INTERANNUAL VARIABILITY IN TERRESTRIAL CARBON EXCHANGE USING AN ECOSYSTEM FIRE MODEL
Description: We have incorporated a
semi-mechanistic fire model into the SEVER Dynamic Global Vegetation Model (DGVM).
The model produces estimates of net primary productivity (NPP), heterotrophic
respiration (HR) and fire carbon emission (FE) for the globe. This model was
run for the period 1957-2002 with the NCEP climate reanalysis data as an input.
Results were compared with the ATSR area burnt maps and a Time Dependent
Inverse (TDI) model fluxes of CO2. We find that on interannual time
scales NPP variability explains major part of flux variability simulated by the
TDI model, followed by the HR and FE contributions.
Author's Names: Sergey Venevsky, Prabir K. Patra, Shamil Maksyutov, et al
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THE AGE OF CARBON RESPIRED FROM TERRESTRIAL ECOSYSTEMS
Description: Carbon
enters ecosystems through a single process, photosynthesis, and nearly all is
returned to the atmosphere through respiration, some 50-80% of which occurs
below-ground. Soil (belowground) respiration integrates CO2 derived
from C that has resided in the ecosystem for periods of differing duration,
ranging from relatively recent photosynthetic products that fuel root
metabolism, to CO2 derived from decomposition of plant and soil
organic matter that may be decades to centuries old. A comparison of the radiocarbon content of CO2
respired by roots, microbes, and soils with the record of radiocarbon in
atmospheric CO2 allows direct estimation of the mean age of C being
respired [Trumbore 2000; Wang et al. 2000, Cisneros Dozal et al. 2005; Borken
et al. 2005].
Author's Names: S.E. Trumbore, E.A Schuur, E. A. Davidson, PB Camargo, et al
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SIGNALS OF PHOTOSYNTHESIS AND RESPIRATION AT BOREAL FORESTS IN RESPONSE TO ENVIRONMENT ...
Description: The isotopic composition of the ecosystem respiration (d13CER) and the isotopic
discrimination of the ecosystem (DEco) were retrieved from intensive campaigns (1998 to 2000) and
from weekly diurnal sampling (2003) at a boreal forest site (Fraserdale, Canada,
49°53'N, 81°34'W). The results show that
d13CER was less sensitive to
temperature (T) variation compared with DEco, suggesting that the photosynthesis CO2 flux
was likely more sensitive to temperature than the ecosystem respiration CO2
flux during the same period of time at the study site.
Author's Names: L.Huang, B. Chen, P.P. Tans, K.Higuchi, D.Worthy, et al
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THE UNDERPINNINGS OF LAND-USE HISTORY: THREE CENTURIES OF GLOBAL GRIDDED LAND-USE ...
Description: To accurately assess the
impacts of human land-use on the Earth System, information is needed on the
current and historical patterns of land-use activities. Previous global
studies have focused on developing reconstructions of the spatial patterns of
agriculture. Here, we provide the first global gridded estimates of the
underlying land conversions (land-use transitions), wood harvesting, and
resulting secondary lands annually, for the period 1700-2000. For input, we
used two existing datasets of global gridded land-use history—HYDE [Klein Goldewijk 2001] and SAGE [Ramankutty & Foley 1999], a new
reconstruction of national wood harvest that we spatially disaggregated to a
global gridded product, and model estimates of the spatial distribution of
plant carbon density and its recovery. Since these do not fully constrain the
problem, we added assumptions related to four additional factors: the residence
time of agricultural land, the inclusiveness of wood harvest statistics, the
priority for land conversion and logging (e.g. primary- or secondary-land), and
the spatial pattern of wood harvest within countries. In order to estimate
uncertainty and characterize model sensitivity, a set of 216 alternative reconstructions
was derived using different assumptions. We estimate that the accumulated
global wood harvest 1700-2000 was approximately 112 Pg C including slash.
Author's Names: G.C. Hurtt, S. Frolking, M.G. Fearon, B. Moore III, et al
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ESTIMATING LANDSCAPE-LEVEL CARBON FLUXES FROM TOWER CO2 MIXING RATIO DATA
Description:
Variations
of the CO2 mixing ratio in the atmosphere near the surface result
from several processes, including photosynthesis and respiration of the
underlying ecosystems, vertical mixing near the surface and in the planetary
boundary layer (PBL), and entrainment of air above the PBL. We developed a
novel approach for isolating ecosystem metabolism signals at the landscape
scale (102-104 km2) in an hourly CO2
record using a vertical diffusion scheme coupled with an ecosystem model.
Author's Names: J.M. Chen, B. Chen, K. Higuchi, D. Chan, et al
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Added on: 28-Jul-2005 Downloads: 145
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IN AND OUT OF AFRICA: ESTIMATING THE CARBON EXCHANGE OF A CONTINENT
Description: Understanding
the diverse elements of the global carbon cycle has been the focus of much
recent research [Prentice et al.
