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  • 1
    Electronic Resource
    Electronic Resource
    Multi-gas assessment of the Kyoto Protocol (1999)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 401 (1999), S. 549-555 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The Kyoto Protocol allows reductions in emissions of several ‘greenhouse’ gases to be credited against a CO2-equivalent emissions limit, calculated using ‘global warming potential’ indices for each gas. Using an integrated global-systems model, it is shown that a ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/44069
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  • 2
    Electronic Resource
    Electronic Resource
    TROPICAL DEFORESTATION AND THE GLOBAL CARBON BUDGET (1996)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Environment and Resources 21 (1996), S. 293-310 
    Details
    ISSN: 1056-3466
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The CO2 concentration of the atmosphere has increased by almost 30% since 1800. This increase is due largely to two factors: the combustion of fossil fuel and deforestation to create croplands and pastures. Deforestation results in a net flux of carbon to the atmosphere because forests contain 20-50 times more carbon per unit area than agricultural lands. In recent decades, the tropics have been the primary region of deforestation. The annual rate of CO2 released due to tropical deforestation during the early 1990s has been estimated at between 1.2 and 2.3 gigatons C. The range represents uncertainties about both the rates of deforestation and the amounts of carbon stored in different types of tropical forests at the time of cutting. An evaluation of the role of tropical regions in the global carbon budget must include both the carbon flux to the atmosphere due to deforestation and carbon accumulation, if any, in intact forests. In the early 1990s, the release of CO2 from tropical deforestation appears to have been mostly offset by CO2 uptake occurring elsewhere in the tropics, according to an analysis of recent trends in the atmospheric concentrations of O2 and N2. Interannual variations in climate and/or CO2 fertilization may have been responsible for the CO2 uptake in intact forests. These mechanisms are consistent with site-specific measurements of net carbon fluxes between tropical forests and the atmosphere, and with regional and global simulations using process-based biogeochemistry models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.energy.21.1.293
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  • 3
    Electronic Resource
    Electronic Resource
    The Role of Nitrogen in the Response of Forest Net Primary Production to Elevated Atmospheric Carbon Dioxide (1995)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Ecology, Evolution, and Systematics 26 (1995), S. 473-503 
    Details
    ISSN: 0066-4162
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.es.26.110195.002353
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  • 4
    Electronic Resource
    Electronic Resource
    Modelling carbon responses of tundra ecosystems to historical and projected climate: a comparison of a plot- and a global-scale ecosystem model to identify process-based uncertainties (2000)
    Oxford, UK : Blackwell Publishing 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 are developing a process-based modelling approach to investigate how carbon (C) storage of tundra across the entire Arctic will respond to projected climate change. To implement the approach, the processes that are least understood, and thus have the most uncertainty, need to be identified and studied. In this paper, we identified a key uncertainty by comparing the responses of C storage in tussock tundra at one site between the simulations of two models – one a global-scale ecosystem model (Terrestrial Ecosystem Model, TEM) and one a plot-scale ecosystem model (General Ecosystem Model, GEM). The simulations spanned the historical period (1921–94) and the projected period (1995–2100). In the historical period, the model simulations of net primary production (NPP) differed in their sensitivity to variability in climate. However, the long-term changes in C storage were similar in both simulations, because the dynamics of heterotrophic respiration (RH) were similar in both models. In contrast, the responses of C storage in the two model simulations diverged during the projected period. In the GEM simulation for this period, increases in RH tracked increases in NPP, whereas in the TEM simulation increases in RH lagged increases in NPP. We were able to make the long-term C dynamics of the two simulations agree by parameterizing TEM to the fast soil C pools of GEM. We concluded that the differences between the long-term C dynamics of the two simulations lay in modelling the role of the recalcitrant soil C. These differences, which reflect an incomplete understanding of soil processes, lead to quite different projections of the response of pan-Arctic C storage to global change. For example, the reference parameterization of TEM resulted in an estimate of cumulative C storage of 2032 g C m−2 for moist tundra north of 50°N, which was substantially higher than the 463 g C m−2 estimated for a parameterization of fast soil C dynamics. This uncertainty in the depiction of the role of recalcitrant soil C in long-term ecosystem C dynamics resulted from our incomplete understanding of controls over C and N transformations in Arctic soils. Mechanistic studies of these issues are needed to improve our ability to model the response of Arctic ecosystems to global change.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2000.06009.x
