Grantee Research Project Results
Final Report: A Regional Assessment of Land Use Effects on Ecosystem Structure and Function in the Central Grasslands
EPA Grant Number: R824993Title: A Regional Assessment of Land Use Effects on Ecosystem Structure and Function in the Central Grasslands
Investigators: Burke, Ingrid C. , Mosier, Arvin , Pielke, Roger , Parton, William J. , Lauenroth, William K.
Institution: Colorado State University
EPA Project Officer: Chung, Serena
Project Period: October 1, 1996 through September 30, 1999
Project Amount: $1,590,428
RFA: Global Climate (1996) RFA Text | Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Climate Change
Objective:
The objectives of this research project were to: (1) assess regional patterns in key ecosystem attributes (both structure and function) across the central grassland region in its current condition compared to pre-settlement condition: landuse, plant community structure, carbon storage, net primary productivity, atmosphere-biosphere interactions, and trace gas flux; and (2) evaluate the consequences of potential changes in landuse and climate across the region for ecosystem structure and function.To accomplish these objectives, we combined remote sensing, spatial databases, simulation models, and fieldwork to improve our understanding of regional patterns and to provide scenarios of potential future conditions. Our research team made major progress in key areas related to regional analysis of ecosystem structure and function, and we built upon this progress by applying our tools and understanding for a regional assessment of landuse and climate change.
Summary/Accomplishments (Outputs/Outcomes):
Our project had three major areas: empirical field analysis of ecosystem responses to landuse management, simulation analysis, and regional assessment of the consequences of landuse management. Our results have been and will continue to be published in numerous peer-reviewed scientific journal articles, scientific conferences, and theses and dissertations. In addition, our results have major implications for understanding and managing ecosystems of the central part of the United States. Below, we briefly summarize our findings and their significance.
The findings are divided into three key areas:
1. Assessment of field-scale ecosystem attributes as they respond to landuse management:
2. Simulation analysis of landuse effects on ecosystem attributes
3. Evaluation of regional scale responses to landuse management
Landuse Effects on Ecosystems: Field Scale
Note: The field portion of this project involved very intensive sampling during three field seasons. Because of the very large logistical challenges of this work, the empirical portion of our work is just completing analysis at this point, with the key papers all presented at the Ecological Society of America meetings this summer, and now being submitted as theses and journal papers. The simulation and regional portions of our work result in products much earlier.
Soil Organic Matter. We found that carbon, nitrogen, and phosphorus were lower in cultivated fields than in native grasslands, with dryland wheat-fallow systems having lost the most soil organic matter.
Applied Significance: To date, there has been no record of the effect of irrigated agriculture on the long term soil fertility of regions. These results indicate that irrigated and fertilized corn crops in this region of the semiarid shortgrass steppe deplete pools of C and N at the soil surface but do not cause a change in C or N below the 5cm layer of soil. The differences in amount and distribution of C and N observed in this study among dryland wheat-fallow and irrigated corn fields indicate that the type of crop grown in this region should be an important consideration for regional studies that evaluate C and N changes due to cultivation.
Net Primary Productivity. Our field data show considerable differences among wheat-fallow, grassland, and irrigated corn systems with respect to above and belowground net primary production. Our data indicate indicates an average difference of 40 g/m2 between total production of rangelands and wheat-fallow systems; because of the alternate year cropping, high yields in dryland wheat do not result in especially high carbon capture if one integrates across years. On the other hand, net primary productivity of irrigated corn is nearly an order of magnitude higher than grasslands or dryland wheat fallow, averaging 1300 g/m2 each year.
Applied Significance: Net primary production is the ecosystem process most closely related to food production (grain yield for row-crops and fodder for rangelands); it also is the best estimate of the rate of carbon capture of ecosystems (balanced by respiration processes, see next section). Our data suggest that given the additional inputs involved with fertilization and plowing, wheat-fallow production agriculture may not be the most productive land management practice for either food production or for net carbon capture. However, irrigation and fertilization result in very large yields for corn, in addition to high rates of carbon capture by plants. In the next section, we address whether these inputs are balanced by net outputs of carbon from the system.
