CHAPTER 5

Carbon Sequestration in Wood and Paper Products

Kenneth E. Skog, USDA Forest Service, Forest Products laboratory

Geraldine A. Nicholson, Maryland Energy Administration

Introduction

Recognition that increasing levels of CO, in the atmosphere will affect the global climate has spurred research

into reducing global carbon emissions and increasing

carbon sequestration. The main nonhuman sources of

atmospheric CO, are animal respiration and decay of biomass (U.S. Congress OTA 1991). However, increases in

atmospheric levels are attributed mainly to fossil fuel

burning and land use change. While efforts to hold down

emissions of CO, continue, increases in CO, emissions

can also be offset, to a degree, by accumulation in carbon

sinks such as plant biomass and oceans. It is therefore prudent to focus research efforts both on increasing carbon in

sinks and reducing carbon emissions.

In 1990, U.S. CO, emissions were 1,367 Tg carbon

equivalent (Clinton and Gore 1993), where Tg is 1 million

metric tons. Wood and paper products play an important

role in mitigating these emissions by sequestering carbon.

There are currently large stocks of carbon in forests, in

wood and paper products in use, and in dumps and landfills. The size of these carbon stocks is increasing. In 1990

approximately 145 Tg of carbon, or 10.6 percent of the

level of U.S. emissions was harvested and removed from

forests for products. If a substantial portion of this carbon

could be prevented from returning to the atmosphere,

it could be a notable contribution to mitigating carbon

buildup in the atmosphere.

We use the term sequestration to refer to the net sequestration, over a period of time, in a stock of carbon: carbon

in forests, carbon in forest products in use (including net

imports), or carbon in forest products in landfills. This

expands the use of the term beyond its common use referring to net sequestration of carbon to forests.

Carbon sequestration to wood and paper products has

been assessed in several other studies. Some studies assess

carbon sequestration for a range of hypothetical conditions

of forest growth, harvest, end use, and disposal (Schlamadinger and Marland 1996). A worldwide study by Winjum

et al. (1998) estimates net flows of carbon out of forests and

into products using the two accounting frameworks used

in this study—the stock change method, and the atmospheric flow method. They use simplified assumptions to

make estimates of net stock changes, and net emissions to

the atmosphere by world region and for selected countries.

They include estimates of logging residue and assumed

decay. Their results, as noted below, are close to ours even

though their methods are very different. Other studies

focusing on the United States, similar to this one, estimate

the actual stocks and flows of carbon from U.S. forests

to products in use, to dumps or landfills, and to burning

and emissions from decay including reconstruction of historical flows and projections (Heath et al. 1996; Row and

Phelps 1996). This study presents similar results with three

improvements: 1) use of greater detail in the changing

composition of end uses of wood and paper products; 2)

inclusion of net imports of wood and paper products in

carbon sequestration estimates; and 3) use of new, much

lower decay estimates for wood and paper in landfills

including separate estimates of CO2 and CH4 portions.

These improvements help provide a clearer understanding

of how sequestration to products may change.

Our purpose is to show an in-depth method of providing historical estimates and projections of U.S. carbon

sequestration to wood and paper products. We compare

those estimates to amounts sequestered in U.S. forests (an

estimate of carbon stock change in the United States). We

also show how amounts used to estimate the net sequestration in products and forests each year may be used to

estimate the net removals of carbon from the atmosphere

to the United States each year (an estimate of carbon flow

to the United States). We discuss how patterns of wood

use have changed and will change and how they will

influence the pattern and amounts of carbon sequestered.

Methods

Historical data and long-range projections were used to

track roundwood and carbon disposition through to end

uses such as housing or paper. To track carbon beyond

end uses to waste products, we estimated burning, disposal, and decay for waste generated in the process of

using primary products, and for rates of product disposal

from end uses, decay, and burning.

The scope of the analysis is focused and limited in a

number of ways. We track carbon harvested and removed

from roundwood harvest sites. The decay and carbon

emissions from logging residue is contained in separate

estimates we display of net sequestration in forests. We

did not estimate the amounts of carbon released due to

fossil fuels burned by harvesting equipment, or to power

primary or secondary wood and paper products mills, or

to make final products using wood (such as housing). We

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-59. 2000 79
Skog and Nicholson

note how much carbon wood and paper products sequester that may offset such emissions. We show estimates

of net sequestration in forests; the estimates include all

carbon accumulation in trees and soil and all deductions

for decay of dead trees including logging residue, and

deductions due to emissions from forest fires. We include

emissions from all burning of wood residue and discarded wood for energy or incineration and, over time,

all regrowth of all trees. Our model projections do not

include projections of biomass plantations for energy production. We did not calculate if, over time, the degree

to which the effect of harvesting and using wood for

fuel increases the growth in forests over the growth that

would occur without wood burning, so as to reabsorb the

carbon emitted by burning. This is an important question for further research. We estimated the amount of harvested and used carbon and its disposition starting in

1910.

