Abstract
Trees have morphological adaptations that allow methane (CH(4)) generated below ground to bypass oxidation in aerobic surface soils. This natural phenomenon however has not been measured in a landfill context where planted trees may alter the composition and magnitude of CH(4) fluxes from the surface. To address this research gap, we measured tree stem and soil greenhouse gas (GHG) emissions (CH(4) and CO(2)) from a closed UK landfill and comparable natural site, using an off-axis integrated cavity output spectroscopy analyser and flux chambers. Analyses showed average CH(4) stem fluxes from the landfill and non-landfill sites were 31.8 ± 24.4 µg m(-2) h(-1) and -0.3 ± 0.2 µg m(-2) h(-1), respectively. The landfill site showed seasonal patterns in CH(4) and CO(2) stem emissions, but no significant patterns were observed in CH(4) and CO(2) fluxes at different stem heights or between tree species. Tree stem emissions accounted for 39% of the total CH(4) surface flux (7% of the CO(2)); a previously unknown contribution that should be included in future carbon assessments.