Methane (CH₄) is the second most important greenhouse gas after carbon dioxide, contributing approximately 20% of anthropogenic climate change. While public attention often focuses on emissions from agriculture and industry, there are also natural mechanisms that actively remove this gas from the atmosphere. The most important terrestrial methane sink is forest soils, in which specialized bacteria (methanotrophs) oxidize methane and convert it into less harmful substances.

New study published in the magazine Agricultural and Forest Meteorology brings surprising findings based on the previous the largest set of continuous methane flux measurements in the world. Scientists from the Forest Research Institute in Baden-Württemberg monitored 13 forest sites in southwestern Germany for up to 24 years.

Surprising increase in methane uptake

Long-term monitoring showed that the monitored forest soils are extremely active consumers of methane. The average absorption rate reached 1.40 ± 1.29 nmol m⁻² s⁻¹, with some locations measuring values significantly higher than the global average for the temperate zone.

The most significant finding, however, is long-term trend: methane absorption in these forests increased by an average of 3 % per year. This result is in direct contradiction to some recent global studies that have predicted a decline in this soil capacity due to climate change.

Why do forests "suck up" more methane?

The key to understanding this phenomenon is changing climate conditions at the local level. During the period studied, the scientists noted three main factors: decrease in annual precipitation, decrease in soil moisture and increase in soil temperatures.

Although drought is usually perceived negatively, it paradoxically has a positive effect on the methane absorption process. Drier soil contains more pores filled with air instead of water. This increases the so-called gas diffusivity – methane from the atmosphere can thus reach the bacteria in the soil faster and deeper, which decomposes it. Conversely, during periods of heavy rain, the pores fill with water, which blocks the transport of methane and can even lead to its production in wet layers.

Methodology and importance of long-term data

The research combined two measurement methods: analysis of soil gas concentration profiles and direct measurements using soil chambers. Thanks to an innovative model calibration approach (RCI-FGM), uncertainties associated with soil heterogeneity were eliminated and highly reliable data were obtained.

The study highlights that short-term measurements (often lasting only 1–2 years) can be misleading because methane uptake is subject to strong seasonal and interannual fluctuations. Only long-term data reveals the true impact of climate change.

What does this mean for the future?

The results suggest that the ability of forest soils to absorb methane is strongly dependent on regional precipitation patterns. If the trend of warming and drying out of the landscape in Central Europe continues, forests could play an even more important role as methane "scavengers" of the atmosphere than previously thought.

However, the authors of the study warn against being overly optimistic for the entire planet. In areas where precipitation increases due to climate change, the exact opposite effect may occur - weakening this important natural sink for greenhouse gases. This research clearly confirms that accurate climate models must take into account local specificities of soil moisture and precipitation, to be able to correctly predict the future development of the global climate. JRI&CO2AI