Net Ecosystem Production. Using a Bowen Ratio system, we collected realtime data on net carbon exchange in wheat and irrigated corn fields. Wheat fields (during the year they are in wheat and the year they are in fallow) appear to be losing small amounts of carbon each year to the atmosphere. Cornfields appear to be sequestering carbon, that is taking up CO2 from the atmosphere at a rate of 250 g/m2/yr, when one accounts for grain removal, the carbon balance is negative at about ?200 g/m2/yr. These are the very first results that empirically show that landuse management in even high production agriculture systems may still not sequester carbon from the atmosphere.
Applied Significance: The Kyoto Protocol, if ratified, will provide the opportunity for the U.S. to offset its industrial emissions by using estimates of terrestrial sequestration of carbon. Our data provide first, and indication that different landuse management practices have very different effects on terrestrial sequestration. Second, they provide estimates of carbon exchange that could be used for carbon accounting.
Soil Water Dynamics. The seasonal patterns in soil water were similar for both wheat and native grassland. There was very little indication that the fallow period resulted in storage of substantial amount of water.
Applied Significance: Our result that fallow fields do not store soil water has crucial implications for land management in much of the western half of the Great Plains. Historical land management practices have long included a fallow rotation in this region, which results in very high soil erosion and high losses of carbon (to the atmosphere, as CO2). In addition, half of the land at any time is in a fallow rotation, effectively reducing grain production by 50 percent. Our result this year, as well as one last year on net primary production, suggests that a fallow rotation is not necessary, and that we could double regional production in the semiarid portion of the Great Plains.
Trace Gas Flux. On this EPA project, we developed a database that contains all of the major measurements made on CO2, N2O, and CH4 fluxes in managed and native ecosystems of the Central Grasslands.
Applied Significance: The key trace gases discussed above, CO2, N2O, and CH4, are major greenhouse gases whose atmospheric concentrations are dramatically influenced by landuse management. Making measurements of these trace gases meaningful for anyone interested in large-scale contributions of agriculture to climate has always been a problem because of the high variability of these processes. The tests above have led to the development of simulation models so that we can extrapolate our knowledge over major regions, both in the Great Plains and in the rest of the world.
Simulation Analysis: Landuse Consequences. EPA-STAR supported the development of the DAYCENT ecosystem model (Del Grosso, et al., 2000, in press). DAYCENT is the daily time step version of the CENTURY model. The monthly time step used in CENTURY is sufficient to model changes in soil organic matter (SOM) and plant growth in response to changes in land use and climate. However, smaller time scale resolution is required to accurately simulate trace gas fluxes to and from soils. The model has been tested against field data and effectively simulates the production of trace gases over short (days) and longer (annual) time scales, which provide important estimates that are not attainable in the field.
Using the model, Del Grosso, et al. (2000, in press) showed that agricultural soils that are depleted of SOM have the potential to store C as a result of land use change. However, the benefits of increased SOM are offset by the greenhouse effects of N2O emissions associated with fertilizer addition, irrigation, tillage, and legume cropping.
Applied Significance: This result indicates that cropland management in the Great Plains results in increased atmospheric CO2 and N2O, both important greenhouse gases. The model suggests that human activities that result in food production (row-crop agriculture) may have a negative effect over large scales by leading to increased greenhouse gas concentrations.
