is also common for portions of a large ownership to be inventoried annually or periodically, and non-inventoried portions are “grown” or “projected” using forest growth models to update the inventory to a target point in time. The Custom Tool was not designed to apply growth models to project inventories over time, and rather assumes that the entire inventory supplied by a user represents a specific point in time. 

Where more than one inventory set is supplied to estimate annual forest carbon stock changes, those dates must be at least one year apart. The Custom Tool estimates annual change by computing the time interval between inventory dates (in decimal years) and then divides carbon stock changes by the interval to obtain annual stock change. This is useful for both retrospective estimates (e.g., using two prior inventories to estimate stock change over a recent period) and prospective estimates (e.g., using a current inventory and an inventory projected with a harvest scheduling model to estimate future stock changes).

4.3 Stand/Stratum Identifiers

For the purposes of the Custom Tool, the forest “stand” is a land area managed as a unit by the landowner In the US, stands are generally considered to be forest areas that are sufficiently homogeneous in terms of species composition, age class, and site quality that they are subject to the same silvicultural treatments. In managed forests of the US, stands are often spatially contiguous, but they do not need to be for the purposes of the Custom Tool. For example, some forest landowners aggregate groups of similar stands into strata that may consist of numerous noncontiguous stands spread across a broader landscape (e.g., all hardwood-dominated streamside management zones in an administrative unit). For the Custom Tool, a stratum can be treated the same as a stand (e.g., a single record in the stand description file).

Most owners of larger areas of forest land use a hierarchical system of administrative units. For example, a single ownership “parcel” or “tract” may contain numerous stands, then a “compartment” may contain multiple tracts, a “district” may contain numerous compartments, and a “region” may contain multiple districts. The Custom Tool accommodates such hierarchical designations by allowing users to supply up to four administrative identifiers for each stand, but a stand cannot be in more than one unit of a given administrative level (e.g., it cannot be included within two tracts), and the stand “number” must be unique within the lowest (smallest) administrative level.

The unique identifier for a stand, therefore, is the combination of up to four administrative levels and a stand number; this is referred to as the “stand key”. Stand keys must be consistent between the stand description file and the stand detail file.

In the example shown in Table 2, stand 16B must be unique within the Wilson tract (there may be other stand 16Bs in other tracts), and if there is a record for this stand in the stand detail file, the key must exactly match the key in the stand description file.

Table 2: Example of a stand key

4.4 Stock changes and geographic consistency

For reporting carbon stock changes between two points in time, it is critical that the estimates be computed for a land base that remains consistent between those points in time. Otherwise, land acquisitions could appear as carbon stock increases and dispositions would appear as carbon stock losses, obfuscating the actual carbon stock change on the landscape. 

It is challenging to enforce that consistency at the stand level, because most large landowners report that stand boundaries may change over time due to silvicultural treatments or natural disturbances. Therefore, the consistency of the land base is enforced at the administrative unit level as defined by the user. Annual carbon stock change will only be calculated for administrative units whose area (in acres, as provided in the input files) is the same across each inventory data set supplied to the tool.

4.5 Geographic location identifiers

The Custom Tool (and the FACT Default Forest Carbon Tool) operate by matching a landowner’s forest stand characteristics with “similar” plots from the FIA database. For the purpose of FACT, similar is defined as plots/stands of the same region, forest type or tree species group, stand origin, and age (see Glossary for definitions). The regions used in the Custom Tool are subregions of the conterminous U.S. (CONUS) used in the “Managed Forest Systems” chapter within the USDA Quantifying Greenhouse Gas Fluxes: Methods for Entity-Scale Inventory Technical Bulletin (Murray, et al. 2024) displayed in Figure 1. 

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).  

Geographic locations supplied to the Custom Tool are intentionally vague. This is both to protect confidentiality of user data and because specific locations are not necessary for matching with similar FIA data. Therefore, for each stand, a user must provide either a county code or an FIA survey unit (aggregates of counties defined in the FIA database documentation (Burrill, et al. 2024) and portrayed as light gray lines in the map above). See Annex IV for information about these codes.

4.6 Stand Description File

The stand description file contains one record per stand, which includes a unique identifier (stand key) as a combination of up to four administrative units and a stand number, a geographic location, descriptive information about the stand including forest type, stand age, and stand origin, and the area of the stand in acres. A full description of the stand description file is provided in Annex II.

The stand description file provides enough information for carbon stock estimates based on regional averages, similar to the way the FACT Default Forest Carbon Tool works. It also provides critical information used in converting tree volume/weight estimates (such as forest type and region) into carbon stock estimates.

4.7 Stand Detail File

The stand detail file may contain zero to multiple records per stand. For stands where no tree volume data are collected by the user, there will be no records in this file and estimates will be based on stand description information alone. Where tree volume data have been collected, this file will contain volume by tree species group, product class, and (optionally) tree diameter class. A full description of the stand detail file is provided in Annex III.

5.1 Error checking

Prior to processing the user-supplied inventory data for carbon stock estimates, the Custom Tool scans all input data for errors. Errors that prevent further processing include invalid codes, missing required fields, or faulty linkages between stand keys in the stand description and stand detail files. Where errors are detected, the Custom Tool notifies the user of the types of errors and the locations (records) within the input files where the errors were detected and the user is prompted to correct those errors and upload the remediated file(s).

After the input files are determined to be free of errors, they are processed as described in the methodology described in Section 6 of this document. During that processing, the Custom 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 parameter such as tree diameter or stand age is beyond the range for which sufficient FIA data are available, or 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, carbon stock estimates are computed based on a default (such as averages for the forest type group in other regions).

5.2 Summary metrics and graphical outputs

Upon processing of the user-supplied data, several summary metrics and graphical outputs are rendered, as detailed below. Additional summary statistics are displayed at the top of the user interface, including the total land area, the number of stands, and the inventory dates. 

Summary statistics (Figure 2) include:

• Total carbon stock: Total forest carbon stock for the forest stand(s).
• Annualized carbon stock change: Where data for two inventory dates are provided,  annual changes in carbon stocks for the selected forest stand(s) across the two inventory dates is presented. 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.

In addition to summary metrics, the user interface also generates a set of graphical outputs. These include:

• Total Carbon by Pool bar chart (Figure 2) presenting total forest carbon stocks by pool. Where data for two inventory dates are provided, the bar chart will offer side-by-side comparisons of carbon stock estimates by pool for the two inventory dates. 
• Carbon Stock Change by Pool bar chart (Figure 3) presenting changes in total forest carbon stocks by pool. 
• Carbon Stock Table (Figure 4) that provides a numerical breakdown of carbon stocks by pool for each administrative unit delineated by the user. A toggle in the upper left corner of this table enables users to select between inventory data provided. 

FIGURES 2, 3, 4 (coming soon)

5.3 Summary report

Summary-level information is also provided to the user in reports/tables that can be generated and saved via the user interface. [To be determined: what are the options and the contents of these?]

5.4 Data download

In addition to summary results provided in the user interface and saved reports, users can download data files in the same framework (data structures) as the data they uploaded. Additional columns will be appended to the records uploaded by the user containing carbon stock estimates associated with the input records of the stand description file(s). For example, if the user uploaded two sets of inventory data for two dates, with stand description and stand detail files for each, the files available for the user to download after processing are depicted in Figure 5.

Figure 5: Input and output files for multiple inventory dates

The stand description results files will contain all the stand description input columns as well as columns for carbon stock per acre (t CO₂e/ac) for aboveground live tree carbon, belowground live tree carbon, sapling and understory carbon, dead wood carbon, litter carbon, and soil carbon, all for the corresponding point in time.

Because estimating carbon stock in live trees at the stand level requires aggregating products within species groups and diameter classes, the carbon stock results will not offer the same level of detail (stand/species group/product class/diameter class) as in the input files.

The stock change results file will contain annual carbon stock changes in the aboveground live tree pool (t CO₂e/yr) only for the administrative units that have consistent area between the two points in time. Output records will contain values for the (up to four) administrative levels, total acres in each unit, total carbon stocks by pool at each point in time, and the annual change in carbon stock for the aboveground live tree pool.

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 the Custom Tool and the DFCT. For some components of forest carbon inventory, where the estimates are dependent on stand age or tree diameter class, it was necessary to develop models (fitting equations to the data). Where modeling was not needed, such as carbon fractions or conversions of green weight to merchantable dry weight, lookup tables (e.g., average values for combinations of region and forest type) were developed or factors were obtained from scientific publications.

When modeling was needed, two general types of models were developed: (1) those that predict forest carbon stocks per acre at the stand level (such as soil carbon per acre, litter carbon per acre, etc.) from stand description data, and (2) those that are applied to groupings of trees (from stand detail data) to convert tree volumes or weights into tree carbon stock estimates.

The general process flow for developing the underlying data tables and models is depicted in Figure 6.

