Forest soils are doing more climate work than most people realize, quietly absorbing methane from the air year after year.
New long-term measurements from southwest Germany show that, in some forests, this underground methane sink has been steadily strengthening rather than fading.
Researchers at the University of Göttingen tracked methane movement across 13 forest plots for nearly 25 years and found that the soils increased their methane absorption by roughly 3 percent per year.
The steady rise – observed across wet and dry periods and gradually warming conditions – challenges simple assumptions that climate change will uniformly reduce the ability of soils to act as methane sinks. It also raises new questions about why some forests improve faster than others.
Forest microbes remove methane
Lower rainfall left more air space in the soil, allowing methane to move downward more quickly instead of lingering near the surface.
Drier ground held more air-filled pores, helping both methane and oxygen travel through the soil – a key factor because microbes that consume methane require oxygen to function.
Across the monitored plots, the team linked stronger methane uptake to lower soil moisture and gradually rising soil temperatures.
Once methane reached the topsoil, methanotrophs – microbes that use methane as fuel – broke it down through reactions that converted the gas into carbon dioxide and water.
Slightly warmer soils tended to speed their metabolism, matching the steady increase in methane uptake seen at many sites.
However, the researchers noted that extremely dry conditions can suppress microbial activity, while long periods of wet soil reduce oxygen levels and allow methane-producing microbes to gain the upper hand.
Tracking methane through soil
Thin tubes fed samples every two weeks from several depths, building soil gas profiles, readings of gas levels through the soil.
Lab tests tracked methane and other gases, showing whether concentrations fell with depth in ways that signaled uptake.
To check those calculations, the researchers also set a sealed chamber on the forest floor and watched methane drop. That double-check mattered because small errors add up, and a false trend can appear after years of data.
Methane matters to climate
A NASA indicator notes that methane traps more heat than carbon dioxide but lasts only about 7 to 12 years.
When soil absorbs methane, it lowers the amount that reaches the atmosphere, cutting warming pressure in the years ahead. Forest soils rarely get credit for this service, yet their performance can rise or fall with weather.
Greater methane absorption will not solve the problem on its own, but it could buy time while emissions cuts catch up.
Rainfall controls methane absorption
Earlier research has not always found rising methane uptake. A 2018 study in the United States, which tracked forests across several sites, reported that methane absorption fell sharply as precipitation increased, with losses reaching as high as 89 percent at one location.
Such contrasts highlight how results can diverge when regions follow different rainfall paths, and why meta-analyses that combine many studies may sometimes overgeneralize local patterns.
“We observed a significant long-term increase in methane uptake in the forest areas we studied,” said Maier.
Rainfall plays a central role because it controls soil moisture, which in turn determines how easily methane and oxygen travel through soil pores.
In southwest Germany, precipitation gradually declined during the monitoring years, while parts of the northeastern United States experienced wetter conditions – helping explain why methane trends moved in opposite directions.
Climate projections generally estimate temperature changes more reliably than local rainfall, meaning that a single global map of future methane uptake could be misleading if regional moisture patterns shift differently under warming.
Forests change, soils respond
Forest disturbances can quietly reshape how soils handle methane by altering the structure that gases move through.
In some monitored plots, bark beetle outbreaks forced tree removal, and the researchers tracked those areas separately in later years to account for the change.
When the canopy opens, sunlight reaches the forest floor more easily, often drying the soil faster. At the same time, heavy machinery used during logging can compact the ground, squeezing the tiny pores that methane needs to travel through.
Because these local changes can sometimes outweigh broader climate trends, long-term monitoring must track forest disturbances alongside weather patterns to understand what is really driving methane uptake.
Future forest methane absorption
Even within one landscape, methane uptake varied widely between plots, showing that soil texture and land-use history strongly shaped results.
Researchers compared beech and spruce forests and still found large differences in how much methane the soils absorbed.
Cross-checks reduced uncertainty, but stony soils and patchy moisture still limited how precisely the team could measure uptake, and scaling this work to whole countries would likely introduce errors because neighboring soils and tree stands can behave very differently.
The long-term record also linked higher methane uptake to drier soil conditions and warmer years, challenging simple global narratives that methane consumption is universally declining.
More sites will need decades of consistent monitoring – especially in regions becoming wetter – before forecasts can reliably guide climate policy.
The study is published in Agricultural and Forest Meteorology.
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