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Published online 23 June 2008
Published in J Environ Qual 37:1376-1382 (2008)
DOI: 10.2134/jeq2007.0290
© 2008 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
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Indicators of Carbon Storage in U.S. Ecosystems: Baseline for Terrestrial Carbon Accounting

Christine Negra*, Caroline Cremer Sweedo, Kent Cavender-Bares and Robin O'Malley

The H. John Heinz III Center for Science, Economics and the Environment, 900 17th Street NW, Suite 700, Washington, DC 20006

* Corresponding author (negra{at}heinzctr.org).

Received for publication June 1, 2007.

   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 Methods
 Results
 Discussion
 REFERENCES
 
Policymakers, program managers, and landowners need information about net terrestrial carbon sequestration in forests, croplands, grasslands, and shrublands to understand the cumulative effects of carbon trading programs, expanding biofuels production, and changing environmental conditions in addition to agricultural and forestry uses. Objective information systems that establish credible baselines and track changes in carbon storage can provide the accountability needed for carbon trading programs to achieve durable carbon sequestration and for biofuels initiatives to reduce net greenhouse gas emissions. A multi-sector stakeholder design process was used to produce a new indicator for the 2008 State of the Nation's Ecosystems report that presents metrics of carbon storage for major ecosystem types, specifically change in the amount of carbon gained or lost over time and the amount of carbon stored per unit area (carbon density). These metrics have been developed for national scale use, but are suitable for adaptation to multiple scales such as individual farm and forest parcels, carbon offset markets and integrated national and international assessments. To acquire the data necessary for a complete understanding of how much, and where, carbon is gained or lost by U.S. ecosystems, expansion and integration of monitoring programs will be required.


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
Methods
 Results
 Discussion
 REFERENCES
 
THE quantity of carbon in ecosystems influences the provision of a wide range of ecosystem services such as ecological productivity and climate regulation. Carbon-containing greenhouse gases in the atmosphere contribute to climate change by trapping solar energy. Large quantities of carbon can be sequestered or released to the atmosphere by soils and biota in U.S. ecosystems, and there is growing interest in the potential for enhanced carbon sequestration by ecosystems to help to offset industrial and other carbon emissions (Goodale et al., 2002; Dilling et al., 2003; Suyker et al., 2003; Bellamy et al., 2005; Millar et al., 2007; Peters et al., 2007).

Ecosystem types have characteristic carbon storage patterns. For example, forests, unlike grasslands, commonly contain considerable aboveground carbon. However, there is also considerable variability in carbon levels within ecosystem types. For example, soil carbon storage in croplands can vary dramatically at local and regional scales. The amount of carbon found in a given terrestrial area is affected by the number and type of plants and animals and the moisture and temperature conditions that control plant growth and decay, as well as underlying soil properties and land use history (Ogle et al., 2003).

Contemporary changes in the amount of carbon stored in forests, croplands, grasslands, and shrublands are influenced by both land management and environmental conditions (Khan et al., 2007; Magnani et al., 2007; Gruber and Galloway, 2008). Shifts in farming and forestry practices have the potential to alter carbon sequestration processes (West and Post, 2002; Lal, 2004), as do climate regimes, such as temperature and moisture conditions, and disturbance patterns, such as wildfire or pest outbreaks (Lucier et al., 2006; Bond-Lamberty et al., 2007; Mildrexler et al., 2007; Heimann and Reichstein, 2008; Kurz et al., 2008).

