Forests are an essential ally in combating climate change. Trees consume carbon dioxide in order to grow, pulling the gas out of the air and storing it in wood, bark and leaves. But when a tree dies and decomposes, that carbon is set free.

To forecast the level of greenhouse gases in the atmosphere, scientists must accurately model the rate at which forests store and release carbon. This requires understanding how fast tree species grow, how long they live, and what happens when they come together to form a forest.

To address those fundamental questions, an international team of nearly 120 researchers joined forces to build a massive dataset of life histories for trees in forests. Their study, published recently in Science, shows that the lives of trees are more complex than ecologists had thought. The findings could help improve both carbon forecasts and conservation strategies.

“One of the big compelling arguments for why we need to save biodiversity is because natural ecosystems store lots of carbon,” said ecologist Thomas Crowther, founder of the Crowther Lab at ETH Zürich in Switzerland and senior author on the study. “But in order to understand how they store carbon, the most important thing we need to understand is how long that carbon stays within ecosystems.”

The conventional wisdom in ecology is that most animals fall somewhere on the fast-slow continuum: Something can grow fast and die young, like a rat, or grow slow and die old, like a human.

“There’s a compromise of energy allocation to either surviving long, and therefore attaining longevity, or growing fast,” said ecologist Rob Salguero-Gómez at the University of Oxford in the U.K., who was not part of the research.

Scientists had wondered whether trees fall neatly on this same continuum. However, the long lives of trees, which often outlive generations of researchers, make it harder to study their lifespans than those of animals.

“For short-lived species, it’s a lot easier. Because they have short lifespans, you can track individuals and calculate average life expectancy,” said ecologist Lalasia Bialic-Murphy, the study’s first author and a lead scientist in the Crowther Lab.

Through years of collaboration, the research team compiled 3.2 million tree measurements—including rates of trunk growth, ages and mortality data—representing more than one thousand species. The records spanned South America and North America, ranging from warm tropical forests to cold boreal regions, and dating as far back as 1926.

“The paper includes a fascinating volume of data. It’s quite an unprecedented effort,” Salguero-Gómez said.

Instead of the expected fast-slow continuum, the team found four distinct “growth strategies”—how quickly a tree grows versus how long it lives. One group consisted of species that grew quickly but died young, such as the slender matchwood (Didymopanax morototoni) of Central and South America. The slow-growing trees, however, fell into three sub-groups with either short, medium, or long lifespans—like the ancient, auburn coast redwood (Sequoia sempervirens) of North America.

Lifespan differences among these slow-growing groups were sizable. Even the slow growers with the shortest lifespans lived an average 204 years. But the longest-lived trees grew for 1,724 years, on average.

“That has a pretty big implication for a species that grows at a similar pace, but holds that carbon for substantially longer periods of time,” Bialic-Murphy said.

The data also showed that forests with a more diverse mix of growth strategies are better at trapping carbon. A possible explanation, Bialic-Murphy said, is that species with different growth strategies don’t compete for the same resources. That leaves enough light, water, and nutrients for all of them to grow productively.

However, forest diversity is threatened: More than one-third of tree species face the risk of extinction, according to a recent IUCN announcement. That’s a critical factor for carbon storage in policy-making, Bialic-Murphy said.

A study of this size doesn’t come together overnight. “Building these mass collaborations is the most rewarding but the most challenging process,” said Crowther, who worked for nearly a decade to assemble and connect the global team. “But then, the real challenge is finding the wording and the context that satisfies everyone’s perspective.”

Citation:

• Bialic-Murphy, L., McElderry, R.M., Esquivel-Muelbert, A., van den Hoogen, J., Zuidema, P.A., Phillips O.L., … Crowther, T.W. (2024). The pace of life for forest trees. Science, 386(6717). doi:1126/science.adk9616

Collin Blinder is a graduate student in the Science Communication M.S. Program at the University of California, Santa Cruz. Other Mongabay stories produced by UCSC students can be found here.