Forests and the Methane Cycle Workshop

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During the first week of June a workshop took place covering the topic of “Forests and Methane Cycling.”  The meeting was jointly organised by MethaneNet and Mari Pihlatie of the University of Helsinki, and was held on the idyllic banks of Lake Kuivajärvi at Hyytiälä Forestry Field Station in Finland.  The aim of the event was to synthesise current knowledge on forest methane cycling from various ecoregions, and at different spatial and temporal scales.

A general introduction set the scene for the workshop, but also raised important questions concerning methods for upscaling fluxes, and the appropriateness of different metrics in reporting data.  After this it was on to individual presentations, beginning with a boreal focus.  Speakers discussed both micrometeorological and chamber approaches to measuring methane in northern coniferous forests, which allow complex methane dynamics to be elucidated.  For example, at Hyytiälä there is evidence that suggests the forest floor is a methane sink, whilst the trees act as a small source; similar results from trees have been reported elsewhere.  This introduced the question: “are trees the missing source of methane in boreal forests?”

For the afternoon session, the science switched from the boreal zone to the tropics.  It was noted that carbon cycling in tropical wetlands is still poorly understood.  Furthermore, the possibility was presented that unquantified methane emissions from tree stems might be the reason for the regional discrepancy between bottom-up and top-down estimates of atmospheric methane sources.  The mediating role of tree physiology on greenhouse gas emissions was also broached.

Day 2 of the workshop was a more interactive affair, with conversations about knowledge gaps and the future direction of forest methane research.  There was time for two field trips, however.  The first was to SMEAR II; an atmospheric research facility where measurements of greenhouse gases from soil and trees are ongoing using chamber methods.  Greenhouse gases are also measured using micrometeorological methods on a 124 m tower.  Our second trip was to the scenic Siikaneva peatland, where greenhouse gases are measured using chamber and eddy covariance methods.

The workshop organizer Dr Mari Pihlatie of the University of Helsinki said “this workshop was an eye opener to see how big uncertainties we still have in understanding the role of trees in methane dynamics in forest ecosystems. Also, the meeting gave an excellent opportunity to initialize collaboration between research groups and disciplines to work towards a comprehensive understanding of the methane cycling in forest ecosystems.” Dr Vincent Gauci of MethaneNet added: “the workshop highlighted that we are at a relatively early stage of developing fundamental knowledge of how forested wetlands and upland ecosystems participate in the methane cycle.  The future of this field of research will have important implications for characterisation and modelling of ecosystem sources of this gas under a range of global change scenarios.”

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