Forest Service | 2019

Greenhouse Gas Emissions and Removals from Forest Land 

and Urban Trees in the United States, 1990-2017

Introduction

As a signatory to the United Nations Framework Convention on Climate Change (UNFCCC), the United States has 

been reporting an economy-wide inventory of greenhouse gas (GHG) emissions and removals since the mid-1990s 

(U.S. EPA 2019). Forest land, harvested wood products (HWPs), and urban trees within the land sector collectively 

represent the largest net carbon (C) sink in the United States, offsetting more than 11 percent of total GHG emissions 

annually (U.S. EPA 2019). Estimates of GHG emissions and removals are compiled by U.S. Department of Agriculture 

Forest Service scientists and are based primarily on national forest inventory (NFI) data collected and maintained by the 

Forest Inventory and Analysis (FIA) program within the USDA Forest Service. This report—the first in a new series of 

annual updates—provides an overview of the status and trends of GHG emissions and removals from forest land, 

HWPs, and urban trees in settlements in the United States from 1990 to 2017. The national estimates summarized here 

are based on the compilation reported in the Land Use, Land-Use Change, and Forestry chapter of the U.S. EPA (2019) 

submission to the UNFCCC. The national scale estimates reported here will also be disaggregated by individual State in 

future Resource Updates and are currently available upon request (see contact information, page 4).

Forest Carbon Cycle

Carbon is continuously cycled among ecosystem pools 

and the atmosphere as a result of biogeochemical 

processes in forests (e.g., photosynthesis, respiration, 

decomposition, and disturbances such as fires or pest 

outbreaks) and anthropogenic activities (e.g., 

harvesting, thinning, and replanting). As trees 

photosynthesize and grow, C is removed from the 

atmosphere and stored in living tree biomass. As trees 

die and otherwise deposit litter and debris on the 

forest floor, C is released to the atmosphere and is also 

transferred to the litter, dead wood, and soil pools by 

organisms that facilitate decomposition. 

The net change in forest C is not equivalent to the net 

flux between forests and the atmosphere because 

timber harvests do not cause an immediate flux of all 

harvested biomass C to the atmosphere. Instead, 

harvesting transfers a portion of the C stored in wood 

to a "product pool." Once in a product pool, the C is 

emitted over time as carbon dioxide (CO2) in the case 

of decomposition, and as CO2, methane (CH4), nitrous 

oxide (N2O), carbon monoxide (CO), and other 

nitrogen oxides (NOx) when the wood product 

combusts. The rate of emission varies considerably 

among different product pools. 

For estimating C stocks or stock change (flux), C in 

forest ecosystems can be divided into the following 

five storage pools (IPCC 2006):

• Aboveground biomass, which includes all living

biomass above the soil including stem, stump,

branches, bark, seeds, and foliage. This category

includes live understory.

• Belowground biomass, which includes all living

biomass of coarse living roots greater than 2

millimeters (mm) diameter.

• Dead wood, which includes all nonliving woody

biomass either standing, lying on the ground (but

not including litter), or in the soil.

• Litter, which includes the litter, fumic, and humic

layers, and all nonliving biomass with a diameter

less than 7.5 centimeters (cm) at transect

intersection, lying on the ground.

• Soil organic C (SOC), including all organic

material in soil to a depth of 1 meter but

excluding the coarse roots of the belowground

pools.

In addition, there are two harvested wood pools 

included when estimating C flux:

• Harvested wood products (HWP) in use.

• HWP in solid waste disposal sites (SWDS).

United States Department of Agriculture

Box 1: Carbon Pools

RESOURCE UPDATE FS-178
Total Emissions and Removals

Forest land, HWPs, and urban trees in settlements have collectively represented a net GHG sink over the UNFCCC 

reporting period, with interannual variability driven, in large part, by natural and anthropogenic disturbance (e.g., wildfire, 

harvesting), land conversions, and changes in HWPs in use (Table 1.; U.S. EPA 2019). In 2017, forest land, HWPs, and 

urban trees in settlements collectively represented an estimated net update of 730.9 million metric tons of carbon dioxide 

equivalent (MMT CO2 eq.). The category “Forest land remaining forest land” was the largest net sink in the land sector 

with an estimated uptake of 517.8 MMT CO2 eq. Conversions of forest land were the largest source of emissions within the 

categories included in this report, with estimated emissions of 126.1 MMT CO2 eq. (Table 1; U.S. EPA 2019). 