The direct and indirect effects of emerging carbon trading programs, coupled with potential changes in climate and disturbance patterns, will have important implications for carbon storage in forests, croplands, grasslands, and shrublands. Furthermore, the expanding biofuels industry is likely to have substantial impacts on carbon storage (Fargione et al., 2008; Searchinger et al., 2008). Internationally, efforts to offset carbon emissions through enhanced terrestrial carbon storage are underway or under discussion, inspired in part by the Kyoto Protocol (Saikku et al., 2008; Zheng et al., 2008) and evolving plans for participation beyond the expiration of the current protocol in 2012 (Basu, 2007; UNFCCC, 2007a,b; Wara, 2007). In the U.S., several private and regional initiatives to offset carbon emissions (such as the Regional Greenhouse Gas Initiative and the Western Regional Climate Action Initiative) have already begun (Marris 2007a,b; Callaway, 2007) and may expand with future development of a U.S. carbon credit trading regime (Point Carbon, 2006; Chameides and Oppenheimer, 2007; Marris, 2007c). As legislative and market attention increasingly focuses on U.S. biofuels production as an alternative to fossil fuels and a strategy for mitigating greenhouse gas emissions, there may be significant implications for terrestrial carbon storage (Stavins and Richards, 2005; USDA, 2006; Righelato and Spracklen, 2007).

To verify that there is real value underlying purchased carbon offsets, carbon trading programs require accountability based on objective reporting systems that establish credible baselines and accurately document the achievement of durable carbon sequestration (Hall et al., 2001; Post et al., 2004; Chameides and Oppenheimer, 2007; Lovett et al., 2007). Similarly, evaluation of policy and market incentives for expansion of biofuels production should demonstrate that these incentives achieve net reduction in atmospheric carbon. For example, it will be increasingly important to document that carbon releases from land use conversions necessary to plant biofuel feedstocks are minimized, thereby helping to ensure that biofuel production strategies do not result in net increase in atmospheric greenhouse gas emissions (Hill et al., 2006; Naylor et al., 2007; Scharlemann and Laurance, 2008).

Ecological indicators are useful tools for tracking the effects of changing management and environmental conditions in the U.S. and for applying common metrics across geographic scales and ecosystem types. The National Research Council has recommended tracking the total amount of carbon sequestered or released by ecosystems by calculating the difference between total non-plant respiration (carbon dioxide produced by detrivores and animals) and net primary production (NRC, 2000). As an outgrowth of the Montreal Process (Montreal Process for Conservation and Sustainable Management of Temperate and Boreal Forests; http://www.rinya.maff.go.jp/mpci/), the USDA Forest Service has published indicators for ecosystem biomass and carbon pools as well as the contribution of forest ecosystem components to the total global carbon budget (USDA Forest Service, 2004). In 2002, a forest carbon storage indicator in the Heinz Center's State of the Nation's Ecosystems report presented total carbon stored in trees in timberlands; however, data were not available to report on other forest carbon pools, carbon in grasslands and shrublands, or soil organic matter in farmlands (The H. John Heinz III Center for Science, Economics, and the Environment, 2002).

In this paper, we report on two new indicator metrics for carbon storage developed through multi-sector expert consultation for inclusion in the 2008 State of the Nation's Ecosystems that complement previous indicator design and reporting work by the Heinz Center and others. The new carbon storage indicator integrates design considerations for multiple ecosystem types, focuses on change in carbon storage over time, and is intended to be sensitive to shifts in carbon storage resulting from multiple factors. Existing national-scale monitoring data are used to populate indicator metrics and we highlight additional data types needed for comprehensive carbon storage reporting. Although primary emphasis is on national-scale reporting, indicator metrics can be applied to sub-national scales and a broad range of contexts such as terrestrial carbon management and can be used to inform development of mechanisms for consistent carbon accounting.


   Methods
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Methods
Results
 Discussion
 REFERENCES
 
Indicator Design
The indicator design process for the State of the Nation's Ecosystems engages stakeholders from four sectors– private business, government, academia, and non-governmental organizations– and is focused on metrics of ecosystem condition rather than stressors or drivers of change. Indicator metrics are designed to integrate the effects of multiple drivers so that specific management or environmental factors are not viewed in isolation (O'Malley et al., 2003). In 2002, the Heinz Center identified six major ecosystem types– forests, farmlands, grassland, and shrublands, coasts and oceans, fresh waters, and urban and suburban areas– to guide the development of a national ecological indicator framework (The H. John Heinz III Center for Science, Economics, and the Environment, 2002). In 2005, the Heinz Center's multi-sector advisory board identified the need to develop an indicator of carbon storage that is applicable to these major ecosystem types and provides information relevant to ecosystem productivity and the contribution of U.S. ecosystems to the global carbon budget.

