Reduced global warming potential after wood ash application in drained Northern peatland forests

•Wood ash addition to peatland forests increases C sequestration in tree biomass.•Increased tree growth decreases the GHG source strength of peatland forests.•In general, GHG effluxes showed no or minor changes after wood ash addition.•Wood ash addition is a suitable GHG mitigation option for peatland forests. Past land use change has converted vast areas of Northern peatland by drainage to agricultural or forested land. This change often reduces the greenhouse gas (GHG) sink strength of peatlands or turns them even from sinks to sources, which affects the global climate. Therefore, there is a need for suitable mitigation options for GHG emissions from drained peatlands. Addition of wood ash to peatland forests has been suggested as such a measure, but the overall effect on the global warming potential (GWP) of these ecosystems is still unclear. In order to fill this knowledge gap, we investigated three drained peatland forests in Sweden that had been fertilized with wood ash and monitored stand growth as well as the GHG emissions from soil, i.e. net effluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Our results show that over the first five to eight years after wood ash application, tree growth was enhanced at all sites. This was accompanied by generally little changes in the GHG emissions. Overall, we found that wood ash application reduced the GWP of drained peatland forests. Even though that our study was limited to eight years after wood ash application, we can conclude that in the short term wood ash application may be a suitable mitigation option for GHG emissions from Northern drained peatland forests.