Sequestration, Storage, & Emissions:
Peeling away the bark.
People often conflate sequestration and storage.
But that’s a deep-rooted misconception.
Let’s start with sequestration,
which is the active process of removing CO2 from the atmosphere through photosynthesis1
before it’s converted into carbon and stored as solid wood.
Remember this?
In a single year, the U.S. emits roughly 6,340 MMT of CO2e.2
For a recap, return to Chapter 01
What about emissions?
Annual Passenger Vehicle Travel Emissions
1,016 MMT CO2e3
Emissions from Forestry Harvest Operations
4.2 MMT CO2e4
Emissions from Forest Products Manufacturing Facilities
76 MMT CO2e5
Emissions from Biomass Combustion at Forest Products Manufacturing Facilities
137 MMT CO2e6
Emissions from the Combustion of “Biomass-Wood” for Energy Production
309.3 MMT CO2e6
Annual Wildfire Emissions (Not an industrial emission, but it’s here for reference because we know you’ll ask about it.)
140.82 MMT CO2e7
What’s the difference between biogenic and industrial emissions?8
Each year, growing trees sequester 1,082 MMT of CO2e.9
That’s more than annual U.S. emissions from passenger vehicle travel.
And that’s just sequestration.
Sequestration is a complicated force of nature. The best available data (what we just looked at) is the human attempt to measure a natural process—transfers, emissions, puts and takes of the forest carbon cycle. It’s messy. Here’s a deeper dive.10
Sequestered
(gross CO2e captured through one year’s growth)
Private Working
Public Working
Private Non-Working
Public Non-Working
This is how much CO2e is currently stored by America’s forests.
Each year, sequestered CO2e is added to the ever-growing storage sink11 (much like new earnings being deposited into a savings account).
Stored
(total sink + yearly sequestered)
Private Working
Private Working
106,530 MMT of CO2e
in 351 million acres
Public Working
Public Working
55,313 MMT of CO2e
in 151 million acres
Private Non-Working
Private Non-Working
16,263 MMT of CO2e
in 82 million acres
Public Non-Working
Public Non-Working
31,515 MMT of CO2e
in 111 million acres
National Parks
2,030 MMT
Almost there…
Yeah, private working forests are pretty impressive.
But why is this bar so tree-mendously long?
There are two main reasons. One, there are more private working forest acres than any other forest type. And two, for private working forests, markets keep forests as forests. Forest products markets incentivize private forest owners to invest in their forests, keep them healthy, and keep them growing—pulling carbon out of the atmosphere and storing it long term. The data clearly shows that the continuous cycle of growing, harvesting, and replanting yields an IMPRESSIVE carbon benefit on the landscape.
So far, we’ve been talking “gross sequestration”1 because we were answering the question, “How much carbon do trees suck out of the atmosphere each year?” But unfortunately for us, and fortunately for earth science teachers, it’s more complicated than that.
To understand the real change in carbon getting pulled out of the atmosphere, we need to look at “net sequestration.”13
At the same time tree growth is adding carbon to the live tree carbon storage pool…
All Forests’ Gross Sequestration
1,082 MMT CO2e9
(How much trees added to the storage columns.)
…other forces14 are removing it. Trees in the forest die.15 They decay over time. And we harvest trees.16
The Forest Service calculated that the amount of carbon actually added to the forest carbon pool in 2021 was 760.1 MMT CO2e 11. Folks refer to this as “net sequestration,”17 because it takes into account all the additions to and subtractions from the forest carbon.
Net Carbon Stock Change (“Net Flux” / “Net Sequestration”)
760.1 MMT [CO2e]18
(How much the columns grow by.)
At landscape scale, we can see that private working forests, which account for 47% of all forests, are responsible for:
- Sequestration
Gross sequestration figures are reflective of the basic process of tree growth between two periods of time.
return - Total U.S. Emissions
This is the total gross United States greenhouse gas (GHG) emissions from 2018. This datapoint is from the EPA GHG Inventory (Table 2-1).
Give it to me straight. What does this include, what does it not include? Most of this is due to fossil fuel combustion – electric power generation and tail pipes – but it also includes emissions from things like landfills and enteric fermentation in domestic livestock (that’s how scientists say “cow burps”). This doesn’t include emissions from Land Use, Land Use Change and Forestry (LULUCF). You can read more about LULUCF emissions in this citation.
