U.S. Department of the Interior

U.S. Geological Survey

Professional Paper 1787

Baseline and Projected Future Carbon Storage and 

Greenhouse-Gas Fluxes in the Great Plains Region 

of the United States
Cover. Agricultural fields and an abandoned farmstead in eastern Montana in the Great Plains 

region. The Great Plains region of the United States has experienced significant land-use change 

since European settlement, with vast swaths of grasslands converted to agricultural lands. Access 

to water, technological changes, a growing biofuels industry, fluctuating demands for agricultural 

products, and government policies have resulted in periodic historical shifts in land use in the region 

and may drive major land-use changes in the next several decades. Land use and land management 

in the region have significant implications for carbon storage and greenhouse-gas fluxes. 

(Photograph by Terry Sohl.)
Baseline and Projected Future Carbon Storage and 

Greenhouse-Gas Fluxes in the Great Plains Region 

of the United States

By Zhiliang Zhu (editor), Michelle Bouchard, David Butman, Todd Hawbaker, Zhengpeng Li, 

Jinxun Liu, Shuguang Liu, Cory McDonald, Ryan Reker, Kristi Sayler, Benjamin Sleeter, 

Terry Sohl, Sarah Stackpoole, Anne Wein, and Zhiliang Zhu

The USGS maps how much carbon is stored in ecosystems and projects future changes 

using streamgage, soil, and natural-resource inventory data; remote-sensing techniques; 

and computer models

U.S. Department of the Interior

U.S. Geological Survey

Professional Paper 1787
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Zhu, Zhiliang, ed., Bouchard, Michelle, Butman, David, Hawbaker, Todd, Li, Zhengpeng, Liu, Jinxun, Liu, Shuguang, 

McDonald, Cory, Reker, Ryan, Sayler, Kristi, Sleeter, Benjamin, Sohl, Terry, Stackpoole, Sarah, Wein, Anne, and 

Zhu, Zhiliang, 2011, Baseline and projected future carbon storage and greenhouse-gas fluxes in the Great Plains 

region of the United States: U.S. Geological Survey Professional Paper 1787, 28 p. (Also available at http://pubs.

usgs.gov/pp/1787/.)
iii

Contents

Acknowledgments.......................................................................................................................................vii

Executive Summary.......................................................................................................................................1

Introduction.....................................................................................................................................................3

Ecosystems of the Great Plains Region .....................................................................................................3

Land-Use and Land-Cover Changes in the Great Plains Region ...........................................................6

Projected Climate Change in the Great Plains Region ............................................................................8

Wildland Fire and Emissions in the Great Plains Region ........................................................................8

Land Management in the Great Plains Region .......................................................................................10

Carbon Storage and Greenhouse-Gas Fluxes of Terrestrial Ecosystems 

in the Great Plains Region ............................................................................................................11

Carbon Fluxes in the Aquatic Ecosystems of the Great Plains Region...................................................18

Integrated Analysis .....................................................................................................................................18

References Cited..........................................................................................................................................24

Figures

1. Map showing the spatial extent of this assessment ..............................................................5

2. Graphs showing the distributions of the four primary terrestrial ecosystems 

and developed lands of the Great Plains region projected over time for each of 

the IPCC-SRES scenarios—A1B, A2, and B1...........................................................................7

3. Graphs showing the trends of baseline and simulated future burned area due to 

wildland fires and their emissions for each of the three IPCC-SRES scenarios, 

by year, in the Great Plains region.............................................................................................9

4. Graphs showing the trends of terrestrial carbon stocks over time in the Great Plains 

region, for the four primary ecosystems and all lands under each of the three 

IPCC-SRES scenarios—A1B, A2, and B1—using two biogeochemical models .............13

5. Maps showing the spatial distribution and uncertainty of carbon sequestration 

and emission in the Great Plains region, by ecosystem between the baseline 

and 2050........................................................................................................................................15

6. Graphs and maps showing temporal trends of projected future greenhouse-gas 

emissions and their spatial distribution in 2010 in the Great Plains region ......................16

7. Chart showing the minimum through maximum ranges of net flux values (in 

teragrams of carbon per year) for all of the major components of the estimated 

baseline (current) carbon budget for the Great Plains region............................................19

8. Bar charts showing the estimated and projected net changes in the total area 

and the carbon stocks of the three primary ecosystems in the region (agricultural 

land, grasslands/shrublands, and forests) between 2005 and 2050, under the three 

IPCC-SRES scenarios—A1B, A2, and B1 ...............................................................................22

9. Chart showing the net impacts of combined LULC changes on carbon stocks 

in the Great Plains region..........................................................................................................23
iv

Conversion Factors

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

meter (m) 3.281 foot (ft) 

Area

square meter (m2

) 10.76 square foot (ft2)

hectare (ha) 2.471 acre

square kilometer (km2

) 0.3861 square miles (mi2)

Volume

cubic meter (m3

) 35.31 cubic foot (ft3)

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

kilogram (kg) 2.205 pound avoirdupois (lb)

megagram (Mg) [metric ton (t)] 1.102 ton, short (2,000 lb)

teragram (Tg) 1.102×106 ton, short (2,000 lb)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

The resolution of pixels in spatial datasets follows the conventions used in the spatial data and 

modeling communities. The format is “n-meter resolution,” where n is a numerical value for the 

length. The usage translates into a pixel with a length of n on all sides that covers an area of 

n meters × n meters. 

How Megagrams, Gigagrams, Teragrams, and Petagrams 

Relate to Metric Tons

1 megagram (Mg) = 1 million grams (106

 g) = 1 metric ton (t)

1 gigagram (Gg) = 1 billion grams (109

 g) = 1,000 metric tons

1 teragram (Tg) = 1 trillion grams (1012 g) = 1 million metric tons (Mt)

1 petagram (Pg) = 1 quadrillion grams (1015 g) = 1 billion metric tons (Gt)

Tables

1. Assumptions about primary driving forces affecting land-use and 

land-cover change .......................................................................................................................7

2. Ranges of annual baseline (observed) values and projected future estimates 

for the amount of area burned by wildland fires and their emissions, by IPCC-SRES 

scenario and assessment year, for the Great Plains region ...............................................10

3. Baseline land area and carbon stock and projected 2050 land area, carbon stock, 

and annual net flux density, under each of the three IPCC-SRES scenarios for

 terrestrial ecosystems in the Great Plains region................................................................12
v

Abbreviations, Acronyms, and Chemical Symbols

ARMS Agricultural Resource Management Survey

C carbon

CCCma CGCM3.1 Canadian Centre for Climate Modelling and Analysis’s Coupled 

Global Climate Model version 3.1

CH4 methane

CO carbon monoxide

CO2 carbon dioxide

CO2-eq carbon dioxide equivalent

CSIRO–Mk3.0 Australia’s Commonwealth Scientific and Industrial Research 

Organisation Mark 3.0

DIC dissolved inorganic carbon

EDCM Erosion-Deposition-Carbon Model

EISA Energy Independence and Security Act of 2007

EPA U.S. Environmental Protection Agency

FIA U.S. Forest Service Forest Inventory and Analysis Program

FLM fuel loading model

FOFEM First Order Fire Effects Model

FORE–SCE “forecasting scenarios of land cover change” model

GCM Global Circulation Model

GEMS General Ensemble Modeling System

GHG greenhouse gas

GWP global warming potential

HadCM3 Hadley Centre Coupled Model

HR heterotrophic respiration

HWP harvested wood products

IMAGE 2.2 Netherlands Environmental Assessment Agency’s Integrated Model to

Assess the Global Environment version 2.2

IPCC Intergovernmental Panel on Climate Change

IPCC-SRES Intergovernmental Panel on Climate Change’s Special Report on 

Emission Scenarios

k gas transfer velocity

LANDFIRE Landscape Fire and Resource Management Planning Tools Project

Landsat USGS and NASA Satellite Program

LULC land use and land cover
vi

MIROC 3.2-medres Model for Interdisciplinary Research on Climate version 3.2, 

 medium resolution

MODIS Moderate Resolution Imaging Spectroradiometer

MTBS Monitoring Trends in Burn Severity

N O2 nitrous oxide

NCAR CCSM National Center for Atmospheric Research’s Community Climate 

 System Model

NFDRS National Fire Danger Rating System

NHD National Hydrography Dataset

NLCD National Land Cover Database

NPP net primary productivity

NWIS National Water Information System

PRISM parameter-elevation regressions on independent slopes model

SOC soil organic carbon

TOC total organic carbon

USDA U.S. Department of Agriculture

USGS U.S. Geological Survey
vii

Acknowledgments

Many people helped with the development of the methods and the models, the preparation and 

analysis of data, and the preparation of this report. We are especially grateful to the following 

personnel. Guidance on the wildland-fire-model codes and computation was provided by 

Mark Finney, Matt Jolly, and Robert Keane of the U.S. Department of Agriculture (USDA) Forest 

Service’s Missoula Fire Sciences Laboratory; Elizabeth Reinhardt of the USDA Forest Service’s 

Office of the Climate Change Advisor; and Jodi Riegle of the U.S. Geological Survey (USGS). 

Guidance on the use of the USDA Forest Service forest inventory and assessment data was 

provided by Samuel Lambert, Elizabeth LaPoint, Patrick Miles, Ronald Piva, Jeffery Turner, and 

Brad Smith of the USDA Forest Service’s Forest Inventory and Analysis Program. Software, data, 

and computation support was provided by Stacie Bennett, Devendra Dahal, Brian Davis, Layth 

Grangaard, Ronald Kanengieter, Jennifer Oeding, Rob Quenzer, and Gail Schmidt of Stinger 

Ghaffarian Technologies, Inc., and by Claudia Young of Earth Resources Technology, Inc. The 

development of soil and wetland data was provided by Norman Bliss of Arctic Slope Regional 

Corporation Research and Technology Solutions and by Kristin Byrd of USGS. 

David Clow, Edward Stets, and Robert Striegl of the USGS helped with the development of 

hydrologic methods and estimates. Greenhouse-gas (GHG) field datasets for model development 

and calibration and an evaluation of GHG emission factors were provided by Robert Gleason and 

Brian Tangen of the USGS. 

We would like to thank Robert Gleason (USGS), Geoffrey Henebry (South Dakota State 

University), and Mark Liebig (USDA Agricultural Research Service) for peer review of this report. 

Finally, special thanks are offered to Christopher Torbert of the USGS for his dedication to 

managing the project.

Executive Summary

This assessment was conducted to fulfill the requirements 

of section 712 of the Energy Independence and Security Act 

(EISA) of 2007 and to improve understanding of carbon (C) 

and greenhouse gas (GHG) fluxes in the Great Plains region in 

the central part of the United States. The assessment examined 

carbon storage, carbon fluxes, and other GHG fluxes (methane 

(CH4) and nitrous oxide (N2O)) in all major terrestrial ecosystems (forests, grasslands/shrublands, agricultural lands, 

and wetlands) and freshwater aquatic systems (rivers, streams, 

lakes, and impoundments) in two time periods: baseline 

(generally in the first half of the 2010s) and future (projections 

from baseline to 2050). The assessment was based on 

measured and observed data collected by the U.S. Geological 

Survey (USGS) and many other agencies and organizations 

and used remote sensing, statistical methods, and simulation 

models. The major findings are as follows:

• The Great Plains region (2.17 million square 

kilometers) is predominantly grasslands/shrublands 

(48 percent of the total area) and agricultural lands 

(42 percent). Forests (5.35 percent), wetlands 

(1.4 percent), water bodies (1.16 percent), and other 

lands (developed and barren lands, 1.73 percent) 

complete the rest of land cover in the region. Land-use 

and land-cover (LULC) change is a major driver of 

changes in carbon storage. Future LULC change in the 

region, projected using the Intergovernmental Panel 

on Climate Change (IPCC) scenarios, is largely driven 

by the demand for agricultural commodities (including 

biofuels), resulting in the significant expansion of 

agricultural land (1.4 to 9.2 percent of the total area by 

2050, depending upon which scenario is used in the 

calculation) at the expense of grasslands/shrublands 

(–2.2 to –9.3 percent) and forests (0.0 to –0.5 percent). 

