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  • 1
    Electronic Resource
    Electronic Resource
    Long-term dynamics of pine and hardwood litter in contrasting environments: toward a global model of decomposition (2000)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 6 (2000), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: We analysed data on mass loss after five years of decomposition in the field from both fine root and leaf litters from two highly contrasting trees, Drypetes glauca, a tropical hardwood tree from Puerto Rico, and pine species from North America as part of the Long-Term Intersite Decomposition Experiment (LIDET). LIDET is a reciprocal litterbag study involving the transplanting of litter from 27 species across 28 sites in North and Central America reflecting a wide variety of natural and managed ecosystems and climates, from Arctic tundra to tropical rainforest. After 5 years, estimated k-values ranged from 0.032 to 3.734, lengths of Phase I (to 20% mass remaining) from 0.49 to 47.92 years, and fractional mass remaining from 0 to 0.81. Pine litter decomposed more slowly than Drypetes litter, supporting the notion of strong control of substrate quality over decomposition rates. Climate exerted strong and consistent effects on decomposition. Neither mean annual temperature or precipitation alone explained the global pattern of decomposition; variables including both moisture availability and temperature (i.e. actual evapotranspiration and DEFAC from the CENTURY model) were generally more robust than single variables. Across the LIDET range, decomposition of fine roots exhibited a Q10 of 2 and was more predictable than that of leaves, which had a higher Q10 and greater variability. Roots generally decomposed more slowly than leaves, regardless of genus, but the ratio of above- to belowground decomposition rates differed sharply across ecosystem types. Finally, Drypetes litter decomposed much more rapidly than pine litter in ‘broadleaved habitats’ than in ‘conifer habitats’, evidence for a ‘home-field advantage’ for this litter. These results collectively suggest that relatively simple models can predict decomposition based on litter quality and regional climate, but that ecosystem-specific problems may add complications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2000.00349.x
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of nitrogen deposition and insect herbivory on patterns of ecosystem-level carbon and nitrogen dynamics: results from the CENTURY model (2004)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 10 (2004), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Atmospheric nitrogen deposition may indirectly affect ecosystems through deposition-induced changes in the rates of insect herbivory. Plant nitrogen (N) status can affect the consumption rates and population dynamics of herbivorous insects, but the extent to which N deposition-induced changes in herbivory might lead to changes in ecosystem-level carbon (C) and N dynamics is unknown. We created three insect herbivory functions based on empirical responses of insect consumption and population dynamics to changes in foliar N and implemented them into the CENTURY model. We modeled the responses of C and N storage patterns and flux rates to N deposition and insect herbivory in an herbaceous system. Results from the model indicate that N deposition caused a strong increase in plant production, decreased plant C : N ratios, increased soil organic C (SOC), and enhanced rates of N mineralization. In contrast, herbivory decreased both vegetative and SOC storage and depressed N mineralization rates. The results suggest that herbivory plays a particularly important role in affecting ecosystem processes by regulating the threshold value of N deposition at which ecosystem C storage saturates; C storage saturated at lower rates of N deposition with increasing intensity of herbivory. Differences in the results among the modeled insect herbivory functions suggests that distinct physiological and population response of insect herbivores can have a large impact on ecosystem processes. Including the effects of herbivory in ecosystem studies, particularly in systems where rates of herbivory are high and linked to plant C : N, will be important in generating accurate predictions of the effects of atmospheric N deposition on ecosystem C and N dynamics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1529-8817.2003.00791.x
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  • 3
    Electronic Resource
    Electronic Resource
    Simulated grazing responses on the proposed prairies National Park (1980)
    Springer
    Environmental management 4 (1980), S. 165-170 
    Details
    ISSN: 1432-1009
    Keywords: ELM simulation model ; grazing effects ; Introduced animals ; Tallgrass prairie ; U.S. National Park service
