Tree diversity increases carbon sequestration

According to new research published in Global Change Biology, the world’s oldest experiment in tropical tree diversity provides compelling evidence that forests with multiple tree species are more carbon than single-species plantations capture.

The study, led by scientists from the University of Freiburg, found that after 16 years of growth, forests planted with five native tree species were 57% higher than single cultures, even though they experienced severe drought during observation and hurricane.

These findings arrive at a critical time, with global investment in forest restoration being a natural-based solution to climate change, with current global initiatives aiming to restore 350 million hectares of forest by 2030.

“This is important because the long-term carbon balance of forests will depend to a large extent on their stability to interference in the face of climate change. Diversified forests show greater ecological stability and the stored carbon is released The risk of returning to the atmosphere is lower than that of a single culture. Resources.

16 years of tropical forest growth

The team collected data from the Sardinilla experiment in Panama, where in 2001, scientists planted a combination of 22 species with different native tree species on previous pastures in 2001. The experimental site has plots of one, two, three or five trees, creating a controlled environment to isolate tree diversity from other variables.

This study is particularly valuable for its 16-year period. Although previous studies have proposed the benefits of tree diversity, most studies have examined young forests or are unable to separate the diversity impact from other environmental factors.

The researchers measured ten different carbon-related variables, tracking how carbon moves in forest ecosystems above and below. This comprehensive approach allows them to not only check the amount of carbon storage, but also the carbon flow between different forest components, including tree biomass, leaf waste, rough woody debris and soil.

After 16 years, the average carbon content per hectare of experimental forests in trees was 35.9 tons, while the carbon content per hectare of about 11.2 tons per hectare from the soil was obtained, resulting in a net carbon of 24.7 hectares.

Diversity effect strengthens over time

A key finding is that five species forest plots store 35.7 tons of carbon in the above-ground tree biomass, while only 22.8 tons in the single species plots – an increase of 57%. The researchers also found that the leaves were produced 64% higher than monocultured forests.

Perhaps most importantly, despite the extreme climates of the forest, including El Nino-driven drought in 2015 and Hurricane Otto in 2016. These positive diversity effects remain. The benefits of diversity actually enhance the growth of trees on the ground.

“We observed a significant increase in overground carbon stocks driven by overground carbon diversity,” Dr. Schnabel noted. “Our structural equation modeling shows that higher tree growth in the mixture enhances leaf waste and rough wood debris carbon flux to the soil, resulting in a tightly connected carbon cycle on the ground.

Interestingly, despite the fact that the diversity of trees significantly improved the above-ground carbon storage, the researchers found that the ground had no similar benefits. During the study period, soil organic carbon showed a net decrease in all levels of diversity, with no significant differences between plots and single cultures.

Impact on forest restoration

These findings have direct implications for global forest restoration projects. Much of the current afforestation work focuses on single species plantations, often using non-native trees. This study shows that using a mixture of native trees will bring greater climatic benefits while potentially providing higher biodiversity value.

Despite the obvious advantages of various forests in carbon sequestration, researchers warned against overestimating the climate mitigation potential of afforestation.

“The average annual net CO2 absorption of planted forests is 5.7 tons of CO2 equivalent per hectare and year. Therefore, this will require 11 hectares of tree growth in this type of forest to make up for Frankfurt and Emissions from a one-way flight between Panama City. The study was initiated and the Sardinilla experiment was led until 2024.

Find the right balance

Researchers stress that forest restoration plans must be carefully designed to avoid competing with agricultural land needs or to replace other natural ecosystems (such as grasslands). According to their paper, feasible solutions are provided for degraded lands suitable for forest growth.

For those who keep in mind forest restoration projects with climate goals, the message is clear: not only does hybrid cultivation surpass single cultures in terms of carbon storage, but also resilient to climate extremes and biodiversity benefits.

As Dr. Schnabel notes, “As we show here, mixed-grown forests as a nature-based solution not only enhance carbon reserves and flux, but also reduce restoration. The sensitivity of forests to stress and interference and, as well, also reduces, thus increasing carbon durability while also providing higher levels of biodiversity and broader ecosystem services.”

This study is part of Treedivnet, the world’s largest experimental network for tree diversity, and represents an important contribution to understanding how forest composition affects climate mitigation potential. As countries and organizations invest billions of dollars in forest restoration, the study shows that maximizing tree diversity should be a key consideration in achieving the best climate benefit.