Hospital stays among migrants in Austria much lower than among Austrians

Complexity Science Hub

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Hospitalization rate of cohorts with different countries of origin and ratio of readmission rate in the next year of each cohort and their (age, sex, region of residence, and month of hospital visit) matched cohort of Austrian patients – left: females (without pregnancy-related hospital stays), right: males. Countries in bold exhibit statistically significantly different readmission rates compared to matched Austrian counterparts. 

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Credit: © Complexity Science Hub

Researchers at the Complexity Science Hub (CSH) analyzed 13 million inpatient hospital stays involving around 4 million individuals in Austria: Although about 20% of the population in Austria does not hold Austrian citizenship, this group accounts for only 9.4% of hospital patients and 9.8% of total hospital nights.

An estimated 300 million people – about 3.6 percent of the global population – are international migrants. Yet studies consistently show that migrants access healthcare services less frequently than native populations. For example, a global analysis of data from 84 countries between 2018 and 2021 found that in only half of them do migrants have equal access to healthcare.

In Austria, where one in five residents is a migrant, the question of how migrants engage with the healthcare system is of particular urgency. It was also the starting point for a recent study conducted by researchers at CSH and the Medical University of Vienna, which was published in the Journal of Migration and Health.

"Reliable data on medical care for migrants can help identify access barriers and gaps in healthcare provision, improve quality of life, enable efficient resource planning, and shape stereotypical debates based on facts," says Elma Dervic, researcher at CSH and lead author of the study.

FEWER HOSPITAL STAYS

The researchers examined data on around 13 million hospital stays in Austria between 2015 and 2019. Their results show that people who live in Austria but do not hold Austrian citizenship have significantly lower hospitalization rates. This applies to all nationalities except German citizens, who record the most hospital stays per capita and whose usage patterns resemble those of Austrians – both in terms of the hospital departments they are admitted to and their primary and overall diagnoses. All other nationalities show clear differences.

For men, the hospitalization rate per capita is highest among Austrians (0.235), followed by Slovaks (0.229) and Italians (0.226). North Macedonians (0.125), Croatians (0.131), and Serbians (0.133) have the fewest hospital stays. The hospitalization rate reflects the likelihood that a person of a given nationality will be admitted to hospital within one year. For instance, the rate for Turkish women in 2019 was calculated by dividing the number of female Turkish patients by the number of female Turkish residents living in Austria.

For women (excluding pregnancy-related stays), Germans (0.223) have the most hospital stays – ahead of Syrian (0.209) and Austrian women (0.207). The hospitalization rate is lowest among Russian women (0.109), North Macedonian women (0.118), and Serbian women (0.126).

MORE READMISSIONS

While overall hospitalization rates are lower among migrants than Austrians, readmission rates (how often patients are readmitted to the hospital within one year) are higher. "This could indicate that people without Austrian citizenship go to the hospital later in the course of an illness," explains Dervic.

Among men, Syrians have the highest readmission rate – followed by Russians and Afghans. Only Hungarians have a significantly lower rate than Austrians.

Among women (excluding pregnancy-related stays), the readmission rate is highest for Afghan women – followed by Serbian, German, and Bulgarian women. It is lowest among North Macedonian women. However, Turkish, Italian, Hungarian, Romanian, Croatian, and Bosnian women also have readmission rates below those of Austrian women.

"HEALTHY MIGRANT" OR ACCESS BARRIERS

Readmission rates could be particularly revealing in order to gain insights into the healthcare of migrants - and to understand why they are hospitalized less frequently, according to the researchers.

Firstly, there is the so-called “Healthy Migrant Effect.” It refers to the idea that people who migrate to another country tend to be relatively healthy and often young – meaning they arrive in better health than the average population. “If this effect were the main reason for the lower hospitalization rates among migrants in Austria, we would also expect their readmission rates to be low,” explains Dervic. Moreover, the researchers controlled for age in their analysis, meaning they compared only individuals within the same age groups.

Secondly, however, if access barriers (such as language or cultural barriers) play a role in the lower hospitalization rates, migrants might still suffer from significant health issues but avoid hospitals until much later. This would then result in higher readmission rates, as illnesses are more advanced at the time of the initial hospital visit.

For example, people from Hungary, Romania and – in the case of women – Turkey show lower readmission rates, which might be consistent with the “Healthy Migrant Effect.” Patients from Russia, Serbia and – in the case of men – Turkey show higher readmission rates, which is more indicative of barriers to access.

MEN LESS LIKELY TO BE HOSPITALIZED

Male patients of all nationalities have lower hospitalization rates than women of the same nationality. For certain nationalities, the differences are particularly pronounced: 32% more Turkish women than Turkish men were admitted to the hospital, 26% more among Germans, and 28% more Serbian women than Serbian men.

DIFFERENT DIAGNOSES

When comparing initial admissions, clear differences emerged between Austrian and non-Austrian patients. For example, non-Austrians were admitted less frequently to general and vascular surgery, but more frequently to internal medicine departments (including cardiology and nephrology), hematology, oncology, and radiology – which could be a sign that these people more often suffer from chronic or severe illnesses, according to the researchers. Additionally, psychiatric diagnoses were made less frequently among non-Austrians. This suggests that mental illnesses are underdiagnosed among migrants," explains Peter Klimek from CSH and MedUni Vienna. All of these differences were substantially smaller among patients with German citizenship.