Figure 6: Process flow for deriving models from data underlying the Custom Forest Carbon Inventory Tool

The following sections describe the process used for (1) extracting estimates from the FIA database for specified groupings for FIA plots, (2) developing tables of estimates or factors in cases where modeling was not necessary, (3) fitting models for each grouping to derive trends of carbon stocks across stand ages for the stand-level estimates, (4) fitting models for each grouping to derive trends of carbon stocks across diameter classes for the tree-level estimates, and (5) the construction of lookup tables containing model coefficients or other values that are used in the Custom Tool.

6.1 FIA Data Retrieval

Data were retrieved from the FIA database using the FIA EVALIDator tool (USDA 2026) through its application programming interface. In conducting the EVALIDator queries, data from the two most recent non-overlapping evaluation groups were used. For example, the most recent measurement published for Maine at the time of development was from 2024, and contained data from plots measured in 2020, 2021, 2022, 2023, and 2024. The next most recent evaluation group with no overlapping measurement years was the 2019 evaluation group, containing plot measurements from 2015, 2016, 2017, 2018, and 2019.

The population of interest was all FIA plots from unreserved forestland, defined by the FIA as forest land not withdrawn from management by statute or administrative designation, and therefore generally available for multiple uses, including timber production. EVALIDator queries allow for the selection of grouping variables (such that estimates are developed for each combination of grouping variables) and filters (to isolate plots with specific characteristics from the estimates). Data from EVALIDator were extracted at the plot level so that outputs included the values of each grouping variable and the desired estimate (e.g., aboveground live tree carbon) for each plot in the population.

For modeling by stand age, the plot-level EVALIDator results were matched with recorded stand ages for each plot (rather than the stand age classes available from EVALIDator).

From the datasets resulting from each EVALIDator query, the models for stand-level and tree-level estimates were developed. Annex IV contains lists of the specific EVALIDator attributes used in the queries for each estimate of interest at the stand level, and Annex V contains details for the tree-level data.

6.2 Lookup tables developed without modeling

In many cases, estimates do not vary consistently across stand age classes or tree diameter classes, and therefore modeling was not necessary for some stand-level and tree-level estimation processes. For example, FIA computes soil organic carbon (SOC) stocks using a model that estimates SOC based on climate, geophysical variables, and forest type (Domke, et al. 2017). Therefore, FIA-based estimates of SOC are not expected to vary across stand ages in a predictable manner, so averages of SOC density by region and forest type were developed for the purposes of the Custom Tool and the Default Tool (see Table 15 in the Custom Tool User Documentation Tables). Another example at the tree level is the application of conversion factors to translate tree green weight to dry weight. These conversions depend only on species-specific factors contained in the FIA database. Therefore, average conversion factors by species group and region were developed using that source, which were further refined into weighted averages for the tree species in the tree species groups by region. 

The lookup tables used by the Custom Tool that did not require modeling are listed in Table 3, with references to the Table number in the Custom Tool User Documentation Tables containing the results.

Table 3 List of estimates and factors not requiring modeling.

6.3 Stand-level modeling

The estimates needed at the stand level included carbon densities (t CO₂e/ac) for all carbon pools, by stand age, for each grouping used in matching the forest conditions supplied by the user to comparable FIA plots. These groupings include the region (Figure 1), broad forest type groups, FIA forest type group, and stand origin (natural or artificial regeneration). For each combination of these groupings, a model was fit to estimate the carbon stock density (for each pool) as a function of stand age. With 11 regions, 32 forest type groups, and 2 stand origins, there are potentially 704 unique combinations of these groups. However, the ability to model all of these combinations was limited by available data.  For example, there were no FIA data for Douglas-fir forest type group plots, either planted or natural, in the Southeast region.

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. 

During model fitting, a multi-stage approach was used, corresponding to the grouping hierarchy (Figure 7). When a model could not be fit (with statistically significant parameter estimates at alpha = 0.1) for a specific combination of  groupings (for example, Southeast region, bottomland hardwood, oak/gum/cypress forest type group, planted stand origin), then the lowest level grouping (stand origin) was dropped, and in a second stage, the model was fit to the remaining groupings (region, broad grouping, and forest type group). If a significant model did not result, then the lowest-level grouping (forest type group) was dropped and a third stage model was fit to just region and major forest type group (softwoods/hardwoods). Where this hierarchical approach continued to render no significant model results, then a model was fit to just region. The result of the modeling effort was a set of parameter estimates (y₀, b, and k) for each combination of the grouping variables (documented in the Custom Forest Carbon Inventory Tool User Documentation Tables file).

Figure 7: Hierarchical approach for model fitting. Where statistically significant parameter estimates could not be achieved with all grouping variables (region, forest type, age, and stand origin), grouping variables were sequentially removed in a predefined hierarchical order to increase the number of FIA plots contributing to model estimation.

6.4 Tree-level modeling

The estimates needed at the tree level include several factors to convert user inputs to tree carbon estimates. The processing flow for stand detail data is depicted in Figure 8. User inputs (volumes/weights of inventoried trees in a stand, by tree species groups, product classes, and diameter classes) may be in a variety of units (cubic feet, cords, thousand board feet, tons). All inputs must be converted to green weight, which requires a variety of conversion factors.

Additional conversion factor ratios are needed to estimate total aboveground biomass from merchantable biomass, and carbon from dry weight (biomass), belowground carbon from aboveground carbon, etc. Many of these conversion factors are developed from models based on ratios of FIA data, others are based on factors reported in the literature, or factors that do not vary with age or diameter and therefore need no modeling.

The groupings used for tree-level modeling are region, major species group (hardwood/softwood), FIA tree species group, and stand origin. Within each combination of groupings, a model was fit to estimate the factors needed as a function of tree diameter (DBH). In addition to the Hugershoff model used in stand-level modeling, tree aboveground to merchantable bole conversion factors were modeled using a modified version of the negative exponential decay function:

y = y₀e^-kx + c

where y is the factor of interest, y₀, k, and c are coefficients, and x is the midpoint of the tree DBH class. During model fitting, the same multi-stage approach was used to fit models to fewer grouping levels as needed to obtain significant parameter estimates.

The factors developed using this modeling approach are listed in Table 4, with the model form used.

Figure 8: Processing flow for stand detail data

6.5 Tables of model coefficients

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 Custom Tool to perform all of the necessary calculations to develop carbon stock estimates from user inventory data at the stand and tree level. These tables are available in the Custom Tool User Documentation Tables file.

Table 4: Tree-level factors developed using modeling

This section describes the processing flow that the Custom Tool uses to combine user-provided stand description and stand detail data with the pre-processed underlying data derived from FIA data. It begins with computing carbon stocks from the stand description data, then computes live tree carbon stocks from the stand detail data. It then adds carbon in un-inventoried trees (saplings) and understory to get totals for aboveground and belowground biomass. Finally, it combines all estimates for each point in time.

If two dates of inventory data are provided, it repeats the above steps for the second date, and finally computes carbon stock changes for geographically consistent administrative units.

7.1 Compute carbon stock estimates from stand description data

For carbon pools not measured in conventional forest inventories (sapling and understory, dead wood, belowground carbon, soil carbon, etc.), the Custom Tool provides estimates based on descriptive information about the stand, obtained for each stand from the stand description file. 

The user-supplied information on region, forest type group, stand origin, and stand age for each stand is used to select the  appropriate model coefficients or values from lookup tables to calculate forest carbon densities (tons/ac), and then multiplied by stand area (acres) to get total carbon stock for each carbon pool. 

Tables of model coefficients and lookup values for estimating forest carbon densities are contained in the CFIT_User_Documentation_Tables.xlsx Excel workbook (herein referred to as the CFIT workbook). The tables contain values with more digits than are reported below (shortened here for convenience). 

All carbon stock estimates will be in tons C (and tons C/acre) and are converted to metric tonnes of carbon dioxide equivalents (t CO₂e) at a later step.

7.1.1 Identify the region for each stand.

The user-provided county FIPS codes or FIA survey unit codes are used to identify the region, based on what is documented in the County_Master table in the Valid Codes workbook or the the FIA_Unit table which documents FIA survey unit codes.

Where a user provides both a County FIPS code and an FIA Unit code, the County FIPS code takes precedence due to its greater spatial resolution.

Example: a record in the stand description file indicates the County_FIPS code is 22115. Looking this value up in the County_Master table of the Valid Codes workbook, we find this is Vernon county (parish) in Louisiana (22 is the state FIPS code for Louisiana, and 115 is the code for Vernon county, LA). This county belongs to FIA survey unit number 3 in Louisiana, or FIA_UNIT code 2203. The region code is SC (South Central).

Similarly, FIA_unit 2203 in the FIA_unit table in the Valid Codes workbook lists the corresponding region code is SC (South Central).