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  • 5
    Electronic Resource
    Electronic Resource
    Modelling carbon responses of tundra ecosystems to historical and projected climate: sensitivity of pan-Arctic carbon storage to temporal and spatial variation in climate (2000)
    Oxford, UK : Blackwell Publishing 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: Historical and projected climate trends for high latitudes show substantial temporal and spatial variability. To identify uncertainties in simulating carbon (C) dynamics for pan-Arctic tundra, we compare the historical and projected responses of tundra C storage from 1921 to 2100 between simulations by the Terrestrial Ecosystem Model (TEM) for the pan-Arctic and the Kuparuk River Basin, which was the focus of an integrated study of C dynamics from 1994 to 1996. In the historical period from 1921 to 1994, the responses of net primary production (NPP) and heterotrophic respiration (RH) simulated for the Kuparuk River Basin and the pan-Arctic are correlated with the same factors; NPP is positively correlated with net nitrogen mineralization (NMIN) and RH is negatively correlated with mean annual soil moisture. In comparison to the historical period, the spatially aggregated responses of NPP and RH for the Kuparuk River Basin and the pan-Arctic in our simulations for the projected period have different sensitivities to temperature, soil moisture and NMIN. In addition to being sensitive to soil moisture during the projected period, RH is also sensitive to temperature and there is a significant correlation between RH and NMIN. We interpret the increases in NPP during the projected period as being driven primarily by increases in NMIN, and that the correlation between NPP and temperature in the projected period is a result primarily of the causal linkage between temperature, RH, and NMIN. Although similar factors appear to be controlling simulated regional-and biome-scale C dynamics, simulated C dynamics at the two scales differ in magnitude with higher increases in C storage simulated for the Kuparuk River Basin than for the pan-Arctic at the end of the historical period and throughout the projected period. Also, the results of the simulations indicate that responses of C storage show different climate sensitivities at regional and pan-Arctic spatial scales and that these sensitivities change across the temporal scope of the simulations. The results of the TEM simulations indicate that the scaling of C dynamics to a region of arctic tundra may not represent C dynamics of pan-Arctic tundra because of the limited spatial variation in climate and vegetation within a region relative to the pan-Arctic. For reducing uncertainties, our analyses highlight the importance of incorporating the understanding gained from process-level studies of C dynamics in a region of arctic tundra into process-based models that simulate C dynamics in a spatially explicit fashion across the spatial domain of pan-Arctic tundra. Also, efforts to improve gridded datasets ofhistorical climate for the pan-Arctic would advance the ability to assess the responses of C dynamics for pan-Arctic tundra in a more realistic fashion. A major challenge will be to incorporate topographic controls over soil moisture in assessing the response of C storage for pan-Arctic tundra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2000.06017.x
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  • 6
    Electronic Resource
    Electronic Resource
    Modelling the soil-plant-atmosphere continuum in a Quercus–Acer stand at Harvard Forest: the regulation of stomatal conductance by light, nitrogen and soil/plant hydraulic properties (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 19 (1996), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Our objective is to describe a multi-layer model of C3-canopy processes that effectively simulates hourly CO2 and latent energy (LE) fluxes in a mixed deciduous Quercus-Acer (oak–maple) stand in central Massachusetts, USA. The key hypothesis governing the biological component of the model is that stomatal conductance (gs) is varied so that daily carbon uptake per unit of foliar nitrogen is maximized within the limitations of canopy water availability. The hydraulic system is modelled as an analogue to simple electrical circuits in parallel, including a separate soil hydraulic resistance, plant resistance and plant capacitance for each canopy layer. Stomatal opening is initially