The way different tree species are distributed in a forest affects their productivity, as biologists have found. Accordingly, trees generate more biomass and dismantle more carbon if the tree species are randomly mixed. In contrast, trees planted in blocks grow worse. The researchers therefore recommend planting as mixed up as possible during the afforestation trees or in rows of alternating species.
According to an evaluation of the Federal Statistical Office, German forests and their ecosystems recorded and bound around 14.3 million tons of carbon in 2021. This corresponds to around 52.5 million tons of carbon dioxide and thus about six percent of the annual CO2 emissions of Germany. Because of this effect as a climate stuff, afforestation is an important means of climate protection. But what type of reforestation and arrangement of the new trees is particularly effective?
Species distribution and productivity
A research team led by Rémy Beugnon from the German Center for Integrative Biodiversity Research (IDIV) has now examined how different planting strategies of different tree species in the forest affect their productivity and CO2 recording. For this purpose, the researchers created simulations based on data from field trials. To do this, they examined the leaf fall and the decomposition rate of 180 pairs of tree of different species at a forested test location near the city of Dexing in the southeast of China. In addition, they analyzed the carbon and nitrogen content of the leaves.
In addition, Bugnon and his team modeled different arrangements of different tree species in the event of a reforestation: planting the species in larger and smaller blocks, single and double series as well as in random arrangement. With the help of this data, the researchers then simulated how the spatial arrangement of the species affects the growth of the individual trees, the decomposition of the litter and other plant remains as well as their nitrogen and carbon cycles. They also compared the differences between plantings with two, four and eight tree species.
The more random, the better
It showed that trees that grew in random arrangement had an eleven percent higher biomass than those that were in rows or blocks. A more uniform distribution of the tree species and thus also the fallen leaves also had a positive effect on the utilization of nutrients and organic material. With greater spatial heterogeneity, more carbon can be broken down, as the examinations showed: While 36.5 percent of the carbon was broken down after nine months after nine months, it was 47.1 percent in random. “These changes increase the decomposition rates and thus increase the total amount of carbon and nitrogen that is processed by the ecosystem,” report Beugnon and his colleagues. The main thing was that the higher the number of tree species. Accordingly, it would be best if foresters mixed up tree species completely – and above all not in blocks.
This has been confirmed for a long time: “The knowledge from biodiversity research has been showing for decades that it is advantageous for productivity and carbon storage when different tree species are planted in mixed stocks,” explains Beugnon. “However, this approach is rarely implemented, which is largely due to the fact that there are no practical guidelines that take into account the constraints of the real forestry.” Because for foresters and forest owners, a mixed arrangement of different tree species is mostly cumbersome: species -rich forests are considered to be too expensive or even not practically incompatible. You can also make the wood harvest and thinning out of the forest.
Row planting as a compromise
The researchers therefore recommend a compromise: “A completely random planting design […] (is) the ideal scenario from an ecological point of view, but makes it difficult to management. An interesting compromise could be to plant trees in rows, which means that the forest function can be significantly improved compared to block designs, while forest management remains practical. ” In the future, Beugnon and his team want to review the simulations in long-term field experiments. Then the research recommendations for sustainable yet economic forests could issue.
Source: German Center for Integrative Biodiversity Research; Specialist articles: Nature Communications, DOI: 10.1038/S41467-025-61389-7