For our historical estimates (post-1909) and projections,

we tracked carbon added to, and emitted from, stocks

of wood and paper products in the United States. Net

sequestration to U.S. carbon sinks come from wood in

trees harvested in the United States and from net imports

(imports minus exports) of logs and wood and paper

products. Historical harvest and product use data are

needed to estimate future emissions from products that

were manufactured in the past. Carbon contained in harvested timber and net imports is tracked through primary

processing into products and end uses (fig. 5.1) (adapted

from Row and Phelps 1996). Wood or paper residues

are generated at all phases of processing and are either

reused in a product, burned with or without energy, or

dumped (historically) or landfilled (currently). Wood and

paper products are tracked to various end uses, where

they have a limited life span and are retired from use and

sent to landfills or burned. The fate of logging residues

were not considered in this model, since decay and emissions from these residues are modeled as part of the forest

ecosystem and included in estimates of change in carbon

sequestered in forests (Heath and Birdsey 1993; Birdsey

and Heath 1995).

Historical data on wood harvest and end use from 1910

through 1986 are from USDA Forest Service surveys and

estimates (USDA Forest Service 1920, 1933, 1948, 1958,

1965, 1973, 1982, 1989; Wadell et al. 1989). Historical wood

harvest, from 1910 through 1986, was tracked from primary products, to end uses, to dumps or landfills (Nicholson 1995). Projections of wood harvest and primary

product production were made using the models that

were used for the 1993 Resource Planning Act (RPA)

Assessment Update (Haynes et al. 1995; Ince 1994). These

projections were made by the North American Pulp and

Paper (NAPAP) model and Timber Assessment Market

(TAMM)/ATLAS forest sector models. Historical information and projections from NAPAP and TAMM/ATLAS

Carbon Sequestration in Wood and Paper Products

Figure 5.1—Cycling of carbon through wood and paper products.

were processed by the WOODCARB model to make

carbon estimates through 2040 for:

• net carbon sequestered in products in use each year

(carbon in minus carbon out);

• net carbon sequestered in landfills or dumps each year

(carbon in minus carbon out);

• carbon released by burning where useable energy was

produced each year; and

• carbon released by decay or burning without energy

produced each year.

The NAPAP model simulates operation of markets

and projects consumption of pulpwood; use, and change

of processing technology; and consumption of pulp and

paper. It projects consumption of hardwood and softwood pulpwood, four categories of recycled paper, and

production and trade of 13 categories of pulp and paper.

The TAMM model and the ATLAS timber inventory

projection model simulate the operation of solid wood

markets and project consumption of timber, production

of lumber and panel products, and end use of lumber

and panels in construction, manufacturing, shipping, and

other applications (see Mills et al. this volume). The

TAMM model also tracks imports and exports of logs,

lumber, and panels. The ATLAS model uses NAPAP and

TAMM calculations of timber removals to project U.S.

forest inventory. The WOODCARB model is an addition

to the TAMM model that tracks carbon in all timber

removed from U.S. land plus carbon in net imports of

logs and wood and paper products.

The following sections explain the methods used to

track the flow of carbon in wood from forests, through

products and end uses, to landfills and emission by decay

or burning.

80 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-59. 2000
Carbon Sequestration in Wood and Paper Products Skog and Nicholson

Carbon Transfer Table 5.1—Carbon per unit of roundwood, by region in kg/m3

(lb/ft3).

From Forests to Harvested Roundwood

The carbon in wood harvested each year was estimated

through 2040, beginning with wood harvested in 1910

and following each year’s wood harvest through to its

final disposition. Carbon in wood residue left on harvest

sites is not included, Cubic feet of roundwood removed in

each of nine U.S. regions is converted to weight of carbon

using factors shown in table 5.1 (Birdsey 1992). Carbon in

logs imported is added to the roundwood sources, and

carbon in logs exported is deducted. The distribution of

uses of imported logs is assumed to be the same as the

distribution of uses for domestic sawlogs.