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RESOURCE UPDATE FS-178

Table 1.—Emissions and removals (net flux) from land use, land-use change, and forestry (MMT CO2 eq.)

Non-CO2 emissions from drained organic soils 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 

Non-forest land converted to forest landb (119.1) (119.4) (119.7) (120.0) (120.3) (120.6) (120.6) (120.6)

(762.6) (704.6) (741.0) (699.0) (742.8) (738.7) (730.9) a For details on how estimates were compiled see U.S. EPA 2019. b Estimated emissions and removals include the net changes to C stocks stored in all ecosystem pools. c Estimates of emissions and removals from urban trees in settlements were compiled using percentage tree cover in carbon sequestration density per unit of tree cover. 

Notes: Totals may not sum due to independent rounding. Parentheses indicate net C uptake (i.e., a net removal of C from the atmosphere). 

Forest Land Remaining Forest Land and Harvested Wood Products

Within the category of “Forest land remaining forest land,” aboveground live biomass is the largest contributor to the net 

uptake over the reporting period followed by belowground live biomass and dead wood (Table 2). Harvested wood 

products in use and in solid waste disposal sites (SWDS) are also an important contributor to the net sink in the land sector. 

a For details on these estimates and how they were compiled see U.S. EPA 2019. 

Notes: Totals may not sum due to independent rounding. Parentheses indicate net C uptake (i.e., a net removal of C from the atmosphere).

Table 2.—Emissions and removals (net flux) from forest land remaining forest land (MMT CO2 Eq.)

Carbon Poola 1990 1995 2000 2005 2010 2015 2016 2017

Forest Ecosystem (547.8) (538.1) (518.9) (531.4) (520.9) (549.4) (529.3) (517.8)

Aboveground biomass (378.7) (371.0) (353.8) (361.2) (365.8) (377.5) (371.3) (357.1)

Belowground biomass (90.7) (88.9) (84.8) (86.1) (86.6) (88.6) (87.1) (83.9)

Dead wood (76.0) (76.9) (77.1) (78.9) (78.3) (82.6) (81.9) (77.4)

Litter (4.2) (2.8) (3.9) (5.1) (1.6) (3.3) (1.2) (3.8)

Soil (mineral) 1.2 0.8 (0.0) (0.6) 5.8 0.5 9.2 2.3 

Soil (organic) (0.1) (0.1) 0.0 (0.1) 4.8 1.3 2.2 1.3 

Drained organic soil 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 

Harvested wood (123.8) (112.2) (93.5) (108.0) (67.3) (95.9) (99.6) (103.3)

Products in use (54.8) (51.7) (31.9) (44.6) (5.7) (31.4) (33.5) (35.7)

SWDS (69.0) (60.5) (61.5) (63.5) (61.6) (64.4) (66.1) (67.6)

Total Net Flux (671.6) (650.4) (612.4) (639.4) (588.2) (645.2) (628.9) (621.1)

Emissions and Removals Categorya

Forest land remaining forest landb

Non-CO2 emissions from fire

N2O emissions from forest soils

Forest land converted to non-forest landb

Harvested wood products

Urban trees in settlementsc

Total Net Flux

1990 1995 2000

(547.8) (538.1) (518.9)

2.4 1.0 12.4 

0.1 0.3 0.5 

121.7 123.1 124.5 

(123.8) (112.2) (93.5)

(96.2) (110.1)

(748.3)

(103.1)

2005 2010

(531.4) (520.9)

8.6 5.4 

0.5 0.5 

126.1 127.8 

(108.0) (67.3)

(116.8) (124.3)

2015

(549.4) (529.3) (517.8)

20.8 8.0 8.0 

0.5 0.5 0.5 

126.2 126.2 126.1 

(95.9) (99.6) (103.3)

(124.5) (123.9) (123.9)

2016 2017
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RESOURCE UPDATE FS-178

Forest Land Conversions

Land use conversions to and from forest land result in substantial emissions and removals each year. In this section all 

emissions and removals included for land conversions to and from forest land, as reported in the U.S. EPA (2019), are 

included in Table 3. Forest land conversion to settlements was the largest source of emissions in the conversion 

categories while cropland conversion to forest land resulted in the largest annual uptake. Considering all forest land 

conversions included in the U.S. EPA (2019) report, there have been net emissions in each year over the reporting period, 

with the most recent estimated net emissions of 5.5 MMT CO2 eq. 

Table 3.—Emissions and removals (net flux) from conversions to and from forest land (MMT CO2 eq.)

a For details on these estimates and how they were compiled see U.S. EPA 2019. 

