United States

Department of

Agriculture

Forest

Service

Northern

Research Station

General Technical

Report NRS-77

Forest Carbon Estimation Using

the Forest Vegetation Simulator: 

Seven Things You Need to Know

Coeli M. Hoover and Stephanie A. Rebain 
Abstract

Interest in options for forest-related greenhouse gas mitigation is growing, 

and so is the need to assess the carbon implications of forest management 

actions. Generating estimates of key carbon pools can be time consuming 

and cumbersome, and exploring the carbon consequences of management 

alternatives is often a complicated task. In response to this, carbon reporting 

capability has been added to the Forest Vegetation Simulator (FVS) growth 

and yield modeling system, allowing users to produce carbon reports along 

with traditional FVS outputs. All methods and computations are consistent with 

Intergovernmental Panel on Climate Change (IPCC) Good Practice Guidance 

and U.S. voluntary carbon accounting rules and guidelines. We briefly describe 

the FVS system, outline the carbon pools estimated, and provide an overview of 

the data requirements, capabilities, features, and limitations of the model and the 

carbon reports. We also review common questions and pitfalls encountered by 

users when running the model.

Visit our homepage at: http://www.nrs.fs.fed.us/

Published by: For additional copies:

USDA FOREST SERVICE USDA Forest Service

11 CAMPUS BLVD., SUITE 200 Publications Distribution

NEWTOWN SQUARE, PA 19073-3294 359 Main Road

Delaware, OH 43015-8640

February 2011 Fax: 740-368-0152

Manuscript received for publication May 2010

The Authors

Coeli M. Hoover is a research ecologist with the U. S. Forest Service, 

Northern Research Station, in Durham, NH. Stephanie A. Rebain is a 

forester with the U. S. Forest Service, Forest Management Service Center, 

in Fort Collins, CO.

Cover

Cover art designed and drawn by Eric Fiegenbaum; used with his permission.

FVS Web site: http://www.fs.fed.us/fmsc/fvs/


Introduction

The growing number of climate change agreements 

and action plans at scales ranging from local to 

international has led to a greater need for information 

on forest carbon stocks now and in the future. While 

estimates and tools (Proctor et al. 2005, Smith and 

Heath 2008, Smith et al. 2007, U.S. EPA 2008, http://

nrs.fs.fed.us/carbon/tools) are available at the county, 

state, and national levels, developing carbon estimates 

from inventory data for multiple forest stands or entire 

forests is generally an unwieldy process. As forest 

carbon markets and greenhouse gas policies continue 

to develop, the question of how forest management 

practices positively or negatively affect carbon storage 

becomes increasingly important to answer. Accounting 

for carbon in harvested wood presents an additional 

challenge when addressing questions related to 

management options and carbon storage. 

Because of this increased demand for forest carbon 

information, a tool was needed to calculate forest 

carbon stocks at smaller scales and to estimate forest 

management impacts on carbon. The following criteria 

were established: the tool should be accessible to 

managers, include the ability to assess the carbon 

consequences of forest management treatments, 

and produce estimates consistent with most current 

U.S. and international carbon accounting rules and 

guidelines. The FVS carbon reports were developed 

to meet this need. We provide here a brief overview of 

the FVS growth and yield framework, including data 

requirements; describe the FVS carbon reports and 

their underlying calculations; discuss their capabilities, 

strengths, limitations, and appropriate use; and list 

seven questions and answers important to know when 

working with FVS. 

Forest Vegetation Simulator

(FVS) Overview

The Forest Vegetation Simulator (FVS) is the U.S. 

Forest Service’s nationally supported framework for 

forest growth and yield modeling. At its core, FVS 

is an individual-tree, distance-independent growth 

model; it predicts changes in tree diameter, height, 

crown ratio, and crown width, as well as mortality, 

over time. FVS has both empirical and theoretical 

components. For instance, diameter growth is 

predicted from equations fit from large datasets 

collected in a particular geographic area. Conversely, 

in many of the FVS geographic variants, densityrelated mortality is predicted by comparing the current 

stand density to a theoretical maximum density for 

that stand type. FVS originated as the Stand Prognosis 

Model in the 1970s (Stage 1973, Wykoff et al. 1982) 

and, over time, growth equations developed for other 

parts of the United States were incorporated into the 

Prognosis framework. It has also been expanded to 

meet the needs of contemporary forest managers and 

is now a true stand dynamics model. Much of this 

expansion occurred through the addition of extensions 

to the core growth model. Extensions of FVS model 

impacts of various disturbance agents such as fire, 

insects, and disease, and they provide additional 

outputs such as economic analyses. As a result, model 

output pertains to a wide range of natural resource 

disciplines and includes variables related to stand 

density and structure, canopy cover, snag dynamics, 

fire hazard, and surface fuel loading, among others 

(see Appendix A for a partial listing of available 

FVS outputs). Users can also include standard forest 

management activities to see how they affect these 

forest attributes. Consequently, the FVS model is used 

extensively throughout the United States to support 

forest management decisionmaking; approximately 20 

geographic variants, each with regionally appropriate 

default settings, are available (Crookston and Dixon 

2005, Dixon 2002). A map and list of available FVS 

variants are provided in Appendix B.
FVS has specific input requirements and file formats. 

