Researchers have carried out a large-scale inventory of German forests for the fourth time. According to the analysis, our forests are trending to become larger, wilder and home to more diverse inhabitants. There are also more older trees and more mixed forests. But because there are fewer trees in them due to weather and environmental damage, forests now store less CO2 from the air. As a result, in recent years they have even become a carbon source instead of a CO2 sink.
Every ten years, researchers commissioned by the federal government carry out an inventory of German forests. They check how the forest is doing and whether it is managed sustainably. In 2022, this Federal Forest Inventory (BWI) took place for the fourth time. The result is the most comprehensive inventory of German forests to date.
German forests are becoming wilder and more diverse
To do this, the researchers measured half a million trees and described the specific situation there at 80,000 locations in the forests. The list of forest characteristics examined includes almost 150 criteria, including, for example, the number, type and diameter of trees, but also what grows on the ground and how much dead wood is there. For the first time, they also collected samples to determine genetic diversity. The researchers then evaluate these samples in order to calculate the overall forest and timber development from the data.
The tree balance revealed both positive and negative developments in our forests. In some respects, they are in better condition today than they were ten years ago. For example, thanks to reforestation, there are around 15,000 hectares more forest area than in 2012. In total there are now 11.5 million hectares of forest – a third of the country. In addition, the forests are developing into mixed forests with more deciduous trees and fewer spruces. The forests are slowly becoming more natural again, i.e. wilder, and contain more old and therefore thicker trees. In 2022, the forest was on average 82 years old – five years older than in 2012. This also increased biodiversity because old trees offer more living space and nutrients for animals and microbes than young trees, as the authors report.
Mixed CO2 balance
But there are also negative developments: the forest has suffered so much since 2017 that, despite the larger area, there is now less wood in the forests. The reason: Many trees died due to storms, drought and infestation by pests such as bark beetles. Older trees also grow slower than young ones and there were not enough young, fast-growing trees. This means that forests can now absorb and store less carbon dioxide (CO2) from the air. They have therefore changed from a carbon sink to a carbon source in recent years.
The bottom line is that the carbon balance of German forests remains unchanged; In net terms, the forest has been almost CO2-neutral over the past ten years. “Roughly the same amount of carbon is currently stored in the living biomass in the forest as ten years ago,” says Thomas Riedel from the Thünen Institute for Forest Ecosystems in Eberswalde. Specifically, that’s 1,184 million tons of carbon, and together with dead wood and soil, that’s around 2,200 million tons. However, this is the result of two trends that almost cancel each other out: “By 2017, the amount of carbon stored had increased by 52 million tons. After that, however, the living biomass released 42 million tons of carbon into dead wood and wood products,” explains Riedel. Dead wood decomposes and releases carbon into the soil in the form of humus and into the atmosphere as CO2. As a result, our forests became a source of CO2 instead of a sink in the last five years of the measurement period.
Sources: Federal forest inventory 2022 / Johann Heinrich von Thünen Institute, Federal Research Institute for Rural Areas, Forests and Fisheries