Grantee Research Project Results
1999 Progress 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 Period Covered by this Report: October 1, 1998 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:
Our objective is to conduct an integrated assessment of landuse for the central grasslands of the United States, utilizing the suite of databases and simulation models that we have developed over the past decade. Our research will provide estimates of the impact of landuse on ecosystem attributes (both structural and functional) at the regional scale and of the sensitivity of these ecosystem attributes to changes in climate.Progress Summary:
Through our work during the past year, we have found that landuse management in the Great Plains significantly alters regional scale climate, specifically with irrigation management increasing thunderstorm activity. These results indicate that global scale predictions of the effects of landuse management are limited within our region. In addition, we have found that: (1) row-crop agriculture leads to increasing production of greenhouse gases, potentially enhancing the rate of global warming; (2) wheat fields are neither losing nor gaining carbon from the atmosphere, but irrigated corn is sequestering net carbon from the atmospere; and (3) the fallow rotation widely used within the dry portions of the Great Plains does not increase water availability and is thus not a necessary practice. Elimination of the fallow period could double grain production from the dryland wheat-fallow region.
Simulation Analysis of the Effects of Landuse Management on Regional Climate. Our work has shown that land surface processes are an integral component of the Earth's climate system. An accurate understanding of climate and its variability cannot be obtained without including these land surface effects. Among the most important is the effect on the atmosphere of human-caused landscape changes. We have shown that alterations in landscape, such as converting the short grass steppe to irrigated agriculture, provides additional fluxes of water vapor into the atmosphere. This additional water vapor permits thunderstorms to be more intense and to produce more rainfall than they would have if the landscape had remained natural. The effect of these human-affected thunderstorms can propagate hundreds and even thousands of miles from the location of landscape disturbance. Tropical deforestation, for example, has been shown in our studies to have an effect on the entire Earth's weather. We also have demonstrated that increased concentrations of carbon dioxide (CO2) can significantly affect the flux of water vapor into the atmosphere.
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 that 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? Policymakers then could react to the greater threats, rather than selecting one environmental issue at a time.
Simulation Analysis of the Effects of Landuse on Carbon Sequestration and N2O Greenhouse Gas Emissions. A well validated soil organic matter model (DAYCENT) was used to address the feasibility of managing land to sequester carbon (C) in soil after accounting for the greenhouse warming potential of soil nitrous oxide (N2O) emissions and the CO2 emissions associated with nitrogen (N) fertilizer production. The model simulated the long-term changes in soil C levels, N2O emissions, and aboveground productivity in agricultural and rangeland systems. The model was run for 100 years of conventional winter wheat/fallow rotations and another 100 years of alternative land use. Simulations showed that corn, corn/alfalfa, and silage cropping provided substantial (1.5-1.8 kg C m-2) net C storage for the first 25-year period, but net C sequestration fell to less than 0.25 kg C m-2 for the fourth 25-year period. The highest potential to store C is during the first 25 years, with an exponential drop in C storage capacity beyond the first 25 years when N2O emissions are considered in all systems. Conventional tillage and no tillage winter wheat/fallow systems both showed a net input of CO2 to the atmosphere during each 25-year period when N2O emissions were considered. Native grassland under light to moderate grazing stored small amounts of C, but addition of 1 g N m-2 yr-1 greatly increased net C sequestration in rangeland simulations. All of the practices, except unfertilized grassland, showed significant inverse correlation between soil C storage and N2O emissions.
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.
Comparisons of Grassland and Winter Wheat From Field Data. Our progress with regard to new ecosystem production, net primary production, and soil water dynamics is discussed below.
Net Ecosystem Production. Over the past year, we have been developing a Bowen Ratio system to collect realtime data on net carbon exchange in wheat and irrigated corn fields. A colleague on a related project, Dr. Jack Morgan, is collecting data on rangelands. To date, we are finding some very interesting and important results. First, wheat fields appear to be nearly at steady-state with respect to carbon balance; this means that no net carbon is being lost to the atmosphere. Second, cornfields appear to be sequestering carbon (i.e., taking up CO2 from the atmosphere). These are the first results that empirically show that landuse management can indeed sequester carbon.
Applied Significance?The Kyoto Protocol, if ratified, will provide the opportunity for the United States to offset its industrial emissions by using estimates of terrestrial sequestration of carbon. Our data provide an indication that different landuse management practices have very different effects on terrestrial sequestration. They also provide estimates of carbon exchange that could be used.
Net Primary Production (Plant Production as Related to Grain Yield). A regional-scale analysis, using U.S. Department of Agriculture (USDA) data of grassland and summer fallow winter wheat conducted under U.S. Environmental Protection Agency (EPA) funding, predicted a difference of 158 g/m2 in average annual aboveground net primary production between native grasslands and summer-fallow winter wheat for our research sites in north central Colorado (Lauenroth, et al., 2000), with wheat being higher. Field data collected for 2 years indicate an average difference of 40 g/m2, although the variability between years is large (1998 was 10 g/m2; 1999 was 70 g/m2). Part of the discrepancy between the model and the data is likely the result of the model being based on long-term data (30 years) and the field result being based on only 2 years. An additional explanation is that because our research sites are at the dry extreme of the regression model range, it is quite possible that the model overestimates the difference.
Applied Significance?Food production is nearly perfectly related to net primary production. Understanding regional patterns in net primary production is crucial for predicting national level food production. Our results suggest that field-scale experiments are necessary for completing such regional analyses, because the large-scale USDA databases that exist to date do not adequately represent the subregions.
Soil Water Dynamics. Our detailed sampling of soil water indicates that seasonal patterns in soil water were similar for both wheat and native grassland. In general, wheat sites were wetter than the grassland sites, but there was a considerable amount of variability in that relationship. In the top 15 cm of the soil, the driest and wettest values were both found on the grassland sites. At 30-45 cm and 75-90 cm, the driest values occurred on the grassland sites, while the wettest occurred late in 1999 on the wheat sites. There was very little indication that the fallow period resulted in storage of a 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.
Future Activities:
Continue work as described in the original application to achieve the grant goals.Journal Articles on this Report : 10 Displayed | Download in RIS Format
Other project views: | All 63 publications | 43 publications in selected types | All 34 journal articles |
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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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Gutmann MP, Cunfer GA, Burke IC, Parton WJ. Farm programs, environment, and land use decisions in the Great Plains, 1969-1992. Environmental History. |
R824993 (1999) |
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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) |
Exit Exit |
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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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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. Influence of the spatial distribution of vegetation and soils on the prediction of cumulus convective rainfall. Reviews of Geophysics 2001;39(2):151-177. |
R824993 (1999) |
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Supplemental Keywords:
modeling, Bowen Ratio towers, effects of agriculture on regional ecosystem function, carbon sequestration, mesoscale climate dynamics, greenhouse gas emissions and agriculture, grain yield, wheat, corn, Great Plains., 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.