Input data may be stored in text files or within a 

database. Either way, a variety of site-specific data is 

input. Stand-level variables include a measure of site 

quality, such as site index or habitat type, slope, aspect, 

elevation, inventory design specifications, and other 

parameters (see Appendix C for a description of input 

variables). If these values are not provided, default 

values are used. Default values are also provided for 

forest floor and various diameter classes of down dead 

wood; users should enter their own data if available. 

Necessary tree-level variables include species and 

diameter. Additional variables such as tree status 

(live or dead), height, crown ratio, and others may 

be included; otherwise they will be estimated using 

default relationships. Each geographic variant has 

various submodels that describe growth and mortality; 

users should become familiar with the various model 

relationships and the input data requirements and 

structure, all of which are documented in publications 

on the FVS Web site. 

The Fire and Fuels Extension (FFE)

Fire is a component of many forest ecosystems, 

and the Fire and Fuels Extension (FFE) (Reinhardt 

and Crookston 2003) was developed to provide 

managers with a way to assess the intensity and 

effects of potential fires and to model the effects of 

fuel management treatments on fire potential. Many 

components of stand-level carbon (e.g., snags, down 

dead wood, forest floor) are estimated and reported 

in the FFE, so carbon reporting functions are part 

of the FFE rather than a separate extension to the 

model system (for a detailed description of the 

development history, see Hoover and Rebain 2008). 

Calculation methods are consistent with the U.S. 

Carbon Accounting Rules and Guidelines for the 

1605(b) Voluntary Greenhouse Gas Reporting Program 

(available at http://www.eia.doe.gov/oiaf/1605/gdlins.

html) and the Intergovernmental Panel on Climate 

Change (IPCC; Penman et al. 2003) Good Practice 

Guidance for national greenhouse gas inventories. A 

complete description of the carbon reporting methods 

and assumptions is provided in the Fire and Fuels 

Extension documentation (Rebain 2010). 

Carbon Reports: Pools

and Options

Two carbon reports can be requested: the Stand 

Carbon Report and the Harvested Carbon Report. The 

Stand Carbon Report includes the major carbon pools 

as defined by the U.S. Carbon Accounting Rules and 

Guidelines and the IPCC Good Practice Guidance: 

aboveground live tree, belowground live tree (coarse 

roots), belowground dead tree, standing dead trees, 

down dead wood, forest floor, and understory (shrubs/

herbs). In addition, the merchantable portion of live 

tree carbon is reported, as well as total stand carbon, 

total carbon removed during harvest, and carbon 

released from fire (if harvests or fires are simulated). 

Users may choose measurement units: pool amounts 

can be reported in tons per acre, metric tons per 

hectare, or metric tons per acre, a hybrid unit. Carbon 

stock estimates are produced by applying conversion 

factors to the biomass estimates generated as part of 

the standard calculations carried out by FVS and the 

FFE. Biomass, expressed as dry weight, is assumed 

to be 50 percent carbon (Penman et al. 2003) for all 

pools except forest floor, which is estimated as 37 

percent carbon (Smith and Heath 2002). Carbon pools 

in the Stand Carbon Report are defined as follows (for 

additional details, consult Hoover and Rebain 2008 or 

the Fire and Fuels Extension documentation):

• Total Aboveground Live: carbon in live trees, 

including stems, branches, and foliage. Choice of 

calculation methods: either volume based default 

FVS-FFE methods (Rebain 2010, Reinhardt and 

Crookston 2003) or national biomass equations 

(Jenkins et al. 2003). 

• Merchantable Aboveground Live: carbon in the 

merchantable portion of live trees; choice of 

calculation method as above.

• Belowground Live: carbon in coarse roots of live 

trees; carbon in fine roots is assumed to be part of 

the soil pool, not currently reported in FVS.

• Belowground Dead: carbon in coarse roots of dead 

or cut trees. 
Figure 1.—Screen shot of sample Stand Carbon Report, with a thin from below simulated in 2015.

• Standing Dead: carbon in dead trees, including 

stems and any branches or foliage still present, 

but excluding roots. 

• Down Dead Wood: all woody surface material 

regardless of size.

• Forest Floor: all surface organic material 

excluding wood (i.e., litter and duff); this 

definition is not an exact match with those used in 

1605(b) reporting. Under the 1605(b) guidelines, 

fine woody debris (<3 inches) is included in the 

forest floor pool; in the FFE carbon reports, this 

material is included in the down dead wood pool. 

Future modifications include adding a category, 

fine woody debris, to the Stand Carbon Report and 

tracking this material separately.

• Herbs and Shrubs: carbon in live herbs and shrubs.

