Methane emissions from trees – insights on constraining their fluxes, drivers, pathways and significance.

Abstract:

Our understanding of tree stem greenhouse gas emissions, particularly methane, is gaining rapid research momentum. Until recently, tree stem methane emissions have been largely overlooked in global inventories. Methane stem emissions occur in both lowland and upland trees and in some cases are highly significant. Although methane efflux through the bark medium is a unifying attribute, many uncertainties remain regarding the precise methane source, pathways, sinks and flux magnitudes along the forest sediment–stem–atmosphere continuum. In addition, the large variability in methane fluxes across stem height and stem location, hydrological conditions, tree species, scaling approaches and climatic drivers, at both spatial and temporal scales - compounds complexities in resolving this novel pathway. Here we present several lines of investigation our research group are currently utilising to address some of these questions within Southern Hemisphere lowland forests. We explore a combination of in situ macro and micro-chamber methods, vertical, radial and seasonal sampling regimes, stable isotope tracing, incubation and inoculation experiments, 3D surface scanning and scaling techniques, flow path modification and labeling experiments, and inter-species comparisons to help constrain the sink-source behaviour, dynamics and interconnected processes driving tree stem methane emissions down-under.