Regional Patterns and Consequences of Landuse
Analysis of the Environmental Controls Over Landuse. We completed a regional dataset such that we now have spatial data on precipitation, temperature, soil (texture, depth), slope and aspect, and irrigation capabilities (distance to nearest surface water, natural or human-made). We tested the relationships among these variables and found that average annual precipitation is the most important predictor of landuse, but that each of the other variables adds predictive power to a relationship predicting which areas are cropped. Our equations predict over 81 percent of the landuse correctly within the region; the balance is likely due to socioeconomic controls over landuse. In addition, we have recently applied the output of three general circulation models to our regional predictions of landuse. This analysis predicts that between 9 and 15 percent of the region will revert from cropland to rangeland under the climatic conditions resulting from doubled CO2. This has a great deal of significance for the potential of the region to supply grain, as well as the carbon balance of the region.
Applied Significance: Our analysis suggests that the likely directional climate change due to greenhouse gas emissions will result in a reduction in arable land in the most productive portion of the United States.
Net Primary Production. A regional-scale analysis, using USDA data, of grassland and summer fallow winter wheat conducted under EPA funding suggested that in a large part of the Great Plains region, the fallow system used does not improve yield over multiple years; in fact, it decreases the potential yield. These results are supported by our field data on soil water.
Applied Significance: If our analysis is correct and a large part of the Great Plains that is currently under the summer-fallow management system with alternate year cropping could be converted to continuous cropping, it would have very significant ecological and economic effects on the region. Grain yield per unit area would effectively be doubled (a factor of 1.75 in our analysis) for the converted area. Carbon balance could be dramatically shifted as well, for two reasons. First, carbon inputs would increase as a result of a crop being grown every year. Second, the cultivation associated with maintaining summer-fallow fields is widely recognized to dramatically increase both decomposition and erosion; reducing cultivation frequency by continuous cropping could potentially decreased carbon losses from systems.
Regional Assessment of Nitrogen Balance as a Result of Cropland Practices. Funding from this grant supported an analysis of regional nitrogen budgets in the Great Plains as a result of cultivation management practices. Data from national sources (USDA) were collected and analyzed, and these data were used in a report to the Office of Science and Technology Policy "Integrating the Nation's Environmental Monitoring and Research Networks and Programs: Our analysis suggests that: (1) average N fertilization rates have doubled over the past 30 years across the Great Plains; (2) fertilization rates vary significantly across crops and geographically across the region; (3) between 20 and 30 kg N/ha is added to crops via fertilization more than is exported in grain or silage; and (4) there have been additional losses across the region from native soil organic matter, due to cultivation. This N may be lost via ammonia volatilization, NO or N2O losses, or by nitrate leaching. The partitioning among these losses is very important for understanding the N balance of the Central Grasslands region, and its influence on greenhouse gas concentrations, photochemistry of the atmosphere, and eutrophication of surface waters, but there are insufficient data for partitioning those loss vectors at this time.
Applied Significance: One of the most important regional scale impacts of humans on the globe is the increase in available nitrogen, which is resulting in a considerable reduction in freshwater and oceanic water quality, in addition to increase in greenhouse gas production. Our data suggest that our region is considerably over-fertilized and contributing to this large-scale human impact.
Remote-Sensing Estimates of Regional Productivity. We analyzed the effect of land use (irrigated agriculture, non-irrigated agriculture, native grasslands and Conservation Reserve Program areas [CRP]) on the seasonal dynamics of carbon gains, an integrative estimator of ecosystem function in the eastern portion of Colorado. Row-crop agriculture significantly increased total carbon gains. Irrigated areas showed an increase of NDVI-I of 46 percent with respect to native grasslands. Rain-fed agriculture showed an increase of only 7 percent over native grasslands. NDVI-I from CRP areas did not differ significantly from the values observed for grasslands. Landuse also had an important effect on the seasonality of carbon gains.
Applied Significance: These results suggest that the regional impacts of irrigated agriculture for primary production are significant, resulting in large increases. However, our bowen ratio field scale data, presented above, demonstrate that much of that carbon may ultimately be exported and lost through livestock-human foodchains. Clearly, large-scale irrigated agriculture alters the amplitudes of carbon cycling, as well as the timing.