• Greenhouse-gas emissions from natural and manmade 

wildland fires are a key component of the assessment. 

The amount of area burned and the GHG emissions 

for the Great Plains region are highly variable both 

spatially and temporally, but the estimates for the 

amount of area burned are not expected to increase 

substantially over time, and the resulting GHG 

emissions are expected to increase just slightly for a 

range of climate projections. Grassland fires are the 

most common type of fire in the region, and they yield 

average GHG emissions (including carbon monoxide 

(CO), carbon dioxide (CO2), and methane (CH4 )) of 

0.18 to 24.72 teragrams of carbon-dioxide equivalents 

per year (TgCO2-eq/yr). Currently, the national GHG 

inventory report by the U.S. Environmental Protection 

Agency (EPA) does not include data on the emissions 

from fires in grasslands/shrublands areas. If included, 

fire emissions could increase by up to 8 percent of the 

current reported amount for the Nation.

• The total area covered by aquatic systems in the 

Great Plains region is small (1.16 percent); however, 

lateral transfer over the water surface ranged from 

0.07 to 0.31 teragrams of carbon per year (TgC/yr) 

within the region, and vertical evasion into the 

atmosphere emitted 12.8 to 24.6 TgC/yr as CO2 from 

rivers, streams, lakes, and impoundments. Because 

the methods used to estimate aquatic fluxes are not 

explicitly coupled with methods used to calculate terrestrial estimates, it is uncertain how much of the aquatic 

fluxes actually may stem from terrestrial sources.

Baseline and Projected Future Carbon Storage and 

Greenhouse-Gas Fluxes in the Great Plains Region 

of the United States

By Zhiliang Zhu1 (editor), Michelle Bouchard,2 David Butman,3 Todd Hawbaker,4 Zhengpeng Li,2

Jinxun Liu,5 Shuguang Liu,6 Cory McDonald,7 Ryan Reker,2 Kristi Sayler,6 Benjamin Sleeter,8

Terry Sohl,6 Sarah Stackpoole,4 Anne Wein,8 and Zhiliang Zhu1

1U.S. Geological Survey, Reston, Va.

2Arctic Slope Regional Corporation Research and Technology Solutions, 

Sioux Falls, S.D.

3Yale University, New Haven, Conn.

4U.S. Geological Survey, Denver, Colo.

5Stinger Ghaffarian Technologies, Inc., Sioux Falls, S.D.

6U.S. Geological Survey, Sioux Falls, S.D.

7U.S. Geological Survey, Boulder, Colo.

8U.S. Geological Survey, Menlo Park, Calif.
2 Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in the Great Plains Region

• The baseline (average of 2001–2005) carbon stock 

estimate for terrestrial ecosystems in the Great Plains 

region is approximately 7,500 TgC (only the top 

20 centimeters (cm) of the soil layer was considered 

with regard to soil organic carbon), which is 

distributed in agricultural lands (45.8 percent), 

grasslands/shrublands (34.9 percent), forests 

(15.5 percent), wetlands (2.9 percent), and other 

lands (0.9 percent). Annual carbon sequestration 

in the region ranged between 20 and 99 TgC/yr 

during 2001 to 2005. 

• By 2050, the total potential carbon stock for terrestrial 

ecosystems in the region is projected to increase 

to a range of 9,665 to 10,228 TgC, depending on 

the projection scenarios. The increase in carbon 

stock translates to a potential total sequestration of 

2,165 to 2,728 TgC between baseline and 2050, or 

a mean annual sequestration of 48 to 61 TgC. The 

projected amount of carbon that would be stored by 

2050 for the region is distributed in agricultural lands 

(47 percent), grasslands/shrublands (29 percent), 

forests (20.4 percent), wetlands (2.9 percent), and other 

lands (0.75 percent). Two factors—(1) the projected 

expansion of agricultural lands and (2) the tendency 

of croplands in the region to be associated with 

favorable ecosystem conditions (such as fertile soil 

and temperate climate, which lead to relatively high 

soil carbon stock)—explain why agricultural lands 

may still contain the most carbon stocks by 2050. The 

increase of forest carbon density and sequestration are 

projected on existing forests owing to the effects of 

CO2 fertilization and a projected low level of forest 

harvesting. Temporally, the rate of sequestration is 

expected to remain steady and decrease slightly over 

the projection period as the result of the projected 

increased LULC change and gradual saturation of 

carbon storage capacity. 

• Methane (CH4 ) emissions from wetlands and nitrous 

oxide (N2O) emissions from agricultural lands are 

high for the Great Plains region. When combined, 

they yield a baseline total of 240 TgCO2-eq/yr 

(82 TgCO2-eq/yr from CH4 and 158 TgCO2-eq/yr

from N2O). By 2050, N2O emissions are expected 

to increase by 7 to 11 percent. The expected change 

of CH4 emissions will range from a slight decrease 

of 1.6 percent to an increase of 16 percent. Up to 

85 percent of the amount of GHG emissions may 

be offset by carbon sequestration in the region in 

terms of the impact on atmospheric warming. 

• Carbon storage and sequestration are affected by 

LULC and LULC change in the Great Plains region. 

Conversions between major ecosystems (for example, 

converting grasslands/shrublands and forests to 

agricultural lands) may lead to a cumulative reduction 

in stored carbon between 26 and 157 TgC from the 

baseline to 2050 (depending on the scenario), or up to 

a 4 percent loss of the mean total carbon sequestration 

of the region during the same time period. Although 

afforestation in the region may result in a small 

increase in the total carbon stock, the potential loss of 

carbon from the conversion of forests to agricultural 

land is much greater. The loss of carbon storage may 

be most noticeable in the northern portion of the region 

because of the relatively low agricultural productivity. 

• Climate is another important factor affecting carbon 

storage and sequestration in the Great Plains region. 

Although climate projections were simulated for the 

IPCC scenarios, the effects of climate fluctuations 

and change have not yet been fully examined. The 

effects of climate change in the region may include 

droughts (such as those that occurred between 2002 

and 2003), floods (such as those in 2011), as well 

as extreme fluctuations in temperature and moisture 

availabilities, which could change the direction of 

carbon sequestration by the region’s ecosystems. 

• Uncertainties in the assessment results remain high 

because of (1) insufficient input data for various 

components of the assessment, and (2) inherent 

uncertainty related to the structure and the parameterization of methods and models that were used in 

the assessment. An improved approach that would 

integrate all the major uncertainty elements is needed 

for future assessments.

• This assessment provides new data and maps to users 

showing where carbon storage opportunities and 

vulnerabilities are located and how they are distributed 

over time. Within the limits of the resolution of a 

national assessment, the data and maps may be used 

to inform climate change mitigation and adaptation 

decisions while empowering the protection and 

restoration of other valuable ecological services that 

are important to society’s welfare and quality of life. 

Conserving natural land cover (such as forests and 

grasslands/shrublands) and maintaining agricultural 

soil sequestration (while finding ways to reduce 

nitrous oxide and methane emissions) are effective 

land-management practices for protecting carbon 

stocks in the region.
Ecosystems of the Great Plains Region 3

Introduction

This is the first of a series of reports that assess carbon 

sequestration and greenhouse-gas (GHG) fluxes in regional 

ecosystems; this report covers the Great Plains region of the 

United States. The assessment has two specific objectives: 

(1) fulfill the requirements of the 2007 Energy Independence 

and Security Act (EISA; U.S. Congress, 2007), section 712, 

which directs the Department of the Interior to examine the 

major ecosystems in all 50 states of the Nation and estimate 

the amount of and changes in carbon storage and GHG 

(carbon dioxide (CO2), methane (CH4), and nitrous oxide 

(N2O)) fluxes in and out of ecosystems and evaluate the 

effects of major controlling processes such as climate change, 

land use, and wildfire on ecosystems; and (2) improve the 

understanding of the capacity and vulnerability of carbon 

storage and sequestration in ecosystems in a spatially and 

temporally meaningful fashion by using the technical 

capabilities of the U.S. Geological Survey (USGS) and 

other agencies and organizations

This regional assessment was conducted using the 

methodology of Zhu and others (2010), which was based on 

the integrated use of remote sensing, existing resource and 

soil inventories, data collected specifically for the assessment, 

statistical analyses, and empirical and process-based modeling. 

Unless noted specifically in this report or in references cited, 

the major input datasets, methods, and models are described in 

the methodology (Zhu and others, 2010). The national assessment is organized by five major ecosystems: four terrestrial 

ecosystems (including forests, grasslands/shrublands, 

wetlands, and agricultural lands), and one aquatic ecosystem 

(including rivers, lakes, impoundments, estuaries, and coastal 

waters9). The thematic definitions of the ecosystems and their 

spatial boundaries are outlined in Zhu and others (2010).

 The assessment accounts for the current (baseline) 

and future projected changes in carbon and GHG fluxes. 

Following standard conventions found in the literature on 

this topic, negative values for carbon fluxes denote carbon 

uptake, or sequestration, unless noted otherwise. The term 

“baseline” is defined as the average current annual conditions 

to be assessed. Different components of the assessment have 

different baseline years, which are limited by input data 

characteristics: land use and land cover (LULC, 1992–2005), 

wildland fires (2001–2008), terrestrial carbon and GHG fluxes 

(2001–2005), and aquatic carbon fluxes (1970s to present). 

The input datasets used for the assessment include those 

developed by the USGS and other agencies and organizations. 

The output datasets are in the form of either annual digital 

maps (250-meter (m) resolution) or annual statistics. Because 

the assessment was conducted at national and broad regional 

scales, the resulting information and data products should be 

applied and (or) used only at the regional scale or broader. 

9

Estuaries and coastal waters are not included in this assessment of the 

Great Plains region.

Ecosystems of the Great Plains Region

The Great Plains region is divided into three U.S. 

Environmental Protection Agency (EPA) Level II ecoregions: 

the Temperate Prairies, the West-Central Semi-Arid Prairies, 

and the South-Central Semi-Arid Prairies (EPA, 1999) (fig. 1). 

The Great Plains region is characterized by generally flat to 

gently rolling topography, with a moderately humid climate in 

the east that gradually transitions to moderately dry conditions 

in the western Great Plains. A strong temperature gradient also 

exists; during the winter, bitterly cold temperatures prevail in 

the north while the south is characterized by mild and pleasant 

temperatures. The dominant natural vegetation is tied to the 

precipitation gradient: shortgrass steppe in the dry western part 

of the region, mixed-grass prairie in the central part, tallgrass 

prairie in the moderately humid east, and woodlands in the 

south and east (Burke and others, 1991). 

The hydrology of the northern portion of the Great 

Plains region is dominated by the Missouri River basin, 

which is the second largest watershed in the United States 

and drains about one-sixth of the conterminous United States 

(Galat and others, 2005). The southern portion is dominated by 

the drainage basins of the Arkansas and the Red Rivers, which 

flow from the northwest to the southeast and are tributaries to 

the Mississippi River (Matthews and others, 2005). With some 

exceptions (for example, the Prairie Pothole region), the vast 

majority of enclosed water bodies in the Great Plains region 

are manmade. The main stem of the Missouri River houses 

the largest reservoir system in North America (Roth, 2005), 

and the region contains a high density of small ponds and 

impoundments as well. 

The native grasslands of the Great Plains are one of 

the most endangered ecosystems in North America (Cully 

and others, 2003; Samson and others, 2004) and have 

undergone the greatest reduction in size of any ecosystem 

in North America (Samson and Knopf, 1994). Between 

60 and 70 percent of the eastern Great Plains has been plowed 

and cultivated, compared with slightly less than 30 percent 

of the western Great Plains (Hartman and others, 2011). 