What about biogenic carbon emissions? The total gross GHG emissions does not include biogenic carbon emissions (emissions from combustion of biomass, like wood and biofuels and “natural” emissions like those from the decomposition of vegetation) because those are accounted for in the LULUCF emissions instead. Including them in the total gross GHG emissions would result in double counting when the net emissions are determined.
Why? It’s nearly impossible to accurately report biogenic carbon emissions. Think about countries where many homes rely on wood stoves and open fires for cooking and heating. Or dead plants decaying in a wetland. Plus, unlike fossil fuel, the biogenic carbon cycle is actually a two-way street, meaning that carbon can also be “removed” from the atmosphere while plants grow. There really isn’t any way to measure those emissions alone, and since there is so much transfer both ways between the atmosphere and land in any given year, there needed to be a different approach to accounting for them.
Let’s zoom in on wood, which comes from forests (the “F” in LULUCF). If we measure or estimate the amount of carbon in forests every year, we can calculate how much the carbon stocks change from year to year. This change is called the carbon flux. The carbon flux includes gains in carbon from, for example, tree growth, and losses in carbon from, for example, wood being removed from the forest and burned for energy. The GHG Inventory reports carbon flux for forest land, cropland, grassland, wetland, and settlements (places where people live), all under the heading of LULUCF.
The good news is that by combining the gross U.S. GHG emissions with the carbon flux from LULUCF, we can get an estimate of the total amount of GHGs actually released to the atmosphere (net emissions) without having to measure all the biogenic carbon emissions. The bad news is that by using this accounting approach, multiple types of biogenic carbon emissions and carbon sinks are combined in a single number and you can’t separate one from the other. That’s why we’ve tried to look at this a little bit differently, which you will see as you scroll.
return - U.S. Passenger Vehicle Emissions
We use passenger vehicles as a reference simply because, well, everyone does! Cars off the road has been the standard mechanism for perspective on climate data for years, so we’re putting this data in the context most people are used to. If you have a car, this is where the emissions from your tailpipe are counted.
In 2021 there were more than 102 million passenger vehicles registered in the U.S.
When folks think of “passenger vehicles” they think of cars. This figure includes emissions from cars, yes, as well as the gasoline and diesel emissions from light-duty trucks. This figure comes from the EPA GHG Inventory (Table 3-13). More information on vehicles can be found on the Bureau of Transportation Statistics site, here.
return - Emissions from Forestry Operations
This includes emissions from operations in the forest, including fuel consumption from harvesting equipment, fertilization, and burning slash piles. The best available U.S.-wide information is from this study using data from 2005. We recognize that this is old data, but it is the only data we have at this point. We’re looking for ways to update this information for future use.
return - Emissions from Forest Products Manufacturing Facilities
This includes direct emissions associated with the manufacture of pulp, paper, paper products, and wood products, plus emissions associated with the generation of electricity that is purchased, plus emissions of CH4 and N2O from biomass combustion at the facility.
This figure does not include direct emissions from the combustion of biomass (biogenic CO2) because EPA does not include those emissions in the total gross GHG emissions reported in the GHG Inventory. However, we can take component pieces of data to calculate total biogenic CO2 emissions: approximately 137 MMT CO2e. The sources for this calculation are:
– Energy use information is from the U.S. Energy Information Administration’s 2018 Manufacturing Energy Consumption Survey (EIA MECS).
– Biogenic CO2 emission factors come from EPA. Emission factors for purchased electricity emission factors come from EPA’s Emissions & Generation Resource Integrated Database (eGRID).
– Fossil and biomass CH4 and N2O factors come from the NCASI/ICFPA GHG calculator.
return - Biomass Emissions
Important clarification! This biomass emissions box is presented for perspective only. Biomass emissions are not industrial emissions, so they would not be included in these gray boxes.
This is the sum of emissions from biomass combustion at forest products manufacturing facilities, 137 MMT CO2e and emissions from the combustion of “biomass-wood” for Energy Production, 309.3 MMT CO2e.
return - Annual Wildfire Emissions
This figure is from the EPA GHG Inventory (Table 6-13).
Important clarification! This wildfire emissions box is presented for perspective only. Wildfires are not an industrial emission, so they would not be included in these gray boxes. EVERYONE asks about wildfire emissions, which is one of the reasons why the EPA provides it as one of the only details from the LULUCF emissions accounting subtotals. See citation 20 for more information about LULUCF.
