HR: 08:45h
AN: B31B-04 INVITED     [PDF]
TI: Trace Gas Emissions in Temperate Forests and Impact of Forest Conversion
AU: * Butterbach-Bahl, K
EM: klaus.butterbach@imk.fzk.de
AF: Institute for Meteorology and Climate Research, Atmospheric Environmental Research (IMK-IFU), Forschungszentrum Karlsruhe GmbH, Kreuzeckbahnstr. 19, Garmisch-Partenkirch, 82467 Germany
AU: Papen, H
EM: hans.papen@imk.fzk.de
AF: Institute for Meteorology and Climate Research, Atmospheric Environmental Research (IMK-IFU), Forschungszentrum Karlsruhe GmbH, Kreuzeckbahnstr. 19, Garmisch-Partenkirch, 82467 Germany
AB: Temperate forest ecosystems play a significant role as sources and sinks for primarily and secondarily active trace gases such as N2O, NO and CH4. In recent decades the magnitude of the biosphere-atmosphere exchange of these trace gases has been substantially altered due to direct and indirect anthropogenic activities. E.g. measurements at different forest sites across Europe exposed to different loads of atmospheric N-deposition clearly show, that N-oxides emissions are positively correlated to N-deposition, whereas CH4 uptake rates are negatively affected. Furthermore, stand properties such as tree species composition as well as stand age have also been demonstrated to strongly affect the exchange of these trace gases. Results of continuous measurements of N-oxide emissions at the H”glwald Forest site, Germany, show that e.g. NO-emissions from a spruce site are approx. 6 fold higher (5-7 kg NO-N ha-1 yr-1) than N2O emissions (0.5-1 kg N2O-N ha-1 yr-1), whereas at an adjacent beech site -stocking on a comparable soil- N2O-emissions are 3-5 kg N2O-N ha-1 yr-1 and NO emissions are 2-2.5 kg NO-N ha-1 yr-1. These results are further supported by microbiological process studies, which show that the forest type can alter the magnitude of the key microbial processes mineralization and nitrification by its effect on soil moisture conditions and substrate quality. However, estimates of trace gas exchange between temperate forest soils and the atmosphere remain fragmentary if the effect of direct anthropogenic management activities such as clear cutting and reforestation are neglected. Therefore, in 1999 we started a multi-year experiment at the H”glwald Forest, Bavaria, in which we investigated the effect of the conversion of a spruce forest into a beech forest either by clear cutting or selected cutting on N2O, NO and CH4 emission/ deposition. The results of this study show, that clear cutting strongly enhanced N2O emissions from approx. 0.5 kg N2O-N ha-1 yr-1 to $>5$ kg N2O-N ha-1 yr-1 not only for one year but for several consecutive years, whereas NO emissions remained at an high level in the year after clear cutting (> 5 kg NO-N ha-1 yr-1), but declined thereafter. CH4 uptake decreased sharply after clear cutting to values close to zero and did not recover even 4 years after site management. If our results are extrapolated for a typical rotation span of a plantation (80-100 years), it becomes evident that increased rates of N2O losses and reduced rates of CH4 uptake within the first decades of forest conversion will reduce the net greenhouse gas balance of forests -including the net ecosystem exchange of CO2- by up to 35 percent. Compared to these dramatic effects, selected cutting exhibited only in the first year significant effects on exchange rates of N2O-, NO- and CH4, thus, indicating that this forest management practice is more sustainable with regard to the protection of the atmosphere.
DE: 0315 Biosphere/atmosphere interactions
SC: Biogeosciences [B]
MN: 2003 Fall Meeting