Atmosphere-Biosphere Interactions: Mesoclimate (Pielke, et al.). We coupled a meteorological model, the Regional Atmospheric Modeling System (RAMS), and a plant model, the General Energy and Mass Transfer Model (GEMTM). This coupled modeling system was used to investigate regional weather conditions in the central grasslands of the United States for three experimental scenarios; land cover is changed from current to potential vegetation; radiative forcing is changed from 1xCO2 to 2x CO2, and; biological CO2 partial pressures are doubled. Results indicated that the biological effect of enriched CO2, and land-use change exhibit dominant effects on regional meteorological and biological fields, which were observed for daily to seasonal time scales and grid to regional spatial scales.
We also coupled atmospheric (RAMS) to another ecosystem (CENTURY) modeling system. This atmospheric and ecosystem coupled modeling system exchanged information on a weekly time step. The coupled model was used to simulate the two-way biosphere and atmosphere feedbacks from January 1 through December 31, 1989, focusing on the central United States. Validation was performed for the atmospheric portion of the model by comparing with United States summary-of-the-day meteorological-station observational data sets, and for the ecological component by comparing with AVHRR remote-sensing NDVI data sets. The results show that seasonal vegetation phenological variation strongly influences regional climate patterns through its control over land-surface water and energy exchange.
Applied Significance: Increased CO2 can permit plants to be more water efficient, but also allow greater plant growth. In our model simulations for the central Great Plains, we found that the net effect of these two influences on plants was a significant cooling over seasonal time scales. As a result of such land surface effects, our ability to accurately predict the future climate is questioned. Existing model simulations of the Earth's expected future climate have neglected these influences. As an alternative approach, we propose environmental assessments which are based on a vulnerability perspective. In other words, what aspect of a resource is most at risk from human and natural caused environmental change? Policy makers could then react to the greater threats, rather than selecting one environmental issue at a time.
Synthesis Products. In addition to the empirical, simulation, and regional analysis described above, the EPA-STAR support has allowed us to produce and contribute to several synthesis papers that summarize the methodologies and lessons we have learned from conducting regional scale analyses. These papers include three chapters in new books on the ecology and biogeochemistry of managed lands in our region (Lauenroth, et al., 1999; Burke, et al., 1997), and progress and methods in regional analysis (Burke, et al., 2000; Aber, et al., 1999).
Applied Significance: Such synthesis products have a large impact on the scientific community in terms of sharing our methodologies so that similar assessments can be conducted elsewhere.
Journal Articles on this Report : 29 Displayed | Download in RIS Format
Other project views: | All 63 publications | 43 publications in selected types | All 34 journal articles |
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Burke IC, Lauenroth WK, Cunfer G, Barrett JE, Mosier A, Lowe P. Nitrogen in the central grasslands region of the United States. BioScience 2002;52(9):813-823. |
R824993 (Final) |
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Chase TN, Pielke Sr. RA, Kittel TGF, Baron JS, Stohlgren TJ. Potential impacts on Colorado Rocky Mountain weather due to land use changes on the adjacent Great Plains. Journal of Geophysical Research: Atmospheres 1999;104(D14):16673-16690. |
R824993 (Final) |
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Chase TN, Pielke Sr. RA, Kittel TGF, Nemani RR, Running SW. Simulated impacts of historical land cover changes on global climate in northern winter. Climate Dynamics 2000;16(2-3):93-105. |
