Quantifying Carbon Accumulation and Loss in Afforested Peatlands

During the 20th Century, new tree planting techniques combined with tax incentives encouraged the establishment of forest plantations across large areas of peatland in the UK. As many of the stands reach harvesting age the question arises whether the bogs should be restored or restocked with new trees.
Bad a’Cheo Forest (Caithness, Scotland), which was afforested in 1968, is once such plantation. Ground elevation and peat depth surveys were compared against re-interpolated data from before afforestation, and across the full forestry rotation. Significant subsidence has taken place since drainage, with an average reduction of 53 cm (13 %) in peat depth under forest stands, suggesting a possible loss of carbon from the peat.
To confirm this Icelandic cryptotephra, most notably Hekla 4 (2310 ± 20 BCE), were used to define isochrones in peat cores, allowing for comparison of carbon stocks. ITRAX core scanning was used on 27 cores from Bad a’Cheo and on eight additional cores from four other sites around the Flow Country to rapidly identify the presence of elements indicative of tephra deposits. Hekla 4 was found significantly closer to the surface in afforested bogs (average 134.4 ± 16.3 cm) than in undrained bogs (244.0 ± 44.6 cm).
Forestry had caused an average loss of stored carbon from peat of 66.8 t C ha-1 at Bad a’Cheo, and an average loss of 103 t C ha-1 across all sites. At Bad a’Cheo carbon uptake in primarily aboveground forest biomass, partially compensated for this, producing a net loss of 19.49 t C ha-1 of afforested peatland over 50 years. High variation in the data produced uncertainty in the estimates, with possible outcomes ranging from a total net gain of carbon across peat and forestry of 266.72 t C ha-1 to a significant net loss of 305.69 t C ha-1.