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| Titel |
Forest response to increased disturbance in the central Amazon and comparison to western Amazonian forests |
| VerfasserIn |
J. A. Holm, J. Q. Chambers, W. D. Collins, N. Higuchi |
| 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 ; 11, no. 20 ; Nr. 11, no. 20 (2014-10-20), S.5773-5794 |
| Datensatznummer |
250117648
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| Publikation (Nr.) |
 copernicus.org/bg-11-5773-2014.pdf |
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| Zusammenfassung |
| Uncertainties surrounding vegetation response to increased disturbance rates
associated with climate change remains a major global change issue for Amazonian
forests. Additionally, turnover rates computed as the average of mortality
and recruitment rates in the western Amazon basin are doubled when compared
to the central Amazon, and notable gradients currently exist in specific wood
density and aboveground biomass (AGB) between these two regions. This study
investigates the extent to which the variation in disturbance regimes
contributes to these regional gradients. To address this issue, we evaluated
disturbance–recovery processes in a central Amazonian forest under two scenarios
of increased disturbance rates using first ZELIG-TROP, a dynamic vegetation
gap model which we calibrated using long-term inventory data, and second
using the Community Land Model (CLM), a global land surface model that is
part of the Community Earth System Model (CESM). Upon doubling the mortality
rate in the central Amazon to mirror the natural disturbance regime in the
western Amazon of ∼2% mortality, the two regions continued to
differ in multiple forest processes. With the inclusion of elevated natural
disturbances, at steady state, AGB significantly decreased by 41.9% with
no significant difference between modeled AGB and empirical AGB from the
western Amazon data sets (104 vs. 107 Mg C ha−1, respectively).
However, different processes were responsible for the reductions in AGB
between the models and empirical data set. The empirical data set suggests that
a decrease in wood density is a driver leading to the reduction in AGB. While
decreased stand basal area was the driver of AGB loss in ZELIG-TROP, a forest
attribute that does not significantly vary across the Amazon Basin. Further
comparisons found that stem density, specific wood density, and basal area
growth rates differed between the two Amazonian regions. Last, to help
quantify the impacts of increased disturbances on the climate and earth
system, we evaluated the fidelity of tree mortality and disturbance in CLM.
Similar to ZELIG-TROP, CLM predicted a net carbon loss of 49.9%, with an
insignificant effect on aboveground net primary productivity (ANPP).
Decreased leaf area index (LAI) was the driver of AGB loss in CLM, another
forest attribute that does not significantly vary across the Amazon Basin,
and the temporal variability in carbon stock and fluxes was not replicated in
CLM. Our results suggest that (1) the variability between regions cannot be
entirely explained by the variability in disturbance regime, but rather
potentially sensitive to intrinsic environmental factors; or (2) the models
are not accurately simulating all tropical forest characteristics in response
to increased disturbances. |
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