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Del Grosso SJ, Parton WJ, Mosier AR, Ojima DS, Potter CS, Borken W, Brumme R, Butterbach-Bahl K, Crill PM, Dobbie K, Smith KA. General CH4 oxidation model and comparisons of CH4 oxidation in natural and managed systems. Global Biogeochemical Cycles 2000;14(4):999-1019. |
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Del Grosso SJ, Parton WJ, Mosier AR, Ojima DS, Kulmala AE, Phongpan S. General model for N2O and N2 gas emissions from soils due to denitrification. Global Biogeochemical Cycles 2000;14(4):1045-1060. |
R824993 (Final) |
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Eastman JL, Coughenour MB, Pielke Sr. RA. Does grazing affect regional climate? Journal of Hydrometeorology 2001;2(3):243-253. |
R824993 (Final) R826730 (2000) |
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Eastman JL, Coughenour MB, Pielke Sr. RA. The regional effects of CO2 and landscape change using a coupled plant and meteorological model. Global Change Biology 2001;7(7):797-815. |
R824993 (1999) R824993 (Final) R825412 (Final) R826730 (2000) |
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Epstein HE, Burke IC, Lauenroth WK. Regional patterns of decomposition and primary production rates in the U.S. Great Plains. Ecology 2002;83(2):320-327. |
R824993 (1999) R824993 (Final) |
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Frolking SE, Mosier AR, Ojima DS, Li C, Parton WJ, Potter CS, Priesack E, Stenger R, Haberbosch C, Dorsch P, Flessa H, Smith KA. Comparison of N2O emissions from soils at three temperate agricultural sites: simulations of year-round measurements by four models. Nutrient Cycling in Agroecosystems 1998;52(2-3):77-105. |
R824993 (1998) R824993 (Final) |
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Groffman PM, Brumme R, Butterbach-Bahl K, Dobbie KE, Mosier AR, Ojima D, Papen H, Parton WJ, Smith KA, Wagner-Riddle C. Evaluating annual nitrous oxide fluxes at the ecosystem scale. Global Biogeochemical Cycles 2000;14(4):1061-1070. |
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Kelly RH, Parton WJ, Hartman MD, Stretch LK, Ojima DS, Schimel DS. Intra-annual and interannual variability of ecosystem processes in shortgrass steppe. Journal of Geophysical Research–Atmospheres 2000;105(D15):20093-20100. |
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Lauenroth WK, Burke IC, Gutmann MP. The structure and function of ecosystems in the central North American grassland region. Great Plains Research–A Journal of Natural and Social Sciences 1999;9(2):223-259. |
R824993 (1999) R824993 (Final) |
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Lauenroth WK, Burke IC, Paruelo JM. Patterns of production and precipitation-use efficiency of winter wheat and native grasslands in the central Great Plains of the United States. Ecosystems 2000;3(4):344-351. |
R824993 (1998) R824993 (1999) R824993 (Final) |
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Liston GE, Pielke Sr. RA. A climate version of the regional atmospheric modeling system. Theoretical and Applied Climatology 2000;66(1-2):29-47. |
R824993 (1999) R824993 (Final) |
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Lu L, Pielke Sr. RA, Liston GE, Parton WJ, Ojima D, Hartman M. Implementation of a two-way interactive atmospheric and ecological model and its application to the central United States. Journal of Climate 2001;14(5):900-919. |
R824993 (1999) R824993 (Final) |
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Martin RE, Scholes MC, Mosier AR, Ojima DS, Holland EA, Parton WJ. Controls on annual emissions of nitric oxide from soils of the Colorado shortgrass steppe. Global Biogeochemical Cycles 1998;12(1):81-91. |
R824993 (Final) |
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Matson PA, Parton WJ, Power AG, Swift MJ. Agricultural intensification and ecosystem properties. Science 1997;277(5325):504-509. |
R824993 (Final) |
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Mosier AR, Parton WJ, Valentine DW, Ojima DS, Schimel DS, Heinemeyer O. CH4 and N2O fluxes in the Colorado shortgrass steppe: 2. long-term impact of land use change. Global Biogeochemical Cycles 1997;11(1):29-42. |
R824993 (1998) R824993 (Final) |