To identify the range of relevant carbon storage metrics to be considered for this new indicator, Heinz Center staff consulted 32 public and private sector experts and reviewed available literature. A multi-sector advisors workshop was convened in February 2006 to identify carbon stocks that account for the majority of net carbon loss or accumulation, to define appropriate reporting strategies, and to evaluate potential data sources. Based on key indicator design considerations identified through consultations, workshop discussions, and engagement with the State of the Nation's Ecosystems project's oversight committees, indicator metrics were developed. Two levels of internal review were provided for this indicator and its metrics by standing four-sector advisory committees. As part of the review process for the 2008 State of the Nation's Ecosystems report, the new carbon storage indicator was presented to several hundred external peer reviewers.

Data Sources
Data from ongoing national-scale monitoring programs characterized by robust sampling or estimation methodologies, transparent reporting, and independent review were sought to populate the indicator metrics. Suitable data sources were identified for key components of forests, croplands, grasslands, and shrublands. Data gaps are discussed in the Results section. Note that the reporting ranges in Fig. 1 were selected, in cooperation with data providers, to distinguish minimal rates of change (± 0.04 metric tons acre–1 yr–1, or 0.1 metric tons ha–1 yr–1) from meaningful change in carbon density.


Figure 1
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  		Fig. 1. Carbon gained or lost, by ecosystem type, over time. Estimates for forests provided by USFS for above- and below-ground biomass (excluding soil). Estimates for croplands, grasslands, and shrublands provided by NREL for soil carbon (top eight inches) on private lands only. Coverage: lower 48 states.

 
Estimates of change in forest carbon storage were derived from the FORCARB model, based on data gathered in the lower 48 states through the Forest Inventory and Analysis (FIA) program, and were provided by the USDA Forest Service (Heath et al., 2003; Smith et al., 2006; Smith et al., 2007; USEPA, 2007). Carbon storage estimates are based on field estimates of the size of trees of various species, along with statistical models of the relationships between tree stem volume and carbon contained in branches, leaves, the forest floor, dead wood, and soil. The interval from 1995 to 2005 represents annualized (interpolated per state or sub-state classification) estimates. All estimates are based on data prepared for the U.S. forest carbon inventory included in the USEPA's Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2005 (2007).

Estimated changes in carbon storage in cropland, grassland and shrubland soils were derived from the Century Ecosystem Model by the Natural Resource Ecology Laboratory at Colorado State University (Parton et al., 1987, 1988, 1994; USEPA, 2007). The Century Ecosystem Model integrates baseline soil carbon measurements and soil properties with change factors including land use data (tillage intensity, soil additions) and weather conditions. Estimates relate to change in carbon stocks in the top eight inches of soil for approximately 90% of privately-owned lands classified as croplands, grasslands, or shrublands for the conterminous U.S. These estimates were based on land use and management histories from the USDA National Resources Inventory (NRI), which only surveys private lands (see http://www.nrcs.usda.gov/technical/NRI/). Stock changes for croplands, grasslands, and shrublands during the 1980-2000 time period coincide with the most detailed data on land use and management available from the NRI. Aboveground carbon in annually cropped soils are excluded, as are organic soils, very gravelly, cobbly, or shaley soils, areas transitioning to non-agricultural use, and soils used to produce vegetables, perennial and horticultural crops, tobacco, or rice. These estimates are also based on data prepared for the USEPA inventory report (USEPA, 2007).