Other categories reported are Total Removed Carbon 

including carbon removed through cutting live or 

dead trees or hauling away surface fuel, and Carbon 

Released from Fire, which includes carbon in fuel 

consumed by simulated wildfires, prescribed burns, 

and pile-burns. This category is useful for comparing 

the carbon consequences of fuel management 

alternatives, because fire behavior, fuel consumption, 

and therefore carbon released, are based on the burn 

parameters entered. An example of the Stand Carbon 

Report, including a simulated thinning, is shown in 

Figure 1. Note that the Total Removed Carbon column 

is non-zero only in the year of harvest, 2015. 

Because FVS is a stand dynamics model, the carbon 

pools change over time. For instance, the aboveground 

and belowground live and dead pools are initially 

based on the inventory data provided, but then change 

due to tree growth, mortality, and removals. In the 

case shown in Figure 1, the total aboveground live 

carbon is initially 46.8 tons/acre, then drops to 28.4 

tons/acre after live trees are removed as part of the 

harvest, and then increases over the next 30 years to 

34.9 tons/acre as the residual trees grow. Harvesting 

caused the live belowground carbon (live root carbon) 

to decrease from 10.4 to 6.6 tons/acre as some of this 

carbon is moved from the live belowground pool to 

the dead belowground pool. The dead belowground 

carbon decreases over time due to decay. The standing 

dead carbon then decreases over time from 3.3 to 0.2 

tons/acre as these snags fall to the ground and become 

down dead wood.

Down dead wood and forest floor biomass are pools 

that users can initialize from inventory data. If sitespecific data are not available, default values are 

provided for forest floor and various diameter classes 

of down dead wood. During a projection, these 

estimates fluctuate to take into account surface fuel 

decay as well as additions, such as litterfall, snagfall, 

and harvesting residues. As an example, in Figure 

1, the down dead wood increases from 4.6 tons/acre 

to 12.9 tons/acre, because, in this example, crown 

material was left as slash during the harvest. The 

--------------------------------------------------------------------------------------------------------------

 ****** CARBON REPORT VERSION 1.0 ******

 STAND CARBON REPORT

 ALL VARIABLES ARE REPORTED IN TONS/ACRE

STAND ID: 11P MGMT ID: NONE

--------------------------------------------------------------------------------------------------------------

 Aboveground Live Belowground Forest Total Total Carbon

 ----------------- ----------------- Stand ------------------------- Stand Removed Released

YEAR Total Merch Live Dead Dead DDW Floor Shb/Hrb Carbon Carbon from Fire

--------------------------------------------------------------------------------------------------------------

2005 46.8 30.0 10.4 0.7 3.3 4.6 7.1 0.3 73.3 0.0 0.0

2015 28.4 20.5 6.6 5.3 2.0 12.9 7.3 0.3 62.7 11.9 0.0

2025 30.5 21.9 7.2 3.4 0.4 6.6 6.7 0.3 55.1 0.0 0.0

2035 32.6 23.5 7.7 2.3 0.2 4.3 6.8 0.3 54.2 0.0 0.0

2045 34.9 25.3 8.3 1.5 0.2 3.2 7.0 0.3 55.4 0.0 0.0
herb and shrub estimates are initially based on stand 

attributes such as dominant species and density, and 

they change over time as stand conditions change. 

More details can be found in the FVS and FFE 

documentation (Dixon 2002, Rebain 2010, 

Reinhardt and Crookston 2003).

The Harvested Carbon Report tracks the fate of carbon 

in harvested merchantable material, including salvaged 

logs. Carbon in removed merchantable biomass is 

allocated into various pools and followed over time; 

for example, a product in use may be discarded, 

transferring carbon from the product pool into the 

landfill pool. Both merchantability specifications and 

allocation to harvested carbon pools differ by FVS 

variant. Choices made about units and methods of 

calculation for the Stand Carbon Report carry over 

to the Harvested Carbon Report. Carbon in harvested 

merchantable biomass is allocated following the 

methods of Smith et al. (2006) to the following pools:

• Products in use

• Products in landfills

• Carbon emitted from combustion with energy 

capture

• Carbon emitted from combustion or decay without 

energy capture 

Carbon in forest products and in landfills is 

summarized in the Merchantable Carbon Stored 

column of the Harvested Carbon Report, while the 

Merchantable Carbon Removed column reflects all of 

the carbon in merchantable biomass that was removed 

from the stand and is the sum of the four pools above. 

Over time, stored carbon from a particular harvest will 

shift to one of the other categories.

An example of the Harvested Carbon Report is given 

in Figure 2. In this example, 11.9 tons/acre of carbon 

was removed from the stand during the harvest, but 

initially only 7.5 tons/acre of that was stored in forest 

products. Over time, carbon stored in forest products 

in use declines, as some moves to landfills and some 

decays or is burned. At the end of the simulation, 4.3 

tons/acre of the initial removal was still storing carbon.