Why are wildfire emissions so hard to pin down? Wildfire emissions are hard to estimate, and there are a variety of numbers whizzing around out there. One major reason for this is that wildfires are not always “forest fires” – many wildfires burn through grasslands and brushlands, as well as forest land, and total area burned is often lumped together. Some reported numbers are state-specific, some are for a specific year, and some report emissions over a longer period of time. For national stats, it can be unclear if a reported number includes Alaska or not. This number does include Alaska.
For reference: The infamous Camp Fire occurred in 2018. Wildfires in California released an estimated 45.5 MMT of CO2e that year, according to the California Air Resources Board.
return - Biogenic vs. Industrial Emissions
As with many climate science terms, lots of people use terms differently. If you’re unsure, you should always ask. Some people will say biogenic and industrial carbon instead of emissions, while others might refer to industrial emissions/carbon as geologic emissions/carbon, or fossil fuel emissions/carbon.
Biogenic emissions come from natural biological processes, such as plant respiration, organic decomposition, and biomass burning (like wood or crop residue). These emissions are part of a natural carbon cycle. The carbon released by plants and organic matter is often reabsorbed by new plant growth, helping to maintain a balance within a shorter timeframe.
Industrial emissions, on the other hand, result from human-driven activities like fossil fuel combustion for energy, transportation, and industrial manufacturing. This process releases carbon stored underground for millions of years, contributing “new” carbon to the atmosphere. Unlike biogenic sources, these emissions are not reabsorbed quickly, leading to a net increase in atmospheric carbon levels.To recap, biogenic emissions are part of a renewable cycle, often balanced by reabsorption, while industrial emissions increase atmospheric carbon over the long term, intensifying climate impacts.return - Growing Trees Sequester 1,082 MMT of CO2e
This figure is calculated through an analysis of the RPA and FIA data. The analysis was done by the National Council of Air and Stream Improvement, Inc. (NCASI).
Private working forests account for about 80% of our gross forest carbon sequestration. To put that into context, private working forests sequester more carbon than is emitted by passenger vehicles each year.
return - Here’s a deeper dive
This figure is calculated through an analysis of the RPA and FIA data. The analysis was done by the National Council of Air and Stream Improvement, Inc. (NCASI). You can read about it in full here.
return - Carbon Storage
How do you calculate forest carbon storage? Which pools are included?
Forest carbon exists in a number of “pools” or forest components, such as living trees, dead trees, understory vegetation, forest floor, standing and down dead wood, and soil. The U.S. Forest Service Forest Inventory and Analysis (FIA) program has data on all of these components. The living tree pool is measured on every plot, while many of the other pools are based on modeled estimates. The numbers in the forest carbon map include all pools measured or estimated by FIA.
FIA data were downloaded from this link and analyzed using procedures recommended by FIA carbon scientists.
What about soil carbon?
The carbon storage totals shown on this page include soil carbon. Soil carbon is a very large pool. It is very slow to change, and relatively unaffected by forest management over the long term. It is also highly variable within a forest, so it would take a tremendous amount of sampling to get precise estimates for smaller areas.
While the FIA program has started to measure soil carbon on many plots, the data currently available nationwide are estimates based on forest type that were developed from overlaying forest type maps with soil carbon maps. They represent broad averages across large regions. Therefore, these estimates do not change over time unless an FIA plot changes forest type (for example, due to harvest or gradual forest species change).
return - Carbon Storage Breakdown
Carbon storage generally refers to the measurement of carbon in a carbon storage pool at a specific point in time. Forest-carbon storage pools can include things like standing trees, soil carbon, litter, landfills, and wood products. Storage changes like a bank account does, with income (sequestration) being added to the current account (stock), and expenses (emissions) being deducted.
Storage data in the U.S. is often reported in two different ways: as the “CONUS”/contiguous 48 states (excluding Alaska and Hawaii), or as all 50 states. This page uses 50-state figures across acreage, sequestration and storage for consistency, but both breakdowns are provided below for easy reference.
