The potential of U.S. grazing lands to sequester carbon and mitigate the greenhouse effect

473 Pages·2001·6.822 MB·English

by  R F Follett, J M Kimble, R Lal

The Potential
U.S. Grazing Lands
of
Sequester Carbon
to
Mitigate
and the
Greenhouse Effect
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The Potential
U.S. Grazing Lands
of
Sequester Carbon
to
Mitigate
and the
Greenhouse Effect
R.F. Follett • J.M. Kimble • R. Lal
LEWIS PUBLISHERS
Boca Raton London New York Washington, D.C.
L1554/disclaimer Page 1 Tuesday, August 1, 2000 11:08 AM
Library of Congress Cataloging-in-Publication Data
The potential of U.S. grazing lands to sequester carbon and mitigate the greenhouse
effect / edited by R.F. Follett, J.M. Kimble, and R. Lal.
p. cm.
Includes bibliographical references.
ISBN 1-56670-554-1 (alk. paper)
1. Soils--Carbon content--United States. 2. Carbon sequestration. 3. Greenhouse effect,
Atmospheric--United States. 4. Greenhouse gases--Environmental aspects--United
States. 5. Rangelands--United States. I. Follett, R. F. (Ronald F.), 1939-II. Kimble, J.
M. (John M.) III. Lal, R.
S592.6.C35 P68 2000
631.4′1—dc21 00-042832
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v
Executive Summary
The Potential of U.S. Grazing Lands to Sequester Carbon and Mitigate the Green-
house Effect, edited by R.F. Follett, J.M. Kimble, and R. Lal, describes grazing lands,
the areas they occupy, and their important role in sequestering C to help mitigate
the greenhouse effect. The editors and 36 other authors prepared the 17 chapters,
which each includes extensive references. Chapter 16 provides a summary and
overview of C sequestration in grazing land soils and estimates the overall poten-
tial of U.S. grazing land to sequester C, while Chapter 17 considers research
needs and priorities.
Grazing lands represent the largest and most diverse single land resource in
the U.S. and in the world. In the U.S., rangelands and pastures together make up
about 55% of the total land surface, and more than half of the earth’s land surface
is grazed. Grazing lands occupy an even larger area than cropland in the U.S. —
212 Mha (524 million acres) of privately owned and over 124 Mha (300 million
acres) of publicly owned land, or more than twice the area of cropland. The large
area grazing land occupies, its diversity of climates and soils, and the potential to
improve its use and productivity all contribute to its great importance for seques-
tering C and mitigating the greenhouse effect and other aspects of climate
change.
Section 1: The Extent, General Characteristics,
and Carbon Dynamics of U.S. Grazing Land
Chapter 1 provides an introduction to the book. It describes the authors’
objectives, the background which prompted them to prepare the book, and the
wide range of questions involved. It also describes (and provides photographs of)
the wide range of ecosystems grazing land includes. It summarizes the negative
effects of human intervention on grazing lands and the best management
practices needed to reverse those effects and effectively sequester C and prevent
its further loss.
The Potential of U.S. Grazing Lands to Sequester Carbon and Mitigate the Greenhouse Effect
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vi Executive summary
Chapter 2 provides the broad-scale perspective on the extent, distribution,
and characteristics of grazing lands. It also provides the analyses of the National
Resources Inventory (NRI) for the areas and descriptions of the privately owned
U.S. grazing lands (rangeland and pasture) used in this book.
Chapter 3 describes the organic C pools and cycles and soil organic C (SOC)
sequestration, while Chapter 4 describes the soil inorganic C (SIC) pools and cy-
cles in grazing land soils.
Section 2: Soil Processes, Plant Process,
and Carbon Dynamics on U.S. Grazing Land
Chapter 5 considers heterogeneity, long-term sustainability, and feedback
loops, including structural features recognizable at the plant, plant community,
and landscape scales as they relate to rangeland areas with different C sequestra-
tion potentials. Chapter 6 explains in greater detail the important biological roles
provided by plant roots and soil microbial biomass for organic C sequestration.
Chapter 7 gives experimentally measured CO -flux data across a transect of
2
grazing land sites extending from north to south in the Great Plains. These data
can be extrapolated to a large part of the Great Plains and show a net sequestra-
tion of C into the soil and vegetation in this important region. The estimates are
similar in magnitude to those made independently by the authors of Chapter 11.
