Assessing soil carbon dioxide and methane fluxes from a Scots pine raised bog-edge-woodland

Scots pine bog edge woodland is a type of habitat typical on raised bogs where trees cohabitate with bog vegetation to form a low-density stand. Even though nowadays this habitat does not cover large areas, in a future scenario it is possible that this environment will expand, either naturally (drier climate) or anthropogenically, as the result of the application of new restoration strategies that could increase net landscape carbon benefits from both peatland and woodland environments. This study is the first reported investigation in Scotland exploring carbon flux dynamics from sparse woodlands on raised bogs. We examined how Scots pine trees directly or indirectly affected soil temperature and moisture, ground vegetation, and consequently carbon dioxide (CO₂) and methane (CH₄) soil fluxes. Soil CO₂ and CH₄ were measured at different distance from the tree and thereafter assessed for both spatial and temporal variability. Our results showed that these low-density trees were able to modify the ground vegetation composition, had no effect on soil temperature, but did affect the soil moisture, with soils close to tree roots significantly drier (0.25 ± 0.01 m³ m^-3) than those on open bog (0.39 ± 0.02 m³ m^-3). Soil CO₂ fluxes were significantly higher in the vicinity of trees (34.13 ± 3.97 μg CO₂ m^-2 s^-1) compared to the open bog (24.34 ± 2.86 μg CO₂ m^-2 s^-1). On the opposite, CH₄ effluxes were significantly larger in the open bog (0.07 ± 0.01 μg CH₄ m^-2 s^-1) than close to the tree (0.01 ± 0.00 μg CH₄ m^-2 s^-1). This suggests that Scots pine trees on bog edge woodland may affect soil C fluxes in their proximity primarily due to the contribution of root respiration, but also as a result of their effects on soil moisture, enhancing soil CO₂ emissions, while reducing the CH₄ fluxes. There is, however, still uncertainty about the complete greenhouse gas assessment, and further research would be needed in order to include the quantification of soil nitrous oxide (N₂O) dynamics together with the analysis of complete gas exchanges at the tree-atmosphere level.