Only 1 percent of the original tallgrass prairie remains in 

the region (Cully and others, 2003). Water availability is the 

most important driver of land use in the Great Plains. Nearly 

20 billion gallons of water are pumped from the High Plains 

aquifer every day for irrigation and drinking water (Karl and 

others, 2009). The dramatic growth of irrigated agriculture 

since 1960 represents a major human-induced hydrologic 

change in North America (Moore and Rojstaczer, 2001). 

LULC change and intensive land-management practices have 

had significant impacts on native plants and animals (Samson 

and Knopf, 1996; Higgins and others, 2002), nutrient cycling 

(Fleischner, 1994), and carbon and GHG fluxes (Fuhlendorf 

and others, 2002). 
110° 100° 90° 50°

45°

40°

35°

30°

25°

WCBP

NGLP

LAP

NGP

NSH

WHP

ST

WHP

NWGLP

CIP

CGP

FH

COTP

TBP

TBP

EP

STP

NEW MEXICO

COLORADO

WYOMING

ARIZONA

UTAH

IDAHO

TEXAS

KANSAS

OKLAHOMA

NEBRASKA

SOUTH

DAKOTA

NORTH

DAKOTA

MONTANA

MINNESOTA

IOWA

MISSOURI

ARKANSAS

LOUISIANA

WISCONSIN

MISSISSIPPI

ILLINOIS

CANADA

Gulf of Mexico

Lake Superior

MEXICO

0 100 200 300 MILES

0 100 200 300 400 KILOMETERS

Base from 2001 National Land Cover Database

(Homer and others, 2007)

4 Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in the Great Plains Region
Index map of Level II ecoregions

in the Great Plains region

Temperate

Prairies

West-Central

Semi-Arid

Prairies

South-Central

Semi-Arid

Prairies

Water

Land cover

Developed

Logging

Mining

Barren

Deciduous forest

Evergreen forest

Mixed forest

Grassland

Shrubland

Cultivated crops

Hay/pasture

Herbaceous wetlands

Woody wetlands

EXPLANATION

Figure 1.

Level II

Ecoregion boundary

Level III

South-Central Semi-Arid Prairies

 WHP Western High Plains

 ST Southwest Tablelands

 CGP Central Great Plains

 FH Flint Hills

 COTP Central Oklahoma/Texas Plains

 EP Edwards Plateau

 STP Southern Texas Plains

 TBP Texas Blackland Prairies 

Temperate Prairies

 CIP Central Irregular Plains

 NGLP Northern Glaciated Plains

 WCBP Western Corn Belt Plains

 LAP Lake Agassiz Plain

West-Central Semi-Arid Prairies

 NWGLP Northwestern Glaciated Plains

 NGP Northwestern Great Plains

 NSH Nebraska Sand Hills

Area of enlarged 

map on facing page

Arkansas River

River

Missouri River

Mississippi

Red River

Ecosystems of the Great Plains Region 5

Estimates of carbon storage, sequestration, and 

GHG fluxes vary widely by ecosystems in the region. The 

estimates for the conterminous United States and coastal 

Alaska provided in the annual national GHG inventory 

report (EPA, 2011a) suggest an average annual net carbon 

flux of –2.36 TgC/yr for grasslands remaining as grasslands, 

–6.56 TgC/yr for lands converted to grasslands, or a combined 

–8.92 TgC/yr for grasslands. Using data from 15 flux towers 

variously located in grassland areas of the Great Plains 

between 2000 and 2008, Zhang and others (2011) showed that 

the annual net flux density ranged from –10 to –38 grams of 

carbon per square meter per year (gC/m2/yr); by extrapolating 

the density value to the total area of grasslands in the region 

(derived from the USGS National Land Cover Database 

(NCLD); Homer and others, 2007), the annual total flux 

ranged from approximately –12.96 to – 49.24 TgC/yr (mean 

value of –31.1 TgC/yr). For croplands, the EPA estimated an 

annual net flux of –5.05 TgC/yr (for croplands that remained 

as croplands), 1.61 TgC/yr (for other lands converted to 

croplands), or a combined annual net flux of –3.44 TgC/yr. 

West and others (2010) determined that the net ecosystem 

carbon balance in 2004 for croplands in the region ranged 

from a high of –48 gC/m2 on more productive lands to as 

low as 60 gC/m2 on drier lands. 

Using data derived from its forest inventory and 

accounting for all the major carbon pools in the region, the 

U.S. Department of Agriculture (USDA) Forest Service 

reported that (1) carbon stored in the region’s forests in 

2010 averaged 471, 279, and 1,346 TgC respectively, 

for the Temperate Prairies, the West-Central Semi-Arid 

Prairies, and the South-Central Semi-Arid Prairies; and 

(2) the average carbon stock density for the region’s forests 

was 104 megagrams of carbon per hectare (MgC/ha), or 

10.4 kilograms of carbon per square meter (kgC/m2) (USDA, 

2011). Estimates of regional carbon and GHG flux rates 

for wetlands generally are not found in existing literature. 

Studies conducted by the USGS (Gleason and others, 2005; 

Euliss and others 2006) found that the restoration of Prairie 

Pothole wetlands from croplands may result in an increase 

in soil organic carbon sequestration by up to 187 Tg for the 

region (2.75 MgC/ha) within 10 years of restoration without 

incurring increased emissions of GHG (CO2, CH4, and N2O) 

(Gleason and others, 2009). Regional studies reporting CO2

fluxes from aquatic ecosystems in the Great Plains region 

are not currently available, but a study by Raymond and 

Oh (2007) reported that the Missouri River yielded from 

1.5 to 3.5 gC/m2/yr for dissolved inorganic carbon (DIC) and 

from 0.2 to 2.0 gC/m2/yr for total organic carbon (TOC). 

Figure 1 (pages 4 and 5). Map showing the spatial extent of 

this assessment. The Great Plains region consists of 3 EPA 

Level II ecoregions (the Temperate Prairies, the West-Central 

Semi-Arid Prairies, and the South-Central Semi-Arid Prairies), 

which in turn consist of 16 Level III ecoregions (modified 

from EPA, 1999). The total area of the Great Plains region 

is approximately 2.17 million square kilometers. The landuse and land-cover classes shown on the map represent 

conditions that existed around 2005. 
6 Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in the Great Plains Region

Land-Use and Land-Cover Changes 

in the Great Plains Region 

As part of the methodology, spatial and temporal distributions of current and projected future LULC changes were 

designed to be a foundation for the assessment (Zhu and others 

2010). The baseline LULC data were derived from a slightly 

modified version of the 1992 NLCD (Vogelmann and others, 

2001). The thematic classification framework for LULC nests 

within the primary ecosystems (Zhu and others 2010) and 

provide enough within-ecosystem thematic details to better 

inform the accounting and analysis of carbon stocks and GHG 

fluxes using biogeochemical models. The LULC from 1992 

to 2005 was modeled and calibrated using historical LULC 

data from the USGS Land Cover Trends project (Loveland and 

others, 2002) to produce annual maps of LULC change from 

1992 to 2000. LULC data from the 2001 and 2006 NLCD 

(Homer and others, 2007) were used to map LULC change 

from 2001 to 2005. Mapping of LULC change between 1992 

and 2005 also incorporated annual changes to forested areas 

due to forest harvesting; this information was derived from 

Landsat data and a vegetation change tracker, (a remotesensing model) (Huang and others, 2010). 

Scenario-based modeling of LULC change (between 

2006 and 2050) is designed to provide an overall framework 

within which to assess projected carbon sequestration capacity 

and vulnerability, as well as uncertainty. Future scenarios 

of LULC change were developed through a hierarchical 

downscaling process using a spreadsheet accounting model 

(Zhu and others, 2010; Benjamin Sleeter, unpub. data, 2011). 

The development of future LULC-change scenarios at both 

the national and regional scales began with (1) scenarios A1B, 

A2, B1, and B2, which are defined in the Intergovernmental 

Panel on Climate Change (IPCC) Special Report on Emission 

Scenarios (SRES) (IPCC-SRES; Nakicenovic and others, 

2000) and (2) model simulation results from the Integrated 

Model to Assess the Global Environment (IMAGE) 2.2 

(Strengers and others, 2004). The IMAGE model produced 

projections of major land-use types, including agriculture and 

forest harvest. Future projections of developed lands (such 

as urban areas) and mining lands were estimated through the 

use of proxy data from IMAGE (population and coal usage, 

respectively). Other LULC classes were evaluated based on 

land-use histories and expert judgment.

Because the IPCC-SRES scenarios span a wide range 

of socioeconomic conditions, the results of the downscaling 

process produced a wide range of future LULC and corresponding ecosystem conditions in the Great Plains region 

(fig. 2). For this assessment, three of the four available 

IPCC-SRES scenarios (A1B, A2, and B1) were used. The 

main assumptions that the IPCC used to develop these three 

scenarios (and the subsequent modeled results of future 

climate-change projections) are summarized in table 1.

The regional LULC scenarios, developed using the 

approach described above, were used to guide a spatially 

explicit “forecasting scenarios of land-cover change” 

(FORE-SCE) model to project future LULC distributions 

(Sohl and others, 2007; Sohl and Sayler, 2008). The 

FORE-SCE model used logistic regression to quantify 

empirical relationships between land cover and spatially 

explicit biophysical and socioeconomic variables. The results 

were probability surfaces that quantified the suitability for 

each land-cover type being modeled. A unique landscape-level 

patch-by-patch modeling procedure was then used to place 

patches of LULC change in suitable areas on the landscape; 

historical LULC-change data and other biophysical data were 

used to generate realistic patch sizes and configurations for 

each region. Other biophysical datasets included a recently 

developed potential wetland map (Kristin Byrd, USGS, unpub. 

data, 2011) using USDA soil survey databases (USDA Natural 

Resources Conservation Service, 2006, 2009). Each Level 

III ecoregion in figure 1 was individually parameterized and 

modeled with FORE-SCE for each of the three IPCC-SRES 

scenarios. The 1992 to 2005 period was used to present 

baseline conditions, using as much observed and actual LULC 

and remotely sensed data as possible, as described above. The 

2006 to 2050 modeled LULC provided spatial representations 

of the IPCC-SRES scenarios. When combined, the baseline 

and modeled scenarios resulted in a continuous, consistent 

LULC map database from 1992 to 2050, which was then 

collapsed to form the primary ecosystems as outlined in 

Zhu and others (2010) (fig. 2).

The validation of the LULC modeling results for 

the Great Plains region focused on examining quantity 

agreement (how well the model represented observed data 

for baseline and scenario-based prescriptions for future 

changes), and location agreement (how well the model 

placed LULC change). Quantity agreement was excellent, 

with FORE-SCE almost exactly matching the recent 1992 

to 2005 LULC proportions as well as the projected scenario 

LULC proportions through 2050. Quantitatively assessing the 

location agreement using the recent data from 1992 to 2005 

was complicated by thematic resolution differences, the very 

small amount of LULC change from 1992 to 2005, and the 

attempt to compare a sampled LULC dataset (USGS Land 

Cover Trends; Loveland and others, 2000) to a wall-to-wall 

modeled product. LULC processes are not stationary, which 

makes the assessment of model performance questionable 

for LULC projections (Pontius and Neeti, 2010). In lieu 

of a quantitative assessment, qualitative assessments of 

model performance were conducted using panel reviews 

by regional LULC experts. The experts reviewed both the 

model parameters and the model output for consistency 

with the scenario-based storylines, after which models were 

adjusted and iterative model runs were conducted until the 

model output was judged to adequately reflect the scenariobased storylines. 
4.6

4.8

5.0

5.2

5.4

5.6

Percentage of area of Great Plains region

36

38

40

42

44

46

48

50

A. Forests B. Grasslands/shrublands C. Agricultural lands

D. Wetlands E. Developed lands

40

42

44

46

48

50

52

2000

20052010201520202025203020352040

20452050

20002005201020152020202520302035204020452050

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2000

20052010201520202025203020352040

20452050

Year Year

Year

IPCC-SRES scenario

EXPLANATION

Figure 2.