Total U.S. forestland carbon storage (50 states): 209,650 MMT CO2e
- Private working forests carbon storage: 106,530 MMT CO2e
- Private non-working forests carbon storage: 16,238 MMT CO2e
- Public working forests carbon storage: 55,313 MMT CO2e
- Public non-working forests carbon storage: 31,545 MMT CO2e
Total U.S. forestland carbon storage (CONUS/Contiguous 48 states): 203,730 MMT CO2e
- Private working forests carbon storage: 105,923 MMT CO2e
- Private non-working forests carbon storage: 16,076 MMT CO2e
- Public working forests carbon storage: 52,666 MMT CO2e
- Public non-working forests carbon storage: 29,065 MMT CO2e
- Net Sequestration
This refers to the amount of carbon actually added to storage pools in forest land, harvested wood products, woodlands, and urban trees in settlements. As reported by the U.S. Forest Service here.
return - Emissions from forests
The emissions that are accounted “against” forests are a moving target. This comes down to the fact that the question, “what are the emissions associated with forests and wood products?” has many answers depending on what you want to include.*
If you are not thinking about official carbon accounting, but you are focused on the conceptual “carbon footprint” (or lack thereof) of our forests and wood products, you would come up with a list of emissions in your head that would make sense to attribute to forests. Things like mortality, standing dead trees, rotting logs and limbs, wildfires, timber harvests, combustion for biomass emissions, respiration from photosynthesis, wood products manufacturing, and depending on how far you take it, the gas for the truck that delivered your package, etc.
However, it’s not that simple: do you include all land based GHG emissions from trees, forests? What about the entire supply chain? If you include the entire supply chain, do you count the electricity used by a mill in the forest category or in the energy production category? What about emissions that can’t be measured?
If you’re an average person you will think about forest emissions differently from how the UN guides countries to report emissions data. Because of this, there are differing, correct pieces of data floating around out there that don’t line up.
Emissions are accounted for in different places and categories which makes combining data into a neat story that might fit a conceptual view of forest emissions impossible without double counting.
There is an international standard from the UN that outlines how countries should account for these emissions. This is how the EPA reports emissions data in the Inventory of Greenhouse Gasses. That roughly breaks up industrial emissions and biogenic emissions, and results in a best way to account for the unmeasurable emissions while also avoiding double counting.
This website is not a reflection of how carbon emissions are accounted for by the UN. We are here to cover concepts of the forest carbon cycle, and try to put as much of this data as we can in perspective.
What we wish we could do is show the math exactly that shows the gross sequestration number and then all of the emissions that you cut out to get down to a net sequestration figure. As we mentioned in other citations, the data just doesn’t fit together without double counting.
An example here is the emissions from a log truck. Conceptually, you would think that you would like to account for this carbon under forests. However, if you’re accounting for emissions from an economy-wide perspective, it would be impossible to break up all the different trucks in the country to attribute their emissions to specific sectors. So, those emissions are lumped together with other trucks and are accounted for in industrial emissions under transportation.
*This does include biomass and other forms of biogenic emissions
return - Trees in the forest die
738 MMT CO2e/year. This is the average amount of carbon in trees that die in one year. This represents a transfer of carbon to the dead tree pool. Eventually, over time, as this dead wood decomposes, the carbon it contains will be released back into the atmosphere as a forest emission. (This figure is reported in FIA data.) Note that this does not include WY, because data is not available.
return - We harvest trees
599 MMT CO2e/year. This is the average amount of carbon removed from the forest through harvest in a year. Most of this carbon will be transferred to the harvested wood products carbon pool, but some wood and wood products will be combusted as fuel, releasing carbon as an emission. (This figure is reported in FIA data.) Note that this does not include WY, because data is not available.
return - Net vs. Gross Sequestration
This all gets so complicated because “net sequestration” can mean different things. It can be used in a general business accounting sense, which is how we’ve just used it here: the gross forest carbon sequestration (revenue) minus the forest carbon emissions (operating costs) equals the net sequestration (profit).
But there is another definition of net sequestration that is used in carbon accounting under the United Nations protocol (UNFCCC) that EPA follows when they create the annual GHG Inventory Report.
Remember when we talked about how it’s nearly impossible to accurately report biogenic carbon emissions? And how the UN got around that problem by measuring or estimating how much the carbon stocks change from year to year on forest land and in harvested wood products (HWP)? This change, also called carbon flux, includes gains in carbon from, for example, tree growth, and losses in carbon from, for example, wildfire, wood being removed from the forest and burned for energy, and natural decomposition of dead vegetation. For the purposes of carbon accounting, as reported every year by EPA in the GHG Inventory Report, this carbon flux is called net sequestration.
