Breadfruit’s low carbon storage could be offset by fast growth, study finds

On a hotter and hungrier planet, breadfruit is becoming a popular tree. It offers nutrient- and fiber-dense fruits that can feed a family and provide farming income, and with its long lifespan, it’s been heralded as a good way to remove carbon from the atmosphere and store it in trees, leaves and soil. But until recently, nobody had ever studied just how much carbon breadfruit trees could store.

In a recent study published in Sustainability, researchers from the University of Hawai‘i at Mānoa found that the breadfruit trees growing in orchards in Hawai‘i display low carbon storage compared with similar tree species.The authors attribute this to its lightweight wood, a favorite among Hawaiians for building surfboards and canoes. But that doesn’t mean breadfruit shouldn’t be part of tropical climate solutions.

“It’s easy to look at these results and say breadfruit doesn’t sequester that much carbon, but they offset that light [weight] wood with exceptional growth rates,” says co-author Noa Kekuewa Lincoln, an assistant professor of Indigenous crops and cropping systems at Mānoa.

The researchers measured its carbon storage by comparing its metabolic rate with its total body mass. But Lincoln says these equations miss an important element: time.

“When you look at those amalgamated equations … they’re just looking at the relationship between the size of the tree and how much carbon is stored,” Lincoln says. “The [equations] say nothing about: How long does it take for the tree to reach those sizes?”

Breadfruit can grow up to 4 feet per year, potentially allowing it to put away carbon much faster than other slow-growing trees. When compared with other agricultural products, Lincoln says breadfruit is a clear winner: Unlike crops that must be plowed up or cut down every year, breadfruit trees can live for 50 years or more, keeping all that carbon locked away.

Laura Roberts-Nkrumah, a professor of crop science and production at the University of the West Indies specializing in breadfruit, calls the new study an important first step for this under-studied species. But she says future studies should also measure breadfruit’s carbon storage in the hotter tropical regions where breadfruit evolved. She says she suspects that photosynthesis, and therefore CO₂ uptake, might be higher there than in subtropical Hawai‘i.

Roberts-Nkrumah also points out that the new study doesn’t account for carbon stored in the fruit itself, which could account for significant carbon removal if the fruit is collected and eaten.

“Breadfruit is a food crop species,” she says. “Any method of looking at carbon in a plant that does consider the carbon allocated to fruiting, in my view, underestimates how much carbon is really being taken up.”

Lincoln also notes that the carbon study in orchards is just the first step. His real goal is to figure out how much carbon breadfruit helps to store when planted in agroforestry plots, the traditional method of growing these trees. In agroforestry, breadfruit trees are the scaffolding that support a wide variety of other crops, from traditional produce such as tomatoes at the forest edge to shade-loving coffee or cacao underneath the trees themselves. These crops benefit from the water retention and fertilizer that breadfruit provides and give growers an additional source of food and income.

“We don’t at the end of the day want to promote breadfruit as an orchard crop; we want to look at it within diversified agriculture systems that realize multiple benefits,” Lincoln says.

However, agroforestry plots are much harder to study. “Whereas a monoculture of corn is the same everywhere — you’ve already limited the number of factors at play, one crop and one spacing — no two agroforestry systems are exactly the same,” he adds.

That doesn’t mean Lincoln isn’t going to try. During their research on breadfruit carbon storage, Lincoln and co-author Chad Livingston, a student at Mānoa, also began collecting data on how carbon levels differed based on the spacing of orchard trees. Though their data set was small, there was a clear pattern that trees spaced farther apart — allowing grasses and other plants to grow between them — had higher soil carbon. He is now seeking funding to continue studying this carbon sequestration in the more complex layers of agroforestry plots.

Agroforestry also captures another aspect of breadfruit that Roberts-Nkrumah thinks is important: Its value to people goes much further than just how much carbon it takes up.

“Sustainability is a goal that has to be met at various levels: household, community, environment, country,” she says. When grown in agroforestry plots, she says, breadfruit ticks several of these boxes: It provides food security to growers and food sovereignty to communities, creates a potential source of income in communities when processed into products such as flour, offers nutrient recycling for the ecosystem and creates habitat for animals.

“We cannot ignore those aspects of it when we think about planting breadfruit for carbon sequestration,” Roberts-Nkrumah says. “We have to balance these environmental needs with other aspects of sustainability, and that has to do with the well-being of producers and communities.”

Banner image: Breadfruit is a perennial tropical tree that produces large, carbohydrate-rich fruit. Image by Quang Nguyen Vinh via Pexels (Public domain).

Related audio from Mongabay’s podcast: A discussion of the breadth, history and potential of agroforestry, listen here:

See a related report about breadfruit:

Breadfruit: A starchy, delicious climate and biodiversity solution

Citation:

Livingston, C., & Lincoln, N. K. (2023). Determining allometry and carbon sequestration potential of breadfruit (Artocarpus altilis) as a climate-smart staple in Hawai‘i. Sustainability, 15(22), 15682. doi:10.3390/su152215682