7.1.2 Compute the live aboveground carbon using model parameters from the appropriate lookup table.

Table 11 in the CFIT workbook provides the lookup values for model parameters for live aboveground carbon, which includes trees, saplings, and understory. Model parameters are grouped by  region, forest type code, and stand origin code. The Custom Tool matches the user-provided region with those listed in the REG_11 column, the forest type code in the FORTYPGRPCD column and the stand origin in the STAND_ORIGIN column to retrieve the lookup table values for the three parameters needed: y₀ (from the Estimate.y₀ column), b (from the Estimate.b column), and k (from the Estimate.k column). Live aboveground carbon density (lagcd) can then be computed using the following equation (i.e., Hugershoff model)

lagcd = y₀  * a^b  * exp(-k * a)

Where:

lagcd = live aboveground carbon density in tons per acre

y₀ = parameter retrieved from the lookup table

a = stand age from the stand description file

b = parameter retrieved from the lookup table

exp = exponentiation function (e to the power)

k = parameter retrieved from the lookup table

Finally, to get total live aboveground carbon in the stand (trees and understory), the per-acre lagcd value is multiplied by the stand area from the stand description file.

lagc = lagcd * Stand_area

Example: a record in the stand description file indicates that stand number 28 is in the SC region, forest type 600, Natural stand origin, age 62 years old, and contains 58.69 acres.

In the lookup table, we find the corresponding record contains the following parameters:

y₀ = 1.41424

b = 0.79210

k = 0.003188

The live aboveground carbon density (carbon per acre) is then:

lagcd = (1.41424) * (62^0.79210) * (exp(-0.003188 * 62))

lagcd = 30.510 tC/ac

The total live aboveground carbon in the stand is then:

lagc = 30.510 * 58.69 = 1,790.605 t C

7.1.3 Compute the live belowground carbon using model parameters from the appropriate lookup table.

Table 13 in the CFIT workbook provides the lookup values for model parameters for deadwood carbon density. Model parameters are grouped by region, forest type code, and stand origin code. The Custom Tool matches the user-provided region with those listed in the REG_11 column, the forest type code in the FORTYPGRPCD column and the stand origin in the STAND_ORIGIN column to retrieve the lookup table values for the three parameters needed: y₀ (from the Estimate.y₀ column), b (from the Estimate.b column), and k (from the Estimate.k column). Dead wood carbon density (dwcd) can then be computed using the following from the equation (i.e., Hugershoff model)

dwcd = y₀  * a^b  * exp(-k * a)

Where:

dwcd = dead wood carbon density in tons per acre

y₀ = parameter retrieved from the lookup table 

a = stand age from the stand description file

b = parameter retrieved from the lookup table

exp = exponentiation function (e to the power)

k = parameter retrieved from the lookup table

Finally, to get total dead wood carbon in the stand, the per-acre value is multiplied by the stand area from the stand description file.

dwc = dwcd * Stand_area

Example: a record in the stand description file indicates that stand number 28 is in the SC region, forest type 600, Natural stand origin, age 62 years old, and contains 58.69 acres.

In the lookup table, we find the corresponding record contains the following parameters:

y₀ = 4.82948

b = 0

k = 0

The live belowground carbon density (carbon per acre) is then:

lbgcd = (4.82948) * (62⁰) * (exp(-0 * 62))

lbgcd = 4.8295 t C/ac

The total live belowground carbon in the stand is then:

lbgc = 4.8295 * 58.69 = 283.442 t C

7.1.4 Compute the dead wood carbon using model parameters from the appropriate lookup table.

Table 13 in the CFIT workbook provides the lookup values for model parameters for deadwood carbon density. Model parameters are grouped by region, forest type code, and stand origin code. The Custom Tool matches the user-provided region with those listed in the REG_11 column, the forest type code in the FORTYPGRPCD column and the stand origin in the STAND_ORIGIN column to retrieve the lookup table values for the three parameters needed: y₀ (from the Estimate.y₀ column), b (from the Estimate.b column), and k (from the Estimate.k column). Dead wood carbon density (dwcd) can then be computed using the following from the equation (i.e., Hugershoff model).

dwcd = y₀ * a^b * exp(-k * a)

Where:

dwcd = dead wood carbon density in tons per acre

y₀ = parameter retrieved from the lookup table

a = stand age from the stand description file

b = parameter retrieved from the lookup table

exp = exponentiation function (e to the power)

k = parameter retrieved from the lookup table

Finally, to get total dead wood carbon in the stand, the per-acre value is multipled by the stand area from the stand description file.

dwc = dwcd * Stand_area

Example: a record in the stand description file indicates that stand number 28 is in the SC region, forest type 600, Natural stand origin, age 62 years old, and contains 58.69 acres.

In the lookup table, we find the corresponding record contains the following parameters:

y₀ = 0.52973

b = 0.52053

k = -0.002966

The dead wood carbon density (carbon per acre) is then:

dwcd = (0.52973) * (62^0.52053) * (exp(0.002966 * 62))

dwcd = 5.457 t C/ac

The total dead wood carbon in the stand is then:

dwc = 5.457 * 58.69 = 320.243 t C

7.1.5 Compute the litter carbon using model parameters from the appropriate lookup table.

Table 14 in the CFIT workbook provides the lookup values for model parameters for litter carbon. Model parameters are grouped by region, forest type code, and stand origin code. The CIFT matches the user-provided region with those listed in the REG_11 column, the forest type code in the FORTYPGRPCD column and the stand origin in the STAND_ORIGIN column to retrieve the lookup table values for the three parameters needed: y₀ (from the Estimate.y₀ column), b (from the Estimate.b column), and k (from the Estimate.k column). Litter carbon density (litcd) can then be computed using the following from the equation (i.e., Hugershoff model).

litcd = y₀  * a^b  * exp(-k * a)

Where:

litcd = litter carbon density in tons per acre

y₀= parameter retrieved from the lookup table,

a = stand age from the stand description file

b = parameter retrieved from the lookup table

exp = exponentiation function (e to the power)

k = parameter retrieved from the lookup table

Finally, to get total litter carbon in the stand, the per-acre value is multipled by the stand area from the stand description file.

litc = litcd * Stand_area

Example: a record in the stand description file indicates that stand number 28 is in the SC region, forest type 600, Natural stand origin, age 62 years old, and contains 58.69 acres.

In the lookup table, we find the corresponding record contains the following parameters:

y₀ = 1.39763

b = 0.10016

k = -0.001079

The litter carbon density (carbon per acre) is then:

litcd = (1.39763) * (62^0.10016) * (exp(0.001079 * 62))

litcd = 2.259 t C/ac

The total litter carbon in the stand is then:

litc = 2.259 *58.69 = 132.599 t C

7.1.6 Compute the soil organic carbon using model parameters from the appropriate lookup table.

Table 15 in the CFIT workbook provides the lookup values for soil organic carbon. Because soil organic carbon density is not dependent on stand age or stand origin, this lookup table leads directly to the SOC density (t C/ac) without the need for modeling using the modeling parameters applied for the other forest carbon pools. 

The CIFT matches the user-provided region with those listed in the REG_11 column and the forest type code in the FORTYPGRPCD column to retrieve the soil organic carbon density (socd) estimate directly from the table (SOC columns). 

Finally, to get total soil carbon in the stand, the per-acre value is multiplied by the stand area from the stand description file.

soc =socd * Stand_area

Example: a record in the stand description file indicates that stand number 28 is in the SC region, forest type 600, Natural stand origin, age 62 years old, and contains 58.69 acres.

In the lookup table, we find the corresponding record contains the following estimate:

SOC = 42.28193

The soil organic carbon density (carbon per acre) is then:

socd = 42.28193 t C/ac

The total soil organic carbon in the stand is then:

soc = 42.28193 * 58.69 = 2,481.526 t C

7.1.7 Exception handling

In some cases, there are no records in the lookup tables for certain combinations of region, forest type group, and stand origin. This happens most commonly when a given type of forest is rare in a geographic region, or when a type of forest rarely is planted and only occurs as natural stands. In these cases, there were insufficient data in FIA to derive an estimate.

In these cases, when an attempt to find a matching record in a lookup or coefficient table fails:

1. If no “Planted” stand origin record is found, but a “Natural” stand origin record exists, the values for the Natural stand are applied.
2. If neither “Planted” nor “Natural” records exist for a forest type group within a region, the record for the forest type group in the “US” region is applied. The values in this record represent the averages for the forest type group across all regions.

Furthermore, while users may enter stand ages greater than 100 years, FACT applies a maximum modeled age of 100 years for carbon estimation purposes. As a result, stands older than 100 years are assigned the same estimated carbon density as a 100-year-old stand. 

In all cases when such exceptions occur, warnings are reported to the user that reference the record number, stand description file, and where insufficient data were detected to render results based on user inputs and what, if any, deviations were made in the modeling process. 

(Exact warning messages will be updated once interface design is complete)

7.2 Compute live tree carbon stock estimates from stand detail data

In the stand detail file, there is a record for each combination of stand key, tree species group, tree product class, and tree diameter class. This is necessary because it is possible to have different measurement units (cubic feet, board feet, green tons, etc.) for different products (pulpwood, sawtimber, etc.), and each needs to be converted to common units (initially, green tons).