A1B

A2

1.2 B1

1.4

1.6

1.8

Land-Use and Land-Cover Changes in the Great Plains Region 7

Figure 2. Graphs showing the distributions of the four primary 

terrestrial ecosystems and developed lands of the Great 

Plains region projected over time for each of the IPCC-SRES 

scenarios—A1B, A2, and B1 (from the Intergovernmental 

Panel on Climate Change’s Special Report on Emission 

Scenarios (IPCC-SRES); Nakicenovic and others, 2000). 

A, Forests; B, Grasslands/shrublands. C, Agricultural lands. 

D, Wetlands. E, Developed lands. The Great Plains region 

(total area approximately 2.17 million square kilometers) is 

dominated by the natural land covers of grass and shrubs and 

the agricultural covers of cultivated crops, hay, and pasture. 

Agricultural lands are projected to expand significantly under 

both the A1B and A2 scenarios because of projected increased 

Table 1. Assumptions about primary driving forces affecting land-use and land-cover change. These assumptions were used to 

downscale the A1B, A2, and B1 scenarios of the Intergovernmental Panel for Climate Change’s Special Report on Emission Scenarios 

(Nakicenovic and others, 2000). 

Driving forces A1B A2 B1

Population growth (global 

and United States)

Medium; 8.7 billion by 2050, 

then declining; in the United 

States, 385 million by 2050

High; 15.1 billion by 2100; 

in the United States, 

417 million by 2050

Medium; 8.7 billion by 2050, 

then declining; in the United 

States, 385 million by 2050.

Economic growth Very high; U.S. gross domestic 

product $72,531 by 2050

Medium; U.S. gross domestic 

product $47,766 by 2050

High; U.S. gross domestic 

product $59,880 by 2050.

Regional or global orientation Global Regional Global.

Technical innovation Rapid Slow Rapid.

Energy sector Balanced use Adaptation to local resources Smooth transition to renewable.

Environmental protection Active management Local and regional focus Protection of biodiversity.

crop demands (A1B and A2) and hay and pasture demand for 

cellulosic biofuel (A1B). These expansions are in contrast to 

the projected declines in the amount of area covered by 

grasslands/shrublands or forests under the A1B and A2 

scenarios. Under the B1 scenario, the amount of area covered 

by agricultural lands is projected to decrease for the first half of 

the timeline (baseline years through 2030) and then to increase 

in the latter half (2030–2050); additionally, (1) the amount of area 

covered by wetlands is projected to increase, and (2) compared 

to other scenarios, the amount of area covered by forests and 

grasslands/shrublands is projected to remain steady throughout 

the middle of the timeline and decrease toward 2050. Note that 

the scale of the y-axis is different for each graph.
8 Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in the Great Plains Region

Projected Climate Change in the 

Great Plains Region

The projected long-term future climate change in the 

Great Plains is highly variable but includes the likelihood of 

higher temperatures, higher precipitation in the north, lower 

precipitation in the south, and increases in extreme events 

such as flooding, drought, and heat waves (Karl and others, 

2009). Five global circulation models (GCMs) were used in 

the fire disturbance modeling: (1) Australia’s Commonwealth 

Scientific and Industrial Research Organization Mark 3.0 

(CSIRO-Mk3.0), (2) the Canadian Centre for Climate Modelling and Analysis’s Coupled Global Climate Model version 3.1 

(CCCma CGCM3.1), (3) the (Japanese) National Institute for 

Environmental Studies’ medium-resolution version of their 

Model for Interdisciplinary Research on Climate, version 3.2 

(MIROC 3.2-medres), (4) the National Center for Atmospheric 

Research’s Community Climate System Model version 3.0 

(NCAR CCSM 3.0), and (5) the United Kingdom’s Hadley 

Centre Coupled Model version 3 (HadCM3) (Wood and 

others, 2002, 2004; Maurer, 2007). The MIROC 3.2-medres 

GCM was used in the biogeochemical modeling of the region. 

The MIROC 3.2-medres GCM is representative of the abovenoted trends for temperature and precipitation changes that 

are derived by comparing average annual temperatures from 

1970 to 2010 and from 2010 to 2050, although the changes 

are variable across the scenarios. In particular, the MIROC 

3.2-medres GCM projects annual average temperature 

increases of up to 2.4 degrees Celsius (°C) in the central part 

of the Great Plains region under the B1 scenario. Although 

there is less change in the annual average precipitation 

throughout the region under the B1 scenario, the climate 

under the A2 scenario is projected to be drier throughout 

the Great Plains region. For each of the three IPCC-SRES 

scenarios, the MIROC 3.2-medres GCM projects greater 

reductions in annual precipitation in the southeastern part of 

the Great Plains region. 

Wildland Fire and Emissions in the 

Great Plains Region 

Historically, fire has played a large role in shaping 

the composition, structure, and function of ecosystems in 

the Great Plains region (Collins and Wallace, 1990). Fire 

occurrences have been highly variable through time and 

are dependent on climate, land-use and land-cover changes, 

and human activity (Clark, 1990; Umbanhowar, 1996). 

Before European settlement, fires often were intentionally 

set by Native Americans, in addition to natural fires caused 

by lightning. In modern times, wildfires are infrequent, 

but still occur. Fires that are prescribed as part of landmanagement activities in both grasslands/shrublands and 

agricultural lands are common (McCarty and others, 2009; 

Tulbure and others, 2011), but data that would accurately 

characterize prescribed fires are not available; therefore, only 

wildland fires were analyzed for this assessment.

The baseline (observed) data for the amount of area 

burned and for emissions by wildfires were derived from 

the Monitoring Trends in Burn Severity database (MTBS; 

Eidenshink and others, 2007), which only mapped large fires 

(202 ha or larger east of the Mississippi River, 405 ha or 

larger in the western United States and Alaska) derived from 

Landsat imagery. The MTBS data were selected because of the 

high degree of confidence in the data: each fire is individually 

examined. Various versions of Federal fire databases are 

available but were not used because of the spatial inaccuracies 

and duplicate records that would have introduced uncertainties 

into results (Brown and others, 2002). Data on active fires 

(Giglio and others, 2003) and burned areas (Roy and others, 

2008), which were detected by the Moderate Resolution 

Imaging Spectroradiometer (MODIS) satellite, were considered but were not used because they contained no information 

about the causes of the fires and they had a coarse spatial 

resolution that complicated the modeling of future trends.

Fire emissions were calculated for each MTBS fire using 

the First Order Fire Effects Model (FOFEM; Reinhardt and 

others, 1997) for each major fire-relevant GHG: CO2, CO, 

and CH4. FOFEM requires data on weather conditions, fuelmoisture contents, and fuel loads. The fuel moisture content 

was estimated by using the National Fire Danger Rating 

System (NFDRS; Bradshaw and others, 1983), which is based 

on a 12-kilometer (km)-resolution, gridded daily weather 

dataset that spans the conterminous United States from 1980 

to 2000 (Maurer and others, 2002). The fuel-load data were 

derived from the Landscape Fire and Resource Management 

Planning Tool Project’s (LANDFIRE’s) Fuel Loading Models 

layer (FLM; Lutes and others, 2009). Because the LANDFIRE 

fuels data derived from Landsat imagery reflected conditions 

around 2001 and after, and the MTBS data cover years 

between 1985 and 2008, fires occurring between 2001 and 

2008 were included as the baseline for fire estimates. 

Simulations of the amount of area burned by fire and 

the corresponding emissions were run for 2001 to 2050 

under each of the IPCC-SRES scenarios (A1B, A2, and 

B1; Nakicenovic and others, 2000). The simulation results 

for 2001 to 2008 were used for validation or for comparison 

with baseline information, whereas the results from 2011 to 

2050 were used to analyze the projected changes in burned 

area and emissions under each scenario over time. First, 

for the simulations, a probability of fire occurrence was 

calculated using logistic regression as well as the baseline 

data on daily weather conditions, fuel-moisture content, 

vegetation types, and fuel types. Next, future daily weather 

sequences were generated by temporally disaggregating 

monthly bias-corrected and spatially downscaled climatechange projections from the five GCMs (CSIRO-Mk3.0, 

CCCma CGCM3.1, MIROC 3.2-medres, NCAR CCSM 3.0, 
Wildland Fire and Emissions in the Great Plains Region 9

Figure 3. Graphs showing the trends of baseline and simulated projected future burned area due to wildland fires and 

their emissions for each of the three IPCC-SRES scenarios (Nakicenovic and others, 2000), by year, in the Great Plains 

region. A, Area burned under the A1B scenario. B, Area burned under the A2 scenario. C, Area burned under the B1 

scenario. D, Emissions from fire under the A1B scenario. E, Emissions from fire under the A2 scenario. F, Emissions from 

fire under the B1 scenario. The baseline values from Monitoring Trends in Burn Severity (MTBS) data are shown as 

dashed black lines. Each gray line represents a range of projected future estimates for 25 simulations (5 global change 

models × 5 replicates). The mean values of the simulated projected future estimates are shown as solid black lines.

and HadCM3) (Wood and others, 2002, 2004; Maurer, 2007) 

with the historical daily weather data (1980–2000) used for 

the baseline assessment. The daily weather sequences were 

processed using the NFDRS algorithms to produce daily fuel 

moisture contents for each GCM and IPCC-SRES scenario 

combination. These data were used with the logistic regression 

to project future patterns of fire ignition. To quantify the future 

potential burned area, each fire’s spread was simulated using 

the minimum travel time algorithm (Finney, 2002) with the 

projected ignition locations, daily weather, and LANDFIRE 

fuel, and topography layers (Rollins, 2009). In the models, 

fires were allowed to spread between 1 and 14 days, depending 

on recent burn durations for each ecoregion. A containment 

algorithm was also applied to each fire to limit the total fire 

size (Finney and others, 2009). After the burned area of each 

fire was established, the emissions were calculated using 

FOFEM. To quantify uncertainty in the future projected 

burned area and emissions, five replicate simulations were 

run for each IPCC-SRES scenario and GCM combination 

for a total of 75 simulations (fig. 3, table 2). 

Comparisons of the simulated scenario data with the 

observed data in MTBS on the amount of area burned and 

resulting fire emissions indicate that the simulated annual 

burned areas and emissions from 2001 to 2010 were generally 

lower than the observed annual burned area and emissions 

from 2001 to 2008. The maximum simulated area burned from 

2001 to 2010 was 4,414 square kilometers (km2 ) under the 

B1 scenario, which was nearly half of the observed maximum 

of 8,159 km2 (table 2). These differences were primarily 

because the simulations did not generate burned areas as 

extreme as that which was observed in 2006, which indicates 

that the model may underestimate the potential influence of 

extreme fire years; however, the differences in mean area 

burned between the observed and simulated values were not 

substantial based on 2-sided t-tests, with p-values of 0.33, 

0.34, and 0.37, for scenarios A1B, A2, and B1, respectively.

Year

8,000

6,000

4,000

2,000

0

20

10

0

Area burned, in square kilometers Emissions, in teragrams of carbon dioxide equivalent

A. A1B B. A2 C. B1

D. A1B E. A2 F. B1

Figure 3.

20002005201020152020202520302035204020452050

20002005201020152020202520302035204020452050

20002005201020152020202520302035204020452050
10 Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in the Great Plains Region

Land Management in the 

Great Plains Region

An objective of this assessment is to analyze the effects 

of land-management activities on carbon storage and GHG 

fluxes. Land-management activities are defined as those 

actions that change the way land is used; for instance, landmanagement activities may help farmers make land more 

productive, or help ranchers conserve their water resources. 

For this assessment, land-management activities were aligned 

with the LULC classes that make up the four terrestrial 

ecosystems, such as tillage practices for agricultural lands. 

