Nature's climate solutions: Mixed forests store more carbon

Forests are essential in sequestering carbon, a process that slows the rate of global warming. But when it comes to the ability to store carbon, not all forests are created equal.

A recent study has revealed that mixed forests with several different species of trees sequester much more carbon than those in which only a single species of tree is present.

The study, led by researchers at the University of Freiburg, offers robust evidence that mixed forests are more effective at sequestering carbon, and thus represent a key weapon in the fight against climate change.

Tropical tree diversity experiment

The research focused on data from the Sardinilla experiment in Panama, which was set up in 2001 and is the world’s longest-running tropical tree diversity experiment in the world.

Originally, pastureland was replanted with tree species. Today, forest growth can be compared on plots that were planted with one, two, three, or five different native tree species.

The forests have now become more mature and scientists can examine long-term trends. The researchers considered multiple carbon stocks in the plots, such as carbon within tree biomass, leaf litter, and mineral soil.

Tree diversity boosts carbon storage

The experts found that forests with five tree species had significantly higher carbon stocks above ground than those with only one species.

Mixed forests captured 57% more carbon in tree biomass when compared to monocultures. This confirms that planting different tree species leads to more carbon storage.

However, belowground carbon stocks and fluxes remained similar, regardless of species diversity.

A resilient carbon sink

The benefits of tree diversity did not fade over time. In fact, they became stronger, even as the forests faced extreme weather events.

The study period included a severe El Niño-driven drought and a hurricane, yet the mixed forests continued to outperform those composed of monocultures.

Study first author Dr. Florian Schnabel is a forest scientist at the University of Freiburg’s Faculty of Environment and Natural Resources.

“This is important, because in the face of climate change, the long-term carbon balance of forests will depend largely on their stability to disturbances. Diverse forests exhibit greater ecological stability and the risk that the stored carbon is released back to the atmosphere is lower than in monocultures,” said Dr. Schnabel.

Mixed forests and climate action

The study’s findings suggest that reforestation projects should prioritize mixed-species forests over monocultures in order to maximize carbon sequestration.

However, the researchers caution against overestimating the climate benefits of planting new forests.

Dr. Catherine Potvin from McGill University in Canada was head of the Sardinilla experiment until 2024, and helped to initiate the study.

“The average yearly net CO₂ uptake of the planted forests was 5.7 tonnes CO₂ equivalents per ha and year. It would thus need one-year tree growth on 11 ha of this type of forest to compensate for the emissions of a single one-way flight between Frankfurt and Panama City,” noted Dr. Potvin.

Embracing forest diversity

The research contributes to a growing collection of evidence that species diversity is central to climate resilience. Mixed forests not only take up more carbon, but also store it more consistently, even in the case of extreme weather events.

When governments and institutions start investing in climate mitigation strategies by planting trees, species diversity is key to making the effects exponentially more powerful.

By creating diverse forests, we can cultivate landscapes that have greater carbon sequestration potential, withstand environmental stress, and provide long-term returns to ecosystems and future generations.

Additional benefits of diverse forests

In addition to carbon storage, mixed forests offer crucial ecological benefits. They promote biodiversity, provide wildlife with food and shelter, and improve conditions for pollinators, seed dispersal agents, and natural pest suppression. These interactions enhance forest health and resilience.

Multispecies forests are also more resistant against disease and pests, as opposed to monocultures where all individuals may succumb to the same pest infestation, leading to heavy financial losses. By reducing this risk, mixed forests maintain long-term stability even under changing conditions.

Furthermore, diverse forests help regulate water, thus maintaining the soil moisture level, preventing soil erosion, and stabilizing environments. Their roots prevent landslides and protect freshwater systems that are vital to communities.

Prioritizing species diversity can lead to more resilient forests that safeguard both the environment and human well-being.

The full results of the study were published in the journal Global Change Biology.

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