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The tallgrass prairie version of the ELM Grassland Model was used to evaluate the potential impact of establishing a tallgrass prairie National Park in the Flint Hills region of Kansas. This total ecosystem model simulates (a) the flow of water, heat, nitrogen, and phosphorus through the ecosystem and(b) the biomass dynamics of plants and consumers. It was specifically developed to study the effects of levels and types of herbivory, climatic variation, and fertilization upon grassland ecosystems. The model was used to simulate the impact of building up herds of bison, elk, antelope, and wolves on a tallgrass prairie. The results show that the grazing levels in the park should not be decreased below the prepark grazing levels (moderate grazing with cattle) and that the final grazing levels in the park could be maintained at a slightly higher level than the prepark grazing levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01866513
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  • 4
    Electronic Resource
    Electronic Resource
    Modeled responses of terrestrial ecosystems to elevated atmospheric CO2: a comparison of simulations by the biogeochemistry models of the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP) (1998)
    Springer
    Oecologia 114 (1998), S. 389-404 
    Details
    ISSN: 1432-1939
    Keywords: Key words Global change ; Carbon dioxide ; Biogeochemistry ; Net primary production (NPP) ; Vegetation/Ecosystem Modeling and Analysis Project (VEMAP)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Although there is a great deal of information concerning responses to increases in atmospheric CO2 at the tissue and plant levels, there are substantially fewer studies that have investigated ecosystem-level responses in the context of integrated carbon, water, and nutrient cycles. Because our understanding of ecosystem responses to elevated CO2 is incomplete, modeling is a tool that can be used to investigate the role of plant and soil interactions in the response of terrestrial ecosystems to elevated CO2. In this study, we analyze the responses of net primary production (NPP) to doubled CO2 from 355 to 710 ppmv among three biogeochemistry models in the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP): BIOME-BGC (BioGeochemical Cycles), Century, and the Terrestrial Ecosystem Model (TEM). For the conterminous United States, doubled atmospheric CO2 causes NPP to increase by 5% in Century, 8% in TEM, and 11% in BIOME-BGC. Multiple regression analyses between the NPP response to doubled CO2 and the mean annual temperature and annual precipitation of biomes or grid cells indicate that there are negative relationships between precipitation and the response of NPP to doubled CO2 for all three models. In contrast, there are different relationships between temperature and the response of NPP to doubled CO2 for the three models: there is a negative relationship in the responses of BIOME-BGC, no relationship in the responses of Century, and a positive relationship in the responses of TEM. In BIOME-BGC, the NPP response to doubled CO2 is controlled by the change in transpiration associated with reduced leaf conductance to water vapor. This change affects soil water, then leaf area development and, finally, NPP. In Century, the response of NPP to doubled CO2 is controlled by changes in decomposition rates associated with increased soil moisture that results from reduced evapotranspiration. This change affects nitrogen availability for plants, which influences NPP. In TEM, the NPP response to doubled CO2 is controlled by increased carboxylation which is modified by canopy conductance and the degree to which nitrogen constraints cause down-regulation of photosynthesis. The implementation of these different mechanisms has consequences for the spatial pattern of NPP responses, and represents, in part, conceptual uncertainty about controls over NPP responses. Progress in reducing these uncertainties requires research focused at the ecosystem level to understand how interactions between the carbon, nitrogen, and water cycles influence the response of NPP to elevated atmospheric CO2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050462
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  • 5
    Electronic Resource
    Electronic Resource
    Analysis of nitrogen saturation potential in Rocky Mountain tundra and forest: implications for aquatic systems (1994)
    Springer
    Biogeochemistry 27 (1994), S. 61-82 
    Details
    ISSN: 1573-515X
    Keywords: alpine tundra ; aquatic ecosystems ; CENTURY model ; Colorado Rocky Mountains ; nitrogen saturation ; subalpine forest