2001, Schimel et al. 2001, Gurney et al. 2002, House et al. 2003]; research that is vital to our understanding of
the missing sink, future atmospheric carbon dioxide concentrations, and future
climate [Fan et al. 1998, Houghton et al.
1998]. Much research has concentrated on carbon dynamics of the large ocean
basins [Lee et al. 1998, Le Quéré et al. 2003] and terrestrial
exchange in North America and Eurasia [Pacala et al. 2000, Schimel et al. 2000]. Despite representing 20% of the global land
mass, Africa has thus far been largely
neglected in these studies. We will examine current understanding of carbon
stocks and fluxes within Africa and discuss
how uncertainty in global carbon dynamics arises in part from uncertainty in
the African components. We outline areas where new measurements and research in
Africa can contribute to understanding at both
continental and global scales.
Author's Names: N. P. Hanan, C.A. Williams, R.J. Scholes, et al
Filesize: 50.76 Kb
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RADIATIVE FORCING FROM A BOREAL FOREST FIRE
Description: We report measurements of energy and carbon fluxes
from a boreal forest fire chronosequence. Taking into account greenhouse gas
emissions and post-fire changes in the surface radiation budget, a boreal forest
fire in interior Alaska
caused the climate to cool. This result suggests that management of forests in
northern countries to preserve carbon sinks may have the opposite effect on
climate as that intended.
Author's Names: J.T. Randerson, S.D. Chambers, M. Flanner, et al
Filesize: 31.78 Kb
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IMPORTANCE OF RECENT SHIFTS IN SOIL THERMAL DYNAMICS ON GROWING SEASON LENGTH, PRODUCTIVITY, ...
Description: In
terrestrial high-latitude regions, observations indicate recent changes in snow
cover, permafrost, and soil freeze-thaw transitions due to climate change. These modifications may result in temporal
shifts in the growing season and the associated rates of terrestrial
productivity. Changes in productivity will influence the ability of these ecosystems
to sequester atmospheric CO2. We use the Terrestrial Ecosystem Model
(TEM), which simulates the soil thermal regime, in addition to terrestrial
carbon, nitrogen and water dynamics, to explore these issues over the years
1960-2100 in extratropical regions (30˚-90˚ N).
Our results reveal noteworthy changes in snow, permafrost, growing
season length, productivity, and net carbon uptake, indicating that prediction
of terrestrial carbon dynamics from one decade to the next will require that
large-scale models adequately take into account the corresponding changes in
soil thermal regimes.
Author's Names: E.S. Euskirchen, A.D. McGuire, D.W. Kicklighter, et al
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MODELING THE HISTORY OF TERRESTRIAL CARBON SOURCES AND SINKS
Description: We
report modeling experiments with a new global dynamic land model (LM3V), to
reconstruct possible causes of the terrestrial carbon sources and sinks over
the past century. The model is unique,
in that it is capable of representing the global history of land use, including
the management of secondary forests (those forests that have re-grown at least
once following harvest). Several published carbon inventories attribute the
majority of the carbon sink caused by land use in the temperate zone to the
management of secondary forests.
Author's Names: S.W. Pacala, G.C. Hurtt, E. Shevliakova, and S. Malyshev
Filesize: 17.72 Kb
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THE IMPACT OF CLOUDS ON ECOSYSTEM CO18O ISOFLUXES IN THE GREAT PLAINS
Description:
Mechanistic
explanations for the downward excursion in d18O of atmospheric CO2
observed during the mid-1990s and the generally large interannnual variability
characteristic of this isotopologue are lacking. We hypothesize that the
excursion and related variations in d18O of atmospheric
CO2 may be linked to global-scale variations in cloud cover.
However, very little is known about the influence of clouds on
biosphere-atmosphere CO18O exchanges. Recent work has demonstrated
the influence of boundary layer clouds on canopy photosynthesis through
increases in the diffuse radiation fraction and relative humidity, combined
with decreases in leaf temperature. In concert, these alterations tend to
increase canopy photosynthesis and conductance, which should also increase CO18O
isofluxes. However, photosynthetic CO18O isofluxes also depend
critically on the d18O of leafwater,
and enhanced cloudiness typically decreases the d18O of leafwater by
enhancing relative humidity and water vapor exchange across stomata. Thus, the net impact of differing cloud regimes on
biosphere-atmosphere CO18O exchanges is difficult to predict.
Preliminary simulations suggest a large impact of diffuse radiation on canopy
photosynthesis by increasing the flux from shade leaves. The impact of this
effect on biosphere-atmosphere CO18O exchanges is diluted somewhat by the lower enrichment in
leafwater d18O on cloudy days
with high diffuse radiation fractions. Our results suggest that these effects
are very dependent on LAI and photosynthetic pathway (C3 or C4).
Author's Names: C.J. Still, W.J. Riley, S.C. Biraud, D. Noone, et al
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