While carbon removed from the stand is reported in 

the year of harvest in the Stand Carbon Report, the 

carbon contained in earlier removals is not included, 

nor is the carbon accounted for once it leaves the 

stand. Consequently, if harvesting is simulated, you 

should request both reports and add the number in 

the Merchantable Carbon Stored column from the 

Harvested Carbon Report to the corresponding value 

Figure 2.—Screen shot of sample Harvested Carbon Report, with a thin from below simulated in 2015. 

------------------------------------------------------------------------------

 ****** CARBON REPORT VERSION 1.0 ******

 HARVESTED PRODUCTS REPORT

 ALL VARIABLES ARE REPORTED IN TONS/ACRE

STAND ID: 11P MGMT ID: NONE

------------------------------------------------------------------------------

 Merch Carbon

 ---------------

YEAR Prducts Lndfill Energy Emissns Stored Removed

------------------------------------------------------------------------------

2005 0.0 0.0 0.0 0.0 0.0 0.0

2015 7.5 0.0 2.5 1.9 7.5 11.9

2025 3.8 1.6 3.6 2.9 5.4 11.9

2035 2.6 2.1 3.9 3.3 4.7 11.9

2045 2.1 2.2 4.1 3.5 4.3 11.9
in the Total Stand Carbon column from the Stand 

Carbon Report to estimate total carbon sequestered. 

As an example, to obtain the total amount of carbon 

sequestered in 2015, add the total stand carbon 

from the Stand Carbon Report (Figure 1, 62.7 tons 

C/ac) and the merchantable stored carbon from the 

Harvested Carbon Report (Figure 2, 7.5 tons C/ac) 

for a total of 70.2 tons C/ac of sequestered carbon in 

2015. This calculation should be repeated for each 

reporting year. Both the Stand Carbon and Harvested 

Carbon reports may be sent to an external database 

or spreadsheet using the database extension of FVS 

(Crookston et al. 2003), allowing quick calculation 

of total carbon estimates for scenarios where harvests 

have occurred. Figure 3 shows the carbon pools over 

time for the stand shown in Figures 1 and 2. 

One of the challenges in accounting for carbon in 

harvested wood products is the role of imports and 

exports—does the location that produced the timber 

receive credit, or is credit assigned to the importing 

location? The Harvested Carbon Report uses the 

production approach to trade; that is, the fate of the 

carbon in the harvested wood products is calculated 

for all harvested wood produced, regardless of whether 

the wood will be used locally or exported. If the wood 

is exported after harvest, the carbon it contains is 

treated the same as other wood harvested from the site; 

it is not transferred or credited to another location. 

This reduces the chances of double counting carbon in 

the harvested wood products pool. The methods and 

coefficients applied in the Harvested Carbon Report 

are described in detail in Smith et al. (2006). 

Figure 3.—Projected carbon changes over time for the stand in Figure 1. Shrub and herb carbon has been 

omitted. The arrow indicates the year of thinning.

Prod. in landfill

Prod. in use

Live tree

Forest floor

Down dead

Standing dead

Live roots

Dead roots

80

70

60

50

40

30

20

10

0

2005 2015 2025 2035 2045

tons C/ac

Year
Increasingly, forest managers are being asked to 

consider the potential carbon consequences of forest 

management actions. The possibility of earning 

income from the sale of carbon credits further 

highlights the need for projections of forest carbon 

stocks into the future. While there are multiple carbon 

registries at this time, many require that forest carbon 

storage be “additional”—that is, above and beyond 

business as usual—to receive credit as an emission 

offset. Determining this baseline level of carbon 

storage can be difficult, but this is another area where 

the carbon reporting functions can help managers. 

Using data from an appropriately designed forest 

inventory, managers can generate baseline carbon 

stock estimates by simulating the “business as usual” 

management actions for any given tract. Alternative 

management scenarios can then be simulated, and the 

carbon stock estimates and average annual change can 

be compared for a variety of management alternatives 

in the same manner that FVS is generally used to 

compare the outcomes of various management options. 

For example, if “business as usual” is to rely on 

natural regeneration after a disturbance, you could 

simulate this in FVS and estimate carbon storage. 

To estimate carbon storage under a second scenario, 

one where desirable tree species are planted instead, 

a second simulation could be run with the planting 

specifications. By comparing the two simulations, you 

can determine how much (if any) additional carbon 

may be stored by planting trees instead of relying on 

natural regeneration.

Generating the Reports – 

Carbon Keywords

The keywords needed to generate carbon reports can 

be found in the FFE menu in Suppose, the graphical 

user interface for FVS. Three main keywords relate to 

the carbon accounting functions. CarbRept requests 

the Stand Carbon Report and CarbCut requests the 

Harvested Carbon Report. The CarbCalc keyword is 

used to select the biomass prediction method, reporting 

units, and annual decay rate of coarse roots. To assist 

with output analysis, both reports can be sent to an 

external database or spreadsheet using the CarbRpts 

keyword in the database extension menu in Suppose. 

A secondary option for FVS users who are not as 

familiar with individual keywords is to request, adjust, 

and export the carbon reports by choosing “Select 

Outputs” and then “FFE Carbon Reports.” 