From Roundwood to Primary Products and

Residue

Annual historical estimates and projections of detailed

product production from the NAPAP and TAMM models

were used to divide roundwood consumed into primary

product, wood mill residue, and pulp mill residue categories (table 5.2). In most areas, solid wood residues are

used almost entirely as raw materials for other processes

or are burned for energy. Only a small portion of residues

is left to decay or is burned without energy (Powell et

al. 1993). Carbon in imports of primary solid wood and

paper products is added to each product category, and

carbon in exports is deducted.

From Primary Products to End-Use Products

and Disposal

Carbon in solid wood products is estimated for nine

end-use categories to estimate the time carbon remains

sequestered in those products (table 5.3). The TAMM projections are used to divide products into these categories.

Pulp and paper products are not tracked to end uses, but

the time in use is estimated directly for various primary

products. When products are placed in end uses, such

as house construction for solid wood and magazine production for paper, some wood or paper is discarded. We

assume 8% loss for solid wood products and 5% for paper

and paperboard products as they are placed into end uses

such as construction or publications. Lost or discarded

wood or paper is tracked to recycling, disposal in landfills

or dumps, or emission by burning. We estimate ~24 percent of paper and paperboard waste (after recycling) was

burned in 1993; this percentage increases to 26 percent for

the year 2000 and thereafter (US EPA 1994).

We adapted an equation used by Row and Phelps to

estimate the fraction of carbon remaining in end use for

each year after the product was placed in use (Row and

Phelps, 1996 p. 37). The key parameter in the equation

Region

Pacific Northwest-west

Pacific Northwest-east

Pacific Southwest

Northern Rocky Mountains

Southern Rocky Mountains

North Central

North East

South Central

South East

Softwood Hardwood

factors factors

242.0 (15.11) 188.4 (11.76)

212.9 (13.29) 188.4 (11.76)

242.0 (15.11) 188.4 (11.76)

215.0 (13.42) 191.7 (11.97)

212.9 (13.29) 188.4 (11.76)

201.0 (12.55) 277.6 (17.33)

194.6 (12.15) 307.7 (19.21)

270.7 (16.90) 317.5 (19.82)

270.7 (16.90) 317.5 (19.82)

is the half-life for carbon in each end use (table 5.4). The

half-life is the time after which half the carbon placed

in use is no longer in use. Disposition of carbon after

use includes recycling, disposal in landfill or dump, or

emission to the atmosphere by burning (with or without

energy produced).

The rate of retirement of wood from end uses is constant for a period, then accelerates for a while near the

median life, and finally slows down after the median life.

Some wood or paper items are expected to have very long

lives in uses such as historical buildings, books in libraries, and antiques. The rate of retirement of paper products

from use is very fast; the half-life is 1 year or less, except

for paper in long-lived publications (free sheet paper),

which has a half-life of 6 years.

Carbon Disposal in Dumps and Landfills

The length of time wood, as opposed to paper, remains

in end uses may have only a minor effect on the net

amount of carbon sequestered in products in the long

run. If, when taken out of use, products are disposed

of in a modern landfill, the literature indicates that they

will stay there indefinitely with almost no decay (Micales

and Skog 1997). What may be more important for carbon

sequestration or emissions is how much wastewood from

discarded wood products or demolition is burned (emitting carbon with or without energy) or how much is recycled (reducing harvest from forests).

Wood and paper sent to landfills (or dumps prior to

1986) includes residue from solid wood mills (in very limited amounts), construction and demolition waste, and

discarded paper, paperboard, and solid wood products.

These same materials are sometimes burned with or without energy. Prior to 1972, most materials were placed

in dumps, where a proportion was burned and contents

were more exposed to oxygen and decayed more comUSDA Forest Service Gen. Tech. Pep. RMRS-GTR-59. 2000. 81
Skog and Nicholson Carbon Sequestration in Wood and Paper Products

Table 5.2—Categories of historical and projected wood consumption used to construct estimates of wood carbon use, disposal, and

decay.