Notes: Totals may not sum due to independent rounding. Parentheses indicate net C uptake (i.e., a net removal of C from the atmosphere). 

Land Area

The land area included in the U.S. EPA (2019) report of GHG emissions and removals includes lands directly influenced 

by human intervention. Direct intervention occurs mostly in areas accessible to human activity and includes altering or 

maintaining the condition of the land to produce commercial or noncommercial products or services; to serve as 

transportation corridors or locations for buildings, landfills, or other developed areas for commercial or noncommercial 

purposes; to extract resources or facilitate acquisition of resources; or to provide social functions for personal, 

community, or societal objectives where these areas are readily accessible to society. Forest Inventory and Analysis data 

from each of the conterminous 48 states and Alaska comprise an estimated 273 million hectares of forest land that are 

considered managed and are included in this report along with an additional 10 million hectares of non-forest land 

converted to forest land. Some differences exist in forest land area estimates in the latest update to the Resources 

Planning Act Assessment (Oswalt et al. 2019) and the forest land area estimates included in U.S. EPA (2019) report, 

which are based on the annual FIA data through 2017 for all states (USDA Forest Service 2018). This difference is due, 

in large part, to the separation of land categories and the managed land definition used in the U.S. EPA (2019) report. 

Sufficient annual inventory data are not yet available for Hawaii but estimates of these areas are included in Oswalt et al. 

(2019). While Hawaii and U.S. Territories have relatively small areas of forest land and thus may not substantially 

influence the overall C budget for forest land, these regions will be added to the forest C estimates as sufficient data 

become available. Agroforestry systems that meet the definition of forest land are also not currently included in the U.S. 

EPA (2019) report since they are not explicitly inventoried (i.e., they are classified as an agroforestry system) by either 

the FIA program or the Natural Resources Inventory of the USDA Natural Resources Conservation Service. Woodland 

area is included in the “grassland remaining grassland” and “land converted to grassland” categories and is not explicitly 

separated in the U.S. EPA (2019) report as a subcategory of grasslands. Combined, forest land and woodland area 

accounts for more than 304 million hectares (Table 4). 

Table 4.—Annual estimates of forest land and woodland area (1000 ha).

a For details on these estimates and how they were compiled see U.S. EPA 2019. 

Notes: Totals may not sum due to independent rounding.

Land Area Categorya 1990 1995 2000 2005 2010 2015 2016 2017 2018

Forest land remaining forest land 269,959 270,720 271,530 271,883 272,609 273,346 273,494 273,623 273,791 

Non-forest land converted to forest land 10,089 10,140 10,194 10,249 10,301 10,341 10,341 10,341 10,341 

Woodlands remaining woodlands 20,576 20,314 19,779 18,925 17,684 16,282 16,015 15,749 15,483 

Non-woodlands converted to woodlands 5,942 5,849 5,656 5,342 4,880 4,456 4,456 4,456 4,456 

Total Area 306,566 307,023 307,160 306,399 305,474 304,425 304,307 304,170 304,072 

Land Conversionsa

Forest land converted to cropland 

Forest land converted to grassland 

Forest land converted to settlements 

Cropland converted to forest land

Other land converted to forest land

Settlements converted to forest land

Wetlands converted to forest land

Total Net Flux

Grassland converted to forest land

1990

50.0 

54.7 

(11.0)

(18.1)

2.6 

17.0 

(47.4)

(41.1)

(1.4)

1995

17.2 

56.3 

(11.1)

(41.2)

3.7 

49.5 

(47.5)

(18.1)

(1.5)

2000 2005

17.4 18.0 

59.9 

(47.8)

(11.0)

(18.2) (18.2)

(41.4)

(1.5) (1.5)

4.9 6.2 

48.9 

58.2 

(11.0)

(47.7)

(41.3)

48.2 

2010 2015 2016 2017

47.1 47.1 

18.5 15.9 

63.2 63.2 

(48.0) (48.0) (48.0)

(10.9) (11.2)

(18.3)

(41.6) (41.7) (41.7)

(1.5) (1.5) (1.5) (1.5)

7.6 5.6 5.5 5.5 

61.8 

(18.3)

47.1 

15.9 

63.2 

(48.0)

(11.1) (11.1)

(18.3) (18.3)

(41.7)

15.8 

47.5
RESOURCE UPDATE FS-178

Planned Improvements

Planned improvements can be broadly assigned to the 

following categories: development of a robust estimation 

and reporting system, individual C pool estimation, 

coordination with other land-use categories, and annual 

inventory data incorporation. Research is underway to 

leverage auxiliary information (i.e., remotely sensed 

information) to operate at finer spatial and temporal scales. 

