Land-use conversion effects on CO2 emissions: from agricultural to hybrid poplar plantation

Land-use changes such as deforestation have been considered one of the main contributors to increased greenhouse gas emissions, while verifiable C sequestration through afforestation projects is eligible to receive C credits under the Kyoto Protocol. We studied the short-term effects on CO₂ emissions of converting agricultural land-use (planted to barley) to a hybrid poplar (Populus deltoids × Populus × petrowskyana var. Walker) plantation in the Parkland region in northern Alberta, where large areas are being planted to hybrid poplars. CO₂ emissions were measured using a static gas chamber method. No differences were found in soil temperature, volumetric moisture content, or soil respiration rates between the barley and Walker plots. The mean soil respiration rate in 2005 was 1.83 ± 0.19 (mean ± 1 SE) and 1.89 ± 0.13 μmol CO₂ m⁻² s⁻¹ in the barley and Walker plots, respectively. However, biomass production was higher in the barley plots, indicating that the agricultural land-use system had a greater ability to fix atmospheric CO₂. The C balance in the land-use systems were estimated to be a small net gain (before considering straw and grain removal through harvesting) of 0.03 ± 0.187 Mg C ha⁻¹ year⁻¹ in the barley plots and a net loss of 3.35 ± 0.080 Mg C ha⁻¹ year⁻¹ from the Walker poplar plots. Over the long-term, we expect the hybrid poplar plantation to become a net C sink as the trees grow bigger and net primary productivity increases.