Historical estimates (1910-1986)

Solid wood products and wood mill residue

Lumber

Structural paneling

Nonstructural paneling

Railway ties

Miscellaneous products

Roundwood for fuelwood

Wood and bark mill residue

Projections (1986-2040)

Hardwood and softwood lumber

Hardwood and softwood plywood

Hardwood and softwood in reconstituted panels

Hardwood and softwood miscellaneous products

Hardwood and softwood for roundwood for fuelwood

Hardwood and softwood wood mill residue

Hardwood and softwood bark mill residue

Paper and paperboard products and pulp mill residue

Paper with long use life

Paper with short use life

Paperboard

Sludge and pulp liquor

Newsprint

Coated free sheet

Uncoated free sheet

Coated groundwood

Tissue and sanitary

Specialty

Kraft packaging

Linerboard

Corrugating medium

Solid bleached board

Recycled board

Construction paper and board

Dissolving pulp

Wood and bark waste

Sludge and pulp liquor

Table 5.3—End-use categories used to estimate time that carbon remains sequestered.

Solid wood products Paper and paperboard

Multifamily housing Use and disposal categories

Mobile homes Newsprint

Residential upkeep and repair Boxes

Nonresidential construction Office paper

Manufacturing Coated paper

Shipping Recycled paper categories

Furniture Old newspaper

Railroad ties Old corrugated containers

Miscellaneous uses Mixed paper

Construction waste Pulp substitutes and high

grade deinking

Demolition waste

pletely. Legislation then required that dumps be phased

out by 1986. Since then, materials have been placed in

landfills. Materials in landfills are periodically covered,

which prevents oxygen from entering. For dumps, we

Table 5.4—Assumed duration of carbon sequestration in end

uses of wood and paper.

End use Half-life of carbon (years)

Single-family homes (pre-1980)

Single-family homes (post-1980)

Multifamily homes

Mobile homes

Nonresidential construction

Pallets

Manufacturing

Furniture

Railroad ties

Paper (free sheet)

Paper (all other)

80

100

70

20

67

6

12

30

30

6

1

estimate that 65 percent of waste was burned. We assume

the remaining waste decayed evenly during a 96-year

period, with a greater proportion of carbon being released

as CO 2 than as CH4 because of a geater mix of oxygen

with the materials.

8 2 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-59. 2000
Carbon Sequestration in Wood and Paper Products Skog and Nicholson

The pattern of landfill decay is markedly different for

wood than for paper. A relatively short time after material

is placed in a landfill, the material is covered and oxygen

is prevented from entering the landfill. While oxygen

is available, white-rot fungus can decay lignin to a limited extent. However, the oxygen is consumed rapidly.

After the oxygen is gone, only anaerobic bacteria remain.

These organisms cannot break down lignin, but they can

break down exposed cellulose and hemicellulose. However, anaerobic bacteria cannot reach cellulose or hemicellulose that is enclosed in lignin (Ham et al. 1993; Wang et

al. 1994). This means that very little decay of solid wood

occurs. Newsprint, which has a lignin content of 20 to 27

percent, is also very resistant to decay. Other papers with

less lignin are somewhat more subject to decay. In general, much less than half of the carbon in wood or paper

is ever converted to CO2 or CH4 (table 5.5) (Micales and

Skog 1997).

Table 5.5—Estimated maximum proportions of wood and paper

that are converted to CO2 or CH4 in landfills.

Product type Maximum carbon converted (%)

Solid wood 3

Newsprint 1 6

Coated paper 1 8

Boxboard 32

Office paper 38

Not only is the decay of wood and paper highly limited in landfills, but the proportion of carbon emitted as

CO2 is limited to ~40 percent, versus ~60 percent as CH4,

due- to the limitation of oxygen and the greater production of CH4 by anaerobic bacteria. Half of the total CO, is

emitted in ~3 years, while half the total CH4 is emitted in

~20 years (Micales and Skog 1997).

where CIC is net sequestration to the inventory of carbon

in the forest per year (carbon inventory change). It

accounts for any emissions from decay of dead trees or

organic material in the soil. It also accounts for emissions

from decay or burning of logging residue left after harvesting. HP is harvest and removal of wood carbon for

products and wood burning per year. We only include

burning of wood after it has been harvested and removed

from the forest. Emissions from forest fires are included

in the estimate of net sequestration in forests (CIC). Harvesting for products could reduce emissions from fire and

increase sequestration in products. This important effect

should be the subject of further research.