For the Great Plains regional assessment, land-management 

variables from agricultural census data and other data sources 

were downscaled and mapped to pixel scale using a Monte 

Carlo statistical procedure (G.S. Schmidt, USGS, unpub. data, 

2011), as follows:

• Crop production was modeled by each IPCC-SRES 

scenario (Nakicenovic and others, 2000) using 

(1) the LULC maps described previously, (2) the 

Netherlands Environmental Assessment Agency’s 

Integrated Model to Assess the Global Environment 

version 2.2 (IMAGE 2.2) (Strengers and others, 2004), 

and (3) USDA crop data (Padgitt and others, 2000; 

Table 2. Ranges of annual baseline (observed) values and projected future estimates for the amount of area burned 

by wildland fires and their emissions, by IPCC-SRES scenario and assessment year, for the Great Plains region.

[Baseline data is from the Monitoring Trends in Burn Severity (MTBS) database. Projected future estimates were derived from the simulation modeling process described above. Carbon-dioxide equivalents include the three major fire-relevant greenhouse gases: CO, CO2, 

and CH4. IPCC-SRES, Intergovernmental Panel on Climate Change’s Special Report on Emissions Scenarios (Nakicenovic and others, 

2000); km2/yr, square kilometers per year; TgCO2-eq/yr, teragrams of carbon-dioxide equivalent per year]

Scenarios Years

Area burned

(minimum to maximum,

in km2/yr)

Emissions

(minimum to maximum,

in TgCO2-eq/yr)

Baseline (observed) 2001–2008 543–8,159 0.18–24.72

A1B 2001–2010 187–2,614 0.42–10.82

2011–2020 146–3,041 0.47–16.92

2021–2030 176–2,474 0.54–10.59

2031–2040 202–2,493 0.36–9.88

2041–2050 242–2,373 0.60–11.92

A2 2001–2010 170–2,746 0.33–9.52

2011–2020 270–2,272 0.62–10.01

2021–2030 132–3,882 0.27–14.54

2031–2040 219–3,264 0.45–9.11

2041–2050 245–2,826 0.59–11.70

B1 2001–2010 264–3,150 0.41–10.63

2011–2020 197–4,414 0.39–12.93

2021–2030 195–3,167 0.45–10.89

2031–2040 169–3,165 0.45–13.41

2041–2050 211–4,332 0.41–10.40

USDA National Agricultural Statistics Service, 2011). 

Crop types and rotation probability were derived

from the same USDA data and used to downscale 

the general class of “cropland” from LULC (as part 

of the agricultural lands ecosystem) to various crops.

• Tillage practices (no tillage, conventional tillage, 

reduced tillage) were downscaled from the tillage 

information provided by the USDA’s Agricultural 

Research Management Survey (ARMS) database 

(USDA Economic Research Service, 2011b), by crop 

type. Because of the lack of data on future projections, 

the projected tillage practice data were assumed to 

remain the same as the baseline data.

• An irrigation map was derived from MODIS imagery 

(USGS, 2002). The projected irrigation data were 

assumed to remain the same as the baseline data.

• Data on fertilizer use were derived from a USDA 

database (USDA Economic Research Service, 2011a). 

Fertilization was assumed to be optimal, thus satisfying 

the requirement for future plant growth. This assumption was based on the observation that the current 

levels of fertilization in the United States can largely 

satisfy the nutrient needs for crop growth. 
Carbon Storage and Greenhouse-Gas Fluxes of Terrestrial Ecosystems in the Great Plains Region 11

• Data on the addition of manure to crops, which directly 

adds carbon into ecosystems in addition to providing 

nutrients, were derived from USDA’s ARMS database 

(USDA Economic Research Service, 2011b) for all 

crop types.

• There are no national data on rangeland grazing, 

which would help determine the grazing intensity 

on grasslands/shrublands. In this assessment, it was 

assumed that all grasslands/shrublands in the region 

would be grazed during the summer. An average 

grazing intensity was calculated based on data from 

Holland and others (1992) to produce a mean value 

ranging from 0.2 to 1.4 Animal Unit Month/ha. This 

range of mean values was comparable with other 

reported grazing intensity measurements in the 

literature (Biondini and others, 1998; Schuman and 

others, 1999; Derner and others, 2006). The total 

carbon removal by livestock grazing in the region 

was calculated using a USDA livestock inventory 

and empirical factors in rangeland management, with 

the assumption that the carbon removal values would 

meet about 70 percent of the total carbon consumption needs by livestock (Holechek and others, 2000; 

USDA National Agricultural Statistics Service, 2011).

• Estimates of fire extent and severity, produced as part 

of the assessment as described previously, were used 

to assess the effects of fire on carbon sequestration. 

The effects of fire on carbon sequestration were 

simulated at annual increments with three burnseverity classes: high, moderate, or low. 

• There were no national data available about cropresidue management. Assumptions were made for the 

amount of aboveground biomass that was removed, by 

crop type. For example, it was assumed that the crop 

type “corn for silage” would have 80 to 90 percent of 

its aboveground biomass (corn plus residue) removed, 

whereas “corn for grain” would only have the corn 

removed and all the residue left in the field.

• Information about the age of forests in the region was 

derived from the U.S. Forest Service’s Forest Inventory and Analysis Program (FIA) database (USDA 

Forest Service, 2011). The data was modeled on an 

annual basis together with LULC classes that identified 

both forest types and mechanically disturbed forested 

land (resulting from forest cutting). Forest thinning 

was not considered for the region. 

Carbon Storage and Greenhouse-Gas 

Fluxes of Terrestrial Ecosystems in the 

Great Plains Region

Climate change, LULC change, land management, and 

ecosystem disturbances are the primary drivers of the changes 

in carbon storage and GHG fluxes. Classes of annual LULC 

maps of the three IPCC-SRES scenarios were merged to 

form four primary terrestrial ecosystems for the assessment, 

according to the definitions outlined in Zhu and others (2010). 

In addition to the LULC data, other key data are needed to 

model baseline and future projected carbon storage and GHG 

fluxes, including (1) soil data (for example, texture, bulk 

density, erodibility, and drainage class by soil layers) from 

the USDA soil survey databases (USDA Natural Resources 

Conservation Service, 2006, 2009) processed and mapped for 

soil organic carbon (SOC) content (Bliss and others, 2009; 

Sundquist and others, 2009; Waltman and others, 2010), 

(2) historical climate data from Oregon State University’s 

“parameter-elevation regressions on independent slopes 

model” (PRISM), and (3) future climate projections from 

MIROC 3.2-medres. Because of the constraints of the model 

structure, only the top 20 centimeters (cm) of the soil layer 

was considered for soil organic carbon data. 

The growth curves of coniferous, broadleaf, and mixed 

forests; forest age; and other forest data (all derived from 

the USDA’s FIA database; Heath and others, 2009; Miles 

and Smith, 2009; Woudenberg and others, 2010; USDA 

Forest Service, 2011) were used to initialize the forested land 

component of the models. The growth curves also were used 

to calibrate the biomass accumulation rates simulated by the 

process-based models. The temporal change of forest growth 

caused by CO2 fertilization, nutrient availability, and climate 

change was simulated using the input data described above; 

however, the temporal change of forest growth due to enhancement from genetics and cultivation was not simulated because 

of insufficient data. Grain yields from the USDA census data 

for all major crops (USDA Economic Research Service, 2011b) 

were used to calibrate the production routines of the processbased models. Temporal (historical and future projected) 

changes in grain yields for all crops were grouped into six 

distinct Michaelis-Menten growth curves using USDA historical 

census data and grain-yield projections from IMAGE 2.2 

(Strengers and others, 2004). The lateral movements of 

soil, carbon, and nutrients; their impacts on the regional 

carbon balance and GHG fluxes; and their linkage to aquatic 

ecosystems were not directly addressed in this assessment.
12 Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in the Great Plains Region

Carbon dynamics and GHG fluxes between the land 

and the atmosphere under the LULC, climate change, and 

land management scenarios (described previously) were 

simulated using three ecosystem models in the General 

Ensemble Biogeochemical Modeling System (GEMS) (Liu 

and others, 2004, in press; Liu, 2009; Zhu and others, 2010). 

The three models are the Erosion-Deposition-Carbon Model 

(EDCM) (Liu and others, 2003), the CENTURY model 

(Parton and others, 1987), and a spreadsheet model described 

in the methodology document (Zhu and others, 2010). The 

process-based models EDCM and CENTURY have been 

tested widely in various ecosystems worldwide (for example, 

Parton and others, 1993; Tan and others, 2006, 2007; Liu and 

others, 2003). The use of the three models helps account for 

inherent uncertainties related to model structure and parameterizations. Using the above-described datasets for LULC, 

areas burned by wildland fires, land management, climate, 

and other biophysical data, the three GEMS-based models 

were run for the each of three IPCC-SRES scenarios (A1B, 

A2, and B1; Nakicenovic and others, 2000) and for one GCM 

(MIROC 3.2-medres) for a total of nine model runs for each 

ecosystem. The results for the Great Plains region are shown 

in figures 4 and 5 and in table 3 below. 

The emissions of N2O and CH4 from the region 

were estimated using the spreadsheet model. Spatial and 

temporal changes in CH4 and N2O were estimated using the 

spreadsheet model with data about LULC, fire, and emission 

factors derived from the literature (Robertson and others, 

2000; Gleason and others, 2009; EPA, 2011a). Baseline 

emissions (expressed as “CO2 equivalent,” or CO2-eq) were 

82 TgCO2-eq for CH4 and 158 TgCO2-eq for N2O. By 2050, 

emissions were estimated to range from 81 to 94 TgCO2-eq

and from 169 to 186 TgCO2-eq, respectively, for CH4 and N2O, 

depending on projection scenario. Changes in carbon stocks 

in ecosystems were simulated by the EDCM and CENTURY 

models because they were capable of simulating the impacts 

of various natural processes and disturbances on the carbon 

cycle. Maps showing the spatial distribution of the total GHG 

emissions in 2010 in the Great Plains region and graphs 

showing projected future emissions are presented in figure 6.

Table 3. Baseline land area and carbon stock and projected 2050 land area, carbon stock, and annual net flux density, under each 

of the three IPCC-SRES scenarios for terrestrial ecosystems in the Great Plains region. Mean annual net flux density and total carbon 

sequestration projections (changes in carbon stocks from mean baseline to 2050) are also given.

[The area of water bodies is given, but carbon-flux analysis was conducted separately (see discussion in section entitled, “Carbon Fluxes of Aquatic 

Ecosystems in the Great Plains”). For annual net flux density estimates, negative values indicate sequestration and positive values indicate emission. Figures 

may not sum to totals because of independent rounding. IPCC-SRES, Intergovernmental Panel on Climate Change’s Special Report on Emissions Scenarios 

(Nakicenovic and others, 2000); km2, square kilometers; TgC, teragrams of carbon; gC/m2/yr, grams of carbon per square meter per year; —, not applicable]

Variables by timeline Forests Grasslands/

shrublands

Agricultural 

lands Wetlands Water Otherlands Total

Baseline Area (×1,000 km2) 116 1,041 920 30 25 38 2,170

Stock (TgC) 1,162 2,614 3,438 216 — 70 7,500

A1B 2050 area (×1,000 km2) 106 840 1,117 28 25 55 2,170

2050 stock (TgC) 1,968 2,369 4,990 262 — 78 9,665

Annual net flux density 

(gC/m2/yr)

–191.5 –6.9 –16.2 –51.9 — 10.0 –22.2

(mean)

A2 2050 area (×1,000 km2) 106 944 1,011 29 25 55 2,170

2050 stock (TgC) 1,980 3,094 4,668 276 — 80 10,099

Annual net flux density 

(gC/m2/yr)

–190.2 –17.0 –19.6 –55.4 — 8.9 –26.6

(mean)

B1 2050 area (×1,000 km2) 115 994 948 37 28 47 2,170

Stock (TgC) 2,163 3,223 4,430 345 — 67 10,228

Annual net flux density 

(gC/m2/yr)

–193.9 –16.2 –20.8 –48.9 — 9.9 –27.9

(mean)

Mean annual net flux density 

(gC/m2/yr)

–192.5 –13.4 –18.8 –52.1 — 9.6 –25.6

(mean)

Mean baseline to 2050 stock 

change (TgC)

875 281 1,258 78 — 5 2,497

Standard error (TgC) 85 197 182 19 — 13 145
2,400

2,200

2,000

1,800

1,600

1,400

1,200

1,000

5,500

5,000

4,500

4,000

3,500

3,000

10,500

10,000

9,500

9,000

8,500

8,000

7,500

7,000

400

350

300

250

200

3,600

3,200

2,800

2,400

2,000

Carbon stocks, in teragrams of carbon

2000 2010 2020 2030

Year

2040 2050

2000 2010 2020 2030

Year

2040 2050

A. Forests B. Grasslands/shrublands

C. Agricultural lands

E. All lands

D. Wetlands

IPCC-SRES scenario and 

 process-based model

EXPLANATION

A1B-EDCM

A1B-Century

A2-EDCM

A2-Century

B1-EDCM

B1-Century

Figure 4.

