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| Titel |
CO2 fluxes in converting a tropical savanna to a managed ecosystem |
| VerfasserIn |
Mila Bristow, Lindsay Hutley, Jason Beringer, Stephen Livesley, Stefan Arndt |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250077659
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| Zusammenfassung |
| Clearing and burning of tropical savanna is a globally significant emission of greenhouse gas
although there is large uncertainty relating to the magnitude of this flux. Australia’s tropical
savannas occupy over 25% of the continental land mass and they significantly influence the
national greenhouse gas budget. The tropical savanna region is also earmarked as
one potential area of agricultural expansion in Australia given predicted rainfall
declines across southern agricultural regions. It is currently unknown what impact a
conversion of savanna woodlands to agricultural cropping will have on carbon and water
budgets.
We measured continuous CO2 exchange using eddy covariance flux towers before, during
and after a land use change event in a savanna woodland in the Northern Territory of
Australia. Our experimental design included flux measurement in an uncleared savanna and at
a second savanna site prior to, during clearing and conversion to agricultural land. In addition,
we measured the biomass of the savanna vegetation to quantify loss of standing carbon during
conversion.
The uncleared savanna was a weak net sink annually (~0.5 t C ha-1yr-1). In the 5
months prior to clearing, the late dry season to the early wet season (Oct 2011 to Mar 2012),
the analogue savanna site was also a weak sink (mean daily sink ~0.05 t C ha-1 d-1).
Clearing shifted the site to a net source of CO2. It remained a permanent CO2 source
regardless of subsequent weather events, with pulses of increased respiration associated with
rainfall events. The cleared debris (63 t biomass ha-1) was burnt in the late dry season a
process that took 10 days (burning, stock piling, re-burning). Using savanna specific fuel
emission factors we calculated the emissions from this fire event assuming all above ground,
and 90% below-ground biomass was incinerated. The burning released a further
25.1 t C ha-1 from cleared debris, plus 6.3 t C ha-1 as a net emission as measured
by the tower, generating huge CO2 emissions to the atmosphere, totalling 31.4 t
C ha-1 (or 115.4 t CO2-e ha-1). The overall difference between uncleared and
cleared savanna sites was equivalent to 12 years of carbon sequestration in this
ecosystem.
Our study clearly demonstrates that the conversion of savanna to agriculture
could lead to much greater C losses from the ecosystem that previously assumed. If
implemented the clearing of tropical savannas in Australia will come at a large
C cost that will have major implications for the national greenhouse gas budget. |
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