Example: Bartlett Experimental Forest 

The Bartlett Experimental Forest (BEF) is a northern 

hardwood forest of about 5,790 acres in the White 

Mountains of central New Hampshire. The BEF, 

originally 2,600 acres, was expanded to its present 

area in 2005 to meet ongoing research needs. The most 

recent inventory was conducted from 2001 to 2003, 

before the expansion. All live stems 2 inches d.b.h. and 

over were tallied on 440 permanent cruise plots, which 

are generally 0.25 acres in size. This information 

on inventory design is used by FVS to produce the 

correct per acre expansion factors. The inventory data 

from these plots were run through the FVS system; 

the resulting current carbon stocks for BEF are 

given in Table 1. Because the carbon stock estimates 

are produced by applying conversion factors to the 

standard biomass estimates generated by FVS and the 

FFE, the accuracy of the carbon reports depends on the 

accuracy and adequacy of the inventory data supplied 

by the user. Users need to make certain that their forest 

inventory design is appropriate and that a sufficient 

number of plots have been measured to ensure meeting 

the error level specified in the inventory design. 

Supplying as much information as possible will also 
improve the projections and estimates; while tree 

height is not a required input variable, adding it will 

improve model performance. Similarly, if data on 

down dead wood and forest floor mass are available, 

including these instead of relying on regional default 

values is advised.

As a simple illustration, the data from BEF were used 

to run projections of carbon stocks over the next 40 

years, with no management actions simulated. The 

current version of the northeast variant was used 

and local values were input for site index, slope, 

aspect, and elevation. Mortality and growth rates 

were left at their default settings, and seedlings were 

added periodically to simulate natural background 

regeneration (only a few of the geographic variants 

include automatic regeneration; aside from stump 

sprouts, users must specify the size and amount of 

seedlings by species). Table 2 shows the carbon stocks 

from this base projection, including average annual 

change in carbon stocks for each 10-year period and 

for the entire projection. If harvesting is simulated, 

the Stand Carbon Report will include the carbon in 

logging slash (by default, crowns are added to the 

down dead wood and forest floor pools), while the 

Harvested Carbon Report includes merchantable 

carbon in wood products and landfills (see Figures 

1 and 2 for examples of these reports). Again, users 

must add the value in the Merchantable Carbon Stored 

column from the Harvested Carbon Report to the value 

in the Total Stand Carbon column in the Stand Carbon 

Report to account for all pools when a harvest occurs. 

This must be done for each reporting year following a 

harvest.

Table 1.—Carbon stocks on the Bartlett Experimental Forest in 2005

Pool Tons C/acre Tons C forest-wide

Aboveground live biomass 44.1 255,339

Belowground live biomass 10.2 59,058

Standing dead 2.9 16,791

Belowground dead biomass 0.7 4,053

Down dead wood 4.5 26,055

Forest floor 7.3 42,267

Shrubs and herbs 0.3 1,737

Total 70.0 405,300

Table 2.—Projected carbon stocks on the Bartlett Experimental Forest, 2005-2045

 Base Growth Scenario Average Annual Change

Year (tons C/acre) (tons C/acre/yr) a

2005 70.0

2015 74.5 0.45

2025 78.8 0.43

2035 82.6 0.38

2045 86.1 0.35

2005-2045 0.40

a

 Average annual change is for each 10-year period, e.g., 2005-2015, 2015-2025
Common Questions: Seven

Things You Need To Know

Should carbon stocks be analyzed, or change 

calculated over time?

The Stand Carbon Report provides an estimate of the 

amount, or stock, of carbon at a specified point in time. 

While carbon stock estimates are important, when 

comparing management alternatives it is most useful 

to compute the rate of change over time (average 

annual change). The average annual change in carbon 

stocks is similar to periodic annual increment and is 

simply calculated by taking the difference between the 

carbon stock at Time 2 and Time 1 and dividing by 

the number of years between the two. This gives the 

rate of change for that time period; note that shortterm and long-term rates may differ for any given 

management alternative. When framing an analysis, 

the management objectives should be considered 

and the time frame should be chosen to reflect those 

objectives. For the BEF case study above (Table 2), 

the rate of average annual change in carbon from 2005 

to 2015 is:

(74.5 tons C/ac – 70 tons C/ac) / 10 years = 

0.45 tons C/ac/year

This calculation can easily be made for any pool; e.g., 

live aboveground biomass only or all live biomass in 

trees. Users may be tempted to run FVS with a cycle 

length of 1 year to generate annual estimates, but 

this practice is discouraged because the default cycle 

lengths are related to the increment data on which the 

growth models were built. Using cycle lengths other 

than the default (10 years in most variants) may result 

in underprediction or overprediction of stand attribute 

values relative to those obtained using the default 

(Wykoff et al. 1982). A few 1-year cycles within 

a simulation will not significantly bias simulation 

results, but creation of whole simulations with 1-year 

cycles is discouraged. To produce annual estimates, 

it is good practice to compute average annual change 

as described above. In general, annual changes in 

carbon stocks are difficult to field verify because the 

carbon increment for a single year will often be within 

the bounds of measurement error, while changes in 

carbon pools over a longer period are generally within 

detection limits. 

