Is methane released from the forest canopy?

Laboratory experiments show that rates of CH₄ emission from plant material depend exponentially on temperature and linearly on UV irradiance. The UV irradiance shall be spectrally weighted and shorter wavelengths results in higher CH₄ emissions. Global upscaling models for estimating aerobic CH₄, based on lab results, have be conducted with varying results, but until now field measurements based on profile and eddy covariance measurements have failed to show CH₄ emissions from forest canopies. To detect CH₄ production or consumption in the canopy of a beech stand we connected a CH₄ analyzer to a canopy air profile system that samples air below and above the canopy from seven different heights. A profile system with many vertical sample points can detect gas concentration gradients with a high sensitivity only under conditions with no or little air movements. Under these conditions we found indications of periodic CH₄ emissions in the canopy, but more data need to be analyzed before the magnitude of the canopy source of CH₄ can be established.