The effect of afforestation on soil carbon dioxide emissions in blanket peatland in Ireland

We studied the effect of afforestation on soil CO2 emissions in blanket peat. The study sites were as follows: two undrained blanket peatland sites, six sites which had been drained and afforested 3, 19, 23, 27, 33 and 39 years previously, and two forest sites which were clearfelled in summer 1996. Soil CO2 emissions were measured using the soda-lime method during 13 sampling campaigns throughout 1997. Each campaign consisted of two consecutive 24-h measurements. Comparison of the average annual CO2 emission revealed no clear pattern in relation to soil type and suggests that afforestation does not always lead to an increase in soil CO2 emissions. In the most recently forested site, CO2 emissions were similar to 1.7 t C ha(-1) a(-1) and drainage had failed to lower the water-table sufficiently to cause a large increase in CO2 emissions. In the 19-, 23-, 27- and 33-year-old sites soil CO2 emissions were similar to 1.0-1.4 t C ha(-1) a(-1) and were similar to, or lower than, levels in the undrained sites. In the 39-year-old site average CO2 emissions were 2.6 t C ha(-1) a(-1). In the clearfelled sites CO2 emissions were lower at between 1.4 and 1.6 t C ha(-1) a(-1). Root respiration appears to account for a large proportion of CO2 emissions, and blanket peat, despite drainage, is resistant to decay. It is concluded that losses of soil C are compensated by C uptake by the trees.