Chapter 8 considers the very complex plant and soil processes related to C
sequestration in tundra, alpine, and mountain meadow systems. Understanding
the feedback relationships between biogeochemical processes and human
activities in these cold environments is increasingly important because human
concerns and opinions and public policy decisions can severely affect these fragile
ecosystems.
Section 3: Managerial and Environmental
Impacts on U.S. Grazing Land
Chapter 9 addresses soil erosion and C dynamics, provides estimates of land
cover and the factors affecting soil erosion, and estimates areas of highly erodible
grazing land and C losses and emissions resulting from soil erosion. It shows how
restoring eroded grazing land soil can sequester a large amount of SOC.
Chapter 10 covers the management of soil’s physical characteristics such as
bulk density, crusting, aggregation, and infiltration characteristics and capacity,
which decrease soil erosion and encourage soil C sequestration.
Follett, Kimble, and Lal, editors
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Executive summary vii
Chapter 11 discusses important considerations for the soil C dynamics of
rangeland. It also discusses the effects of grazing management on changes in
rangeland plant communities and the potential of rangelands to sequester C.
Chapter 12 discusses how pasture management options provide an excellent
opportunity to sequester SOC. Although occupying a smaller total area than
rangelands, pastures generally have more favorable climatic conditions and re-
spond well to the planting of improved species, grazing, and fertility manage-
ment.
Chapter 13 evaluates the effects of fire on soil C sequestration, especially for
tall grass prairie. Many grassland areas have coevolved with fire and grazing.
When properly managed, fire can promote growth of many of the grass species
and help to control the invasion of unwanted species. The increase in plant
growth that results from fire can compensate for the loss of aboveground C with
little or no change in SOC.
Section 4: Using Computer Simulation Modeling
to Predict Carbon Sequestration in Grazing Land
Because of the importance of plant productivity to the sequestration of C,
Chapter 14 focuses on the complex interactions between system components and
how computer simulation modeling can help evaluate the effects of environmen-
tal change and of management strategies to improve rangeland production.
Chapter 15 describes soil C responses to environmental change in grassland
systems and the factors that control soil C dynamics. In addition, Chapter 15 also
demonstrates the predictive capability of computer modeling by simulating
changes in aboveground plant production and SOC during a 50- to 75-year period
after initiation of altered climate conditions and a doubling of CO levels in the
2
Great Plains.
Section 5: Summary and Overview
and Research and Development Priorities
Chapter 16, the synthesis chapter, summarizes information from all the other
chapters and presents an overview of U.S. grazing lands’ potential to sequester C.
Chapter 17 addresses issues that require research and identifies some of the pri-
orities scientists, policy makers, and producers need to consider. Chapter 16 con-
cludes that C sequestration under grazing land (pasture and rangeland) results
from both managed and unmanaged activities. The total soil C sequestration po-
tential for U.S. grazing land is 29.5 to 110.0 (mean = 69.9) million metric tons
The Potential of U.S. Grazing Lands to Sequester Carbon and Mitigate the Greenhouse Effect
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viii Executive summary
(MMT) C/yr and represents a sink 1.6 times the size of the CO -C emission from
2
all U.S. agriculture (42.9 MMTC/yr; Lal et al. 1998) and 4.4 times the CO -C emis-
2
sion from all grazing land agriculture.
This total includes 45% from land conversion and restoration, 7% from un-
managed rates of C sequestration, and 48% due to adoption of improved practices.
Much can be accomplished to decrease the CO emitted from grazing land through
2
land conversion and restoration practices (17.6 to 45.7 MMTC/yr), specifically by
decreasing soil erosion (6.2 to 24.6 MMTC/yr) and with the Conservation Reserve
Program (CRP), which has the potential to sequester SOC (7.6 to 11.5 MMTC/yr).
Other conversion and restoration practices include mined land restoration and
land conversion to pasture, which cumulatively result in the sequestration of an
additional 2.6 to 7.8 MMTC/yr.