Commercial forest inventories generally report “merchantable volume”, which is the volume in the portion of the tree for which local markets exist. This usually consists of the main stem, from ground line or a specified stump height to a limiting diameter of the stem near the top of the tree (for example, a 3” top stem diameter). Merchantable volumes exclude wood in tree tops (the portion of the tree above the threshold stem diameter), branches, and trees in the forest below a threshold diameter at breast height (DBH; usually 5”). However, reporting of carbon in live trees should include those non-merchantable portions of trees and trees too small to be merchantable. The Custom Tool therefore applies a factor based on FIA data to make an appropriate adjustment (depending on the region, tree species, etc.).

All trees also store carbon in their root systems, so belowground live tree carbon is estimated based on published ratios that estimate belowground live tree carbon from the amount of carbon in the tree aboveground. Computing belowground live tree carbon is done for each record after aboveground live tree carbon is computed.

Finally, the tree inventory data provided by users will not include two components that are part of the aboveground and belowground live carbon pools: saplings (trees between 1” diameter and 5” diameter), and understory (vegetation less than 1” diameter). These will be estimated similarly to the forest carbon pools from stand description data (region, forest type, and age).

The general flow of the processing steps for data provided via the stand detail template is depicted in Figure 8. The broad processing steps (referenced in Table 5) are:

1. Convert volumes (in MBF, cubic feet, or cords) to merchantable green weight (short tons). This may require several substeps:
2. 1. Convert MBF International to green tons
   2. Convert cubic feet inside bark to green tons
   3. Convert cords to green tons
   4. Convert MBF Doyle to MBF International (then step 1.a.)
   5. Convert MBF Scribner to MBF International (then step 1.a.)
   6. Convert cubic feet outside bark to cubic feet inside bark (then step 1.b.)
2. Convert merchantable green weight to merchantable dry weight (short tons).
3. Adjust merchantable dry weight from whatever top diameter specified by the user to merchantable dry weight to a 4” top diameter (as used by FIA).
4. Convert merchantable dry weight to a 4” top diameter to total aboveground tree biomass (dry weight in short tons).
5. Convert total aboveground tree biomass to total aboveground tree carbon.
6. Compute the carbon in the merchantable portion of trees.
7. Compute the corresponding total belowground tree carbon.
8. Aggregate all species/product/diameter records to the stand level and multiply by acres.
9. Compute sapling carbon aboveground and belowground.
10. Compute understory carbon aboveground and belowground.
11. Combine to get live aboveground and belowground carbon.

All carbon stock estimates will be in tons C (and tons C/acre) and converted to metric tonnes (t) CO₂e at a later step.

7.2.1 Convert volumes (MBF, cubic feet, or cords) into merchantable green weight (short tons).

7.2.1.1 For volumes provided in MBF International ¼” log rule (volume units code 5)

Table 16 in the Custom Tool User Documentation Tables provides the lookup table values  to convert MBF International ¼” to green tons . A factor (mbfint_fact) is calculated that converts thousand board feet (MBF International ¼” log rule) to green tons based on the user-provided region, species group code, and stand origin code.  The Custom Tool locates the corresponding record in the model parameter lookup table (matching the region in the REG_11 column, the species group code in the SPGRPCD column and the stand origin in the STAND_ORIGIN column) to retrieve the three parameters needed: y₀ (from the Estimate.y₀ column), b (from the Estimate.b column), and k (from the Estimate.k column). The conversion factor (mbfint_fact) is computed using the following equation:

mbfint_fact = y₀  * d^b  * exp(-k * d)

Where:

mbfint_fact = board feet International to green tons conversion factor

y₀ = parameter retrieved from the lookup table

d = diameter class value from the stand detail file (column 8)

b = parameter retrieved from the lookup table

exp = exponentiation function (e to the power)

k = parameter retrieved from the lookup table

Then, to get green tons for the stand/species/product class/diameter combination, the conversion factor is multiplied by the volume_ac (column 9) in the stand detail file.

grnwt_ac = volume_ac * mbfint_fact

Example: a record in the stand detail file indicates that stand number 13 is in the RMN region, and is a natural stand. For this stand, there is a record for species group 24 (other western softwoods), product class 101 (softwood sawtimber), and average tree diameter of 12.626”, containing 2.957 MBF International ¼” per acre. In the LU6_mbfint lookup table, we find the corresponding record contains the following parameters:

y₀ = 0.90129

b = 0.80424

k = 0.04385

The conversion factor is then:

mbfint_fact = (0.90129) * (12.626^0.80424) * (exp(-0.04385* 12.626))

mbfint_fact = 3.982 green tons/MBF Int

The green tons per acre in this stand/species/product/diameter class is then:

grnwt_ac = 2.957 * 3.982 = 11.775 green tons/ac

7.2.1.2 For volumes provided in cubic feet inside bark (volume units code 4)

Table 17 in the Custom Tool User Documentation Tables provides the lookup table values that convert cubic feet inside bark to green tons. A factor (cf_fact) is calculated that converts cubic feet to green tons using the user-provided region, species group code, and stand origin code.  The Custom Tool locates the corresponding record in the model parameter lookup table (matching the region in the REG_11 column, the species group code in the SPGRPCD column and the stand origin in the STAND_ORIGIN column) to retrieve the three parameters needed: y₀ (from the Estimate.y₀ column), b (from the Estimate.b column), and k (from the Estimate.k column). Then the conversion factor (cf_fact) is computed from the equation:

cf_fact = y₀  * d^b  * exp(-k * d)

Where:

cf_fact = cubic feet to green tons conversion factor

y₀ = parameter retrieved from the lookup table

d = diameter class value from the stand detail file (column 8)

b = parameter retrieved from the lookup table

exp = exponentiation function (e to the power)

k = parameter retrieved from the lookup table

Then, to get green tons for the stand/species/product class/diameter combination, the conversion factor is multiplied by the volume_ac (column 9) in the stand detail file.

grnwt_ac = volume_ac * cf_fact

Example: a record in the stand detail file indicates that stand number 25 is in the RMN region, and it is a natural stand. For this stand, there is a record for species group 12 (true fir), product class 102 (softwood pulpwood), and average tree diameter of 5.89”, containing 161.426 cubic feet per acre. In the LU7_cuft lookup table, we find the corresponding record contains the following parameters:

y₀ = 0.02329

b = -0.16819

k = -0.02779

The conversion factor is then:

cf_fact = (0.023298) * (5.89^-0.16819) * (exp(0.02779* 5.89))

cf_fact = 0.02036 green tons/cubic foot

The green tons per acre in this stand/species/product/diameter class is then:

grnwt_ac = 161.426 * 0.02036 = 3.286 green tons/ac

7.2.1.3 For volumes provided in cords (volume units code 8)

Table 18 in the Custom Tool User Documentation Tables provides the lookup table values that convert cords to green tons. The Custom Tool retrieves a factor (cord_fact) that converts cords to green tons using the user-provided region and species group code. The Custom Tool locates the corresponding record in the lookup table (matching the region in the REG_11 column, the species group code in the SPGRPCD column) to retrieve the factor (cord_fact) from the FACTOR column.

Then, to get green tons for the stand/species/product class/diameter combination, the conversion factor is multiplied by the volume_ac (column 9) in the stand detail file.

grnwt_ac = volume_ac * cord_fact

Example: a record in the stand detail file indicates that stand number 47 is in the RMN region. For this stand, there is a record for species group 24 (other western softwoods), product class 102 (softwood pulpwood), and average tree diameter of 7.1255”, containing 0.95346 cords per acre. In the LU8_cords lookup table, we find the corresponding record contains the following factor:

cord_fact = 2.25 green tons/cord

The green tons per acre in this stand/species/product/diameter class is then:

grnwt_ac = 0.95346 * 2.25 = 2.145 green tons/ac

7.2.1.4 For volumes provided in MBF Doyle log rule (volume units code 6)

Table 19 in the Custom Tool User Documentation Tables provides the lookup table values that convert MBF Doyle to MBF International ¼”. First, the broad species group (Broad_Group  column) is retrieved from the Species_group tab in the Valid_Codes file by matching the species group code provided by the user with the Code column. Using the diameter or diameter class provided by the user, and the broad species group, the Custom Tool finds the corresponding record in the lookup table (matching the diameter class in the ClassMidpt column or between the Class_min and Class_max in Table 19). The factor (doyle_fact) is then retrieved from the FACTOR column.

Then, to get MBF International for the stand/species/product class/diameter combination, the conversion factor is multiplied by the volume_ac (column 9) in the stand detail file.

mbfint_ac = volume_ac * doyle_fact

Next, the procedure documented in Section 7.2.1.1 is applied to convert the MBF International (mbfint_ac) value to green tons.