We now focus on the stock of carbon in the atmoThe shift to greater CH4 production in landfills compared with that in dumps is important because CH4 is 25

times more effective than CO2 as a heat-trapping greenhouse gas. In our tracking of CH4 production, we assume

10% of the CH4 is converted to CO, by micro-organisms

as it moves out of the landfill. We assume that the proportion of landfill CH4 that is burned will increase from the

current 15% level to 58% by 2040.

sphere, and estimate how the forest sector adds to or

decreases the size of this stock. We include the emissions

from imports in our variables for emissions from the

United States. The rate of removal from the atmosphere

per year may be expressed as follows (positive terms represent removal from the atmosphere, negative terms represent additions to the atmosphere):

[2]

Calculating Net Removal of Carbon from the

Atmosphere to the United States

One objective of this study is to estimate the combined effect of the forestry sector on net removal of

carbon from the atmosphere through the year 2040. This

includes sequestration to forests, products, and landfills,

and emissions by burning and decay including emissions

from imported products. This section will show why net

annual sequestration of carbon in U.S. stocks (forests,

products, landfills) is greater than the net removal to the

United States from the atmosphere by the amount of net

imports.

where S is net removal of carbon from the atmosphere; G

is gross sequestration of carbon in forest trees and soil per

year, including all growth, even that which is later harvested during the year for products and fuel; WB is emissions of carbon as CO2 from burning wood, paper, or CO2

from burning CH4 for energy production; ECO2 is emissions of carbon as CO2 from decay or burning without

energy; and ECH4 is emissions of carbon as CH4 from

decay in landfills, not including CH4 emitted from wood

products in other places such as sewage systems.

Gross sequestration of carbon to forest trees and soil

per year (G) may be expressed as the change in carbon

inventory in forests during a year plus carbon in material

harvested for products:

[1]

The following steps convert equation [2], which

expresses annual net carbon removal from the atmosphere to the United States in terms of forest sequestration and emissions, into an equation that expresses the

same removal using variables for the annual change in

stock of carbon in products in use (P) and stock of product carbon in landfills (L). Let WB = WBWOOD + WBCH4

where WBWOOD is carbon released from burning wood

and paper, and WBCH4 is carbon released from burnmg

CH4 released from landfills.

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-59. 2000 83
Skog and Nicholson Carbon Sequestration in Wood and Paper Products

We may express the net sequestration to the stock of

products in use (P) as the amount harvested minus the

removal from products in use plus net imports:

[3]

where SL is the amount of carbon shifted to landfills from

the stock of products in use each year.

The net sequestration of carbon to landfills each year

is the amount shifted from products in use (SL) minus

releases:

pare carbon sequestration effects between a forest and a

nonforest industry that both provided, say, housing components, one would need to account for not only the fossil

fuel emissions of these industries but also any carbon

sequestration. The net sequestration effect of using wood

housing components is bolstered by the forest regrowth

and product or landfill sequestration effects calculated

here.

[4]

By solving equation [4] for SL, substituting in equation

[3], and solving for HP, we have

[5]

By substituting equations [1] and [5] in equation [2], we

obtain an expression for total net sequestration per year

that includes the effect of forest growth (CIC), net sequestration to products in use and landfills (P and L), and

emissions from burning and landfill decay (WB, ECO2,

and ECH4):

Some may ask why wood burning does not seem to

add to sequestration since it replaces fossil fuels and trees

grow to absorb the carbon emitted by wood burning. The

answer lies in the fact that equation [7] only indicates the

net sequestration in one year and does not account for

how the value for carbon inventory change (CIC) may

be higher in a future year or years as a result of harvesting and burning wood in the current year. A forest

growth and yield model is needed to evaluate the degree

to which the CIC value is higher in the future due to

harvest and use of wood for energy in the current year.

In the analysis for this study, we used the ATLAS inventory growth and yield model to calculate actual future

increases in forest growth.

Calculating the Greenhouse Gas Effect of

Net Carbon Removal to the United States

[6]

If we focus on the amounts of carbon flows (rather than

the different effects of CO2 and CH4 in the atmosphere),

we may simplify the calculation of carbon removal from

the atmosphere.

[7]

Equation [7] indicates that net removal from the atmosphere is the sum of net sequestration to carbon in forests,

net sequestration to products in use, and net sequestrations to landfills minus net imports.

Annual change in carbon in stocks in the United States

may be expressed as

The greenhouse gas effect of net carbon sequestration

by the forest sector is determined in part by whether

carbon is emitted to the atmosphere as CO, or as CH4. A

CH4 molecule is 25 times more effective in trapping heat

than a CO2 molecule (U.S. Congress OTA 1991). However, CH4

 lasts an average of 10 years in the atmosphere,

while CO2 lasts at least 50 years before breaking down.

