Soil CO₂ and CH₄ effluxes in powerline rights-of-way and their adjacent forests

Global decarbonization implies a large deployment of the power grid to convey electricity from production sites to users. The right-of-way (i.e. the cleared area below the pylons, where vegetation is periodically maintained) is a linear disturbance in the landscape that changes soil and vegetation and the carbon dynamics both within the impacted area as well as in adjacent forests, notably via an edge effect. Our main objective is to assess whether total and heterotrophic soil CO₂ effluxes (F_CO2-T and F_CO2-H), soil CH₄ effluxes (F_CH4) and microclimate (soil temperature and water content)differed between powerline rights-of-way and their adjacent forests compared to forest interior over a large climatic gradient encompassing the temperate and boreal forest in Eastern Canada. Monthly efflux measurements were carried out between May and October 2023 and 2024 in rights-of-way, their adjacent forests and control forests in eight upland forest sites. Compared to the control forest, cumulative F_CO2-T during the snow-free period were higher (+10.75 %) in the edge forests and lower (–7.75 %) in the rights-of-way, while cumulative F_CO2-H were lower (–15.57 %) in the rights-of-way than in the control forests, with no edge effect. Soil was warmer and wetter in rights-of-way compared to control forest, but there was no edge effect on the microclimate. Land use change and edge effect did not alter the apparent temperature sensitivity of F_CO2-T (Q₁₀) or the CH₄ absorption capacity of soils. Altogether, our results showed that the deployment of powerlines in a forest landscape creates spatial heterogeneity in soil CO₂ effluxes with reduced CO₂ cycling in the rights-of-ways and enhanced cycling in the edge forest, while soil CH₄ effluxes are not affected. This suggests that the width of the right of way has implications for assessing the GHG impact of the deployment of power lines.