Forest soil and deadwood CH4 fluxes in response to climate change and forest management

Methane (CH₄) is the second largest contributor to global warming and the importance of reducing CH₄ emissions was recently highlighted through the Global Methane Pledge launched in 2021. Forest soils can act both as sinks and sources of CH₄, largely depending on the hydrological status of the soil, and both direction and magnitude of CH₄ fluxes often vary considerably even across small spatial and temporal scales. Thus, projected changes in precipitation patterns can be expected to affect both total CH₄ budgets and the spatiotemporal distribution of sinks and sources. Forest management – for example clear cutting and nitrogen (N) fertilization – also affects CH₄ cycling in forests with the potential to turn CH₄ sinks into CH₄ sources, but little is currently known about the mechanisms and to what extent fluxes are affected by forest management.

In the ForBioFunCtioN project, we have set up an extensive climate and management manipulation experiment across five Norwegian spruce dominated bilberry forest sites spanning from a recent clear-cut to mature managed (80 years) and old unmanaged (140 years) stands. Treatments include warming with open-top chambers, simulated increased precipitation and additions of N fertilizer and biochar in a total of 12 different treatment combinations (n = 144). We utilize state-of-the-art technology (LI-7810 Trace Gas Analyzer, LI-COR^®) for measurements of soil-atmosphere and deadwood-atmosphere exchange of CO₂ and CH₄.

Here, we present the experimental setup and soil and deadwood flux measurements of CO₂ and CH₄ from June to December 2021. Initial results show that soil CH₄ fluxes vary considerably both between and within sites yet indicate short-term responses of CH₄ fluxes to addition of biochar and N fertilizer in particular.