Soil compensated as carbon store after loss of forest in Germany’s drought

Soil stored almost as much carbon as trees in German forests and even compensated for the negative effects from forest loss during the 2018-2020 drought, found an analysis by the Thünen research institute. 

While many trees in Germany's forests died during the dry years of 2018-2020 and thus ceased to function as carbon stores, the forest soil experienced a peak in carbon storage, the analysis said. In most cases, the areas were cleared, but in others deadwood remained on the ground, in addition to needles and leaves, as well as fine roots that had died in the soil. This abundant layer of litter was broken down by the higher solar radiation and the associated higher temperatures on the bare areas, allowing carbon to enter the soil.

The results caused the researchers to reassess how forests function under different conditions and how that might impact modelling in the future. “We now suspect that in dry years, trees tend to invest in root mass rather than leaf mass in order to better access the water in the soil,” said Nicole Wellbrock from the Thünen Institute. The analysis found that while living trees currently store 1,184 million tonnes of carbon, soils down to a depth of 30 centimetres contain 936 million tonnes of carbon. 

The shift from trees to soil has reversed somewhat after the drought years, reported news service Climate Table. By 2024, CO₂ storage in standing biomass increased again, while storage in the soil decreased. 

“The soil largely buffered the loss of trees as a CO₂ sink during these years,” Wellbrock told Climate Table. “But the effect was not complete and not long-term. We cannot give the all-clear regarding the current strain on the forest ecosystem in the acute climate crisis.”

Germany’s forests are needed to combat climate change, as they absorb CO2 from the atmosphere. They are also essential for climate adaptation efforts, to bring down temperatures in baking cities, boost biodiversity, and aid with rainwater drainage. However, a satellite imagery analysis of Germany’s forests published in September last year found that the tree population continues to decline “dramatically” in the country. More than 900,000 hectares of tree cover have been lost since the end of 2017, roughly equal to 8.5 percent of Germany's total forest area.