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We employed grass and forest versions of the CENTURY model under a range of N deposition values (0.02–1.60 g N m−2 y−1) to explore the possibility that high observed lake and stream N was due to terrestrial N saturation of alpine tundra and subalpine forest in Loch Vale Watershed, Rocky Mountain National Park, Colorado. Model results suggest that N is limiting to subalpine forest productivity, but that excess leachate from alpine tundra is sufficient to account for the current observed stream N. Tundra leachate, combined with N leached from exposed rock surfaces, produce high N loads in aquatic ecosystems above treeline in the Colorado Front Range. A combination of terrestrial leaching, large N inputs from snowmelt, high watershed gradients, rapid hydrologic flushing and lake turnover times, and possibly other nutrient limitations of aquatic organisms constrain high elevation lakes and streams from assimilating even small increases in atmospheric N. CENTURY model simulations further suggest that, while increased N deposition will worsen the situation, nitrogen saturation is an ongoing phenomenon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00002571
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  • 6
    Electronic Resource
    Electronic Resource
    Analysis of factors regulating ecosystemdevelopment on Mauna Loa using the Century model (2000)
    Springer
    Biogeochemistry 51 (2000), S. 161-191 
    Details
    ISSN: 1573-515X
    Keywords: altitudinal gradient ; carbon cycling ; elevation ; Hawaii ; nutrient cycling ; plant productivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We used the Century model to evaluateenvironmental controls over ecosystem developmentduring the first 3500 y of primary succession onpahoehoe (i.e., relatively smooth, solid) lava flowsof wet, windward Mauna Loa, Hawaii. The Century modelis a generalized ecosystem model that simulatescarbon, nitrogen and phosphorus dynamics forplant-soil systems. Preliminary results indicated theneed to modify the model to include the effects ofsoil C accumulation on soil water storage anddrainage. The modified model was parameterized tosimulate observed values of aboveground productivity,biomass and soil element pools on a 3400-y-old site at700 m elevation. Testing the model parameters at 1660m elevation indicated that N inputs were lower andsoil water drainage rates were slower at the higherelevation. We applied the modified and fullyparameterized model to simulate ecosystem attributesduring primary succession at five elevations, andconducted single-factor experiments with the model toidentify the specific influences of variations intemperature, nutrient inputs, and rainfall on modeledecosystem characteristics. Simulated aboveground productivity (ANPP), net N andP mineralization, and biomass element pools allincreased through time at each elevation, and alldeclined with increasing elevation at each point intime. After 3500 y of succession none of theseattributes had reached a stable asymptote, butasymptotes were approached more quickly, andsuccession was therefore faster, at lower than athigher elevations. Simulated soil organic matter(SOM) pools increased with elevation, despite thatplant productivity declined. These results, andsimilar comparisons among rainfall regimes, suggestthat SOM pools were more sensitive to factorscontrolling decay than production rates. Within elevations and temperature regimes, nutrientavailability was the most important factor controllingsimulated rates of plant productivity, biomass, anddetritus accumulation during ecosystem development. Through time, SOM accumulations alleviated nutrientlimitations to plants, but simulated productivityremained highly dependent upon externally suppliednutrients even after 20,000 y. Rainfall had two maineffects on nutrient availability within the model: (1)it increased rates of leaching, and thus depletednutrient supplies; and (2) it exacerbated soil floodingand thereby decreased nutrient turnover rates. Highrainfall on windward Mauna Loa maintains oligotrophicconditions through time despite continuous N and Pinputs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006495408992
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  • 7
    Electronic Resource
    Electronic Resource
    Environmental change in grasslands: Assessment using models (1994)
    Springer
    Climatic change 28 (1994), S. 111-141 
    Details
    ISSN: 1573-1480
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Modeling studies and observed data suggest that plant production, species distribution, disturbance regimes, grassland biome boundaries and secondary production (i.e., animal productivity) could be affected by potential changes in climate and by changes in land use practices. There are many studies in which computer models have been used to assess the impact of climate changes on grassland ecosystems. A global assessment of climate change impacts suggest that some grassland ecosystems will have higher plant production (humid temperate grasslands) while the production of extreme continental steppes (e.g., more arid regions of the temperate grasslands of North America and Eurasia) could be reduced substantially. All of the grassland systems studied are projected to lose soil carbon, with the greatest losses in the extreme continental grassland systems. There are large differences in the projected changes in plant production for some regions, while alterations in soil C are relatively similar over a range of climate change projections drawn from various General Circulation Models (GCM's). The potential impact of climatic change on cattle weight gains is unclear. The results of modeling studies also suggest that the direct impact of increased atmospheric CO2 on photosynthesis and water use in grasslands must be considered since these direct impacts could be as large as those due to climatic changes. In addition to its direct effects on photosynthesis and water use, elevated CO2 concentrations lower N content and reduce digestibility of the forage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01094103