Example: a record in the stand detail file indicates that stand number 25 is in the RMN region. For this stand, there is a record for species group 18 (Engelmann and other spruces; Softwood broad group), product class 101 (softwood sawtimber), and average tree diameter of 14.93”, containing 5.911 MBF Doyle per acre. In the lookup table, we find the corresponding record contains the following factor:

doyle_fact = 1.6689 MBF International/MBF Doyle

(14” class midpoint, softwood Broad_Group)

The MBF International per acre in this stand/species/product/diameter class is then:

mbfint_ac = 5.911 * 1.6689 = 9.865 MBF International/ac

Using the procedure in 7.2.1.1, we compute the MBF International to green tons conversion factor as:

mbfint_fact = 3.4116 green tons/MBF International per ac

And the green tons is then:

grnwt_ac = 3.4116 * 9.865 = 33.655 green tons per acre

7.2.1.5 For volumes provided in MBF Scribner log rule (volume units code 7)

Table 20 in the Custom Tool User Documentation Tables provides the lookup table to convert MBF Scribner to MBF International ¼”. First, the broad species group (Broad_Group  column) is retrieved from the Species_group tab in the Valid_Codes file (matching the species group code provided by the user with the Code column). Using the diameter or diameter class provided by the user, and the broad species group, the corresponding record is selected in the lookup table (matching the diameter class in the ClassMidpt column or between the Class_min and Class_max in Table 20). The factor (scrib_fact) is then retrieved from the FACTOR column.

Then, to get MBF International for the stand/species/product class/diameter combination, the conversion factor is multiplied by the volume_ac (column 9) in the stand detail file.

mbfint_ac = volume_ac * scrib_fact

Next, the procedure documented in Section 7.2.1.1 is applied to convert the MBF International (mbfint_ac) value to green tons.

Example: a record in the stand detail file indicates that stand number 25 is in the RMN region. For this stand, there is a record for species group 18 (Engelmann and other spruces; Softwood broad group), product class 101 (softwood sawtimber), and average tree diameter of 14.93”, containing 5.911 MBF Scribner per acre. In the lookup table, we find the corresponding record contains the following factor:

scrib_fact = 1.1659 MBF International/MBF Scribner

(14” class midpoint, softwood Broad_Group)

The MBF International per acre in this stand/species/product/diameter class is then:

mbfint_ac = 5.911 * 1.1659 = 6.892 MBF International/ac

Using the procedure in 3.1.1, we compute the MBF International to green tons conversion factor as:

mbfint_fact = 3.4116 green tons/MBF International per ac

And the green tons is then:

grnwt_ac = 3.4116 * 6.892 = 23.513 green tons per acre

7.2.1.6 For volumes provided in cubic feet outside bark (volume units code 3)

Table 21 in the Custom Tool User Documentation Tables provides the lookup table values to convert cubic feet outside bark to cubic feet inside bark. A factor (bark_fact) is calculated that converts cubic feet inside bark to cubic feet outside bark using the user-provided region, species group code, and stand origin code. The Custom Tool locates  the corresponding record in the model parameter lookup table (matching the region in the REG_11 column, the species group code in the SPGRPCD column and the stand origin in the STAND_ORIGIN column) to retrieve the three parameters needed: y₀ (from the Estimate.y₀ column), b (from the Estimate.b column), and k (from the Estimate.k column). The conversion factor (bark_fact) is then computed from the following equation:

bark_fact = y₀  * d^b  * exp(-k * d)

Where:

bark_fact = cubic feet outside bark to inside bark conversion factor

y₀ = parameter retrieved from the lookup table

d = diameter class value from the stand detail file (column 8)

b = parameter retrieved from the lookup table

exp = exponentiation function (e to the power)

k = parameter retrieved from the lookup table

Then, to get cubic feet inside bark for the stand/species/product class/diameter combination, the conversion factor is multiplied by the volume_ac (column 9) in the stand detail file.

cuftib_ac = volume_ac * bark_fact

Next, the procedure documented in section in 7.2.1.2 is applied to convert the cubic feet inside bark (cuftib_ac) value to green tons.

grnwt_ac = cuftib_ac * cf_fact

Example: a record in the stand detail file indicates that stand number 6 is in the SE region, and it is a planted stand. For this stand, there is a record for species group 2 (loblolly and shortleaf pines), product class 102 (softwood pulpwood), and average tree diameter of 6.17”, containing 158.312 cubic feet (outside bark) per acre. In the lookup table, we find the corresponding record contains the following parameters:

y₀ = 0.56330

b = 0.207102

k = 0.0102802

The conversion factor is then:

bark_fact = (0.56330) * (6.17^0.207103) * (exp(-0.0102802*6.17))

bark_fact = 0.77066 cf_ib/cf_ob

The cubic feet inside bark per acre in this stand/species/product/diameter class is then:

cuft_ib_ac = 158.312 * 0.77066 = 122.005 cuft_ib/ac

Using the procedure in 3.1.2, we compute the cubic feet inside bark to green tons conversion factor as:

cf_fact = 0.03141 green tons/cubic feet inside bark per ac

And the green tons per acre is then:

grnwt_ac = 122.005 * 0.03141 = 3.8322 green tons per acre

7.2.2 Convert merchantable green weight (short tons) to merchantable dry weight (short tons).

Table 22 in the Custom Tool User Documentation Tables contains the lookup table values to convert merchantable green weight to merchantable dry weight. The Custom Tool retrieves a factor (grn2dry_fact) that converts the green weight to dry weight using FIA averages for the user-selected region and species group. The Custom Tool finds the corresponding record in the lookup table for the region and species group code to retrieve the FACTOR (grn2dry_fact) from the table.

Then, to get dry tons for the stand/species/product class/diameter combination, the conversion factor is multiplied by the green weight (which was either provided by the user or computed in the steps above).

merch_drywt = merch_grnwt * grn2dry_fact

Example: a record in the stand detail file indicates that stand number 37 is in the SC region. For this stand, there is a record for species group 2 (Loblolly and shortleaf pines; Softwood broad group), product class 102 (softwood pulpwood), and average tree diameter of 9.77”, containing 4.089 green tons per acre. In the lookup table, we find the corresponding record contains the following factor:

grn2dry_fact = 0.55101 dry tons/green ton

The merchantable dry tons per acre in this stand/species/product/diameter class is then:

merch_drywt = 4.089 * 0.55101 = 2.253 merchantable dry tons/ac

7.2.3 Adjust merchantable dry weight (short tons) to merchantable dry weight to a 4” top (short tons).

Table 23 in the Custom Tool User Documentation Tables is referenced to adjust dry weight to a user-specified top diameter to dry weight to the FIA-standard 4” top diameter.

FIA data uses a 4” top diameter for computing merchantable volumes and weights. However, many companies use variable top diameters for different products, and the smallest top diameter (usually for pulpwood) may be 2” or 3”. In the step following this one, merchantable dry weight of trees is converted to total aboveground biomass (dry weight) of trees, which should include the top portion of the stem above the 4” top, as well as branches. Without adjusting for user-specified top diameters, there is a potential to overestimate the tree carbon. For example, the volume to a 2” top will be higher than the volume to a 4” top. If an adjustment factor based on the 4” top to volumes to a 2” top is applied, the biomass and carbon in the tree would be overestimated. Therefore, we apply a factor to convert the biomass up to a user-specified top diameter to the corresponding biomass to a 4” top diameter.

Table 23 in the Custom Tool User Documentation Tables contains the lookup table values to convert the merchantable dry weight to a user-specified top diameter (merch_drywt) to merchantable dry weight to a 4” top (drywt_4inch). The Custom Tool retrieves the model coefficients based on the user-provided region and species group code. The Custom Tool locates the corresponding record in the model parameter lookup table (matching the region in the REG_11 column and the species group code in the SPGRPCD) to retrieve the two parameters needed: α (from the Estimate.a column) and β (from the Estimate.b column). The conversion factor (top_adj) is computed using the following equation:

Where:

top_adj = factor used to compute the corresponding dry weight to a 4” top

D = minimum of 42” or the diameter class value from the stand detail file (column 8)

Dt = top diameter (merchantability specification) retrieved from the stand detail file (column 11)

α = parameter retrieved from the lookup table (Estimate.a)

β = parameter retrieved from the lookup table (Estimate.b)

Using the merch_drywt computed in step 7.2.2, multiply by the top_adj factor to obtain merchantable dry weight to a 4” top diameter:

drywt_4inch = merch_drywt * top_adj

Example: a record in the stand detail file indicates that stand number 37 is in the SC region, and it is a planted stand. For this stand, there is a record for species group 2 (loblolly and shortleaf pines), product class 102 (softwood pulpwood), and average tree diameter of 0.77” containing 2.253 merchantable dry weight (to a 2” top) per acre. In the LU13_topadj lookup table, we find the corresponding record contains the following parameters:

α = 2.996

β = 0.735

The conversion factor is then:

Top_adj = 1-49.772.9961-29.772.9960.735

Top_adj = 0.95496

The merchantable dry weight to a 4” top for this stand/species/diameter combination is then:

drywt_4inch = 2.253 * 0.95496 = 2.1515 tons/ac

7.2.4 Convert merchantable dry weight to a 4” top (short tons) to total tree aboveground biomass (short tons).

Table 24 in the Custom Tool User Documentation Tables contains the lookup table values to convert the merchantable dry weight to a 4” top (drywt_4inch) to total tree aboveground biomass. The Custom Tool retrieves the model coefficients based on the user-provided region, species group code, and stand origin code. The Custom Tool locates the corresponding record in the model parameter lookup table (matching the region in the REG_11 column, the species group code in the SPGRPCD column and the stand origin in the STAND_ORIGIN column) to retrieve the three parameters needed: y₀ (from the Estimate.y0 column), k (from the Estimate.k column), and c (from the Estimate.c column). The conversion factor (merch2agb_fact) is computed using the following equation (note this equation is different from previous ones):

merch2agb_fact = y₀ * exp(-k * d) + c

Where:

merch2stem_fact = merchantable to total stem biomass factor

y₀ = parameter retrieved from the lookup table

d = diameter class value from the stand detail file (column 8)

k = parameter retrieved from the lookup table

exp = exponentiation function (e to the power)

c = parameter retrieved from the lookup table

Then, to get total tree aboveground biomass (treeagb_ac) for the stand/species/product class/diameter combination, the conversion factor is multiplied by the dry weight to a 4” top computed in step 7.2.3:

treeagb_ac = drywt_4inch * merch2agb_fact

Example: a record in the stand detail file indicates that stand number 42 is in the PNWW region, and it is a planted stand. For this stand, there is a record for species group 10 (Douglas-fir), product class 101 (softwood sawtimber), and average tree diameter of 12.25”, containing 56.3 green tons per acre. In step 7.2.4 we computed the corresponding merchantable dry weight was 39.328 tons per acre (to a 4” top diameter). In the lookup table, we find the corresponding record contains the following parameters:

y₀ = 5.09132

k = 0.35144

c = 1.15752

The conversion factor is then:

merch2agb_fact = (5.09132) * (exp(-0.35144*12.25)) + 1.15752

merch2agb_fact = 1.22625 tons total aboveground biomass/merchantable ton

The total aboveground biomass per acre in this stand/species/product/diameter class is then:

treeagb_ac = 39.328 * 1.22625 = 48.226 tons/ac

7.2.5 Convert total tree aboveground biomass (dry short tons) to total aboveground live tree carbon.

Table 25 in the Custom Tool User Documentation Tables provides the lookup table values to convert total tree aboveground biomass to total aboveground live tree carbon,. The Custom Tool retrieves a factor (agb2agc_fact) based on the user-provided region and species group that converts the tree biomass to carbon reflecting FIA averages.

Then, to get aboveground tree carbon for the stand/species/product class/diameter combination, the conversion factor is multiplied by the total stem biomass per acre (totstem_ac, which was computed in step 7.2.5).

treeagc_ac= treeagb_ac * agb2agc_fact

Example: a record in the stand detail file indicates that stand number 37 is in the SC region. For this stand, there is a record for species group 2 (Loblolly and shortleaf pines; Softwood broad group), product class 102 (softwood pulpwood), and average tree diameter of 9.77”, containing 4.089 green tons per acre. We computed the merch_drywt to be 2.253 tons/ac (in step 7.2.2), then following steps 7.2.3 and 7.2.4 found the total stem biomass to be 2.464 tons/ac.

In the lookup table, we find the corresponding record contains the following factor: 

agb2agc_fact = 0.477 tons C/ton biomass 

The tree aboveground carbon per acre in this stand/species/product/diameter class is then:

treeagc_ac = 2.464 * 0.477 =1.175 tons C/ac

7.2.6 Compute carbon stored in the merchantable portion of trees.

Users may wish to know what portion of aboveground carbon is stored in the merchantable portions of their stands. Based on the aboveground live tree carbon already computed, the conversion factor used previously in Step 7.2.4 (merch2agb_fact) can be applied to compute the desired proportion.

merchc_ac = treeagc_ac / merch2agb_fact

Example: in Step 7.2.4, we used stand number 42 in the PNWW region, species group 10 (Douglas-fir), product class 101 (softwood sawtimber), and average tree diameter of 12.25”, containing 39.328 dry tons per acre to a 4” top diameter, and a total tree aboveground biomass of 48.226 tons/ac. When converted to carbon (agb2agc_fact = 0.516), this becomes 24.885 t C/acre.

For this stand, we found the merch2agb_fact:

merch2agb_fact = 1.22625 tons total stem/merchantable ton

So dividing by this factor results in the carbon in the merchantable portion of the trees:

merchc_ac = 24.885 / 1.22625 = 20.293 tons C/acre in merchantable portion

7.2.7 Compute corresponding total belowground live tree carbon.

Belowground tree carbon is estimated following the FIA approach that applies equations published in Jenkins, et al. (2003). This approach uses parameters based on broad species group (softwood hardwood) and tree diameters to compute the ratio of belowground carbon to aboveground carbon. The equation to obtain the ratio is:

ratio = exp[B₀ + B₁/(d*2.54)]

Where:

ratio = belowground C divided by the aboveground C

B₀ and B₁ = parameters from Table 5 below

d = diameter class value (in inches) from the stand detail file (column 8)

2.54 cm/inch = factor to convert diameters in inches to diameters in cm

exp = exponentiation function (e to the power)

Table 5: parameters from Jenkins et al. (2003)

To get the belowground tree carbon per acre, the following formula is applied:

treebgc_ac = treeagc_ac * ratio

Example: a record in the stand detail file indicates that stand number 37 is in the SC region. For this stand, there is a record for species group 2 (Loblolly and shortleaf pines; Softwood broad group), product class 102 (softwood pulpwood), and average tree diameter of 9.77”, containing 4.089 green tons per acre. We computed the treeagc_ac to be 1.175 tons/ac (in step 7.2.5).

We compute the ratio as: 

ratio = exp[-1.5619 * 0.6614/(9.77*2.54)] = 0.2154

The belowground carbon per acre in this stand/species/product/diameter class is then:

treebgc_ac = 1.175 *0.2154 =0.253 tons C/ac

7.2.8 Aggregate data to the stand level and multiply by acres

Based on the user-supplied data from the stand detail file, the following estimates have been computed in Steps 7.2.1-7.2.7: 

grnwt_ac = merchantable green weight (short tons) of trees per acre

merch_drywt = merchantable dry weight (short tons) of trees per acre

drywt_4inch = merchantable dry weight to a 4” top (short tons/ac)

totstem_ac = total stem dry weight (short tons/ac)

merchc_ac = carbon in the merchantable portion of trees

treeagc_ac = carbon in aboveground live trees per acre (short tons/ac)

treebgc_ac = carbon in belowground live trees per acre (short tons/ac)

Stand-level totals can now be calculated across all species, products, and diameters (treeagc_ac and treebgc_ac) which are described as:

Sum (merchc_ac, treeagc_ac, treebgc_ac by stand key)

The stand totals (merchc_ac, treeagc_ac, and treebgc_ac) are then multiplied by the stand acres to get totals for all stands:

Merchc = merchc_ac * Stand_area

treeagc = treeagc_ac * Stand_area

treebgc = treebgc_ac * Stand_area

7.2.9 Exception handling

In some cases, there are no records in the lookup tables for certain combinations of region, species group, and stand origin. This happens most commonly when a given type of forest is rare in a geographic region, or when a type of forest rarely is planted and only occurs as natural stands. Processing exceptions are also applied where users enter a zero for diameter, diameter estimates exceed 42 inches DBH, or estimates of the age of the stand exceed 100 years. In these cases, default values are applied as follows:

1. If no “Planted” stand origin record is found, but a “Natural” stand origin record exists, the values for the Natural stand are applied.
2. If neither “Planted” nor “Natural” records exist for a species group within a region:
3. 1. For some modeling tables (LU[6, 7, 8, 11, 14]), values are estimated using regional averages for either hardwood or softwood species when sufficient species-specific information is unavailable. In these cases, parameter values are derived from averages across all hardwoods or all softwoods within the applicable region.
   2. For other modeling tables (LU[12, 13, 15, 16, 17, 18, 19]), parameter values are based on nationwide averages for the applicable species group, rather than region-specific estimates.
   3. For tables LU[9 and 10], all relevant combinations of region and species group are expected to be directly represented within the dataset, allowing parameter values to be assigned without additional averaging assumptions.

In all cases when such exceptions occur, warnings are reported to the user that reference the record number, stand description file, and where insufficient data were detected to render results based on user inputs and what, if any, deviations were made in the modeling process. 

