Forests with a diversity of tree species have larger aboveground carbon storage and greater carbon fluxes compared to monocultures , according to an international study led by the University of Freiburg.
For the study, published in Global Change Biology, the researchers evaluated data from the world's longest-running experiment on the diversity of tropical tree species.
Forests with a diversity of tree species can sequester significantly more carbon than those consisting of only one species. An international study led by the University of Freiburg, published in Global Change Biology, confirms this with data from the world's oldest experiment on tropical tree diversity. The researchers were able to show that forests consisting of five tree species exhibit considerably larger aboveground carbon stores and greater aboveground carbon fluxes—that is, a greater exchange between carbon stores—than monocultures. The study highlights the advantages of species-rich mixed forests for reforestation and climate protection.
Numerous studies have already suggested that greater tree species diversity improves the ecosystem functions of forests , including carbon sequestration. However, previous studies struggled to distinguish this effect from other factors or focused solely on young stands. Therefore, it remained unclear whether the results were also applicable to older forests. To address this question, researchers analyzed data from the world's longest-running experiment on the diversity of tropical tree species. The Sardinilla Experiment in Panama was established in 2001 on a former pasture and comprises 22 experimental plots, each containing one, two, three, or five native tree species. Due to the rapid tree growth in the tropics, these plots already exhibit a comparatively advanced stand development. The team investigated various carbon stores and fluxes, from carbon in aboveground tree biomass and carbon in leaf litter to carbon in mineral soil.
Their studies revealed that forests with five tree species sequester significantly more aboveground carbon and exhibit greater aboveground carbon fluxes than monocultures. For example, the species-rich forests stored 57 percent more carbon in aboveground tree biomass. However, there were no significant differences in soil carbon fluxes and storage.
Remarkably, the positive effect of tree species diversity on aboveground carbon stores increased over time – even though the experiment was affected by extreme weather events such as a severe El Niño-induced drought and a hurricane. "This is a crucial factor because, in the face of climate change, the long-term carbon balance of forests depends heavily on their resilience to disturbances. Species-rich forests have greater ecological stability, and the risk of stored carbon being released back into the atmosphere is significantly lower than in monocultures," explains Dr. Florian Schnabel, a forest scientist at the Faculty of Environment and Natural Resources at the University of Freiburg, lead author of the study and director of the Sardinilla experiment.
The researchers emphasize that reforestation projects should prioritize mixed forests over monocultures for carbon storage. At the same time, they warn against overestimating the importance of newly planted forests in combating climate change. "The average annual net CO2 uptake of the planted forests was 5,7 tons of CO2 equivalents per hectare per year. To offset the emissions of a one-way flight from Frankfurt to Panama City, 11 hectares of this forest would have to grow for one year," says Dr. Catherine Potvin, former leader of the Sardinilla experiment and co-initiator of the study from McGill University in Montreal, Canada.
• Dr. Florian Schnabel is a forest scientist at the Faculty of Environment and Natural Resources at the University of Freiburg and director of the Sardinilla experiment. His research focuses on the relationships between biodiversity and ecosystem functions of forests, sustainable forest management in the face of global change, and the impacts of climate extremes on forests. He is an associate investigator of the Cluster of Excellence "Future Forests."
• The Sardinilla experiment is part of TreeDivNet, the world's largest network of tree biodiversity experiments.
original publication
Schnabel, F., Guillemot, J., Barry, KE, Brunn, M., Cesarz, S., Eisenhauer, N., Gebauer, T., Guerrero-Ramirez, NR, Handa, IT, Madsen, C., Mancilla, L., Monteza, J., Moore, T., Oelmann, Y., Scherer-Lorenzen, M., Schwendenmann, L., Wagner, A., Wirth, C., Potvin, C. (2025). Tree diversity increases carbon stocks and fluxes above- but not belowground in a tropical forest experiment. In: Global Change Biology. DOI: 10.1111/gcb.70089
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