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Mosier AR, Parton WJ, Phongpan S. Long-term large N and immediate small N addition effects on trace gas fluxes in the Colorado shortgrass steppe. Biology and Fertility of Soils 1998;28(1):44-50. |
R824993 (1998) R824993 (Final) |
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Ojima D, Mosier A, Del Grosso S, Parton WJ. TRAGNET analysis and synthesis of trace gas fluxes. Global Biogeochemical Cycles 2000;14(4):995-997. |
R824993 (Final) |
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Parton WJ, Hartman M, Ojima D, Schimel D. DAYCENT and its land surface submodel: description and testing. Global and Planetary Change 1998;19(1-4):35-48. |
R824993 (1998) R824993 (Final) |
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Parton WJ, Holland EA, Del Grosso SJ, Hartman MD, Martin RE, Mosier AR, Ojima DS, Schimel DS. Generalized model for NOx and N2O emissions from soils. Journal of Geophysical Research–Atmospheres 2001;106(D15):17403-17419. |
R824993 (Final) |
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Paruelo JM, Jobbagy EG, Sala OE, Lauenroth WK, Burke IC. Functional and structural convergence of temperate grassland and shrubland ecosystems. Ecological Applications 1998;8(1):194-206. |
R824993 (1998) R824993 (Final) |
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Paruelo JM, Lauenroth WK. Interannual variability of NDVI and its relationship to climate for North American shrublands and grasslands. Journal of Biogeography 1998;25(4):721-733. |
R824993 (1998) R824993 (Final) |
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Paruelo JM, Burke IC, Lauenroth WK. Land-use impact on ecosystem functioning in eastern Colorado, USA. Global Change Biology 2001;7(6):631-639. |
R824993 (1999) R824993 (Final) |
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Pielke Sr. RA, Liston GE, Eastman JL, Lu L, Coughenour M. Seasonal weather prediction as an initial value problem. Journal of Geophysical Research–Atmospheres 1999;104(D16):19463-19479. |
R824993 (1999) R824993 (Final) |
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Pielke Sr. RA, Chase TN, Kittel TGF, Knaff JA, Eastman J. Analysis of 200 mbar zonal wind for the period 1958-1997. Journal of Geophysical Research–Atmospheres 2001;106(D21):27287-27290. |
R824993 (Final) |
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Pielke Sr. RA. Overlooked issues in the U.S. National Climate and IPCC Assessments. Climatic Change 2002;52(1-2):1-11. |
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Weeks Jr. RD, Holtzer TO. Habitat and season in structuring ground-dwelling spider (Araneae) communities in a shortgrass steppe ecosystem. Environmental Entomology 2000; 29(6):1164-1172. |
R824993 (Final) |
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Supplemental Keywords:
atmosphere, trace gases, carbon dioxide, nitrous oxide, methane, soil organic matter, soil carbon, soil nitrogen, soil phosphorus, primary productivity, net ecosystem production, ecological effects, vulnerability, effects of landuse on ecosystems, carbon sequestration, nitrogen excess, ecosystem, soil organic matter, terrestrial ecosystems, climate change, landuse management, agricultural management, agricultural subsidies, Conservation Reserve Program, ecosystem ecology, atmospheric science, climate change, plant ecology, agronomy, agricultural science, agroecosystem ecology, soil sampling, net primary production, net ecosystem production, bowen ratio, remote sensing, regional analysis, regionalization, scaling, mesoscale climate models, ecosystem models, Great Plains, Central Grasslands, agriculture., RFA, Scientific Discipline, Air, Ecosystem Protection/Environmental Exposure & Risk, Ecosystem/Assessment/Indicators, Ecosystem Protection, climate change, Ecological Effects - Environmental Exposure & Risk, Atmospheric Sciences, Ecological Risk Assessment, Ecological Indicators, risk assessment, ecological effects, scaling, environmental monitoring, assessment models, climate change impact, ecosystem assessment, Central Grasslands, land use effects, ecological assessment, integrated assessment, regional scale, soil, terrestrial, assessment methods, carbon storage, land use, climate variabilityProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.