FVS is a stochastic model; however, by default, the 

same random number seed is used and so the same 

simulation file produces the same results with each 

run. Random effects are incorporated in the model 

through the distribution of errors associated with the 

prediction of the logarithm of basal area increment. 

The effects of these differing diameter growth rates 

extend through most of the remaining components 

of the model (Dixon 2002). It is possible to reset the 

random number seed to produce variation in projection 

results with the RANNSEED keyword. Hamilton 

(1991) suggests several projections should be made 

using different random seeds rather than relying on the 

results of a single simulation. When estimating carbon, 

it is good practice to follow this recommendation of 

multiple model runs in a stochastic manner to get 

some knowledge of the expected variation around the 

estimate. 

Does regeneration occur automatically in 

simulations?

Probably not. Some FVS variants, such as Inland 

Empire, Eastern Montana, Central Idaho, and 

Southeast Alaska, have a full establishment model 

that predicts incoming regeneration over time. The 

rest of the variants do not—in these cases the only 

regeneration occurring automatically is from sprouting 

following a harvest or fire. As a result, depending 

on the length of your simulations and the types of 

management practices simulated, you may need to 

decide on regeneration rates and input them through 

keywords. Regeneration amounts may be derived 

from expert opinion or literature sources, or they may 

be inferred through other inventory data sources. 

Regeneration rates should be carefully considered 

since they may have a substantial impact on your 

simulation results.
Does FVS estimate soil carbon?

The soil carbon pool is currently not included in 

the carbon reports. Soil carbon stocks are highly 

variable across the landscape and do not respond to 

management actions in a uniform manner. While some 

estimates of soil carbon are available, they are quite 

general and for that reason are not included at this 

time. The status of forest soil carbon data and models 

is being monitored, and soil carbon may be included in 

the reports in the future.

What about cases where only live trees or 

large trees were inventoried? Will some carbon pools be missing from the reports?

The trees initially included in FVS simulations are 

those in your input dataset. To ensure all carbon pools 

are modeled, you must inventory small and dead trees, 

as well as large, live trees. If estimates of surface 

fuels (down dead wood) are available, they should 

be input to the model as well. If no surface fuel data 

are available, FVS dubs in initial values based on the 

forest type and other stand characteristics, depending 

on the variant you are running.

Does FVS work for all forest types?

FVS variants cover most forested areas of the United 

States. However, these variants were developed to 

generally describe forest growth in that region—each 

variant can and should be calibrated to local site 

conditions. Once a variant is selected, there are 

multiple ways to calibrate FVS to better match the 

site conditions (Hamilton 1994, Ray et al. 2009, 

Vandendriesche and Haugen 2008). One simple thing 

is to make sure important variables that drive the 

growth and mortality equations are included in your 

input dataset. These vary by variant but typically 

include topographic variables (slope, aspect, and 

elevation) and site productivity variables (such 

as site index or habitat type). Reading the variant 

overview documentation for the specific area you are 

modeling is essential to know what to include. FVS 

also has a self-calibration feature that allows growth 

measurements to be entered and then used to adjust the 

default growth equations so that they better match a 

stand’s particular site conditions. 

Which method of biomass calculation is the 

best choice?

This depends on the scale of your analysis as well as 

on site factors. The default setting uses the regional 

volume equations from the National Volume Estimator 

Library, the standard method used by FVS. These 

volume estimates are then converted to biomass using 

species-specific pounds/cubic foot conversion factors. 

Because the volume equations do not include crown 

material, separate crown biomass equations are used 

to calculate the additional carbon in this portion of 

the tree. If you are working with just one geographic 

variant, this method is likely a good choice, since 

the equations are more local. If you are conducting 

analyses using several different geographic variants 

and comparing them, then you may wish to select 

the Jenkins et al. (2003) calculation option, which 

uses national biomass equations. This will eliminate 

possible differences in carbon estimates due to 

differences in the behavior of the regional volume 

equations. If the Jenkins et al. (2003) calculation 

option is chosen, it is used to calculate the live tree 

carbon in both the Stand Carbon Report and Harvested 

Carbon Report.

Does FVS estimate carbon or carbon dioxide 

equivalents?

The output units in the carbon reports are chosen 

by the user; while there are three choices, tons/acre, 

metric tons/hectare, or the hybrid unit of metric 

tons/acre, all output is in mass of carbon regardless 

of the unit selected. Those users who require output 

in terms of carbon dioxide will need to convert to 

carbon dioxide equivalent (CO2

e), which is easily 

done by multiplying the mass of carbon by 44/12, 

the molecular weight ratio of carbon dioxide to 

carbon. For nearly all reporting applications requiring 

the use of CO2

e, the units are metric tons rather than 

English tons.
10

Limitations of the Reports

The carbon reporting function was added to FVS 

primarily as a decision support tool for forest managers 

who need to address the carbon consequences of 

planned management actions and their alternatives. 