controlled to conserve plant water stores and delay the onset of water stress. Stomatal closure at a threshold minimum leaf water potential prevents xylem cavitation and controls the maximum rate of water flux through the hydraulic system. We show a strong correlation between predicted hourly CO2 exchange rate (r2= 0.86) and LE (r2= 0.87) with independent whole-forest measurements made by the eddy correlation method during the summer of 1992. Our theoretical derivation shows that observed relationships between CO2 assimilation and LE flux can be explained on the basis of stomatal behaviour optimizing carbon gain, and provides an explicit link between canopy structure, soil properties, atmospheric conditions and stomatal conductance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1996.tb00456.x
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  • 7
    Electronic Resource
    Electronic Resource
    Recent patterns and mechanisms of carbon exchange by terrestrial ecosystems (2001)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 414 (2001), S. 169-172 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Knowledge of carbon exchange between the atmosphere, land and the oceans is important, given that the terrestrial and marine environments are currently absorbing about half of the carbon dioxide that is emitted by fossil-fuel combustion. This carbon uptake is therefore limiting the extent of ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35102500
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  • 8
    Electronic Resource
    Electronic Resource
    Influence of nitrogen fertilization on methane uptake in temperate forest soils (1989)
    [s.l.] : Nature Publishing Group
    Nature 341 (1989), S. 314-316 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] In the spring of 1988, nine (25 m2) plots were established in each of two forest stands at the Harvard Forest in central Massachusetts: a 62-year-old red pine (ftnus resinosa Ait.) plantation and an ~ 80-year-old mixed black oak/red maple (Quercus velutina Lam./ Acer rubrum L.) stand. Both stands ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/341314a0
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  • 9
    Electronic Resource
    Electronic Resource
    Net flux of carbon dioxide from tropical forests in 1980 (1985)
    [s.l.] : Nature Publishing Group
    Nature 316 (1985), S. 617-620 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The FAO/UNEFs8'9 estimate of deforestation in the tropics is compared in Table 1 with estimates made by Myers10'12 and the FAO's Production Yearbook13. Comparison of the rates given by FAO/UNEP and the Production Yearbook assumes that deforestation of the open and closed forests of the former is ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/316617a0
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  • 10
    Electronic Resource
    Electronic Resource
    Productivity response of climax temperate forests to elevated temperature and carbon dioxide: a north american comparison between two global models (1993)
    Springer
    Climatic change 24 (1993), S. 287-310 
    Details
    ISSN: 1573-1480
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We assess the appropriateness of using regression- and process-based approaches for predicting biogeochemical responses of ecosystems to global change. We applied a regression-based model, the Osnabruck Model (OBM), and a process-based model, the Terrestrial Ecosystem Model (TEM), to the historical range of temperate forests in North America in a factorial experiment with three levels of temperature (+0 °C, +2 °C, and +5 °C) and two levels of CO2 (350 ppmv and 700 ppmv) at a spatial resolution of 0.5° latitude by 0.5° longitude. For contemporary climate (+0 °C, 350 ppmv), OBM and TEM estimate the total net primary productivity (NPP) for temperate forests in North America to be 2.250 and 2.602 × 1015 g C ⋅ yr−1, respectively. Although the continental predictions for contemporary climate are similar, the responses of NPP to altered climates qualitatively differ; at +0 °C and 700 ppmv CO2, OBM and TEM predict median increases in NPP of 12.5% and 2.5%, respectively. The response of NPP to elevated temperature agrees most between the models in northern areas of moist temperate forest, but disagrees in southern areas and in regions of dry temperate forest. In all regions, the response to CO2 is qualitatively different between the models. These differences occur, in part, because TEM includes known feedbacks between temperature and ecosystem processes that affect N availability, photosynthesis, respiration, and soil moisture. Also, it may not be appropriate to extrapolate regression-based models for climatic conditions that are not now experienced by ecosystems. The results of this study suggest that the process-based approach is able to progress beyond the limitations of the regression-based approach for predicting biogeochemical responses to global change.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01091852
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