   Results
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Methods
 Results
Discussion
 REFERENCES
 
Indicator Design Considerations
Several key indicator design considerations emerged from expert consultations and workshop discussions:

  1. Changes in the amount of carbon stored by ecosystems should not be obscured by changes in the areal extent of major ecosystem types. For example, carbon gain resulting from increase in carbon per unit area (e.g., aggrading forests) should be distinguishable from carbon gain due to increased ecosystem area (e.g., land use conversion from cropland to forest).
  2. Indicators should be sensitive to major changes in carbon stocks, especially in carbon-dense systems and lands undergoing conversion to new cover types, climate regimes, or disturbance patterns. For example, wetlands constitute a relatively small percent of the U.S. by area, but they have the potential to release or take up large quantities of carbon in response to changing hydrologic conditions (Johnson et al., 2005). Similarly, some geographic areas may have greater potential for rapid changes in carbon storage, where warming trends may alter patterns of wildfire, hydrology, or pest outbreaks (Goetz et al., 2005; Sitch et al., 2007; Turetsky et al., 2007).
  3. To facilitate detection of meaningful patterns in carbon storage, it is important to measure both changes in carbon stocks over units of time, as well as total carbon stocks. While tracking rates of change is important for identification of major shifts in net gain or loss of carbon, it is also important to characterize, to the extent possible, the total quantity of carbon stored in ecological compartments to understand the scale of historical and possible future shifts. Measurement of change is more feasible for some carbon pools, while measurement of total stocks is more feasible in others. For example, measurement of total soil carbon is constrained by serious technical limitations due to high spatial heterogeneity and variable carbon composition and residence time (Conant and Paustian, 2002; Ogle and Paustian, 2005).

Indicator Metrics
Existing indicators in the State of the Nation's Ecosystems have reported on total carbon stocks for those ecosystem components for which national-scale data were available (trees in timberlands) or provided ‘placeholders’ pending expanded environmental monitoring (see Data Gaps below). The indicator metrics described below were designed to focus on change in carbon storage and provide an integrated, cross-ecosystem view. While these metrics currently present available data for forests, croplands, grasslands, and shrublands, figures are intended to accommodate additional ecosystem types as data become available. In addition to the six major ecosystem types, wetland ecosystems will also be included because of their generally higher carbon density and climate sensitivity.

Changes in carbon stocks are reported as annual estimates averaged over 10-yr time periods– the years included in decadal averages depend on availability of data for each ecosystem type. As new data become available, new decadal averages will be added. The timescale selected for reporting is intended to be sensitive to large-scale net change in ecosystem carbon (e.g., shifts in carbon density resulting from large-scale fire suppression or drier regional climate conditions) and less sensitive to ‘natural’ oscillations in carbon content.

Total Carbon Gained or Lost by U.S. Ecosystems
The indicator metric shown in Fig. 1 is designed to report on change over time in the total amount of carbon stored in major U.S. ecosystem types, parameterized as annual change averaged over 10-yr time blocks. This figure is intended to enable characterization of major U.S. ecosystem types as net sources or sinks for atmospheric carbon (e.g., increased carbon storage in plants, soils, and sediments can offset emissions of carbon dioxide and methane gases to the atmosphere, where they contribute to the greenhouse effect). Due to limitations in available data for the full range of ecosystem types (specifically fresh waters, coastal waters, wetlands, and urbanized areas) and select carbon pools or land ownership types in forests, croplands, grasslands, and shrublands, a complete understanding of net carbon sequestration in U.S. ecosystems is not yet possible.

As shown in Fig. 1, above- and below-ground biomass in the nation's forests (not including soils) gained nearly 150 million metric tons of carbon per year from 1995–2005, with about twice as many forest acres (about 60%) gaining carbon as losing carbon (about 30%). Soils in privately owned croplands gained 11.1 and 16.5 million metric tons of carbon per year during the 1980s and 1990s, respectively, although some cropland acres (35–45%) gained carbon while others (9–13%) lost carbon (the remainder had minimal change in carbon stocks). Soils on the nation's privately owned grasslands and shrublands lost 150 thousand metric tons of carbon per year in the 1980s and gained 1.6 million metric tons per year in the 1990s, although some private grassland-shrubland acres (about 9%) gained carbon while others (5–6%) lost carbon.