Carbon Storage and Greenhouse-Gas Fluxes of Terrestrial Ecosystems in the Great Plains Region 13

Figure 4. Graphs showing the trends of terrestrial carbon stocks over time in the Great Plains region, 

for the four primary ecosystems and all lands under each of the three IPCC-SRES scenarios (A1B, A2, 

and B1; Nakicenovic and others, 2000), using two biogeochemical models. A, Forests. B, Grasslands/

shrublands. C, Agricultural lands. D, Wetlands. E, All lands. Note that the scale of the y-axis is different 

for each graph. EDCM, Erosion-Deposition-Carbon Model; IPCC-SRES, Intergovernmental Panel on 

Climate Change’s Special Report on Emissions Scenarios.
A. Forests B. Grasslands/shrublands

C. Agricultural lands D. Wetlands

110° 100° 90° 50°

45°

40°

35°

30°

25°

14 Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in the Great Plains Region
Total carbon sequestration, in kilograms 

 of carbon per square meter (A–E)

EXPLANATION

Figure 5.

Level II ecoregion boundary

<–5.0

–5.0 to –2.1

–2.0 to –0.6

–0.5 to 0.5

0.6 to 2.0

2.1 to 4.9

≥5.0

≤1.0

1.1 to 2

2.1 to 4.0

4.1 to 8.0

8.1 to 10

>10

Uncertainty of carbon sequestration, 

 in kilograms of carbon per square 

 meter (F)

E. All lands F. Uncertainty

Index map of Level II ecoregions

in Great Plains region

Area of enlarged map

Temperate

Prairies

West-Central

Semi-Arid

Prairies

South-Central

Semi-Arid

Prairies

0 100 200 300 400 MILES

0 200 400 KILOMETERS

Base from 2001 National Land Cover Database

(Homer and others, 2007)

Carbon Storage and Greenhouse-Gas Fluxes of Terrestrial Ecosystems in the Great Plains Region 15

Figure 5 (pages 14 and 15). Maps showing the spatial distribution and uncertainty of carbon sequestration 

(negative) and emission (positive) in the Great Plains region, by ecosystem between the baseline and 2050. 

A, Forests. B, Grasslands/shrublands. C, Agricultural lands. D, Wetlands. E, All lands. F, Uncertainty. The carbon 

sequestration value represented on the maps is the mean of a total of six simulations performed by the EDCM and 

CENTURY models under each of the three IPCC-SRES scenarios (A1B, A1, and B1; Nakicenovic and others 2000). 

Uncertainty is expressed as the standard error of these simulations. EDCM, Erosion-Deposition-Carbon Model; 

IPCC-SRES, Intergovernmental Panel on Climate Change’s Special Report on Emissions Scenarios; <, less than; 

≤, less than or equal to; >, greater than; ≥, greater than or equal to. 
–400

–300

–200

–100

0

100

200

Total

–100

0

100

200

300

400

500

Methane (CH4 )

78

80

82

84

86

88

90

92

94

96

Nitrous oxide (NO2) 

Year

2000 2010 2020 2030 2040 2050

Year

2000 2010 2020 2030 2040 2050

150

155

160

165

170

175

180

185

190

Carbon dioxide (CO2)

Figure 6.

IPCC-SRES scenario

(Graphs)

A1B

A2

B1

Mean

Emissions, in teragrams of carbon-dioxide equivalent per square meter per year

Emissions in 2010, in grams of carbon-dioxide 

 equivalent per square meter per year

(Maps)

EXPLANATION

Level II ecoregion boundary

≤ –250

–250 to –50

–50 to 50

50 to 250

>250

16 Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in the Great Plains Region

Figure 6 (pages 16 and 17). Graphs and maps showing temporal trends of projected future greenhousegas emissions and their spatial distribution in 2010 in the Great Plains region. The projected future CO2

fluxes were estimated using the process-based models EDCM and CENTURY within GEMS; N2O, and CH4 

fluxes were estimated using the spreadsheet model. The high variability of CO2 over time was caused 

by the impacts of the interannual variability of climate and land-management practices. Because the 

spreadsheet model does not account for the climate and land-management effects, the temporal changes 

in N2O and CH4 fluxes only reflect the impact of LULC change. Note that the scale of the y-axis is different 

for each graph. EDCM, Erosion-Deposition-Carbon Model; GEMS, General Ensemble Modeling System; 

IPCC-SRES, Intergovernmental Panel on Climate Change’s Special Report on Emissions Scenarios; 

LULC, land use and land change; ≤, less than or equal to; >, greater than. 
Methane (CH4 ) Total

Nitrous oxide (NO2 Carbon dioxide (CO ) 2

)

110° 100° 90° 50°

45°

40°

35°

30°

25°

Year 2010

Base from 2001 National 

Land Cover Database

(Homer and others, 2007)

0 100 200 300 400 MILES

0 200 400 KILOMETERS

Carbon Storage and Greenhouse-Gas Fluxes of Terrestrial Ecosystems in the Great Plains Region 17
18 Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in the Great Plains Region

Carbon Fluxes in the Aquatic Ecosystems

of the Great Plains Region

Aquatic ecosystems in this regional assessment include 

streams, rivers, perennial ponds, lakes, and impoundments. For 

this report, the term “riverine” refers to both rivers and streams 

and “lacustrine” refers to both lakes and impoundments. For 

aquatic ecosystems, the baseline estimates were calculated using 

input data that spanned the recent decades (varying between the 

1970s and the present, depending on the type of data) and were 

produced for two major fluxes: lateral carbon flux in riverine 

systems and CO2 evasion (efflux) from both riverine and lacustrine systems. Lateral flux describes the transfer of dissolved 

and particulate carbon by riverine systems from terrestrial 

landscapes to inland water bodies, major rivers, and coastal 

areas. Carbon-dioxide evasion occurs when surface water is 

supersaturated with CO2 relative to the atmosphere. Lateral 

fluxes can be estimated using concentration and streamflow 

data available from the USGS. For this assessment, a multiple 

regression approach was used, which estimated daily flux as a 

function of streamflow, seasonality, and time, and where daily 

fluxes were totaled and expressed on an annual basis. More 

details on the methods used for calculation of carbon loads 

(TgC/yr) in lateral flux can be found in Zhu and others (2010). 

In this regional assessment, 59 streamgages provided 

adequate recent water-quality and discharge data that were 

used to estimate total organic carbon (TOC) fluxes, and 

149 streamgages had enough recent data to estimate dissolved 

inorganic carbon (DIC) flux. These data were collected on 

streamgages between 2000 and 2010. On average, rivers 

in the Great Plains region transferred 0.07 to 0.31 TgC/yr 

(mean=0.19 TgC/yr) from upland terrestrial systems to 

inland waters and coastal areas. Annual DIC yield ranged 

between 1.9 and 2.2 gC/m2 (mean=2.1 gC/m2) whereas the 

TOC ranged from 0.57 to 0.92 gC/m2 (mean=0.73 gC/m2). 

These values were within the estimated carbon yields for 

the Missouri River made by Raymond and Oh (2007), who 

reported 1.5 to 3.5 gC/m2/yr as DIC and 0.2 to 2.0 gC/m2/yr 

as TOC. Inorganic carbon represented about 60 percent of 

the total lateral carbon flux. A recent study of carbon fluxes 

to coastal areas in the United States found that the export 

of inorganic carbon was three times greater than the export 

of TOC (Edward G. Stets, USGS, unpub. data, 2011). The 

processes that contribute to riverine inorganic carbon transport 

include the oxidation of organic matter, the dissolution of 

carbonate minerals, and the transfer of products from both 

terrestrial ecosystems and in-stream respiration. 

Partial-pressure CO2 concentrations and CO2 flux were 

calculated by stream order within each ecoregion and were 

based on alkalinity, temperature, and pH measurements 

from 966 stations made between the 1970s and the present 

and archived in the USGS’s National Water Information 

System (NWIS) (Butman and Raymond, 2011). For lacustrine 

systems, the water-to-air CO2 efflux was calculated based 

on the concentration gradient between dissolved CO2

and overlying atmospheric concentrations. The regional 

distribution of dissolved CO2 was estimated from calculated 

values for lacustrine systems in the EPA National Lakes 

Assessment (EPA, 2011b) (n=342). The gas transfer velocity 

(k) of CO2 was calculated for each ecoregion as a function 

of mean annual wind speed and water temperature. The 

lacustrine surface areas for each ecoregion were obtained 

from the USGS’s National Hydrography Dataset (NHD; 

U.S. Geological Survey, 2011), and ice cover was estimated 

based on mean monthly skin-surface temperature. 

Using the above empirical data and modeling techniques, it was possible to scale up CO2 evasion estimates 

to give a total vertical CO2 flux for the Great Plains 

region from riverine and lacustrine systems. Although the 

percent of total surface area of the region that is covered 

by rivers and streams (0.32 percent) is less than lakes or 

impoundments (1.26 percent), the estimate of CO2 evasion 

from riverine systems was higher (37 to 73 TgCO2-eq/yr, 

mean=55 TgCO2-eq/yr) than that from lacustrine systems 

(10 to 17 TgCO2-eq/yr, mean=13 TgCO2-eq /yr). The greater 

rate of CO2 evasion from riverine systems can be explained by 

higher transfer velocities and higher dissolved CO2 concentrations in rivers and streams.

Integrated Analysis 

By integrating carbon estimates of the four major 

terrestrial ecosystems, emissions of wildland fires, and 

aquatic fluxes, an overall regional baseline carbon budget 

was constructed, as shown in figure 7. This figure shows 

relations between carbon fluxes for all of the ecosystems in 

the region. The range values indicate minimum and maximum 

estimates of the baseline years for a given component of the 

assessment. For biomass and soil organic carbon boxes, the 

minimum and maximum values are from different years of 

the baseline. The total sequestration is estimated to range 

from 20 to 99 TgC/yr (mean=65 TgC/yr). As shown in the 

figure, there is uncertainty concerning (1) overlaps between 

terrestrial ecosystems and aquatic ecosystems and (2) the 

effects of wildland fire on carbon stocks. For example, in the 

figure, the carbon evasion flux (12.8–24.6 TgC) is attributed 

to the flux from lacustrine and riverine ecosystems; however, 

some portion of this evasion may already be accounted for in 

the terrestrially derived heterotrophic respiration (HR) term. 

Additionally, not all carbon from the lateral flux process is 

exported from the region. Riverine or lacustrine systems 

within the region may store terrestrially derived carbon in 

sediments; carbon sequestration in sediments is unknown at 

this point as work is ongoing.