You may be wondering if we can get an estimate of the annual forest-related biogenic emissions by subtracting net sequestration from gross sequestration as reported here. It would be nice if it were that simple, but it is not. Gross sequestration is the amount of carbon sequestered in growing trees while net sequestration, as used in the EPA GHG Inventory Report includes forest carbon in aboveground biomass (like trees) belowground biomass (like plant roots), dead wood, litter, and soil, as well as carbon in harvested wood products in use and in solid waste disposal sites, so it’s kind of like subtracting apples from oranges.
The limit isn’t your imagination, it’s the data.
What you might think we can do:
ALL FOREST SEQUESTRATION minus ALL FOREST EMISSIONS equals NET CARBON SEQUESTRATION.
What we can actually do:
MEASUREMENT OF CARBON STOCKS THIS YEAR minus MEASUREMENT OF CARBON STOCKS LAST YEAR equals
NET SEQUESTRATION/CARBON FLUX/CARBON STOCK CHANGE.
return - Sequestration Breakdown
Sequestration data in the U.S. is often reported in two different ways: as the “CONUS”/contiguous 48 states (excluding Alaska and Hawaii), or as all 50 states. This page uses 50-state figures across acreage, sequestration and storage for consistency, but both breakdowns are provided below for easy reference.
Total U.S. forestland gross sequestration (50 states): 1,581 MMT CO2e
- Private working forests gross sequestration: 1,151 MMT CO2e
- Private non-working forests gross sequestration: 12.9 MMT CO2e
- Public working forests gross sequestration: 325 MMT CO2e
- Public non-working forests gross sequestration: 92 MMT CO2e
- Private working forests gross sequestration: 1,148 MMT CO2e
- Private non-working forests gross sequestration: 12.9 MMT CO2e
- Public working forests gross sequestration: 312 MMT CO2e
- Public non-working forests gross sequestration: 92 MMT CO2e
This refers to the amount of carbon actually added to storage pools in forest land, harvested wood products, woodlands, and urban trees in settlements.
Net vs. Gross Sequestration
This all gets so complicated because “net sequestration” can mean different things. It can be used in a general business accounting sense, which is how we’ve just used it here: the gross forest carbon sequestration (revenue) minus the forest carbon emissions (operating costs) equals the net sequestration (profit).
But there is another definition of net sequestration that is used in carbon accounting under the United Nations protocol (UNFCCC) that EPA follows when they create the annual GHG Inventory Report.
Remember when we talked about how it’s nearly impossible to accurately report biogenic carbon emissions? And how the UN got around that problem by measuring or estimating how much the carbon stocks change from year to year on forest land and in harvested wood products (HWP)? This change, also called carbon flux, includes gains in carbon from, for example, tree growth, and losses in carbon from, for example, wildfire, wood being removed from the forest and burned for energy, and natural decomposition of dead vegetation. For the purposes of carbon accounting, as reported every year by EPA in the GHG Inventory Report, this carbon flux is called net sequestration.
In 2018, the Forest Service reported net sequestration as 752.9 MMT of CO2e, which is still widely cited. Since then, they have revised the 2018 figure up to 782.4 MMT of CO2e. The EPA reported net sequestration of carbon in forests and HWP as 754.5 MMT CO2 eq. (Total net flux from Table 6-10 of the Inventory of US Greenhouse Gas Emissions and Sinks 1990-2018). You may be wondering if we can get an estimate of the annual forest-related biogenic emissions by subtracting net sequestration from gross sequestration as reported here. It would be nice if it were that simple, but it is not. Gross sequestration is the amount of carbon sequestered in growing trees while net sequestration, as used in the EPA GHG Inventory Report includes forest carbon in aboveground biomass (like trees) belowground biomass (like plant roots), dead wood, litter, and soil, as well as carbon in harvested wood products in use and in solid waste disposal sites, so it’s kind of like subtracting apples from oranges.
The limit isn’t your imagination, it’s the data.
What you might think we can do:
All forest sequestration
–
all forest emissions
=
net carbon sequestration
What we can actually do:
Measurement of carbon stocks this year
–
measurement of carbon stocks last year
=
net sequestration/carbon flux/carbon stock change.
return