The long-term greenhouse effect of a CH, molecule has

been estimated to be ~21 times greater than the effect of

a CO2 molecule (U.S. Congress OTA 1991). To approximate The greenhouse gas effect of net carbon removal (S),

we need to convert carbon emitted as CH4 (ECH4) to its

weight in terms of the heat trapping effect of carbon in

CO,. That is, an atom of carbon in CH4 results in 21 times

more heat trapped than an atom of carbon in CO-,.

[8]

To interpret the difference between equations [7] and

[8], recall from equation [3] that products in use (P) is harvest (HP) increased by net imports minus emissions and

shifts to landfills. So the annual change in stocks includes

net imports while annual removal from the atmosphere

does not.

Equation [7] does not include carbon emissions from

fossil fuels burned for energy in forest sector activities.

The sequestration calculated here is the dividend obtained

by the forestry activities of the sector. If one were to com-

[9]

[10]

where Sg is net carbon removal after converting the CH4

emissions term to CO2 equivalent weight.

About 40% of the carbon from wood and paper decaying in landfills is emitted as CO2

 and about 60% as CH4.

The CO2 is released quickly, while oxygen is present, and

the CH4 is released very slowly after oxygen is depleted

(Micales and Skog 1997). Since half the carbon is emitted

84 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-59. 2000.
Carbon Sequestration in Wood and Paper Products Skog and Nicholson

Table 5.6—Estimates of harvested wood carbon sequestered, emitted, and consumed in U.S. annually in Tg (historical reconstruction

1910 to 1980, with projections to 2040 [RPA Base case]).

Year

Added to

products in

use

Added to

landfills

Emitted by Emitted by decay Total

burning with or burning without consumed

energy energy each year

Historical reconstruction

1910

1920

1930

1940

1950

1960

1970

1980

Base Case projections

1990

2000

2010

2020

2030

2040

24.3 1.1 88.4 10.6 124.4

22.9 3.1 51.9 14.7 92.6

12.8 4.1 44.6 15.5 77.0

14.0 5.3 35.0 20.4 74.7

13.6 6.3 37.4 25.5 82.8

9.0 7.1 34.6 30.6 81.3

12.4 9.2 32.8 35.9 90.3

11.8 27.9 48.1 19.2 107.0

26.0 33.4 74.4 11.4 145.2

25.0 32.5 88.1 14.3 159.9

24.6 38.0 96.8 15.3 174.7

25.6 42.6 103.0 16.4 187.6

24.4 47.0 109.5 17.1 197.9

22.9 50.8 119.0 17.5 210.2

as CH4, converting it to CO2 could have a notable effect in

raising the carbon sequestration by the forestry sector.

Results

Several key factors determine the pattern of historical

and projected carbon sequestration and emissions from

wood and paper products.

The total carbon contained in roundwood harvest plus

net imports declined between 1910 and 1940 (from 124

to 74 Tg/year) in part as a result of steadily decreasing

fuelwood use. After the 1940s the amount of carbon in

roundwood doubled by 1995: 74 Tg/year to 150 Tg/year.

Total carbon in roundwood and net imports is projected

to increase to 210 Tg/year by 2040 as indicated using the

1993 RPA Base case projections for the U.S. forest sector

(table 5.6; fig. 5.1).

Since the early 1900s the use of roundwood in primary

products [lumber, panels, paper and paperboard, fuel)

has shifted from solid wood products and fuelwood, to a

mix of products that includes an increasing proportion of

paper products and more burning of residue from solid

wood products mills and black liquor from pulp mills.

Even though carbon held in solid wood products is

projected to double between 1950 and 2040 (30 to 60

Tg), carbon in pulpwood used in paper production will

Figure 5.2—Annual net sequestration of harvested wood carbon

in products and landfills, and annual emissions from wood burning with energy, and wood and paper decay and other burning in

the United States, 1910 to 1993, with projections to 2040.

increase 600 percent (to 81 Tg) by 2040. Burning of wood

residue and black liquor has also increased relative to

solid wood uses, from 1 Tg in 1910 to 21 Tg in 1990 and

will be 31 Tg in 2040. Fuelwood use, reaching a low of 3

Tg in 1970, is projected to surpass its 1920 level by 2040

and remain slighly higher than burning of wood residue

and black liquor (fig. 5.3).