The Great Plains region features extensive grasslands/

shrublands and agricultural lands. Both of these ecosystems 

have undergone intense land-use changes because of agricultural practices and urban expansion, which are the primary 

processes that influence carbon sequestration and GHG fluxes 

in the Great Plains. Such relations are demonstrated in the 

results of the assessment. 
Integrated Analysis 19

Areas of the LULC classes (and hence ecosystem areas) 

exhibited modest changes between 1992 and 2005 (the baseline 

period for LULC analysis) highlighted by distinctive local 

increases in developed land (particularly in the southern Great 

Plains), declines in forest cover, and steady trends in overall 

agricultural lands and grasslands/shrublands. Socioeconomic 

factors, particularly the demand for agricultural lands, are the 

primary drivers of changes in LULC in the region, and this is 

reflected in both the mapped and projected future LULC that 

make up the ecosystems for this assessment. Under the A1B 

scenario, a very high demand for biofuels, including cellulosic 

biofuel, is projected to drive strong increases in both the 

cultivated crop (traditional biofuels) and hay/pasture (cellulosic 

biofuels) agricultural classes over time. Under the A2 scenario, 

the projected increases in cultivated crops are driven by strong 

population increases, but the overall projected increases in 

agricultural land are smaller than under scenario A1B. Under 

both the A1B and A2 scenarios, the projected increases in 

agricultural land, as well as significant increases in developed 

land, result in declines in “natural” land covers (grasslands/

shrublands, forests, and wetlands) by 2050. Under the environmentally focused B1 scenario, the projected initial increases 

in natural land cover are reversed after 2030 as the population 

increases; there also is a move towards less intense, more 

environmentally friendly agricultural practices, which result 

in a projected need for an increase in agricultural land. Under 

the B1 scenario, the overall natural land cover is projected to 

decline only slightly between the baseline years and 2050.

Areas burned and resulting emissions in baseline years 

demonstrate the large interannual variability in fire activity 

in the region. Among the three Level II ecoregions included 

in the Great Plains region, annual burned areas and emissions were greatest in the South-Central Semi-Arid Prairies 

(averaging 1,675 km2 and 5.83 TgCO2-eq) and lowest in the 

Temperate Prairies (averaging 63 km2 and 0.41 TgCO2-eq). 

When the baseline results were analyzed for the entire Great 

Plains region, the observed amount of area that burned 

varied widely, from as much as 8,159 km2 in 2006 to as 

little as 453 km2 in 2004, which yielded a mean burn rate of 

1,713 km2/yr. The vast majority of area burned was grasslands/

shrublands. Greenhouse-gas emissions from the fires were 

strongly related to the area burned: the highest was in 2006 

at 24.72 TgCO2-eq and lowest was in 2004 at 0.18 TgCO2-eq, 

with an average of 5.96 TgCO2-eq.

The simulated projected burned areas and emissions from 

2011 to 2050 also have a large interannual variability (table 2, 

fig. 3), which is similar to the observed MTBS data. Under 

each of the three scenarios (Nakicenovic and others, 2000), 

there were projected increases in trends in the simulated 

burned area and emissions, but differences among them were 

small; however, the increasing trends in the amount of burned 

area were not significant based on the Mann-Kendall trend 

test (Mann, 1945) of area burned versus time (τ=0.03, 0.03, 

and 0.00, and p-values=0.15, 0.14, and 0.94, for scenarios 

A1B, A2, and B1, respectively, where τ ranges between –1.0 

(decreasing trend) and 1.0 (increasing trend) and p-values 

Figure 7. Chart showing the minimum through maximum 

ranges of net flux values (in teragrams of carbon per year, or 

TgC/yr) for all of the major components of estimated baseline 

(current) carbon budget for the Great Plains region. The arrows 

above the top row of boxes show the directions of the net 

fluxes in relation to the atmosphere. The bottom boxes show 

the net fluxes within the region. The negative values in the total 

biomass and soil organic carbon boxes indicate carbon uptake

Figure 7.

Net primary

productivity

(NPP)

601 to 881

Soil organic

carbon

(SOC)

16 to –36 

Fire

0.05 to 6.74 

Heterotrophic

respiration

(HR)

565 to 727 

Total biomass

–37 to –83 

Harvested wood

products 

(HWP)

–0.3 to –0.96 

Lateral flux

out of region

(not available) 

Sediment burial

(not available)

Lacustrine

evasion

2.8 to 4.6 

Lateral flux

within region

0.07 to 0.31 

Methane

2.91 to 2.94 

Riverine

evasion

10.1 to 20.7 

or sequestration; positive values indicate carbon emission. The 

dashed lines indicate uncertainty in delineating boundaries 

between related components, such as between terrestrial and 

aquatic fluxes, because the methods are not fully coupled. The 

heterotrophic respiration values account for both ecosystem 

respiration and consumption (both grain consumption and 

grazing by livestock). Both lacustrine and riverine evasion 

refers to CO2 evasion, with the value converted to carbon. 
20 Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in the Great Plains Region

indicate the degree to which τ is significantly different than 0, 

or no trend). The projected trends for emissions were slightly 

different. Under all three scenarios, emissions increased but 

only by slightly varying amounts when CO2-eq versus time 

was analyzed (τ=0.04, 0.05, and 0.03 and p-values=0.0226, 

0.0039, and 0.0978, for scenarios A1B, A2, and B1, respectively). The slightly increasing trends in burned area and 

emissions are a conservative estimate of the potential change 

in the Great Plains as the simulations underestimated the 

influence of extreme fire years; extreme events are expected to 

increase in occurrence under a warming climate (IPCC, 2007). 

The effects of fire on carbon sequestration were modeled using 

both the EDCM and CENTURY process-based models. The 

findings were similar to those in the recent literature (Ansley 

and others, 2002); the effects of fire on carbon sequestration 

(reducing the amount of carbon stored in ecosystems in the 

region) were small, averaging 0.08, 0.11, 0.12 and 0.12 TgC/yr 

for the baseline assessment years (2001–2005) and under the 

A1B, A2, and B1 scenarios (2006–2050), respectively. 

A unique feature of this assessment was the examination 

of the movement of carbon through aquatic systems. The 

results for the baseline period showed that, although the total 

area covered by aquatic ecosystems in the region is small (less 

than 2 percent of the total land surface), aquatic systems are 

active sites of carbon transfer and cycling. In addition, these 

results demonstrate that riverine systems are not closed “pipelines” that transfer carbon from upland ecosystems to coastal 

areas (Cole and others, 2007). Instead, there is considerable 

loss of carbon as water and sediments move laterally through 

the system. Climate conditions are projected to be wetter in the 

north and drier in the south (Karl and others, 2009), and these 

projected increases in temperature, evaporation, and drought 

will have impacts on water resources. Given the strong link 

between water flow and lateral carbon fluxes (Schlesinger and 

Melack, 1981; Schindler, 1997; Runkel and others, 2004), in 

areas where lower precipitation and higher evaporation are 

projected, lower carbon fluxes may be possible. 

Work to develop a region-specific estimate of carbon 

sequestration in sediments is ongoing; however, the 

dominance of small, artificial impoundments combined 

with the high prevalence of agricultural lands in the Great 

Plains suggests that sediment burial of organic carbon 

represents a significant carbon sink in this region. Downing 

and others (2008) measured organic carbon burial rates of 

between 148 and 17,000 gC/m2/yr in agriculturally eutrophic 

impoundments in Iowa. If burial rates are similarly high 

throughout the Great Plains region, sediments could be 

sequestering at least as much carbon as is lost by means of 

CO2 efflux from aquatic ecosystems.

Estimates of CH4 and N2O emissions were calculated 

by using the spreadsheet model, which relied on LULC 

change as the primary data without considering other landmanagement activities. Emissions of CH4 were estimated at 

an average rate of 82 TgCO2-eq/yr from 2005 to 2010 and 

increase in future years (81 to 94 TgCO2-eq/yr by 2050, or a 

–1.62 to 16 percent change) (fig. 6). The CH4 emission rate 

estimated by this study is higher than the EPA estimates for 

the entire Nation, which vary from 15 to 27 TgCO2-eq/yr 

(EPA, 2011a) and for which EPA only considered CH4

emissions from forests and rice cultivation but not from other 

major emitters such as wetlands. Under the B1 scenario, 

wetland areas in the region are projected to increase and 

decrease under the A1B and A2 scenarios (fig. 2). The 

projected trends in CH4 emissions reflect those changes in 

wetland areas (fig. 6); however, it should be noted that the 

CH4 uptake by grasslands/shrublands and agricultural lands 

was not considered in the assessment. For N2O, a mean 

annual emission of approximately 158 TgCO2-eq from 2005 

to 2010 was estimated. This estimate is comparable to the 

EPA estimates (EPA, 2011a), which reported that the national 

N2O emissions from agricultural soils and forests varied 

from 210 to 226 TgCO2-eq/yr. Future N2O emissions are 

projected to increase (169 to 186 TgCO2-eq/yr by 2050 or a 

6.7 to 11 percent increase) as a function of the increase in 

agricultural land areas. About 85 percent of the total global 

warming potential (GWP) of CH4 and N2O may be offset by 

carbon sequestration in the Great Plains region. Nevertheless, 

the net GWP would still emit about 100 TgCO2-eq/yr in the 

region (fig. 6). Greenhouse-gas emissions and their uncertainty 

(indicated by a wider spread among scenarios) are projected 

to increase under all three of the IPCC-SRES scenarios. 

These increases only reflect the changes in LULC (especially 

wetlands) because CH4 and N2O emissions were estimated by 

considering only LULC change using the spreadsheet model.

Between 2001 and 2005 (baseline years for the carbon 

sequestration and GHG flux assessment), grasslands/shrublands 

covered 48 percent of the Great Plains region but stored 

35 percent of the total carbon (table 3). Agricultural lands 

covered 42 percent of the land area and stored 46 percent of 

the region’s carbon because of their extensive land area and 

the relatively high carbon density (3.74 kgC/m2). Forests, 

wetlands, and other lands cover 5.35, 1.4, and 1.73 percent of 

the region’s land areas and stored 15.5, 2.9, and 0.93 percent 

of the total carbon, respectively. Between the carbon 

uptake by biomass and by soil, the region featured a total 

sequestration rate that ranged between 20 and 99 TgC/yr, 

which is approximately 3 to 13 percent of the region’s net 

primary productivity (NPP). The net ecosystem carbon 

production rate, when evaluated as CO2 equivalents, is 

approximately 1.16 to 6.58 percent of total GHG emissions of 

the United States in 2009 (EPA, 2011a). In addition to carbon 

sequestration, other key processes in the region included 

heterotrophic respiration (82 to 94 percent of NPP) and aquatic 

lateral and vertical fluxes (approximately 13 to 26 TgC/yr). 

Following recommendations from Lovett and others (2006) 

and Chapin and others (2006), the baseline estimate of carbon 

loss resulting from the effects of grazing was included in 

the total heterotrophic respiration estimate. The loss of soil 

organic carbon (SOC) (16 TgC) is the result of the severe 

drought in the region between 2002 and 2003. By comparison, 

carbon loss resulting from fire emissions was a relatively small 

portion of the overall carbon budget in the region (fig. 7). 
Integrated Analysis 21

Overall, the assessment projects that the Great Plains region 

will remain an overall carbon sink, with projected sequestered 

carbon ranging from 2,165 to 2,728 TgC (mean 2,497 TgC) 

between the baseline years and 2050, depending on the scenarios 

(table 3). These projections translate into an annual carbon 

sequestration of 48.12 to 60.62 TgC (176.5 to 222.3 TgCO2-eq), 

which is about 2.66 to 3.35 percent of total GHG emissions of 

the U.S. in 2009 (EPA, 2011a); however, the overall strength of 

sequestration by all major ecosystems is expected to decrease 

over time (see carbon-dioxide graph in figure 6). Agricultural 

lands would increase in area but maintain carbon stocks, 

grasslands/shrublands would lose land area and carbon stocks, 

and forests would lose land area but gain carbon stocks. On an 

annual averaged basis, all of the major ecosystems in the region 

are projected to be carbon sinks, with forests possessing the 

highest averaged per-area carbon sequestration (192.5 gC/m2/yr), 

followed by wetlands, agricultural lands, and grasslands/

shrublands (52.1, 18.8, and 13.4 gC/m2/yr, respectively). Over 

the 50 years between 2001 and 2050, forests would sequester 

the most carbon per unit of land, followed by wetlands, 

agricultural land, and grasslands/shrublands.