Change in Carbon per Unit Area in U.S. Ecosystems
The indicator metric shown in Fig. 2 reports change over time in carbon density, the amount of carbon found per unit area, parameterized as annual change averaged over 10-yr time blocks. Change in carbon storage is normalized by the areal extent of major U.S. ecosystem types so that the effects of land management and climatic variation can be distinguished from the effects of land conversion to new ecosystem types. This metric can be used to better understand changes in the capacity of ecosystems to provide carbon-related ecological services such as soil fertility, water storage, resistance to soil erosion and soil biodiversity enhancement.


Figure 2
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  		Fig. 2. Change in carbon density, by ecosystem type, over time. Estimates are based on data shown in Fig. 1 and areal extent of forests, croplands, and grasslands and shrublands. Note unit conversion: 1 metric ton = 1.10 U.S. short tons; 1 acre = 0.40 hectare.

 
As shown in Fig. 2, 56% percent of forest acres gained 0.04 to 0.8 metric tons of carbon annually (0.1 to 2.0 metric tons per hectare), and even higher carbon gains (> 0.8 metric tons of carbon annually per acre, or > 2.0 metric tons of carbon annually per hectare) occurred in 6% of forest acres. More than 0.8 metric tons of carbon were lost per acre annually (> 2.0 metric tons of carbon per hectare annually) on 3% of forest acres, and 29% of forest acres had carbon losses of 0.04 to 0.8 metric tons per acre per year (0.1 to 2.0 metric tons per hectare per year). The remaining 6% of forest area experienced minimal change in carbon storage per acre annually. Between 1990 and 1999, almost all of cropland acres with more than "minimal change" (increase or decrease) in soil carbon density, changed at a rate of 0.04 to 0.8 metric tons of carbon per acre (0.1 to 2.0 metric tons of carbon per hectare) yearly. A smaller percentage of cropland soils showed "minimal change" in the 1990s than in the 1980s. Additional data are required to determine if this decrease is part of a larger trend over time. Between 1990 and 1999, almost all of private grassland and shrubland acres with more than "minimal change" (increase or decrease) in soil carbon density, changed at a rate of 0.04 to 0.8 metric tons of carbon per acre (0.1 to 2.0 metric tons of carbon per hectare) yearly. In the 1980s and 1990s, about 85% of private grassland and shrubland areas had no substantial change in carbon density, nationally.

Changes in the amount of carbon in ecosystems can result from changes in both the amount stored per acre (carbon density) and the area of that ecosystem. The indicator metrics described above show that U.S. forests gained more total carbon than croplands, grasslands, and shrublands (Fig. 1) and a greater percentage of forest acreage experienced a net gain in carbon density (Fig. 2). The positive change in forest carbon storage from 1995–2005 may be due to improved forest management practices that increase biomass on existing forest lands, and the regeneration of previously cleared forest areas, rather than a change in forest area. The more modest increases in soil organic carbon in croplands, grasslands, and shrublands may be due to enrollment of lands in the Natural Resource Conservation Service's Conservation Reserve Program or adoption of conservation tillage and other soil management techniques.

Additional Reporting Elements
To complement reporting on terrestrial carbon stocks, additional indicator elements will be included in the State of the Nation's Ecosystems report. As monitoring data or estimates become available, reporting on carbon storage in aquatic systems (wetlands, rivers, lakes, coastal areas) will be included. In the 2008 report, trends in concentration of two major carbon-based atmospheric gases– carbon dioxide and methane– will be presented as an index of deviation from long-term, preindustrial average concentrations (note that changes in global gas concentrations cannot be quantitatively linked to changes in U.S. carbon stocks). These two gases are important targets for climate change mitigation and are associated with numerous ecological processes such as plant growth and decomposition.

