Forests With More Diverse Trees Capture More Carbon, Study Finds

The vast array of Earth’s plants and animals is what makes our world so exciting and beautiful. When it comes to forests, having a diversity of tree species comes with an added bonus that benefits the entire planet: a higher rate of carbon sequestration.

A new study has found that forests with greater tree diversity are more productive, which potentially means extra efficiency in capturing carbon from the atmosphere.

An international team of researchers has found that faster-growing trees that capture carbon more quickly tend to be on the smaller side and have shorter lifespans. This means they store less carbon and release it back into the atmosphere at a faster pace as well, a press release from University of Birmingham said.

On the other hand, trees that grow more slowly are larger, live longer and tend to capture more carbon, especially in an exceptionally diverse forest.

“At the community level, we find that more diverse forests, which include a wider mix of fast-growing short-lived and slow-growing long-lived species, sequester more carbon. This result suggests that more demographically diverse forests are better able to tap into a larger resource pool within a given environment (e.g., include tree species that acquire nutrients from different soil profiles), which minimizes direct competition for limited resources,” lead author of the study Dr. Lalasia Murphy, a lecturer in the department of environmental systems science at ETH Zurich, told EcoWatch in an email. “Alternatively, this emergent trend could be due to positive facilitation among species. Either way, this result emphasizes the importance of forest biodiversity.”

More specifically, certain types of trees have the ability to capture higher amounts of carbon than others.

“Forests with diverse tree species can capture carbon more effectively, meaning that promoting forest biodiversity in forests can help capture more carbon. Understanding how these factors are linked can guide restoration and conservation projects. By selecting the right mix of tree species, we may be able to maximize carbon storage and develop strategies that enhance forest resilience to climate change,” said co-author of the study Dr. Adriane Esquivel-Muelbert, a Birmingham-based researcher from Brazil, in the press release.

The research team analyzed 3.2 million tree measurements from 1,127 species growing in forests from northern Canada to southern Brazil, and mapped the life expectancies of trees that were from 1.3 to almost 3,200 years old.

“Slow-growing long-lived species capture carbon at slower rates but also store that carbon for substantially longer periods (100s to 1,000s of years). Keep in mind that species growth-longevity relationships have different implications than community-level trends,” Murphy told EcoWatch.

In the study, the researchers identified four primary types of tree life-cycles: three clusters of slow-growing tree species and those that are fast-growing but have shorter lifespans.

On one end of the growth cluster are species that have small maximum sizes and high life expectancies. On the other end are tree species with large maximum sizes and low life expectancies.

“Tree growth and lifespan trade-offs are crucial for the planet’s carbon balance. The positive relationship between trait diversity and productivity suggests that maintaining diverse forests is crucial for ecosystem health and climate change mitigation,” Esquivel-Muelbert said in the press release.

The team discovered that all four demographic functional types were found in tropical regions, while species located in non-tropical areas were part of two clusters of mostly slow-growing tree species. They found the mean life expectancy of the trees tended to be longer outside the tropics.

The research team mapped the life history traits of species across the Americas and found a strong correlation between tree growth and temperature, with cooler climates being associated with slower growth.

They also found that tropical forests exhibited higher diversity in comparison with boreal and temperate forests.

Murphy clarified why tropical forests have a higher diversity of tree species. “There are several possible explanations for this emergent pattern. Cold temperatures in the boreal regions likely constrain the range of strategies that can persist over evolutionary time, acting as an environmental filter that excludes fast-growing short-lived species. At the same time, more productive tropical forests are thought to have higher levels of competition among species. Theoretically, this should lead to strong selective pressures over evolutionary time, causing species to differentiate to avoid direct competition and coexist (e.g., adopt fast- and slow-growth strategies),” Murphy told EcoWatch. “Basically, we find a wider range of fast-growing short-lived species and slow-growing long-lived species in the tropics and a narrower range of predominantly slow-growing long-lived species in the boreal north.”

If they are not subjected to deforestation, wildfires or other interruptions to their life cycle, tropical forest tree species can have similar life spans to those in boreal forests. 

“In the absence of human disturbance, the oldest trees in tropical forests live as long as the oldest trees in boreal forests,” a press release from ETH Zurich said.

The study, “The pace of life for forest trees,” was published in the journal Science.

“This study provides a broad-scale assessment of tree life expectancy for species across the Americas, with estimates ranging from tens to thousands of years,” Murphy said in the press release. “These findings provide new insights that can be used to inform biodiversity conservation and climate change mitigation.”

To help make forests more diverse, Murphy suggested protecting remaining intact forests and supporting restoration efforts that “prioritize native biodiversity conservation.”

For the study, the scientists used the largest dynamic tree information dataset to date.

“Such large-scale analysis is only possible with large collaborative efforts involving hundreds of researchers monitoring these forests for many years,” said co-author of the findings Dr. Thomas Pugh, an environmental scientist who splits his time between Lund University and the University of Birmingham, in the press release.