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| Titel |
Towards a Full Greenhouse Gas Budget at a Clear-Cut and Stump Harvested Boreal Forest Site in Sweden |
| VerfasserIn |
P. Vestin, M. Mölder, E. Sundqvist, M. Hellström, A. Båth, P. Weslien, L. Klemedtsson, A. Lindroth |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250063294
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| Zusammenfassung |
| Clear-cutting and subsequent site preparation is common forest management practice in
Sweden. In addition, stump harvesting (for bioenergy production) following clear-cutting has
become more common in recent years. The net effects of clear-cutting/stump harvesting on
greenhouse gas (GHG) fluxes are however not well-known. A full assessment of the
benefits of any management practice has to include all greenhouse gases. Recent
development of fast-response gas analyzers has made eddy covariance (EC) measurements
of water vapor (H2O), carbon dioxide (CO2), methane (CH4) and nitrous oxide
(N2O) possible. The applicability of these analyzers is however limited by high cost
and in some cases by high power demand. By using the so-called flux-gradient
method, it is possible to use one set of gas analyzers for a multi-tower setup to reduce
both cost and total power consumption. In addition, using the same analyzers for
measurements at several plots reduces systematic errors and minimizes the need for
calibration.
The effects of clear-cutting and stump harvesting on GHG fluxes were studied at Norunda
forest in central Sweden. Four different plots were established on a new clear-cut. All plots
were clear-cut (early 2009) and site prepared (May 2010). Two of the plots were then stump
harvested. On each of the plots, a 3 m high tower was erected and equipped for flux-gradient
measurements of CO2, H2O, CH4(May 2010 – October 2011), and N2O (June 2011 -
October 2011) exchanges. Friction velocities and sensible heat fluxes were measured by
sonic anemometers (Gill Windmaster, Gill Instruments Ltd). Air was continuously
sampled at two heights in the towers and gas concentrations were analyzed for CH4,
CO2, H2O (LGR DLT-100, Los Gatos Research) and N2O (QCL Mini Monitor,
Aerodyne Research). In addition, EC flux measurements of CO2 and H2O (Li-7500,
LI-COR) were carried out on two of the plots (one of each treatment). The EC
measurements allows for verification of CO2 and H2O fluxes from the flux-gradient
measurements.
The clear-cut became waterlogged after harvest in 2009. Two of the plots (one of each
treatment) were significantly wetter than the other two. All plots were on average sources of
CO2, with daily average fluxes ranging between -2.5 and +5.8 μmol m-2s-1. The ingrowth
of new vegetation was faster on the wetter plots, resulting in lower average CO2 emissions.
Preliminary results indicate a switch from a weak CH4 sink to a significant CH4 source at all
plots (higher emissions from the two wetter plots). Daily average CH4 fluxes ranged between
-7.9 and +218.4 μmol m-2h-1. There were significant N2O emissions on all plots during the
main growing season of 2011, with large emissions following heavy rain events. N2O
fluxes ranged between -63.7 and +403.7 μg m-2h-1 but without clear differences
between wetter and drier plots as in the case with CO2 and CH4. Available data
(including EC flux data for verification of the flux-gradient measurements) will be added
to the time series and presented (in terms of CO2 equivalents) at the conference. |
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