Data Gaps
This indicator is intended to provide comprehensive geographic coverage of carbon storage in U.S. ecosystems, however a complete picture is not yet available. No national-scale carbon storage data are currently being collected on public grasslands and shrublands, wetlands (including peatlands; coastal, and freshwater), ocean waters and sediments, fresh waters, or urban and suburban areas. Data for wetland and peatland systems are of particular interest because of their potential to store or release large amounts of carbon. For example, as wetlands dry out or are drained for agriculture or development, carbon is released to the atmosphere. In some areas, former wetland areas are more sensitive to disturbances such as fires, which can further accelerate carbon loss. In Alaska alone, wetlands and peatlands are estimated to contain 43.2 Gt C (peatland, freshwater mineral, and estuarine pools combined) (USCCSP, 2007).

In addition, estimates for important carbon pools in forests, croplands, grasslands and shrublands are unavailable:

Forests: Some studies suggest that forest soils make up nearly half of the carbon found in forests; preliminary work is being done to estimate carbon in forest soils (Woodbury et al., 2007). Estimates of carbon storage in forests of Alaska and Hawaii are not available, since the underlying survey on which the estimates are calculated has not yet been expanded to these areas on a consistent basis. In 1995, the Forest Service estimated 16.0 billion metric tons of carbon (Gt C) in Alaskan forests, the majority in the soils (12.0 Gt C) (Birdsey and Heath, 1995). Planned improvements for Forest Service soil carbon estimates include incorporating land use changes into modeling analyses and accounting for areal changes and effects of afforestation and deforestation (USEPA, 2007).
Croplands, grasslands, and shrublands: Estimates for public croplands (a relatively minor component of U.S. croplands) are not currently available. Several hundred million acres of grasslands and shrublands in the public domain represent an important gap in carbon estimates. Carbon estimates do not include above-ground plant matter, although the practice of returning crop residues to soils (e.g., no-till and other conservation measures) is accounted for in croplands estimates. For grassland and shrubland systems, above-ground plant matter is believed to be a secondary component (5–30% of carbon stocks). There are no estimates available for either Alaska or Hawaii. Planned work at the Natural Resources Ecology Laboratory and the Conservation Effects Assessment Project (USDA NRCS, 2008) may address these data gaps.

Ecosystem inventory programs are essential to comprehensive carbon storage reporting and validating carbon models (Hicke et al., 2007; Lovett et al., 2007). Model-based estimation techniques are also important tools for tracking changes in terrestrial carbon stocks (Bricklemyer et al., 2007). As carbon inventory programs and associated estimation tools for the full range of ecosystem types are developed, total change in carbon content in individual ecosystem types could be summed to produce an estimate of the total amount of carbon gained or lost by all U.S. ecosystems. As common monitoring protocols and carbon storage indicator metrics are aligned globally, changes in global carbon storage could be compared to changes in atmospheric concentrations of carbon-based greenhouse gases. Large-scale carbon models represent an evolving set of estimation tools that integrate remote sensing, field measurements, and ecological process knowledge to generate spatially-explicit information about carbon dynamics and may make an important contribution to carbon storage reporting at multiple scales (Potter et al., 2006; Mildrexler et al., 2007; Peters et al., 2007).


   Discussion
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 Methods
 Results
 Discussion
REFERENCES
 
Net carbon sequestration by terrestrial ecosystems subtracts from atmospheric carbon pools (carbon dioxide, methane) that contribute to the greenhouse effect. The amount of carbon in ecosystems affects to some degree their capacity to provide services such as soil fertility, water storage, food and fiber production, and food and habitat for organisms. In the context of emerging voluntary and mandatory carbon markets and initiatives to promote production of biofuel feedstocks, comprehensive and consistent information about carbon storage in ecosystems is needed for effective local land management and regional and national policy assessment (Pinchot Institute for Conservation, 2006; USEPA, 2007).

