Post-harvest patterns of carbon dioxide production, methane uptake and nitrous oxide production in a Pinus radiata D. Don plantation

Forest harvest results in the removal of a large reservoir of terrestrial carbon with potential significant effects on net CO2 emissions, but concomitant effects on other atmospheric trace gas fluxes are poorly understood.We measured CO2, CH4 and N2O fluxes between soils and the atmosphere over 3 years at a recently harvested site under Pinus radiata on a volcanic soil of high-fertility status using replicated, large, in situ chambers to enclose three harvest residue treatments. Temporal changes in CO2 and N2O emissions were also measured over a wider harvested area using small chambers. The residue (slash) treatments were a control (‘no-slash’), ‘normal-slash’ typical of the site and ‘high-slash’ (three times normal-slash). Mass loss was inversely related to all size categories of slash, and averaged 98% for litter and 34% for large wood (76–120 mm diameter). C:N ratios generally declined as a result of increased N concentrations. Overall, CO2-C production was significantly higher (P = 0.02) in the ‘normal-slash’ (by 27%) and ‘high-slash’ (by 72%) than in the ‘no-slash’ treatments. An interaction between treatment and time explained (P = 0.05) the CO2-C flux data better than did the interaction between treatment and soil moisture (P = 0.07). Evidence from small-chamber CO2-C flux data collected over a wider area before and after harvest suggested little apparent effect of soil disturbance during harvest. Averaged over 3 years, the annual CO2-C efflux from the large chambers was 8.3 ± 1.1 Mg ha−1.Methane uptake was apparently depressed by surface soil disturbance during harvest, because it increased after harvest by 70% in the ‘normal-slash’ and ‘high-slash’ treatments to average 12 ± 1 kg CH4 ha−1 year−1. Neither NH4+ nor NO3−-N concentrations had any measurable effect on CH4 uptake. Despite the high N fertility of the harvest site, N2O emissions were low overall (0.56 ± 0.17 kg N2O-N ha−1 year−1) and differed little between treatments, apart from a spike shortly after harvest.Overall, during the time frame of the first commitment period under the Kyoto Protocol, the three greenhouse gases (CO2, CH4 and N2O) contributed 87, −1 and 14%, respectively, to combined emissions on a CO2-equivalent basis from this fertile harvest site.