Trees can sometimes act as methane sources, through methanogens inside the trees or by channeling methane produced in soils. Trees can also sometimes act as sinks, through methanotrophs on their surfaces. Currently, there is insufficient literature on this phenomenon: which types of trees are sources and which are sinks; when (diurnal and/or seasonally) and where (geographically) do they act as sources and when / where do they act as sinks; and which parts of trees (e.g. roots, branches, bark, leaves, etc.) are sources or sinks.

Spatially and temporally resolved quantification of different tree parts as sources or sinks of methane has not been achieved primarily due to the difficulty of measuring precise fluxes on small spatial scales. 

There are existing commercially available technologies that can measure gas fluxes from leaves that are easily accessible (e.g. within the lowest ~6 feet of the tree) (1). However, at present there are limited measurement technologies for woody and subterranean surfaces and significant logistical challenges associated with applying technologies to the upper levels of trees.

The understanding of arboreal methane sources and sinks would benefit from the development of low cost, compact, durable, high sensitivity, and precise methane sensors specifically designed for trees. Measuring the gas fluxes from both foliage and woody surfaces anywhere on a tree, over long time scales and in a variety of conditions would enable a more holistic understanding of the methane flux attributable to a tree over its entire spatial extent and lifetime.

A low cost and portable sensor would enable nimble deployment to ensure comprehensive coverage of individual trees as well as wide spatial coverage to explore a diversity of geographic locations, durations, and tree types.

The primary metric for success is development and field demonstration of a device that is compact, durable, high sensitivity, and precise that can be manufactured either commercially or in-house at large scale and low cost. The device should be widely applicable, with the ability to measure methane fluxes from a diversity of tree parts to facilitate a wide range of scientific applications.

If successful, the development of tree methane flux measurement technologies would:

• Open avenues of research to determine whether methane source/sink attributes of trees can be modified.
• Assist in the assessment of any potential future approaches that seek to enhance methanotrophy or suppress methanogenesis on trees.
• Improve our understanding of tree-based methanogenesis and methanotrophy.
• Improve our understanding of currently unknown methane sinks.
• Potentially discover co-benefits or risks to forestation that are currently unexplored and pathways to minimize risks and maximize co-benefits.
• Help determine the role of different tree types as methane sources or sinks relative to their impacts as carbon dioxide sinks.