(Exact warning messages will be updated once interface design is complete)

7.3 Compute sapling carbon

Tables 26 (for aboveground sapling carbon density) and 27 (for belowground sapling carbon density) in the Custom Tool User Documentation Tables provide the lookup tables for sapling carbon. The Custom Tool matches the user-provided region, forest type code, and stand origin code to locate the corresponding record in the model parameter lookup table (matching the region in the REG_11 column, the forest type code in the FORTYPGRPCD column and the stand origin in the STAND_ORIGIN column) and retrieve the three parameters needed: y0 (from the Estimate.y0 column), b (from the Estimate.b column), and k (from the Estimate.k column). Sapling carbon density (sap_ag_cd and sap_bg_cd, for aboveground and belowground) is then computed using the following  equation:

sap_xx_cd = y₀  * a^b  * exp(-k * a)

Where:

sap_xx_cd = sapling carbon density in tons per acre for xx= ag or bg

y₀ = parameter retrieved from the lookup table

a = stand age from the stand description file

b = parameter retrieved from the lookup table

exp = exponentiation function (e to the power)

k = parameter retrieved from the lookup table, with parameters retrieved from Table 26 for aboveground and Table 27 for belowground

Finally, to get total aboveground and belowground sapling carbon in the stand, the per-acre value is multiplied by the stand area from the stand description file.

sap_ag = sap_ag_cd * Stand_area

Sap_bg = sap_bg_cd * Stand_area

Example: a record in the stand description file indicates that stand number 28 is in the SC region, forest type 600, Natural stand origin, age 62 years old, and contains 58.69 acres.

In the aboveground  lookup table, we find the corresponding record contains the following parameters: 

y₀ = 1.01458

b = 0.72218

k = 0.03501

The sapling aboveground carbon density (carbon tons per acre) is then:

Sap_ag_cd =(1.01458) * (62^0.72218) * (exp(-0.03501 * 62))

Sap_ag_cd = 2.28 tC/ac

The total sapling aboveground carbon in the stand is then:

Sap_ag =2.28 * 58.69 = 133.82 tC

Similarly, the parameters retrieved from the belowground lookup table are:

y₀ = 0.18773

b = 0.66060

k = 0.03110

The sapling belowground carbon density (carbon tons per acre) is then:

sap_bg_cd = (0.18773) * (62^0.66060) * (exp(-0.03110 * 62))

sap_bg_cd = 0.42 tC/ac

The total sapling belowground carbon in the stand is then:

sap_bg =0.42 * 58.69 = 24.47 tC

7.4 Compute understory carbon

Table 28 (for aboveground understory carbon density) and 29 (for belowground understory carbon density) in the Custom Tool User Documentation Tables provide the lookup tables for understory carbon. The Custom Tool matches the user-provided region, forest type code, and stand origin code to locate the corresponding record in the model parameter lookup table (matching the region in the REG_11 column, the forest type code in the FORTYPGRPCD column and the stand origin in the STAND_ORIGIN column) to retrieve the three parameters needed: y0 (from the Estimate.y0 column), b (from the Estimate.b column), and k (from the Estimate.k column). Understory carbon density (und_ag_cd and und_bg_cd, for aboveground and belowground) is then estimated using the following equation:

Und_xx_cd = y₀  * a^b  * exp(-k * a)

Where:

und_xx_cd = understory carbon density in tons per acre for xx= ag or bg

y₀ = parameter retrieved from the lookup table

a = stand age from the stand description file

b = parameter retrieved from the lookup table

exp = exponentiation function (e to the power)

k = parameter retrieved from the lookup table, with parameters retrieved from Table 28 for aboveground and Table 29 for belowground

Finally, to get total aboveground and belowground understory carbon in the stand, the per-acre value is multiplied by the stand area from the stand description file.

und_ag = und_ag_cd * Stand_area

und_bg = und_bg_cd * Stand_area

Example: a record in the stand description file indicates that stand number 28 is in the SC region, forest type 600, Natural stand origin, age 62 years old, and contains 58.69 acres.

In the aboveground lookup table, we find the corresponding record contains the following parameters: 

y₀ = 0.8648

b = -0.13245

k = -0.0037

The understory aboveground carbon density (carbon tons per acre) is then:

Und_ag_cd = (0.8648) * (62^-0.13245) * (exp(0.0037 * 62))

Und_ag_cd =0.63 t C/ac

The total understory aboveground carbon in the stand is then:

Und_ag = 0.63 * 58.69 = 36.96 t C

Similarly, the parameters retrieved from the belowground lookup table are:

y0 = 0.09609

b = -0.13245

k = -0.0037

The understory belowground carbon density (carbon tons per acre) is then:

und_bg_cd = (0.09609) * (62^-0.13245) * (exp(0.0037 * 62))

und_bg_cd = 0.07 t C/ac

The total sapling belowground carbon in the stand is then:

und_bg = 0.07 * 58.69 = 4.11 t C

7.5 Combine estimates for all carbon pools at the stand level and store outputs

Live aboveground and belowground carbon is comprised of three components each: tree carbon based on inventory measurements, sapling carbon based on FIA modeled data, and understory carbon based on FIA modeled data.  These three components are summed to get total live aboveground and belowground carbon:

lagc_detail = treeagc + sapagc + undagc

lbgc_detail = treebgc + sapbgc + undbgc

In the list below, the “detail” in the variable name indicates this estimate comes from stand detail (rather than stand description) data. While lagc and lbgc were computed based on the stand description data (in steps 7.1.2 and 7.1.3), the more reliable estimates from the stand detail data will be utilized for any stand for which stand detail data were provided.

The primary estimates for each stand will be:

lagc_detail (or lagc from step 7.1.2 for stands without detail data)

lbgc_detail (or lbgc from step 7.1.3 for stands without detail data)

merchc (for stands with detail data),

nonmerchc (for stands with detail data; nonmerchc = lagc_detail – merchc)

dwc = dead wood carbon (from step 7.1.4)

litc = litter carbon (from step 7.1.5)

soc = soil organic carbon (from step 7.1.6).

These estimates rendered in short tons C. Therefore, as a final step, they need to be converted to metric tonnes (t CO₂e) based on the following two steps

1) Multiply the carbon in short tons by 0.9071847 metric tonnes per short ton

2)Multiply the result by 3.666667 tonnes CO₂e per tonne C to obtain t CO₂e.

7.6 Computing annual carbon stock changes

The Custom Tool can compute carbon stock change estimates if a user uploads complete inventory datasets for two points in time at least a year apart. 

Using those files, the Custom Tool completes an error-check for each inventory dataset separately  

The error checking evaluates consistency between datasets in describing the administrative aggregates and their reported area (acres) at both inventory dates. The Custom Tool does this by summarizing and comparing the total stand areas for all administrative units for the two inventories. Where there are discrepancies detected in area estimates for administrative aggregates, the Custom Tool produces a warning message that describes the nature of the error that prevents stock change computation.

Table 6: Example situations for stock change calculations. Stock changes can be computed only for South Districts B and C, and for PNW District A. Carbon stocks at time 1 and time 2 can be reported for all 6 administrative units.

Then stock change computation can proceed for those administrative units whose area did not change between inventories.

The stock change computation is performed using all carbon pools except for soil organic carbon. Soil carbon stocks are assumed to be static across inventory years due to the higher level of uncertainty and protracted timelines associated with soil carbon changes. Therefore the equations for estimating carbon stock change is as follows:

Stock₁ = lagc₁ + lbgc₁ + dwc₁ + lit₁

Stock₂ = lagc₂ + lbgc₂ + dwc₂ + lit₂

Tot_chng = Stock₂ – Stock₁

Ann_chng = Tot_chng / years_between

Where:

c_pool_n = carbon in a pool at inventory date n, summed to the designated administrative unit

Stock_n = total forest carbon stock (excluding soil carbon) at inventory date n for the designated administrative unit

Tot_chng = overall stock change between inventories,

years_between = time (in decimal years) between the two inventories

Ann_chng = average annual forest carbon stock change (in t CO₂e/year) for the administrative unit between the inventories.=

Example: The entries in bold, underlined text in the table below show where the administrative unit area changed between inventories, preventing calculation of stock change for those areas. 

For the other units, the stocks at time 1 and time 2 are shown. If the Inventory time 1 was July 1, 2023 and the inventory time 2 was December 31, 2024, then the years_between would be 1.5.