While this tool may be used to develop carbon 

sequestration estimates for carbon credit trading, the 

reports were not originally designed for this purpose 

and may not include some carbon pools that may 

be of interest to those engaged in reporting overall 

carbon emissions and sequestration. These include 

management related emissions such as the carbon 

emitted from equipment use when harvesting and 

transporting timber, transporting nursery stock for 

planting, etc. A complete carbon footprint analysis 

would include life-cycle analysis of all aspects of 

forest management, such as the emissions associated 

with the production, transportation, and application 

of fertilizer. FVS was designed as a growth and yield 

model; the carbon reporting functions simply convert 

standard FVS outputs to biomass and then to carbon 

using the assumptions detailed above and referenced 

in the model documentation. Full entity-wide carbon 

accounting is beyond the scope of FVS. 

Summary

By building on the existing capabilities of the FFE, 

we integrated easy-to-use, comprehensive carbon 

accounting capabilities into FVS. Managers familiar 

with the model can now estimate carbon stocks 

and assess the carbon implications of different 

management practices along with more traditional 

management objectives by using just a few additional 

keywords. It is important to note that the usual 

recommendations and guidance for running 

simulations in FVS apply; the carbon reports 

simply build on standard FVS outputs. Those 

wishing to use the carbon reporting functions in 

FVS should be aware of the inventory and stand data 

requirements for their particular FVS variant, and 

calibrate the model to local conditions as much as 

possible. When using FVS for any purpose, including 

estimating carbon stocks, it is critical to begin with 

data from an appropriately designed forest inventory 

that meets a suitable level of error (generally ± 10 or 

20 percent). FVS is constantly being improved and 

updated. As a result, the estimates of carbon may 

change based on the version of the software you 

are using. A list of bulletins describing updates and 

improvements to the various FVS components is 

maintained on the FVS Web site.

FVS is an extensive and complex model that can 

simulate nearly any forest management treatment. 

With this flexibility and complexity comes a fairly 

steep learning curve; it is strongly recommended 

that users have prior FVS experience or attend 

FVS training before attempting to use the model.

Training sessions are held throughout the year; 

information on FVS training sessions can be found 

on the FVS Web site. 

Acknowledgments

The authors would like to thank Linda Heath, Chad 

Keyser, and Mariko Yamasaki for feedback on an 

early draft of the manuscript. The final manuscript 

benefited from reviews and suggestions from Elizabeth 

Reinhardt, Robert Smith, Erin Smith-Mateja, and 

Michael VanDyck. We are grateful to Eric Fiegenbaum 

for creating the cover art and to Michael VanDyck for 

providing the map in Appendix B.
11

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symposium; 2002 November 19-21; New Orleans, 

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12

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13

Appendix A – FVS Output tables

Table A-1—List of some available FVS output; this is not an exhaustive list.

Report or Post Processor Variables Included

Summary Statistics Report Trees per acre, basal area, stand density index, quadratic mean 

diameter, stand top height, volume, and others

Output Tree List Detailed individual tree output

Stand and Stock Table post processor Trees per acre, basal area, and volume by species and diameter 

class

SVS post processor Stand Visualization System image files

Compute variables Virtually anything can be computed; includes trees per acre, basal 

area, volume, canopy cover, and other attributes by species and 

size class for live or harvested trees, fuel loading by size class, 

snags, tree biomass by species and size class, and many others

Potential Fire Report Canopy base height, canopy bulk density, crowning index, torching 

index, potential fire type, flame length, mortality, smoke production, 

and fuel models

Fuels Report Surface fuel and standing tree biomass in tons/acre

Summary Snag Report Snags per acre by size and decay class (hard/soft)

Detailed Snag Report Detailed snag output by species, size, decay class, and year of 

death

Fuel Consumption Report Fuel consumption and smoke production for simulated burns

Burn Conditions Report Fire behavior for simulated burns

Mortality Report Mortality by size and species for simulated burns

Structure Class Report Canopy cover, stand structure class, and others
14

Appendix B – FVS Variants

Southeast Alaska and Coastal British Columbia (AK)

Blue Mountains (BM)

Inland California and Southern Cascades (CA)

Central Idaho (CI)

Central Rockies (CR)

Central States (CS)

East Cascades (EC)

Eastern Montana (EM)

Klamath Mountains (NC)

Lake States (LS)

Northeast (NE)

Inland Empire (IE)

Pacific Northwest Coast (PN)

Southern (SN)

South Central Oregon and Northeast California (SO)

Tetons (TT)

Utah (UT)

Westside Cascades (WC)

Western Sierra Nevada (WS)
15

Appendix C – Stand and Tree Input Variables

Table C-1.—List of tree variables that can be input into FVS. Items in bold type are required.