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-59. 2000 85
Skog and Nicholson Carbon Sequestration in Wood and Paper Products

Table 5.7—United States net carbon accumulation, emission, net Imports, and removal from the atmosphere by yeara.

Net carbon flux (Tg)

1990 2000 2010 2020 2030 2040

Change in forests, CIC 274 189 192 176

Change in products in use, P 26.02 24.99 24.51 25.58

Change in landfills, L 33.38 32.48 39.37 42.53

Wood burning, WB 74.38 88.07 96.58 102.83

Emitted CO2, ECO2 11.43 14.02 14.83 15.77

Emitted CH4 from landfills, ECH4 0 0.23 0.5 0.61

Change in stock of carbonb

333.4 246.47 255.88 244.11

Net imports of wood products,

paper, and paperboard (I - E) 2.33 3.26 3.67 3.87

Removal from atmosphere, S

c

331.07 243.21 252.21 240.24

Removal from atmosphere in CO2 equivalents, Sg

d

331.07 238.61 242.21 228.04

aBase case projections

bChange in stock of carbon = CIC + P + L

c S = CIC + P - (I - E) + L (net carbon removal from atmosphere)

d Sg

 = CIC + P - (I - E) + L - 20(ECH4) (net carbon removal from atmosphere in CO2 equivalents)

166 161

24.27 22.86

46.89 50.74

109.27 118.86

16.49 16.98

0.62 0.55

237.16 234.6

2.84 1.50

234.32 233.1

221.92 222.1

Overall, the rate of net sequestration of carbon to products in use and landfills increased -170 percent between

1970 and 1990—from 22 to 59 Tg/year. This net sequestration reflects disposal and decay of products taken out

of use, sent to landfills or burned; and decay of wood

and paper in landfills. This increase was due in part to

the increase in product consumption; roundwood use

increased 51 percent between 1970 and 1991, 35 to 53 ×

107 m

3

 (12.5 to 18.7 × 109 ft3) (Heath and Birdsey 1993).

It is also due to a sharp increase in the rate of accumulation of carbon in landfills with the shift from dumps

to landfills in the 1970s and 1980s. Net accumulation in

dumps or landfills increased from 9.2 Tg/year in 1970

to 33.4 Tg/year in 1990. This increase in net accumulation was due to virtual elimination of open air burning in

dumps and a decrease in the rate of decay of wood and

paper in landfills compared with that in dumps.

Using the 1993 RPA Base case projections for the forest

products sector, the annual rate of carbon sequestration

to forest trees, understory, floor, and soil is projected to

decline from 274 Tg in 1990 to 161 Tg in 2040 (table 5.7)

(Birdsey and Heath 1995). This trend reflects a slowdown

in the rate of accumulation in the North as forests reach

an age of slower tree growth and slower increases in soil

carbon, and a reduced harvest on public land in the West

along with more intensively managed areas of former old

growth. It also reflects increased management intensity in

the South, where accumulation is balanced by removals

(Birdsey and Heath 1995).

The annual rate of carbon accumulation in landfills or

dumps and products is projected to increase from 59 Tg in

1990 to 75 Tg in 2040. This is due entirely to the increasing

Figure 5.3—Initial product uses of roundwood harvested in the

United States, 1910 to 1993, with projections to 2040.

rate of accumulation in landfills. The net annual sequestration to products in use actually decreases slightly from

26 Tg in 1990 to 23 Tg in 2040. This decline is due in

part to the increasing proportion of wood that is used

in paper products, which have a shorter use-life than do

solid wood products.

Our estimate of 59 Tg carbon added to landfills, dumps,

and products in 1990 is close to the estimate of Winjum et

al. (1998) of 57 Tg stored in commodities for five years or

more for the United States.

Carbon emissions from burning with energy production are projected to increase as a result of notable increases

86 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-59. 2000
Carbon Sequestration in Wood and Paper Products Skog and Nicholson

in burning of black liquor and roundwood (directly from

forests) for fuel. Black liquor and roundwood carbon emissions increase from 54 to 92 Tg between 1990 and 2040.

Burning of mill residue and other wood or paper waste

increases emissions from 20 to 27 Tg during the same

period. Emissions from burning without energy production and from decay are projected to increase from 11 Tg

to 18 Tg between 1990 and 2040. In total carbon, emissions

increase from 86 Tg to 137 Tg between 1990 and 2040.