Total changes are:

South District B: 3,967,248 – 3,819,361 = 147,888 t CO₂e

South District C: 2,336,668 – 2,207,097 = 129,571 t CO₂e

PNW District A: 960,924 – 1,033,095 = -72,171 t CO₂e

Annual changes are:

South District B: 147,888 t CO₂e / 1.5 yrs = 98,592 t CO₂e/yr

South District C: 129,571 t CO₂e / 1.5 yrs = 86,380 t CO₂e/yr

PNW District A: -72,171 t CO₂e / 1.5 yrs = -48,114 t CO₂e/yr

• Burrill, Elizabeth A.; DiTommaso, Andrea M.; Turner, Jeffery A.; Pugh, Scott A.; Christensen, Glenn; Kralicek, Karin M.; Perry, Carol J.; Lepine, Lucie C.; Walker, David M.; Conkling, Barbara L. 2024. The Forest Inventory and Analysis Database, FIADB user guides, volume: database description (version 9.4), nationwide forest inventory (NFI). U.S. Department of Agriculture, Forest Service. 1016 p. [Online]. Available at web address: https://research.fs.usda.gov/understory/forest-inventory-and-analysis-database-user-guide-nfi
• Domke, G.M., C.H. Perry, B.F. Walters, L.E. Nave, C.W. Woodall, and C.W. Swanston. 2017. Toward inventory-based estimates of soil organic carbon in forests of the United States. Ecological Applications 27(4):1223-1235.
• Jenkins, Jennifer C, David C Chojnacky, Linda S Heath, and Richard A Birdsey. 2003. National-Scale Biomass Estimators for United States Tree Species. Forest Science 49 (1): 12–35.
• 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, W. Brad. 1991. Assessing removals for North Central forest inventories. Res. Pap. NC-299. St. Paul, MN: U.S. Department of Agriculture. Forest Service. North Central Forest Experiment Station, 48 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]
• Winn, Matthew F.; Royer, Larry A.; Bentley, James W.; Piva, Ronald J.; Morgan, Todd A.; Berg, Erik C.; and Coulston, John W. 2020. Timber products monitoring: unit of measure conversion factors for roundwood receiving facilities. e-Gen. Tech. Rep. SRS-251. Asheville, NC: U.S. Department of Agriculture Forest Service, Southern Research Station. 148 p.

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)

Administrative Unit: A user-defined analysis boundary based on political or jurisdictional divisions (e.g., states or counties) used to group FIA plots. 

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).  

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.

Carbon stock: The total mass of carbon contained within a defined pool, expressed as t CO₂e 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. 

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. Diameter at breast height is a primary field measurement from which tree volume, biomass and carbon are estimated. (Adapted from FIA Glossary: Standard Terminology)

Doyle log rule: A log scaling rule used to estimate the board-foot volume of logs from log length and small-end diameter measured underbark. It is commonly used in the Central and Eastern United States, although use varies by region and market.

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. 

EVALIDator: An 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.

Federal Information Processing Standards (FIPS) code: A standardized numeric code used to identify geographic areas such as states and counties. 

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) 

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 (CO₂), methane (CH₄) and nitrous oxide (N₂O). (Adapted from ISO 14050:2020, 3.9.1) 

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.

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.  See harvested wood product (HWP) carbon pool glossary term

Harvested wood product (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 carbon pool definitions and accounting approaches.

International ¼-inch log rule: A log scaling rule used to estimate the board-foot volume of logs from log length and small-end diameter measured underbark, using a ¼-inch saw kerf allowance. It is commonly used in the Eastern United States, although use varies by region and market.

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.

Log scaling rules (Doyle, Scribner, International): Common methods used to estimate the board-foot volume of logs from their dimensions (i.e., Doyle, Scribner, International 1/4 inch log rule). These rules use different assumptions and calculation methods, which can produce different volume estimates for the same log, and their use varies regionally across the United States.  

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. 

Merchantability specification: The set of criteria determining which trees, and which portion of a tree, are considered usable for wood products, including minimum diameter at breast height, top diameter, minimum sawlog length and limits on form defect and cull. FIA applies regionally specific merchantability standards. (Adapted from FIA Glossary: Standard Terminology) 

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 FIA. 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.  

Poletimber-size trees: Trees at least 5.0 inches d.b.h. but smaller than sawtimber-size trees; softwoods 5.0–8.9 inches and hardwoods 5.0–10.9 inches d.b.h. Also referred to as medium-diameter trees. See Stand size class. (Adapted from FIA Glossary: Standard Terminology) 

Product class: A category used to classify roundwood according to its intended product or processing pathway. Timber product categories often distinguish wood type and intended product, such as softwood sawtimber, hardwood pulpwood, posts, poles, or fuelwood. 

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.” Also see growing stock removals/harvest removals, which is defined separately in this glossary.

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) 

Scribner log rule: A log scaling rule used to estimate the board-foot volume of logs from log length and small-end diameter measured underbark. It is commonly used in the Western United States and for some Southern pine sawlogs, although use varies by region and market.

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. 

Sink: A carbon pool that takes up more carbon than it releases over a given time period, resulting in net storage. 

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. 

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) 

Source: A carbon pool that releases more carbon to the atmosphere than it takes up over a specified period of time.

Species group: A classification used by FIA that aggregates individual tree species into broader groups based on taxonomic and ecological similarity for consistent summarization and analysis of forest attributes. (Adapted from 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 key: A unique identifier used to distinguish and track a specific forest stand or condition within a dataset, enabling linkage of plot-level observations and attributes across measurements. 

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)

Survey unit: A sub-state geographic area used by FIA to organize forest inventory sampling, estimation, and reporting. Survey units generally consist of groups of counties and may reflect broad ecological or forest-resource similarities.

(Adapted from the USDA Forest Service FIA Database Description and User Guide and EVALIDator)

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.

Understory carbon pool: A component of the aboveground live biomass carbon pool that represents carbon in non-tree vegetation beneath the forest canopy, including woody shrubs, tree seedlings below 1 inch (2.5 cm) d.b.h. and herbaceous plants.

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. 

This file type contains location identification information for each stand in the inventory (administrative levels and units used by the company and location identifiers). The location identifiers are intentionally general to protect confidential information and are used for lookup purposes to find data for geographically similar stands. The stand key, or unique identifier, consists of a combination of the administrative units and stand number.

There should be one record per stand in the user’s inventory.

¹ See CFIT workbook Table 1 for valid code listings by state.

² See CFIT workbook Table 2 for valid FIA survey unit codes.

³ See CFIT workbook Table 3 for valid forest type group codes.

⁴ Valid codes are 0 for naturally regenerated stands, and 1 for artificially regenerated (e.g., planted) stands (see CFIT workbook Table 4).

⁵ Due to lack of FIA data for older stands, any stand age over 100 will be treated as a 100 year-old stand when retrieving carbon stock estimates from FIA data (i.e., carbon stocks estimated based on forest type and age will have the values for 100-year-old stands).

This file type contains volumetric inventory data summarized by tree species groups, product classes (e.g., sawtimber, veneer, pulpwood, etc.), and (optionally) tree diameter classes within a stand. Because inventories may use different units for different product classes (e.g., board feet for sawtimber and cords for pulpwood), there may need to be multiple product records per species in a stand. Furthermore, many inventories provide details by diameter classes, which provides more accurate estimates of tree volume, biomass, and carbon. Thus, there can be multiple records per stand for different combinations of species group, product, and diameter class.

⁵ See CFIT workbook Table 5 for valid species group codes.

⁶ See CFIT workbook Table 6 for valid product class codes.

⁷ For compatibility with FIA, we use two-inch diameter classes with even-numbered midpoints. For example, the 8” diameter class (represented by the number 8) is for trees 7.0” to 8.9” in DBH. Floating-point numbers for average diameters are also acceptable. If no diameter class or average diameter is recorded for a combination of species group and product, enter a zero.

⁸ See CFIT workbook Table 7 for valid volume unit codes.

⁹ See CFIT workbook Table 8 for top diameter values.

Data retrieval using the FIA EVALIDator application requires specification of the attributes of interest. For example, to get soil organic carbon stock per acre on unreserved forestland, an EVALIDator query might use the following attributes in a ratio query:

Numerator: Carbon in organic soil, in short tons, on forest land (ATTR #52)

Denominator: Area of forest land, in acres (ATTR #2)

Filter string to exclude reserved forestland: “and COND.RESERVCD=0”

The stand-level estimates were derived from data retrieved from EVALIDator using the following attribute specifications. All EVALIDator outputs reflect plot measurements from land designated as “unreserved forest land” and produced data at the FIA plot level.

Data retrieval using the FIA EVALIDator application requires specification of the attributes of interest. For example, to the average ratio of inside-bark volume to outside-bark volume for trees, an EVALIDator query might use the following attributes in a ratio query:

Numerator: Sound bole bark volume of live trees (timber species at least 5 inches d.b.h.), in cubic feet, on forest land (ATTR #11012)

Denominator: Sound bole wood volume of live trees (timber species at least 5 inches d.b.h.), in cubic feet, on forest land (ATTR #574174)

Filter string to exclude reserved forestland: “and COND.RESERVCD=0”

The tree-level estimates were derived from data retrieved from EVALIDator using the following attribute specifications. EVALIDator outputs reflect plot measurements from land designated as “unreserved forest land”, and produced data at the FIA plot level. The numbers in “Estimate of Interest” column refer to the step numbers in Figure 8.