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| Titel |
Climate warming impacts on boreal landscape net CO2 exchange |
| VerfasserIn |
Manuel Helbig, Natascha Kljun, Laura E. Chasmer, Ankur R. Desai, William L. Quinton, Oliver Sonnentag |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250145006
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| Publikation (Nr.) |
 EGU/EGU2017-8897.pdf |
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| Zusammenfassung |
| In boreal peatlands of the North American sporadic permafrost zone, climate change
causes permafrost thaw and induces changes in vegetation composition and structure.
Boreal landscape net carbon dioxide (CO2) fluxes in these regions will thus be
modified directly through the changes in the meteorological forcing of ecosystem
processes and indirectly through changes in landscape functioning associated with
thaw-induced land cover changes. How the combined effects alter net ecosystem CO2
exchange of these landscapes (NEELAND), resulting from changes in gross primary
productivity (GPP) and ecosystem respiration (ER), remains unknown. Here, we
quantify indirect land cover and direct climate change impacts on NEELAND for a
boreal forest-wetland landscape in the organic-rich Taiga Plains of northwestern
Canada.
Using 1.5 years of nested eddy covariance flux tower measurements, we observe both
larger GPP and ER at the landscape-level (50% forested permafrost plateaus & 50%
permafrost-free wetlands) compared to the wetland-level (100% permafrost-free wetland).
However, the resulting annual NEELAND (-20±6 g C m−2) was similar to NEE of the
wetland (-24±8 g C m−2). Indirect thaw-induced wetland expansion effects thus appear to
have negligible effects on NEELAND. In contrast, we find larger direct climate change
impacts when modeling end-of-the-21st-century NEELAND (2091-2100) using downscaled
air temperature and incoming shortwave radiation projections. Modeled GPP indicates large
spring and fall increases due to reduced temperature-limitation. At the same time,
light-limitation of GPP becomes more frequent in fall. The projected warmer air temperatures
increase ER year-round in the absence of moisture stress. As a result, larger net CO2 uptake is
projected for the shoulder seasons while the peak growing season net CO2 uptake
declines.
The modeled annual NEELAND is projected to decline by 25±15 g C m−2 for a
moderate (RCP 4.5) and 103±37 g C m−2 for a high warming scenario (RCP 8.5),
potentially reversing recently observed increasing net CO2 uptake trends across the
boreal zone. At the end of the 21st-century, modeled annual NEELAND was not
significantly different from 0 g C m−2 for the RCP 4.5 scenario (+16±42 g C m−2) and
positive for the RCP 8.5 scenario with +94±54 g C m−2. Thus, even without moisture
stress, net CO2 uptake of boreal forest-wetland landscapes may decline – and likely
cease - if anthropogenic CO2 emissions are not reduced. Future NEELAND changes
are thus more likely driven by direct climate than by indirect land cover change
impacts. |
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