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| Titel |
Deciphering the components of regional net ecosystem fluxes following a bottom-up approach for the Iberian Peninsula |
| VerfasserIn |
N. Carvalhais, M. Reichstein, G. J. Collatz, M. D. Mahecha, M. Migliavacca, C. S. R. Neigh, E. Tomelleri, A. A. Benali, D. Papale, J. Seixas |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 7, no. 11 ; Nr. 7, no. 11 (2010-11-18), S.3707-3729 |
| Datensatznummer |
250005065
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| Publikation (Nr.) |
 copernicus.org/bg-7-3707-2010.pdf |
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| Zusammenfassung |
Quantification of ecosystem carbon pools is a fundamental requirement for
estimating carbon fluxes and for addressing the dynamics and responses of the
terrestrial carbon cycle to environmental drivers. The initial estimates of
carbon pools in terrestrial carbon cycle models often rely on the ecosystem
steady state assumption, leading to initial equilibrium conditions. In this
study, we investigate how trends and inter-annual variability of net
ecosystem fluxes are affected by initial non-steady state conditions.
Further, we examine how modeled ecosystem responses induced exclusively by
the model drivers can be separated from the initial conditions. For this, the
Carnegie-Ames-Stanford Approach (CASA) model is optimized at set of European
eddy covariance sites, which support the parameterization of regional
simulations of ecosystem fluxes for the Iberian Peninsula, between 1982 and
2006.
The presented analysis stands on a credible model performance for a set of
sites, that represent generally well the plant functional types and selected
descriptors of climate and phenology present in the Iberian region – except
for a limited Northwestern area. The effects of initial conditions on
inter-annual variability and on trends, results mostly from the recovery of
pools to equilibrium conditions; which control most of the inter-annual
variability (IAV) and both the magnitude and sign of most of the trends.
However, by removing the time series of pure model recovery from the time
series of the overall fluxes, we are able to retrieve estimates of
inter-annual variability and trends in net ecosystem fluxes that are
quasi-independent from the initial conditions. This approach reduced the
sensitivity of the net fluxes to initial conditions from 47% and 174% to
−3% and 7%, for strong initial sink and source conditions, respectively.
With the aim to identify and improve understanding of the component fluxes
that drive the observed trends, the net ecosystem production (NEP) trends are
decomposed into net primary production (NPP) and heterotrophic respiration
(RH) trends. The majority (~97%) of the positive trends in
NEP is observed in regions where both NPP and RH fluxes show
significant increases, although the magnitude of NPP trends is higher.
Analogously, ~83% of the negative trends in NEP are also associated
with negative trends in NPP. The spatial patterns of NPP trends are mainly
explained by the trends in fAPAR (r=0.79) and are only marginally
explained by trends in temperature and water stress scalars (r=0.10 and
r=0.25, respectively). Further, we observe the significant role of
substrate availability (r=0.25) and temperature (r=0.23) in explaining
the spatial patterns of trends in RH. These results highlight the
role of primary production in driving ecosystem fluxes.
Overall, our study illustrates an approach for removing the confounding
effects of initial conditions and emphasizes the need to decompose the
ecosystem fluxes into its components and drivers for more mechanistic
interpretations of modeling results. We expect that our results are not only
specific for the CASA model since it incorporates concepts of ecosystem
functioning and modeling assumptions common to biogeochemical models. A
direct implication of these results is the ability of this approach to detect
climate and phenology induced trends regardless of the initial conditions. |
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