Variable Description

Tree_ID Tree Identification Code

Plot_ID Plot Identification

Tree_Count Tree Count

History History Code 0-5 are live trees, 6 and 7 died during mortality observation, 8 and 9 died 

before mortality observation period

Species Tree Species Code, can be the FVS alpha code, FIA code, or USDA plant symbol

DBH or Diameter Diameter at breast height (dbh) in inches

DG DBH growth in inches

Ht Height in feet

HtG Height growth in feet

HtTopK Height to the point of the tree of top kill in feet

CrRatio If the number is 0-9, then it is considered a crown ratio code. If the number is 10-99, the 

value is considered a percent live crown.

Damage1 - 3 Three damage codes can be input

Severity1 - 3 The associated severity code for each damage code 

TreeValue Tree Value Class Code 1 for desirable, 2 for acceptable, 8 for non-stockable, and any 

other number represents a live cull

Prescription Prescription code 

Age Age of the tree record

Table C-2.—List of stand variables that can be input into FVS. Items in bold type are required.

Variable Description

Stand_ID Stand identification code

Stand_CN Stand control number; a unique stand identifier

Variant The two-character variant identification code

Inv_Year The stand’s inventory year 

Latitude Latitude in degrees of the stand’s location

Longitude Longitude in degrees of the stand’s location

Location Location code representing the Region/Forest/District/Compartment codes

Ecoregion Bailey’s Ecoregion code 

PV_Code or Habitat The habitat type or plant association code

PV_Ref_Code Potential vegetation reference code for the PV_Code

Age Stand age in years

Aspect Aspect in degrees

Slope Slope in percent

ElevFt Elevation in feet

(Table C-2 continued on next page)
16

Appendix C – Stand and Tree Input Variables (continued)

Table C-2. (continued)—List of stand variables that can be input into FVS. Items in bold type are required.

Variable Description

Basal_Area_Factor Basal area factor used in sampling large trees

Inv_Plot_Size The inverse of the fixed plot size in acres used in sampling small trees

Brk_DBH Breakpoint DBH in inches between small tree and large tree plots

Num_Plots Number of plots 

NonStk_Plots Number of non-stockable plots

Sam_Wt Sampling weight used to compute weighted averages

Stk_Pcnt Stockable percent

DG_Trans Diameter growth translation code

DG_Measure Diameter growth measurement period

HTG_Trans Height growth translation code

HTG_Measure Height growth measurement period

Mort_Measure Mortality measurement period

Max_BA Maximum basal area

Max_SDI Maximum stand density index 

Site_Species Site species code

Site_Index Site index 

Model_Type Model type code

Forest_Type Forest type code 

State FIA state code

County FIA county code

Fuel_Model Fire behavior fuel model

Fuel_0_25 Initial tons per acre of 0 to 0.25 inch fuel 

Fuel_25_1 Initial tons per acre of 0.25 to 1 inch fuel 

Fuel_1_3 Initial tons per acre of 1 to 3 inch fuel

Fuel_3_6 Initial tons per acre of 3 to 6 inch fuel

Fuel_6_12 Initial tons per acre of 6 to 12 inch fuel

Fuel_12_20 Initial tons per acre of 12 to 20 inch fuel 

Fuel_20_35 Initial tons per acre of 20 to 35 inch fuel

Fuel_35_50 Initial tons per acre of 35 to 50 inch fuel

Fuel_gt_50 Initial tons per acre of greater than 50 inch fuel

Fuel_Litter Initial tons per acre of litter

Fuel_Duff Initial tons per acre of duff

Photo_Ref Photo series reference number (1 – 32)

Photo_Code Photo reference number
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Printed on recycled paper

Hoover, Coeli M.; Stephanie A. Rebain. 2011. Forest Carbon Estimation Using 

the Forest Vegetation Simulator: Seven Things You Need to Know. Gen. 

Tech. Rep. NRS-77. Newtown Square, PA: U.S. Department of Agriculture, 

Forest Service, Northern Research Station. 16 p.

Interest in options for forest-related greenhouse gas mitigation is growing, and 

so is the need to assess the carbon implications of forest management actions. 

Generating estimates of key carbon pools can be time consuming and cumbersome, 

and exploring the carbon consequences of management alternatives is often a 

complicated task. In response to this, carbon reporting capability has been added to 

the Forest Vegetation Simulator (FVS) growth and yield modeling system, allowing 

users to produce carbon reports along with traditional FVS outputs. All methods 

and computations are consistent with Intergovernmental Panel on Climate Change 

(IPCC) Good Practice Guidance and U.S. voluntary carbon accounting rules and 

guidelines. We briefly describe the FVS system, outline the carbon pools estimated, 

and provide an overview of the data requirements, capabilities, features, and 

limitations of the model and the carbon reports. We also review common questions 

and pitfalls encountered by users when running the model.

KEY WORDS: Forest Vegetation Simulator, forest carbon estimation, forest carbon

 sequestration, harvested wood products
www.nrs.fs.fed.us