Forest methane science

The Climate Case for Forest Methane

Through their bark, trees pull methane out of the air, a potent greenhouse gas that standard carbon accounting leaves out. It was measured only recently, and current forest-carbon methods do not credit it. This page explains the mechanism, measurements, climate metrics, and limits.

How the uptake works

Inside the Bark

Methane-oxidizing bacteria occupy the oxic outer tissue of the stem, the bark and the sapwood just beneath it, though their exact position is not yet resolved. They oxidize atmospheric methane, consuming oxygen and releasing carbon dioxide. The inner heartwood is dead and anoxic, so they cannot persist there. Soil-derived methane can also travel up the stem through the chimney effect. SelvaFlux measures uptake directly from the atmosphere.

A misty tropical mountain rainforest, its canopy meeting the clouds and open sky along the skyline. — Methane is the second most important greenhouse gas after carbon dioxide. Upland forests take it up from the atmosphere at their woody surfaces.

The next figure shows a stem in cross-section.

CH₄ + 2 O₂ →CO₂ + 2 H₂OThe methane-oxidizing bacteria occupy the oxic outer tissue, probably the bark and the sapwood beneath it, though their exact position is not yet resolved. They oxidize atmospheric methane to carbon dioxide, using oxygen. The central heartwood is dead and anoxic, so they cannot persist there.

The next figure shows how one bacterium oxidizes methane.

Inside the cell, methane is oxidized in four steps, through methanol, formaldehyde, and formate to carbon dioxide. Methane monooxygenase catalyzes the first step. It splits O₂, putting one oxygen atom into methanol and reducing the other to water, and spends a reductant (the 2[H]) to break methane’s strong C-H bond. This first step costs energy; the three oxidations that follow release the reducing power the cell runs on. That reducing power is handed to a second O₂ in respiration and ends as water, so a single methane takes two O₂ in all to reach carbon dioxide; the enzyme shown here uses only the first. The full step-by-step balance is below. Over many methane molecules, most of the carbon is oxidized through to carbon dioxide and leaves for the atmosphere, while a smaller fraction is drawn off at formaldehyde and assimilated into the cell.

Oxidizing methane to carbon dioxide is a net climate benefit. Methane traps far more heat than carbon dioxide while it is in the air, on the order of 30 times as much over 100 years and roughly 80 times over the first 20, mass for mass. Converting a methane molecule to carbon dioxide leaves a much weaker greenhouse gas, so the net effect is to reduce warming.

Methanotrophs differ in their affinity for methane. Low-affinity types are active only where methane is abundant, as in wetlands and landfills. High-affinity types oxidize methane at its atmospheric concentration, about 2 parts per million, and are the ones responsible for the atmospheric sink.

At atmospheric concentration the energy yield is very low, less than a cell needs just to maintain itself, so per-cell rates are slow and these bacteria do not live on methane alone. Across the world’s well-drained soils they still remove on the order of 30 million tonnes of methane a year. We found that tree bark adds a sink of the same order of magnitude (Nature 2024). Bark methane-oxidizers have since been characterized by genome sequencing (Leung et al. 2026), though the specific organisms responsible on upland bark are not yet identified.

These bark microbes are not specific to methane. They also oxidize atmospheric hydrogen and carbon monoxide, which supplements their energy at these low concentrations. Across Australian forests, Leung and colleagues (2026) measured bark as a substantial hydrogen sink, on the order of 55 million tonnes a year.

Stoichiometry, step by step

CH₄ + O₂ + 2[H] → CH₃OH + H₂Omethane monooxygenasespends reducing power

CH₃OH → HCHO + 2[H]methanol dehydrogenaseyields reducing power

HCHO + H₂O → HCOOH + 2[H]formaldehyde dehydrogenaseyields reducing power

HCOOH → CO₂ + 2[H]formate dehydrogenaseyields reducing power

4[H] + O₂ → 2 H₂Orespirationyields ATP

CH₄ + 2 O₂ → CO₂ + 2 H₂OoverallΔG ≈ −800 kJ/mol

[H] is a reducing equivalent (carried by NAD(P)H and similar cofactors). The first step spends two; the three oxidations after it yield six, more than enough to repay that and to power the cell. At formaldehyde, some of the carbon is assimilated into biomass instead of continuing to CO₂.

The final figure shows the estimated global distribution.

A world map of forest methane uptake across every continent, with the tropical forests of the Amazon, the Congo Basin, and Southeast Asia standing out. — The flux per unit of bark is small. Summed across the world’s trees, the woody surface it acts on totals about 143 million km² (*Nature* 2024), close to the area of Earth’s land. Integrated over that surface, the uptake is affects the global methane budget. The map shows its estimated distribution.

