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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THE CANADIAN TERRESTRIAL ECOSYSTEM MODEL (CTEM) – THE TERRESTRIAL CARBON CYCLE COMPONENT OF THE ..
Description: The
Canadian Centre for Climate Modelling and Analysis (CCCma) is currently working
towards development of a coupled carbon climate model in which the time-evolving
atmospheric concentrations of greenhouse gases, and in particular CO2,
are computed prognostically on the basis of scenario-specific emissions. The
Canadian Model for Ocean Carbon (CMOC) and the Canadian Terrestrial Ecosystem
Model (CTEM) are the oceanic and terrestrial carbon cycle models implemented in
this coupled framework. This presentation will focus on the terrestrial carbon
cycle component CTEM that is able to grow vegetation from bare ground and
includes processes of photosynthesis, autotrophic and heterotrophic
respiration, phenology, allocation, mortality, land use change, fire, and
competition between plant functional types (PFTs). In the coupled model CTEM
provides a dynamic land surface interface to the climate model by simulating time-varying
vegetation structural attributes as a function of model climate and provides net
fluxes of CO2 between the land surface and the atmosphere. This
presentation provides an overview of how the primary terrestrial ecosystem
processes are modeled in CTEM. It also discusses in some detail the parameterizations
of fire and competition among plant functional types (PFTs). These two
processes have not received adequate attention in the current generation of dynamic
global vegetation models. The fire module of CTEM takes into account all three
aspects of the fire triangle: fuel availability, readiness of fuel to burn
depending on weather conditions, and the presence of an ignition source. The
approach also takes into account the anthropogenic effect on natural fire
regimes. Competition between PFTs is modeled on the basis of a modified form of
Lotka-Volterra equations that, unlike existing applications, allows coexisting
PFTs. Model results at selected locations show that CTEM estimates of vegetation
biomass, leaf area index, fire return interval, biomass burning CO2
emissions and fractional coverages of coexisting PFTs compare reasonably well
with observation-based estimates.
Author's Names: Vivek Arora
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Added on: 25-Jul-2005 Downloads: 45
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THE EFFECTS OF LAND USE CHANGE AND OF SEASONAL VARIATIONS IN CLIMATE ON GPP ACROSS THE ...
Description:
Amazonian
forests play an important and complex role in the global carbon cycle,
contributing substantially to increases (via land use change emissions) and
possibly to net sequestration (in intact forests) of atmospheric CO2.
Predicting these processes of net carbon uptake and release depends crucially
on understanding ecosystem response to both seasonal and interannual
variations. However, prominent ecosystem modeling studies of the Amazonian
carbon cycle [Tian et al., 1998; Botta 2002] appear to make seasonal
predictions (wet-season carbon uptake and dry-season loss) at odds with both
some site-specific observations (which show the opposite pattern, Saleska et al., [2003]) and basin-wide
satellite observations (which imply large-scale increases in the activity of
photosynthetic vegetation during the dry season, Huete et al., [2005]).
Author's Names: S. R. Saleska, M. Pathmadevan, A. Huete, F. Cardoso, et al
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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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THE MEASUREMENT OF CO2 EFFLUX ON FOREST FLOOR IN DECIDUOUS FOREST, JAPAN - THE CASE IN THE DEEP ...
Description:
For more than 1000 years, the forests in mountainous
areas of Japan
have been distinguished by excessive harvesting and litter collection.
Revegetation of these areas over the past 130 years has resulted in the current
forest coverage. However, the forest soils are immature and contain very little
organic carbon. Therefore, the past human impact likely affects the present
carbon cycle and CO2 efflux at the forest floor. It is important to
estimate the carbon cycle and CO2 efflux at the forest floor in such
a heavily affected ecosystem to discuss the relationship between the carbon
cycle and land use management. Therefore, we measured the CO2 efflux
at the forest floor in a deciduous forest heavily affected by human activities
in Japan
and estimated the annual rate.
Author's Names: K. Tamai, Y. Kominami, T. Miyama, Y. Goto and Y. Ohtani
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THE ROLE OF ROOT RESPIRATION IN TEMPERATE DECIDUOUS FOREST IN CENTRAL JAPAN
Description: To
evaluate the role of root respiration (Rr), we
measured spatial and temporal variation of Rr. We measured
root biomass, Rr and soil respiration (Rs) in temperature deciduous forest in central Japan.
The size dependence of Rr was shown
and Rr in fine root (< 2 mm) accounted
more than half of total Rr per unit
area. Moreover, we had measured continuously Rr
and Rs using automated system. Rr responded exponentially to soil temperature. High soil
moisture during and just after rainfall caused limiting factor in Rr. And the contribution of Rr
to Rs changed seasonally.
Author's Names: M. Dannoura, Y. Kominami , K. Tamai, M. Jomura, et al
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Added on: 28-Jul-2005 Downloads: 25
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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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Added on: 29-Jul-2005 Downloads: 149
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TOWARDS A BETTER QUANTIFICATION OF CROPLANDS EXTENT AND MANAGEMENT CONTRIBUTION TO CARBON CYCLING
Description: The
development of agriculture responding to increasing demand for food raises the
question of the role of cultivated land in relation to carbon sources and
sinks, their spatial patterns and temporal variability.
Author's Names: P.C. Smith, N. Viovy, Y. Meurdesoif, S. Gervois, et al
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WATERSHED SCALE CHANGE IN THE CARBON AND WATER CYCLES BY FORESTRY ACTIVITIES IN A ...
Description:
To evaluate the deforestation
and forestation effects on the carbon and water cycles, micrometeorological and
hydrological observations were conducted in a conifer-broadleaf mixed forest in
northernmost Japan
in the series of these activities. The
clear-cutting of trees changed the carbon balance of the ecosystem to the net
source in the plant-growing period, although the undergrowth, Sasa bamboos, still keeps large biomass
after the tree-cutting and the half-hourly flux indicate carbon sequestration
in the daytime. Strip-cutting of Sasa bamboos and planting of the larch
saplings did not cause the distinct change in the emission rate. On the other
hand, the evapotranspiration rate recovered to the same level with that in the
mixed forest within 2 years after the clear-cutting. We attributed the increase
in the evapotranspiration rate partly to the acclimation in the transpiration
capacity of Sasa bamboos.
Author's Names: K. Takagi, M. Nomura, K. Fukuzawa, H. Shibata, et al
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WEEKLY OBSERVATIONS OF STABLE ISOTOPE COMPOSITION OF ECOSYSTEM-ATMOSPHERE CO2 ...
Description:
The
stable isotope composition of atmospheric CO2 is being monitored in
five AmeriFlux sites (four forests and one grassland) by collecting air samples
inside and above canopies at weekly intervals. Measurements of concentration, d13C and d18O of
atmospheric CO2
have continuously been made from 100-ml flask
samples since 2001. These measurements, in concert with eddy covariance
flux
measurements, provide mechanistic insights relating observed isotope
changes
and the controls over carbon sequestration and loss on seasonal and
interannual
bases. Data and a brief project description are available via the
Internet at:
http://ecophys.biology.utah.edu/Research/DOE_TCP/index.html.
Author's Names: C.-T. Lai, and J.R. Ehleringer
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