As in past submissions, emissions and removals associated 

with natural (e.g., wildfire, insects, and disease) and 

human (e.g., harvesting) disturbances are implicitly 

included in the report given the design of the annual NFI, 

but not explicitly estimated. In addition to integrating 

auxiliary information into the estimation framework, 

alternative estimators are also being evaluated which will 

eliminate latency in population estimates from the NFI, 

improve annual estimation and characterization of 

interannual variability, facilitate attribution of fluxes to 

particular activities, and allow for easier harmonization of 

NFI data with auxiliary data products. Finally, estimates of 

emissions and removals from woodlands were compiled 

for the reporting period but were not included in the U.S. 

EPA (2019) report. Preliminary estimates suggest that in 

2017, “Woodlands remaining woodlands” emitted 3.0 

MMT CO2 eq., “Woodlands converted to non-woodlands” 

emitted 11.6 MMT CO2 eq., and “Non-woodlands 

converted to woodlands” was a small sink at 0.5 MMT 

CO2 eq. Emissions and removals from woodlands will be 

incorporated in future U.S. EPA reports.

4

Literature Cited

Oswalt, S.N.; Smith, W. B.; Miles, P.D.; Pugh, S.A., coords. 2019. Forest resources of the United States, 2017: a technical document supporting 

the Forest Service 2020 RPA Assessment. Gen. Tech. Rep. WO-97. Washington, DC: U.S. Department of Agriculture, Forest Service. 223 p. 

https://doi.org/10.2737/WO-GTR-97.

International Panel on Climate Change [IPCC]. 2006 IPCC guidelines for national greenhouse gas inventories. Hayma, Japan: Institute for Global 

Environmental Strategies. https://www.ipcc-nggip.iges.or.jp/public/2006gl/ (accessed 15 April 2019).

USDA Forest Service. 2018. Forest inventory and analysis national program: FIA data mart. Washington, DC: U.S. Department of Agriculture 

Forest Service. http://apps.fs.fed.us/fiadb-downloads/datamart.html (accessed 1 November 2018).

U.S. Environmental Protection Agency [EPA]. 2019. Inventory of U.S. greenhouse gas emissions and sinks: 1990-2017. EPA 430-R-19-001. 

Washington, DC: U.S. Environmental Protection Agency. https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissions-and-sinks.

There were several improvements made in the 

compilation of the forest land, HWPs, and urban trees in 

settlements in the U.S. EPA (2019) report.

• Included, for the first time, more than 24.5 million

hectares of managed forest land in interior Alaska.

• Replaced the regional approach for C estimation in the

western United States with the state-level method used

in the eastern United States so C stocks and stock

changes are now estimated consistently for the entire

1990 to 2017 time series in all states with

remeasurements in the NFI.

• Consistent estimation nationally resolved unbalanced

area estimates which may have resulted in over or

underestimates in C stock changes, particularly soil C,

in past reports.

• Incorporated forest stand-level fuel estimates as well

as combustion factors related to fire severity

classifications in the compilation of fire emissions

estimates.

• Settlement land area was used with percentage tree

cover in developed land as a proxy for percentage tree

cover in settlement area. This improved alignment with

other estimates in the settlements category.

How to Cite This Publication

Domke, Grant M.; Walters, Brian F.; Nowak, 

David J.; Smith, James, E.; Ogle, Stephen M.; 

Coulston, John W. 2019. Greenhouse gas 

emissions and removals from forest land and 

urban trees in the United States, 1990-2017.

Resource Update FS-178. Newtown Square, PA: 

U.S. Department of Agriculture, Forest Service, 

Northern Research Station. 4 p. 

https://doi.org/10.2737/FS-RU-178.

Contact Information

Grant M. Domke, Research Forester

USDA Forest Service, Northern Research Station

1992 Folwell Ave.

St. Paul, MN 55108

Ph: 651-649-5138 Fax: 651-649-5140

gmdomke@fs.fed.us

Northern FIA: http://nrs.fs.fed.us/fia/

National FIA: http://fia.fs.fed.us

USDA is an equal opportunity provider, employer, and lender

The published report is available online at http://doi.org/10.2737/FS-RU-178

Box 2: 2019 Highlights