In the Great Plains region, grasslands/shrublands are 

projected to lose 246 TgC under the A1B scenario or projected 

to gain 480 and 609 TgC under the A2 and B1 scenarios, 

respectively, depending on the projected changes in land areas 

(fig. 2). These projections translate into an annual net flux 

density ranging from –6.9 to –17 gC/m2 from 2001 to 2050. 

The grasslands/shrublands estimates are lower than an estimate 

by Zhang and others (2011) but higher than the EPA estimate 

(EPA, 2011a). For the effect of grazing on carbon flux, model 

runs were initialized based on limited data and assumptions, 

as described previously. The results show that the effects of 

grazing on carbon flux in grasslands/shrublands could be 

considerable. The mean annual carbon removal estimates 

from grasslands/shrublands (assuming moderate grazing) are 

approximately 107, 99, 104, and 107 TgC, for the baseline 

(2001–2005) assessment and under the A1B, A2, and B1 

scenarios (2006–2050), respectively. These carbon flux results 

are lower than the 150 TgC/yr reported by Holechek and others 

(2000), which was based on USDA livestock inventory data 

(USDA National Agricultural Statistics Service, 2011). 

Using the USDA inventory data, West and others (2010) 

estimated that the total net ecosystem carbon balance on all 

agricultural lands in the United States was 7 TgC in 2004. 

The EPA (2011a) estimated that croplands in the United 

States acted as a carbon sink, with a storage rate of between 

4.75 and 5.37 TgC/yr from 2005 to 2009. Biogeochemical 

models, however, showed higher estimates than the inventory 

approach. Using the CENTURY model, Ogle and others 

(2010) found that croplands in the United States sequestered 

soil carbon at a rate of 14.6 TgC/yr from 1990 to 1995 and 

a rate of 17.5 TgC/yr from 1995 to 2000. Nevertheless, this 

assessment projects an increase in the density of carbon 

stocks in agricultural lands (from 3.74 kgC/m2 for the baseline 

estimate to 4.47 to 4.67 kgC/m2 by 2050) and an estimated 

overall mean annual sequestration of 27.95 TgC. 

For the baseline years, the carbon storage in forest ecosystems of the Great Plains region was estimated to be 1,162 Tg for 

a total forested area of 116,196 km2, or a carbon stock density 

of 10.0 kgC/m2 (table 3). This estimate for total carbon storage 

is lower than a 2010 USDA Forest Service forest inventory 

estimate of 2,096 TgC for a forested area of 234,162 km2, with 

a carbon density value of 8.95 kgC/m2 (Brad Smith, USDA 

Forest Service, unpub. data, 2010). The difference in total 

carbon storage was likely caused by the difference between 

the definitions of forested land used in this assessment and 

the definition used by the USDA Forest Service; a proportion 

of land that the Forest Service defined as forested lands was 

identified as grasslands/shrublands in the NLCD dataset, which 

was used as the basis for forested lands in this assessment. The 

comparable carbon density estimates (slightly higher in this 

assessment compared to the Forest Service estimate) provide 

further evidence of this analysis. When projected to 2050, the 

assessment results suggest that forest ecosystems will remain a 

strong carbon sink, despite the projected loss of forested lands 

over time, and that the carbon stock density in forested lands 

increases from an average of 10 kgC/m2 during the baseline 

years (2001–2005) to between 18.62 and 18.76 kgC/m2 by 2050. 

Spatially, most carbon sequestration opportunities are 

projected to occur in the southern and eastern parts of the Great 

Plains region, where productive soil and favorable climate 

conditions are found (fig. 5). The assessment also projects the 

potential for wetland restoration in the Prairie Pothole region 

of the study area. On the other hand, a projected loss of carbon 

storage is possible in agricultural lands of the northern prairies 

as the result of reduced agricultural productivity and increased 

soil drying. For the entire Great Plains region, all of the major 

ecosystems except for grasslands/shrublands are projected to 

increase their storage of carbon through 2050. Grasslands/

shrublands are expected to lose carbon toward the second 

half of the assessment timeline because of the projected loss 

of land areas of the ecosystem. When these projections are 

combined, a moderately sized carbon sink is present for most 

of the timeline, but the strength of the sink is expected to 

decrease over time, as noted previously. 

Carbon storage and stock changes in the region are 

significantly affected by LULC changes. This assessment 

indicates that the projected net changes in carbon storage are 

closely related to the projected net changes in ecosystem areas 

in the region, but the relationship varies between the three major 

ecosystems: agricultural land, grasslands/shrublands, and forests 

(fig. 8). The size and direction of the projected net changes in 

carbon stored in agricultural lands are directly related to the 

projected net changes in the size and direction of the agricultural 

lands. For the grasslands/shrublands and forests, the size and 

direction of the projected net changes in their land areas have a 

smaller impact on the size and direction of the projected carbon 

storage than that of agricultural lands. The projected loss of 

land areas tended to reduce the projected carbon sequestration 

but did not tend to change its direction, unless the loss in area 

became large enough, such as the projected loss of grasslands/

shrublands that exists under scenario A1B (fig. 8).
–60,000 

–40,000 

–20,000 

0 

20,000 

40,000 

60,000 

Area, in square kilometers Carbon stocks, in teragrams of carbon

–200 

–100 

0 

100 

200 

300 

400 

2005–2010

2010–2015

2015–2020

2020–2025

2025–2030

2030–2035

2035–2040

2040–2045

2045–20502005–2010

2010–2015

2015–2020

2020–2025

2025–2030

2030–2035

2035–2040

2040–2045

2045–20502005–2010

2010–2015

2015–2020

2020–2025

2025–2030

2030–2035

2035–2040

2040–2045

2045–2050

A1B A2 B1

Ecosystem

EXPLANATION

Agricultural lands

Grasslands/shrublands

Forests

22 Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in the Great Plains Region

The transitions of land use between the major ecosystems 

are projected over time as the result of projected LULC 

changes, as discussed previously and shown in figure 2. These 

transitions (for example, forests transitioning to agricultural 

lands) would result in changes in the projected amount of 

carbon stored in biomass and soils and thus in the projected 

gains or losses in stored carbon (fig. 9). When considering 

the effects of land-use transitions alone (without including 

the effects of land-management activities such as fertilization 

or grazing in the analysis), the results from all three models 

(CENTURY, EDCM, and the spreadsheet model in GEMS) 

for the three IPCC-SRES scenarios suggest overall negative 

impacts on projected carbon storage in the Great Plains region 

(fig. 9A), with varying ranges of projected carbon losses between 

the baseline years and 2050: 59 to 157 TgC using EDCM, 

48 to 122 TgC using CENTURY, and 26 to 118 TgC using the 

spreadsheet model. It should be noted that the spreadsheet model 

accounted for changes in carbon storage only in vegetation, 

whereas the CENTURY and EDCM models accounted for 

changes in all major carbon pools in ecosystems. Among the 

three IPCC-SRES scenarios, the projected cumulative total loss 

between the baseline years and 2050 is the largest under the A1B 

scenario (119 to 157 TgC), followed by A2 (84 to 142 TgC) and 

B1 (26 to 59 TgC); this order of impact among the scenarios is 

consistent across all of the models. Given that the mean total 

carbon sequestration of the Great Plains region is projected to be 

2,500 TgC during the study period (table 3), LULC change in 

the region could potentially reduce the total by about 4 percent.

Among the individual transitions between the major 

ecosystems, the conversion of forests to agricultural 

lands was found to be the dominant factor contributing to 

the greatest projected negative impact on carbon stocks 

(fig. 9B). Forest-to-agriculture conversion accounted for 

half of the carbon loss induced by LULC changes, followed 

by conversion of forests to other lands (which explains 

20 percent of the projected carbon loss). The conversion of 

grasslands/shrublands to agricultural lands and vice versa had 

a variable effect on the change in carbon storage, depending 

on the model that was used (see the bar for G2A versus the 

bar for A2G in figure 9B); the results indicated that there 

was structure-related uncertainty in the models. Conversions 

from wetlands to agricultural lands (W2A), and from forests 

to grasslands/shrublands (F2G) also lead to a considerable 

projected loss of carbon stocks. The only consistent projected 

gains of carbon stocks were from the conversions of grasslands/shrublands to forests (G2F), agricultural lands to forests 

(A2F), other lands to forest (O2F), and other lands to grasslands/shrublands (O2G); however, these projected gains were 

much smaller than the projected losses, as shown in figure 9. 

Finally, because of time and resource constraints, there are 

processes and effects that are related to the Great Plains region’s 

carbon cycle that were not addressed in this report, including: 

(1) individual effects of modeled land management, (2) modeling 

of natural vegetation succession, (3) GHG emissions from livestock feedlots, (4) the effects of cover crops on agricultural lands, 

(5) carbon dynamics in deep soil layers, (6) an estimate of carbon 

sequestration in aquatic systems such as lakes and impoundments, 

and (7) a spatially explicit delineation of carbon flux resulting 

from the lateral movements of soil, carbon, and other materials 

and its impact on both aquatic and terrestrial ecosystems. 

Figure 8. Bar charts showing the estimated and projected net changes in the total 

area and the carbon stocks of the three primary ecosystems in the region (agricultural 

lands, grasslands/shrublands, and forests) between 2005 and 2050, under the three 

IPCC-SRES scenarios (A1B, A2, and B1; Nakicenovic and others, 2000). IPCC-SRES, 

Intergovernmental Panel on Climate Change’s Special Report on Emissions Scenarios. 
Land-cover change

B

Scenario and model

Carbon stock change, in teragrams of carbon Carbon stock change, in teragrams of carbon

–80

–60

–40

–20

0

A

F2F

F2GF2A

F2W

F2OG2F

G2GG2A

G2W

G2O

A2F

A2GA2A

A2W

A2O

W2F

W2GW2A

W2W

W2O

O2F

O2G

O2A

O2W

O2O

20

–80

–60

–40

–20

0

A1B and

EDCM

A1B and

spreadsheet

A2 and

spreadsheet

B1 and

spreadsheet

A1B and

CENTURY

A2 and

EDCM

A2 and

CENTURY

B1 and

EDCM

B1 and

CENTURY

Baseline–2010

EXPLANATION

2010–2020

2020–2030

2030–2040

2040–2050

Decade

CENTURY 

Model

Error bar—One standard 

 deviation of the mean 

 carbon change

EDCM 

Spreadsheet

EXPLANATION

Integrated Analysis 23

Figure 9. Bar chart showing the net impacts of combined 

LULC changes on carbon stocks in the Great Plains region. 

A, Carbon stocks by decade as estimated using each 

of the three biogeochemical models (CENTURY, EDCM, 

and spreadsheet) in GEMS under each of the IPCC-SRES 

scenarios (A1B, A2, and B1; Nakicenovic and others, 2000). 

B, Changes in carbon stocks resulting from the transition of 

one land-use type to another between the baseline and 2050, 

using each of the three biogeochemical models (CENTURY, 

EDCM, and spreadsheet) in GEMS. On part B, for the 

individual transitions from one land-cover class to another 

(x-axis labels), the letters F, G, A, W, and O denote forests, 

grasslands/shrublands, agricultural lands, wetlands, 

and other lands, respectively, and the “2” between two 

letters means “transition to.” For example, F2G refers 

to “forests transitioning to grasslands/shrublands.” The 

error bar in part B is one standard deviation of the mean 

carbon change for each of the three IPCC-SRES scenarios. 

EDCM, Erosion-Deposition-Carbon Model; GEMS, General 

Ensemble Modeling System; IPCC-SRES, Intergovernmental Panel on Climate Change’s Special Report on 

Emissions Scenarios; LULC, land use and land change. 
24 Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in the Great Plains Region

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Manuscript approved on November 21, 2011

Edited by Elizabeth D. Koozmin

Illustrations and layout by Caryl J. Wipperfurth

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Zhu and others—Baseline and Projected Future Carbon Storage and Greenhouse-Gas Fluxes in the Great Plains Region of the United States—Professional Paper 1787

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