Empirical and process-based modelling of soil respiration in afforested peatlands

Worldwide peatlands cover about 3% of the Earth’s land surface and it is estimated that they store about 610 Pg C. Some 50 million ha of peatlands have been drained and converted to another land-use. After drainage the aerobic peat starts to decompose emitting large amounts of CO2 and natural peatlands usually change from carbon (C) sinks to C sources. The main objective of this thesis was to develop country-specific peat C decomposition factors (RP) for afforested peatland. In order to achieve this, an experimental setup to partition soil respiration was established on a chronosequence of seven Sitka spruce (Picea sitchensis (Bong.) Carr.) and one lodgepole pine (Pinus contorta Dougl.) plantation on drained blanket peat. In addition, an experiment to assess the correct collar insertion depth for measuring total soil respiration (RTOT) was conducted in the same ecosystems. Finally, the suitability of the process-based ECOSSE model to simulate heterotrophic respiration (RH) in peatland forest was assessed. This study found that a shallow collar insertion depth of 1.5 cm would reduce the measured RTOT by 34 and 21% in a Sitka spruce and lodgepole pine plantations respectively. This study also found that autotrophic respiration represented on average 44% of RTOT. On the other hand, the contribution of RP and litter decomposition to RTOT were 35 and 21%, respectively. The mean CO2-C emission from RP for this land-use change was 3.3 ± 0.2 t CO2-C ha-1y-1 Finally, it was proved that with limited input data, the ECOSSE model was able to simulate the seasonal variation of RH in afforested peatlands. However, the relative constantly deviation between the ECOSSE-simulated RH and the site-specific RH suggests that further model adjustments and calibrations are needed in order to increase the accuracy of the ECOSSE simulations.