We also estimate that nonintensively managed grazing land currently seques-
ters between –4.1 and 13.9 MMTC/yr and includes sequestration of inorganic car-
bonates on extensive rangeland areas in the western U.S. Intensification on U.S.
rangeland through improved management has the potential to sequester 5.4 to
16.0 MMTC/yr, while more intensive grazing management, improved species, and
fertility and manure management of U.S. pastureland has the potential to se-
quester a total of 10.5 to 34.3 MMTC/yr.
Little information is available concerning the response of high-altitude, cold
region grazing land in the U.S. to management inputs, except for mountain mead-
ows. Mountain meadows are estimated to potentially sequester 0.05 to 0.10
MMTC/yr with improved fertility. Because mining provides economic resources
whereby inputs of fertility, reseeding, and other land restoration practices can be
made available, it also has the highest potential rates of SOC sequestration
(> 1000 kg C/ha/yr).
The productivity and sustainability of grazing lands requires that high soil
quality (e.g., biomass productivity potential and environmental quality) be main-
tained. Both nutrients and water-holding capacity of soil directly relate to SOC
content. High-quality soils lead to C sequestration and result in low levels of CO
2
and other greenhouse gas emissions. A wide range of options exist for sequester-
ing C in soil. Appropriate options differ for different soils and ecoregions, and no
single option universally applies. Site-specific adaptation and total ecosystem
management is needed, and the most appropriate combination of options must be
selected. Thus, depending upon the ecosystems, some promising options include:
(cid:1) Growing species with deeper root systems and perhaps those that con-
tain high lignin content, especially in their roots and residues.
(cid:1) Managing rangelands and pastures through controlled grazing, vegeta-
tion management, and other recommended management practices.
Pasture management options also include fertility inputs and improved
species.
(cid:1) Using strategies that increase biomass yields.
Follett, Kimble, and Lal, editors
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Executive summary ix
(cid:1) Using strategies to conserve water and soil resources.
(cid:1) Converting marginal and degraded lands to restorative land uses (e.g.,
establish perennial cover, such as with CRP or afforestation).
(cid:1) Restoring degraded soils.
(cid:1) Enhancing biological N fixation.
Numerous gaps and uncertainties exist related to obtaining exact estimates
for both the emissions of greenhouse gases from grazing lands and for narrowing
the range for the estimated potential of grazing land’s agricultural activities to
sequester C. In spite of these gaps, the authors of this book clearly have estab-
lished that significant amounts of C are sequestered in grazing land soils and,
with careful and appropriate management, even more C can be sequestered. The
diversity of climates and soils of grazing lands and the potential to improve their
use and productivity all contribute to their great importance for sequestering C.
There are 212 Mha of privately owned and over 124 Mha of publicly owned
grazing land in the U.S. — more than twice the area (155 Mha) of cropland soils.
Because of the benefits to producers, the public, and society in general, sequester-
ing C in soil is a win-win scenario with the potential to enhance soil quality and
productivity, restore degraded grazing land resources, and mitigate the green-
house effect. Improved management practices, restoration of degraded soils and
ecosystems, and enhanced biomass productivity on grazing lands can provide a
significant contribution to offsetting U.S. emissions of CO while helping to miti-
2
gate the greenhouse effect.
As Chapter 17 states, however, grazing land systems can contribute to both
the environmental and economic well-being of U.S. agriculture while also seques-
tering C — provided that our national strategic goals include enhancing (1) graz-
ing land condition, (2) environmental quality, and (3) the economic viability of
producers. Realizing this vast potential depends on (1) obtaining research data on
soil carbon dynamics, (2) assessing the cost of soil C by monitoring additional
costs associated with adopting recommended management practices, (3) identify-
ing policy issues that facilitate/encourage adopting the desired practices, and (4)
putting in place the mechanisms needed.
Soil C sequestration research has been ad hoc and piecemeal. We need to de-
velop a systematic research program based on identified knowledge gaps and pri-
orities of issues. The program has to be interdisciplinary and involve soil scien-
tists, agronomists, economists, and policy makers. Similarly, we need to develop
interdisciplinary research teams (including biophysical and social scientists) to
identify appropriate policies for soil C sequestration. Various governmental bod-
ies may need to identify and implement appropriate policies to facilitate wide-
spread adoption of recommended practices.
An important component of the interdisciplinary program is the land
manager. Farmers and land managers need to be involved in program planning
The Potential of U.S. Grazing Lands to Sequester Carbon and Mitigate the Greenhouse Effect
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