Our estimate of 86 Tg of total emissions in 1990 is identical to the estimate of Winjum et al. (1998) for emissions

from all sources in 1990.

In 1990, we were adding carbon to the wood and paper

product stocks at the rate of 59 Tg per year. This rate is projected to increase to 74 Tg per year by 2040 (tables 5.6 and

5.7). If we add sequestration to forest trees, understory,

floor, and soils, the rate of sequestration to U.S. carbon

stocks is 333 Tg/yr in 1990 and 235 Tg/year by 2040.

The annual net removal of carbon from the atmosphere

to the United States is slightly less than the accumulation

in stocks due to net imports supplementing US. stocks.

Net removal of carbon from the atmosphere is 331 Tg for

1990 and is projected to decline to 233 Tg by 2040. Net

removal measured in CO2 equivalent effect on the atmosphere is 331 Tg for 1990 and is projected to decline to

222 Tg by 2040. In 1990, the total carbon removal from

the atmosphere to U.S. forests and forest products was 24

percent of the U.S. fossil fuel carbon emissions level of

1,367 Tg (331/1367).

Our estimates of the cumulative fate of carbon in

the United States since 1910 (including net imports) are

shown in figure 5.5. We estimate total carbon in wood

and bark used for products and fuel between 1910 and

1990 at 7.8 Pg (where Pg is 1 billion metric tons). We estimate 2.1 Pg accumulated in products and landfills, 4.0

Pg in wood and bark burned for energy, and 1.7 Pg in

emissions. Total accumulation over the projection period,

from 1990 to 2040, is 9.0 Pg. Accumulation in products

and landfills is projected to be 3.2 Pg between 1990 and

2040 for a total of 5.3 Pg over the period 1910 to 2040.

Conclusions

Our projections indicate we have accumulated 2.1 Pg

of carbon in the stock of wood and paper products in use

and in landfills and dumps in the United States between

1910 and 1990. This is substantial compared with the 1992

stock of carbon in forest trees (13.8 Pg) and in forest soil

(24.3 Pg).

Annual sequestration to product carbon stocks in the

United States are slightly geater than annual removal of

carbon from the atmosphere. Forest, product, and landfill

stocks increased 333 Tg/yr in 1990 while net sequestration

to forests, products, and landfills was 331 Tg/yr. This difference is because net sequestration to stocks includes net

imports while annual removal from the atmosphere does

not. Net removal from the atmosphere may be increased

by burning CH4 from landfills to convert it to CO2, which

has less greenhouse effect.

The choice of accounting method (measuring stock

changes, or measuring removals from the atmosphere)

could determine how a country would count carbon

imports and exports in offsetting greenhouse gas emissions for the purpose of meeting goals under international agreements. This in turn could influence forest

and industry management in the U.S. If credit is given

for increasing stocks, a country would seek to boost

imports and restrain exports. If credit is given for increasing removals from the atmosphere, there would be an

emphasis on increasing carbon sequestration in forests

and in products from domestic forests that may be aided

by increasing exports and restraining imports. There may

also be more emphasis on decreasing methane emissions

from forest products decay in landfills.

By recognizing what has caused changes in sequestration to carbon stocks in wood products and forests we

can identify some ways sequestration can be increased

even more. We can increase sequestration to the stock of

carbon in products, landfills, and forests while maintaining the same aggregate consumption of wood and paper

products by the following actions:

• shifting product mix to a greater proportion of lignincontaining solid wood, paper, and paperboard products, which decay less in landfills;

• increasing product recycling; and

• increasing product use life.

Carbon dioxide equivalent emissions would also be

reduced by the actions noted. Emissions would also be

reduced by burning more landfill CH4 in place of fossil

fuels.

It may be possible to increase sequestration while

increasing product consumption above projected levels

but this would be determined by the certain effects of

such an increase not assessed in this study:

• How much would annual carbon inventory change in

the forest increase in the future as a result of increased

harvest today?

• How much would manufacturing emissions change

due to substitution of wood and paper for nonwood

products?

• How much would emissions from forest fires decrease

due to reduction in fuels available for fires?

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-59. 2000 87
Carbon Sequestration in Wood and Paper Products

Skog and Nicholson

Acknowledgments

The research for this paper was supported, in part, by

a grant from the Environmental Protection Agency, Office

of policy, Planning, and Analysis.

88

Literature Cited