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A new global analysis reveals a critical oversight in sustainable coffee and carbon-capture initiatives. These programs incentivize the planting of new trees yet fail to reward the preservation of mature shade trees in existing agroforestry farms, despite their far greater carbon storage potential.

According to new research from the Smithsonian's National Zoo and Conservation Biology Institute (NZCBI) and Smithsonian Tropical Research Institute (STRI), published today in the journal , more than twice as much carbon stands to be lost through the removal of non-coffee shade trees than might be gained through tree planting—even if every plantation-style coffee farm in the world planted new shade trees.

Globally, coffee farms cover more than 10 million hectares. Farming systems vary in intensity, from plantation-style monocultures to agroforestry systems with native trees that provide shade, wildlife habitat and carbon storage. Planting new shade trees is currently incentivized through carbon markets, which allow coffee farmers to sell carbon credits generated via tree planting. However, existing agroforestry systems are rapidly converting to monoculture plantations, releasing significant amounts of carbon into the atmosphere while destroying habitat.

Scientists from NZCBI and STRI identified a critical gap in current carbon markets, which compensate coffee farmers for planting new trees but not for protecting standing trees. This potentially creates an incentive to remove existing trees to plant new ones that store less carbon but would be eligible for carbon-credit payments.

"There is a lot of money behind planting trees on degraded coffee farms, yet there are basically no financial incentives, outside of the Smithsonian Bird Friendly certification, to protect standing shade trees," said NZCBI ecologist Ruth Bennett, senior author of the study and leader of Smithsonian Bird Friendly program, which offers a gold standard certification for coffee and cocoa farms that conserve high-quality habitat for wildlife.

"To be clear, planting shade trees on monoculture coffee farms is a positive step, but our findings show tree planting alone can't make up for what you lose when you remove mature shade trees."

The study, conducted in collaboration with The Nature Conservancy and CIRAD, also found carbon-focused tree planting efforts do not necessarily boost biodiversity. Carbon sequestration is optimized by maximizing tree density, while biodiversity benefits more from tree diversity.

"To protect nature and fight climate change, coffee companies need to focus on planting a diversity of the right trees, not just planting a high density of fast-growing trees that capture carbon," said Emily Pappo, the study's first author and a postdoctoral climate fellow at the Smithsonian.

Prior research demonstrated coffee farms that include a diverse mixture of shade trees harbor roughly four times more bird species than coffee monocultures. Such findings are at the heart of the Bird Friendly coffee certification criteria, which ensure farms maintain dense and diverse shade trees. This certification grants farmers access to specialty markets and enables them to set higher asking prices, rewarding them for conserving biodiversity.

Coffee farmers are facing economic pressure and reduced yields due to climate change, and some are responding by removing shade trees on their properties in hopes of producing more coffee, even though scientists believe shade trees may help producers adapt to climate change by assisting with temperature and moisture regulation. At the same time, some large coffee companies are investing millions in tree-planting efforts to meet their climate goals via carbon credits.

Researchers wanted to understand just how much carbon is stored in coffee farming landscapes and evaluate how carbon and biodiversity could change through tree planting or the removal of shade trees.

The researchers gathered data from 67 scientific studies conducted in coffee regions around the world. They examined farms across a spectrum—from bare "sun coffee" monocultures with no trees at all to complex agroforestry systems where coffee grows under a canopy of native forest trees.

The researchers compared the carbon stored in each type of farm, then applied these measurements to existing data on global coffee growing that shows 41% is grown in full sun, 35% with minimal shade and 24% under diverse tree cover. Finally, the team modeled what might happen under various scenarios—calculating the maximum possible carbon gains if every sun farm planted trees, and the potential losses if farms cut down existing shade trees.

The study estimated coffee farms currently store 482 million metric tons of carbon above ground. The modeled scenarios revealed that even if all sun coffee farms added shade trees, they would sequester only 82–87 million additional metric tons of carbon. In contrast, if all shade-grown coffee were converted to monocultures, 174–221 million metric tons of carbon could be released into the atmosphere.

These extreme scenarios expose a fundamental issue with current carbon-market incentives for coffee farms: Mature shade trees store more carbon than newly planted trees, yet only new trees are incentivized via carbon markets. Prioritizing tree-planting above conserving existing shade trees could undermine the effectiveness of the coffee industry's investments in climate solutions.

"If we don't prioritize biodiversity on carbon sequestration projects, it won't accidentally happen," Pappo said. "This means choosing a diverse suite of shade trees with the aim of conserving biodiversity."

To maximize the potential of coffee farming to fight climate change and boost biodiversity, the study authors call for creating carbon payment programs that reward protecting existing shade trees and ensuring these payments are accessible to small farms. For tree-planting efforts, researchers recommend explicitly prioritizing tree diversity in all planting initiatives to support biodiversity. Without these changes, global coffee agriculture may continue to lose carbon and biodiversity despite investments in tree planting.

Going forward, Smithsonian researchers are continuing to develop the Shade Catalog, a resource to help coffee farmers select shade trees that work well alongside coffee while providing benefits to wildlife and ecosystem services. Bird Friendly-affiliated researchers are also working on tools to help farmers find the balance between carbon storage, biodiversity and farm productivity.