The new carbon storage indicator in the State of the Nation's Ecosystems report was designed to be responsive to changes in carbon sequestration that result from significant shifts in land management such as altered forestry and farming practices precipitated by carbon trading programs or expanded biofuels production. The two indicator metrics show recent increases in carbon storage in forests, croplands, grasslands, and shrublands suggesting possible enhancement of carbon-related ecological services; however, this observation is based on incomplete data for these ecosystem types and is not complemented by carbon data for aquatic and urbanized ecosystems. This indicator is intended for use at the national scale; however, indicator metrics can be usefully translated to other decision-making contexts if data is available at relevant geographic scales. Scaleable indicators can function as accountability tools for landowners and carbon market managers and as assessment tools for national policy instruments, such as the Farm Bill.

Indicators in the 2008 State of the Nation's Ecosystems report reflect a multi-sector consensus about the metrics of ecological condition that should be monitored over time. Where information-gathering systems do not exist to populate these indicators with data, the report highlights these data gaps. For example, only partial data are available to demonstrate the utility of the new carbon storage indicator. Data systems that provide ongoing inventory of carbon stocks and establish standards for data quality, verification, estimation methods, and reporting are essential. As we learn more about the biophysical capacity of soils and plants to sequester carbon, we will need to improve our ability to scale up from plot- and county-level information to regional and national frameworks. Over time, evolving expertise in satellite remote sensing, carbon biogeochemistry, and spatial modeling will enable more advanced monitoring of changes in the carbon stocks in vegetation and soils.

To better track how shifts in land management and environmental conditions affect carbon stocks, greater integration and consistency of information is needed to populate indicator metrics. In order for monitoring data to be aggregated from a project or market level to a national level, a consistent set of metrics is needed. Standardized data gathering can enable carbon storage information at the parcel, county, or state scale to be linked. By connecting local monitoring to a system of integrated national reporting, indicators can be used for policy assessment and resource allocation decisions at regional, national, and international scales.


   ACKNOWLEDGMENTS
 
Data providers: Linda Heath and James Smith (USDA Forest Service); Stephen Ogle and Mark Easter (Natural Resource Ecology Lab., Colorado State Univ.). Workshop participants: Tony Janetos (Chair), Linda Heath, Richard Houghton, Gary Kaster, Stephen Ogle, Neil Sampson, Gordon Smith, Eric Sundquist, and Merritt Turetsky. Additional thanks to all those who advised the Heinz Center on development of this indicator: Greg Aplet, Steve Archer, John Blair, Sandra Brown, Bob Corell, Ruth DeFries, Dee Gavora, Robert Gleason, Jennifer Harden, Cesar Izaurralde, Jennifer Jenkins, John Kinsman, John Litynski, Daryl Lund, Dave Nowak, Keith Paustian, Hobie Perry, Chuck Rice, Dave Schimel, Tim Seastedt, Michael Thompson, Tristram West, Chris Woodall, as well as members of the State of the Nation's Ecosystems Design Committee and Indicator Refinement Committee.

Funding Sources: The State of the Nation's Ecosystems project is a collaborative project involving business, environmental organizations, academia, and government. Funding is providing by both public and private sources; federal funds account for about one-half of project expenses and foundation and corporate sources provide the remaining one-half. The H. John Heinz III Center for Science, Economics and the Environment would like to thank the following contributors to Phase 2 (2003-2007) of the State of the Nation's Ecosystems project. Corporate: ChevronTexaco Corp., ExxonMobil Corp., Pioneer Hi-Bred International, Inc., Procter & Gamble Co.; Federal: National Aeronautics and Space Administration, National Oceanic and Atmospheric Administration, National Science Foundation, Office of Naval Research (grant administration), U.S. Dep. of Agriculture, U.S. Dep. of the Interior, U.S. Environmental Protection Agency; Foundations: Foundation for Environmental Research, Robert and Patricia Switzer Foundation, Teresa and H. John Heinz III Charitable Fund Vira I. Heinz Endowment.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 Methods
 Results
 Discussion
 REFERENCES
 
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher.


   REFERENCES
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 NOTES
 ABSTRACT
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 Methods
 Results
 Discussion
 REFERENCES
 





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