Forests are doing more for the climate than they are often credited for. New long-term research shows that forest soils can become increasingly effective at removing methane from the atmosphere as the planet warms, challenging the assumption that climate change will always weaken natural carbon and greenhouse gas sinks.
A study based on nearly 25 years of continuous measurements in southwest Germany has found that forest soils in the region are absorbing methane at a steadily increasing rate. The research, carried out by scientists at the University of Göttingen, shows that methane uptake by soils across 13 forest plots rose by about 3% per year over the monitoring period, even as temperatures gradually increased and rainfall patterns shifted.
Methane is a powerful greenhouse gas that traps far more heat than carbon dioxide, although it remains in the atmosphere for a much shorter time. Any natural process that reduces methane levels can therefore have an outsized impact on slowing near-term warming. Forest soils, it turns out, play a quiet but important role in this process.
How forest soils remove methane
The key to this growing methane absorption lies beneath the forest floor. When soils are relatively dry, they contain more air-filled pores, allowing gases to move more freely. Methane from the atmosphere can travel downward into the soil more efficiently, while oxygen can move downward as well.
This matters because methane-consuming microbes, known as methanotrophs, require oxygen to function. Once methane reaches the top layers of soil, these microbes use it as an energy source, breaking it down into carbon dioxide and water. Slightly warmer soil temperatures tend to speed up microbial metabolism, which helps explain the gradual rise in methane uptake observed at many of the study sites.
The researchers found that lower soil moisture and slowly rising soil temperatures were strongly linked to stronger methane absorption. However, they also stressed that extremes can reverse the effect. Prolonged wet conditions reduce oxygen availability and allow methane-producing microbes to dominate, while very dry soils can suppress microbial activity altogether.
Measuring methane over decades
To capture such long-term trends accurately, the researchers relied on detailed and redundant measurements. Thin sampling tubes were installed at several depths in the soil, allowing gas samples to be collected every two weeks. These samples were analyzed in the lab to determine how methane concentrations changed with depth, a clear signal of whether the gas was being absorbed.
To verify these findings, the team also placed sealed chambers on the forest floor and directly measured how quickly methane levels declined inside them. This double-checking was crucial, as small measurement errors can accumulate over many years and create misleading trends if not carefully controlled.
Why methane uptake matters
Methane traps significantly more heat than carbon dioxide but typically remains in the atmosphere for only seven to twelve years. When forest soils remove methane, they reduce the amount available to drive warming in the near term. While this natural process cannot offset human emissions on its own, it can help slow the pace of climate change while broader emission reductions take effect.
Despite this benefit, forest soils are rarely included prominently in climate discussions or mitigation strategies, partly because their behavior varies so widely across regions and conditions.
Rainfall makes the difference
The findings also help explain why earlier studies have sometimes reported declining methane uptake. Research conducted in the United States in 2018 showed that methane absorption fell sharply in forests experiencing increased rainfall, with losses reaching nearly 90% at one site. These contrasting results highlight how strongly soil moisture controls methane dynamics.
In southwest Germany, precipitation gradually declined over the monitoring period, favoring drier soils and greater methane absorption. In contrast, parts of the northeastern United States became wetter, reducing the soil’s ability to absorb methane. Because climate models generally predict temperature changes more reliably than local rainfall, the researchers caution against assuming a single global trend in forest methane uptake.
Forest changes also matter
Climate is not the only factor shaping how soils handle methane. Forest disturbances can significantly alter soil structure and gas movement. In some of the monitored plots, bark beetle outbreaks led to tree removal, opening the canopy and allowing more sunlight to reach the forest floor. This often dried the soil faster, potentially increasing methane uptake.
At the same time, logging machinery can compact the soil, squeezing the tiny pores that gases need to move through. These opposing effects mean that local land-use history and forest management can sometimes outweigh broader climate trends, underscoring the need to track disturbances alongside weather data.
Even within the same landscape, methane uptake varied widely between plots. Differences in soil texture, stone content, and land-use history all influenced results. Comparisons between beech and spruce forests showed no simple pattern, with some plots absorbing far more methane than others.
The researchers acknowledge that scaling such detailed measurements to national or global levels would introduce significant uncertainty. Still, the long-term data clearly show that, under certain conditions, forest soils can increase their methane absorption over time.
The study, published in Agricultural and Forest Meteorology, challenges the idea that methane consumption by soils is universally declining. Instead, it suggests a more complex picture in which warming, drying, forest structure, and soil properties interact in ways that can either weaken or strengthen this hidden climate service.
To reliably predict how forests will influence methane levels in the future, scientists say decades of consistent monitoring will be needed, especially in regions expected to become wetter. Until then, forest soils remain an underappreciated but potentially valuable ally in the fight against climate change.