What the accounts miss

Forests Remove Methane From the Air

Most methane mitigation focuses on emitting less. Forests also take it back out of the air. This sink was measured directly across upland forests worldwide and published in Nature ().

Direct measurements allow the climate effect of this uptake to be quantified. An approved methodology would allow forest projects to credit it.

Methane and near-term warming

Methane Causes Strong Warming Over a Short Period

Carbon dioxide drives warming over centuries. Methane acts on a much shorter timescale: it lasts perhaps a decade in the air, and while it is up there it traps more heat per tonne than CO₂. Removing methane reduces warming over the following decades.

GWP100 Averages Methane’s Effect Over a Century

The commonly cited value of about 28× averages methane’s warming across 100 years, most of them long after the methane itself is gone. Averaged over a century, a short pulse of warming produces a lower value than a shorter time window. Over 20years, methane’s effect is much larger.

GWP* describes changes in warming from short-lived gases more directly than a 100-year average (). Under the GWP* establishment calculation used here, removing a tonne of methane is equivalent to about 128× a tonne of CO₂ over 20 years. GWP* is SelvaFlux uses this figure only to describe near-term climate benefit.

Climate benefit and current crediting value

Two Metrics Produce Different Values

GWP* values the near-term climate benefit at about 19% of biomass-carbon uptake. GWP100, the metric used for current crediting, values it at about 4%.

Climate benefitmeasured by GWP*~19%

The estimate is about 19%of the forest’s biomass-carbon benefit. The range is 10 to 40% across growth rates and is higher in slow-growing forests.

Current crediting basisunder GWP100~4%

Under current rules, an approved method would credit about 4% of the forest’s biomass-carbon credits, with a range of 2 to 9%. Projected revenue uses this value.

Both start from the methane a hectare of forest takes up each year:

Bark CH₄ uptake46.7 µg/m²/h × 41,200 m²/ha × 8,760 h/yr = 16.8 kg CH₄/ha/yrper-area uptake from , warm tropics, 2 m up the stem; woody surface area 4.12× the ground area, by laser scanning
Credit, GWP10016.8 kg × 27 = 0.45 tCO₂e/ha/yrabout 4% of biomass carbon
Climate benefit, GWP*16.8 kg × 128 = 2.15 tCO₂e/ha/yr128 is methane’s value over its first 20 years as a new sink; about 19% of biomass carbon

The 4% and 19% are shares of biomass growth, about 11.6 tCO₂/ha/yr here (Cook-Patton Nature 2020), and they rise on slower-growing sites. We report the GWP100 credit and the GWP* benefit separately, and do not add them together.

Four panels of annual credit per hectare over a project's 30 years. Reforestation is the left column, protection the right. The top row shows carbon far larger than methane for each. The bottom row shows methane only: the reforestation rate-based (GWP*) credit holds near 1.8 tonnes for 20 years then drops, the 100-year (GWP100) credit is flat near 0.45 tonnes, and both protection methane credits rise gradually. — The same per-hectare credits over a project’s 30 years, reforestation and protection shown separately. Carbon far exceeds methane in both. The panels plot GWP* resolved over time. It front-loads a newly established sink, so the reforestation methane credit holds near 1.8 tCO₂e/ha/yr (about 16% of the carbon) for its first 20 years, then falls. The 19% headline above uses the project-level GWP* value, 2.15tCO₂e/ha/yr.

Caveat:these panels assume a hectare’s woody surface area, the bark and branches that take up the methane, reaches full extent in the first year, well ahead of the biomass carbon. Surface area builds faster than biomass, but how much faster is not yet established, and a slower rise would lower the methane credited in the early years. SelvaFlux is working to measure this rate directly.

Current and Potential Crediting Values

The difference between the two estimates is about 15 percentage points. GWP* gives a climate-benefit estimate of roughly 19%. GWP100 supports a proposed crediting estimate of about 4%.

If registries approve a metric designed for short-lived gases, the creditable figure could exceed today’s 4%. SelvaFlux is seeking approval for this change. Revenue estimates will continue to use GWP100 until registries approve another metric.

Independent corroboration

Results From Other Research Groups

The 2024 Naturestudy mapped methane uptake by tree woody surfaces across upland forests worldwide, strongest in the warm tropics and fading toward cold high latitudes. Independent groups have measured the same effect at their own sites, at per-area rates that match that temperature trend. Separate labs have documented the mechanism behind it, methane-oxidizing microbes in bark and wood. One 2025 paper (Jardine et al.) asks whether part of the uptake is instead tied to the tree’s own respiration, but the weight of evidence favors the microbial process. The picture is not uniform. In some upland forests the stems release more methane than their surfaces take up, and those results are here too. Wetland forests, which emit methane heavily from waterlogged soil, are a separate question and are not used here.

