Wirth C.

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  • Preprint
    Reconciling carbon-cycle concepts, terminology, and methods
    ( 2006-01-06) Chapin, F. Stuart ; Woodwell, G. M. ; Randerson, James T. ; Rastetter, Edward B. ; Lovett, G. M. ; Baldocchi, Dennis D. ; Clark, D. A. ; Harmon, Mark E. ; Schimel, David S. ; Valentini, R. ; Wirth, C. ; Aber, J. D. ; Cole, Jonathan J. ; Goulden, Michael L. ; Harden, J. W. ; Heimann, M. ; Howarth, Robert W. ; Matson, P. A. ; McGuire, A. David ; Melillo, Jerry M. ; Mooney, H. A. ; Neff, Jason C. ; Houghton, Richard A. ; Pace, Michael L. ; Ryan, M. G. ; Running, Steven W. ; Sala, Osvaldo E. ; Schlesinger, William H. ; Schulze, E.-D.
    Recent patterns and projections of climatic change have focused increased scientific and public attention on patterns of carbon (C) cycling and its controls, particularly the factors that determine whether an ecosystem is a net source or sink of atmospheric CO2. Net ecosystem production (NEP), a central concept in C-cycling research, has been used to represent two different concepts by C-cycling scientists. We propose that NEP be restricted to just one of its two original definitions—the imbalance between gross primary production (GPP) and ecosystem respiration (ER), and that a new term—net ecosystem carbon balance (NECB)—be applied to the net rate of C accumulation in (or loss from; negative sign) ecosystems. NECB differs from NEP when C fluxes other than C fixation and respiration occur or when inorganic C enters or leaves in dissolved form. These fluxes include leaching loss or lateral transfer of C from the ecosystem; emission of volatile organic C, methane, and carbon monoxide; and soot and CO2 from fire. C fluxes in addition to NEP are particularly important determinants of NECB over long time scales. However, even over short time scales, they are important in ecosystems such as streams, estuaries, wetlands, and cities. Recent technological advances have led to a diversity of approaches to measuring C fluxes at different temporal and spatial scales. These approaches frequently capture different components of NEP or NECB and can therefore be compared across scales only by carefully specifying the fluxes included in the measurements. By explicitly identifying the fluxes that comprise NECB and other components of the C cycle, such as net ecosystem exchange (NEE) and net biome production (NBP), we provide a less ambiguous framework for understanding and communicating recent changes in the global C cycle. Key words: Net ecosystem production, net ecosystem carbon balance, gross primary production, ecosystem respiration, autotrophic respiration, heterotrophic respiration, net ecosystem exchange, net biome production, net primary production.
  • Article
    The role of historical fire disturbance in the carbon dynamics of the pan-boreal region : a process-based analysis
    (American Geophysical Union, 2007-06-20) Balshi, M. S. ; McGuire, A. David ; Zhuang, Qianlai ; Melillo, Jerry M. ; Kicklighter, David W. ; Kasischke, E. ; Wirth, C. ; Flannigan, M. ; Harden, J. W. ; Clein, Joy S. ; Burnside, T. J. ; McAllister, J. ; Kurz, Werner A. ; Apps, M. ; Shvidenko, Anatoly
    Wildfire is a common occurrence in ecosystems of northern high latitudes, and changes in the fire regime of this region have consequences for carbon feedbacks to the climate system. To improve our understanding of how wildfire influences carbon dynamics of this region, we used the process-based Terrestrial Ecosystem Model to simulate fire emissions and changes in carbon storage north of 45°N from the start of spatially explicit historically recorded fire records in the twentieth century through 2002, and evaluated the role of fire in the carbon dynamics of the region within the context of ecosystem responses to changes in atmospheric CO2 concentration and climate. Our analysis indicates that fire plays an important role in interannual and decadal scale variation of source/sink relationships of northern terrestrial ecosystems and also suggests that atmospheric CO2 may be important to consider in addition to changes in climate and fire disturbance. There are substantial uncertainties in the effects of fire on carbon storage in our simulations. These uncertainties are associated with sparse fire data for northern Eurasia, uncertainty in estimating carbon consumption, and difficulty in verifying assumptions about the representation of fires that occurred prior to the start of the historical fire record. To improve the ability to better predict how fire will influence carbon storage of this region in the future, new analyses of the retrospective role of fire in the carbon dynamics of northern high latitudes should address these uncertainties.