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  • 8
    Electronic Resource
    Electronic Resource
    Modeling the effects of climatic and co2 changes on grassland storage of soil C (1993)
    Springer
    Water, air & soil pollution 70 (1993), S. 643-657 
    Details
    ISSN: 1573-2932
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract We present results from analyses of the sensitivity of global grassland ecosystems to modified climate and atmospheric CO2 levels. We assess 31 grassland sites from around the world under two different General Circulation Models (GCM) double CO2 climates. These grasslands are representative of mostly naturally occurring ecosystems, however, in many regions of the world, grasslands have been greatly modified by recent land use changes. In this paper we focus on the ecosystem dynamics of natural grasslands. The climate change results indicate that simulated soil C losses occur in all but one grassland ecoregion, ranging from 0 to 14% of current soil C levels for the surface 20 cm. The Eurasian grasslands lost the greatest amount of soil C (∼1200 g C m−2) and the other temperate grasslands losses ranged from 0 to 1000 g C m−2, averaging approximately 350 g C m−2. The tropical grasslands and savannas lost the least amount of soil C per unit area ranging from no change to 300 g C m−2 losses, averaging approximately 70 g C m−2. Plant production varies according to modifications in rainfall under the altered climate and to altered nitrogen mineralization rates. The two GCM's differed in predictions of rainfall with a doubling of CO2, and these differences are reflected in plant production. Soil decomposition rates responded most predictably to changes in temperature. Direct CO2 enhancement effects on decomposition and plant production tended to reduce the net impact of climate alterations alone.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01105027
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  • 9
    Electronic Resource
    Electronic Resource
    Analysis of agroecosystem carbon pools (1993)
    Springer
    Water, air & soil pollution 70 (1993), S. 357-371 
    Details
    ISSN: 1573-2932
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract We present analyses of major driving variable controls on soil C in agroecosystems. Historical changes in soil C storage in agricultural soils are characterized by large losses during transition from natural grasslands and forests. A major driver in more recent times is the steadily increasing rate of net primary production of major land areas in agriculture. Simulation and analytical models are used to predict trajectories and potential soil C storage under possible scenarios of changed management and climate. Database and analytical requirements for extrapolation from regional to global scales are outlined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01105007
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  • 10
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    Measuring and mitigating agricultural greenhouse gas production in the US Great Plains, 1870–2000 (2015)
    National Academy of Sciences
    Details
    Publication Date: 2015-08-03
    Description: The Great Plains region of the United States is an agricultural production center for the global market and, as such, an important source of greenhouse gas (GHG) emissions. This article uses historical agricultural census data and ecosystem models to estimate the magnitude of annual GHG fluxes from all agricultural sources (e.g., cropping, livestock raising, irrigation, fertilizer production, tractor use) in the Great Plains from 1870 to 2000. Here, we show that carbon (C) released during the plow-out of native grasslands was the largest source of GHG emissions before 1930, whereas livestock production, direct energy use, and soil nitrous oxide emissions are currently the largest sources. Climatic factors mediate these emissions, with cool and wet weather promoting C sequestration and hot and dry weather increasing GHG release. This analysis demonstrates the long-term ecosystem consequences of both historical and current agricultural activities, but also indicates that adoption of available alternative management practices could substantially mitigate agricultural GHG fluxes, ranging from a 34% reduction with a 25% adoption rate to as much as complete elimination with possible net sequestration of C when a greater proportion of farmers adopt new agricultural practices.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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