Woody-Surface Methane Uptake, Measured Independently

Tree stems take up atmospheric methane at per-area rates that match the 2024 study’s temperature trend. SelvaFlux measures methane uptake at this surface.

Jardine et al. 2025, Trees. An upland tree stem in California was measured taking up atmospheric methane, at a per-area rate in the range the 2024 study found for a temperate-climate stem.
Machacová et al. 2021, New Phytologist. In a well-drained tropical rainforest on Réunion, on volcanic substrate, the stems of six species and their bark cryptogams were net methane sinks, the stronger uptake expected at a warm site.

Methane Uptake by Tree Foliage

Studies have also measured atmospheric methane uptake by leaves. SelvaFlux does not include foliage in its bark-uptake estimates.

Sundqvist et al. 2012, Geophysical Research Letters. Branch chambers on four boreal species in central Sweden measured net uptake of atmospheric methane by their shoots and foliage.
Gorgolewski et al. 2023, Ecosystems. In an upland temperate forest in Ontario, tree foliage was a net daytime methane sink.

The Mechanism: Microbes in Bark and Wood

Independent studies have identified methane-oxidizing microbes in bark and wood.

Jeffrey et al. 2021, Nature Communications. Methanotrophic bacteria in the bark of paperbark trees cut the methane the trees emit by about 36%, with uptake rising where more of these bacteria live.
Jeffrey et al. 2021, New Phytologist. Carbon-isotope measurements up the trunk showed about a third of the methane moving through the stem is oxidized on the way.
Leung et al. 2026, Science. Across eight Australian tree species spanning wetland, mangrove, coastal heath, and upland forests, bark microbes oxidized methane, hydrogen, and carbon monoxide.
Putkinen et al. 2021, New Phytologist. Metagenomic sequencing of boreal Norway spruce needles found monooxygenase genes potentially able to consume methane.

Where the Picture Is Mixed

Net direction varies by species and setting, and we include the contrary results. Wetland forests, heavy methane emitters from waterlogged soil, are a separate question and are not used here.

Epron et al. 2025, Tree Physiology. In a cool-temperate mountain forest, bark methane oxidation was real but about ten times smaller than trunk emissions, so those trees were a net source. The authors caution it is early to treat tree surfaces as a global sink everywhere.
Hettwer et al. 2025, Biogeochemistry. In a Maine conifer forest, living stems of spruce, hemlock, and red maple were net methane emitters across the moisture gradient.
Kasak et al. 2026, Agricultural and Forest Meteorology. In a California blue oak savanna, oak stems were a weak but persistent methane source year-round at all three measured heights, and the ecosystem was a net methane source even though its soils took up methane. Chambers reached 2.7 m up the trunk. The authors’ laser scans put the whole trunk at about 6% of a tree’s woody surface, and they did not measure branches.
Gewirtzman et al. 2025, bioRxiv (preprint). In upland forests, tree stems were net methane emitters at the chamber scale, though the sapwood just beneath the bark, and the heartwood, carried methane-oxidizing genes alongside the methane-producing ones.

At the scale of a country

National Forest Methane Inventories

From satellites, the same measurement can quantify forest methane uptake across a whole jurisdiction or a single project. A jurisdictional estimate gives governments additional information for national forest accounts. We design these programs with national forest institutions and climate funders.

Bark methane uptake is a natural process the forest already carries out. It is reportable for completeness in a national inventory. It does not create a carbon credit, offset, or license to emit.

For governments and jurisdictions

Other forest benefits

Methane Is One Benefit of Standing Forests

Standing forests store carbon, support biodiversity, recycle rainfall, and protect soil. SelvaFlux measures methane uptake. These other benefits are not included in the methane credit.

Other benefits of standing forests

Pilot measurements are underway. We estimate that crediting is 1 to 2 years away.

For impact investors

The homepage explains the projected revenue for forest-project developers.

References

Where the Numbers Come From

Forest methane uptakeGauci, V. et al. (2024). Global atmospheric methane uptake by upland tree woody surfaces. Nature.DOI
Methane warming potency (GWP*, 128× over 20 yr)Lynch, J., Cain, M., Pierrehumbert, R. & Allen, M. (2020). Demonstrating GWP*: a means of reporting warming-equivalent emissions. Environmental Research Letters 15(4), 044023.DOI
Credited basis (GWP100, ~27× for biogenic methane)IPCC (2021). Climate Change 2021: The Physical Science Basis, Working Group I (AR6), Chapter 7.Report
Forest biomass growthCook-Patton, S. C. et al. (2020). Mapping carbon accumulation potential from global natural forest regrowth. Nature 585, 545-550.DOI

Common questions