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

Global decarbonization will require a large deployment of power grids to convey electricity. The right-of-way (i.e., the cleared area below the pylons, where vegetation is periodically maintained) is a land-use change that involves changes in soil and vegetation and their carbon dynamics both within the rights-of-way and in adjacent forests, notably via an edge effect. Our main objective was to assess whether soil CO₂ effluxes (F_CO2), soil CH₄ effluxes and microclimate (soil temperature and water content) differed between powerline rights-of-way and their adjacent forests compared to control forests over a large bioclimatic gradient of upland sites across the temperate and boreal forests of Eastern Canada. Monthly efflux measurements were carried out between May and October 2023 and 2024 in eight rights-of-way and their adjacent edge and control forests. Overall, cumulative total F_CO2 during the snow-free period were lower (–7.57 %) in rights-of-way and higher (+11.20 %) in the edge forests compared to the control forests. However, these results were not consistent across the bioclimatic gradient: balsam fir forests, contrarily to forests from both cooler and warmer bioclimatic domains, showed enhanced soil respiration in rights-of-way. Overall, soils were warmer and wetter in rights-of-way compared to control and edge forests; however, no effects were found on the soil methane uptake. Our study indicated that the presence of a powerline right-of-way influences soil biogenic carbon emissions. Effects are related both to changes in abiotic and biotic conditions. These estimates should improve the assessment of the carbon footprint of power transmission and electricity deployment.