“Our study shows that the different use of the Austrian healthcare system by people of different nationalities cannot be explained solely by the ”Healthy Migrant Effect” or cultural barriers,” says Klimek. "Rather, the use of the healthcare system by migrant population groups must be differentiated by nationality, as there are obviously different patterns of use in different groups. Future measures should specifically facilitate access - especially to outpatient care - for example through better translation services or orientation aids in the healthcare system."

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ABOUT THE STUDY

The study "Healthcare Utilization Patterns Among Migrant Populations: Increased Readmissions Suggest Poorer Access. A Population-Wide Retrospective Cohort Study" by Elma Dervic, Ola Ali, Carola Deischinger, Rafael Prieto-Curiel, Rainer Stütz, Ellenor Mittendorfer-Rutz and Peter Klimek was recently published in Journal of Migration and Health (doi: 10.1016/j.jmh.2025.100340).

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ABOUT THE COMPLEXITY SCIENCE HUB

The Complexity Science Hub (CSH) is Europe’s research center for the study of complex systems. We derive meaning from data from a range of disciplines – economics, medicine, ecology, and the social sciences – as a basis for actionable solutions for a better world. 

CSH members are Austrian Institute of Technology (AIT), BOKU University, Central European University (CEU), Graz University of Technology, Interdisciplinary Transformation University Austria (IT:U), Medical University of Vienna, TU Wien, University of Continuing Education Krems, Vetmeduni Vienna, Vienna University of Economics and Business, and Austrian Economic Chambers (WKO).

csh.ac.at

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Journal

Journal of Migration and Health

DOI

10.1016/j.jmh.2025.100340 

Method of Research

Data/statistical analysis

Subject of Research

People

Article Title

Healthcare utilization patterns among migrant populations: Increased readmissions suggest poorer access. A population-wide retrospective cohort study

Article Publication Date

20-Aug-2025

 

How chefs and scientists are using kombucha and kimchi to study microbiology

North Carolina State University

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Scientists and chefs have collaborated on a new study that demonstrates how fermented foods can be used to drive participatory science projects that both engage the public and advance our understanding of microbial ecology. The study focused on working with food experts and the public to examine the microbial communities associated with kombucha, kimchi and chow chow. This photo shows a study participant preparing a jar of kimchi.

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Credit: Lauren Nichols.

Scientists and chefs have collaborated on a new study that demonstrates how fermented foods can be used to drive participatory science projects that both engage the public and advance our understanding of microbial ecology. The study focused on working with food experts and the public to examine the microbial communities associated with kombucha, kimchi and chow chow.

“One of the things we demonstrated here is that this approach works, it’s relatively inexpensive, and it is easy to scale,” says Erin McKenney, co-lead author of a paper on the work and an assistant professor of applied ecology at North Carolina State University.

“This proof-of-concept study focused on questions that have been answered using conventional approaches, allowing us to determine that the findings from our approach are consistent with established findings,” McKenney says. “But now that we have that proof of concept, we can begin using this technique to address additional questions.”

For the study, the researchers hosted three participatory science workshops at the North Carolina Museum of Natural Sciences in which scientists and chefs instructed K-12 teachers and members of the public on how to make fermented foods. Each workshop focused on a specific fermented food: kimchi, chow chow and kombucha.

While workshop participation varied, the researchers ended up with 18-23 samples of each fermented product.

Liquid samples were taken from each of the fermented foods at different points, to see how the microbial communities in each sample changed as the fermentation progressed. Samples were taken from chow chow and kimchi on days 3 and 10; kombucha samples were taken on days 4 and 8.

The researchers conducted DNA sequencing of each sample to get a snapshot of both the diversity and overall abundance of microbes in the sample.

“The findings were interesting,” says Hanna Berman, co-lead author of the paper and a postdoctoral researcher at NC State. “For example, we found kimchi made with cabbage fosters very different microbial communities compared to kimchi made with daikon radishes. In kombucha, on the other hand, there were no microbial species associated specifically with green tea versus black tea – which come from the same species of plant but are processed differently.

“These findings are in line with previous studies, and it was exciting to see that we were able to answer scientific questions accurately using methods that are also effective at engaging the public,” Berman says.

“The whole concept of helping people understand the diversity of microbes and microbial ecosystems is important,” says Christina Roche, co-lead author of the paper and a researcher at both the North Carolina Museum of Natural Sciences and NC State. “It’s also important to help people understand the beneficial roles that microbes play in our food systems. And we think there is very real value in scientists and chefs coming together to give people tools that can help them explore those ideas on their own and, as an added bonus, produce delicious food.”

“Developing techniques that both advance our scientific understanding of the world and engage the public in scientific endeavors is critical to the mission of both science museums and land-grant universities,” says McKenney. “That makes this work particularly rewarding for everyone involved in this project.”

“We included the recipes that were used for the study in the paper, so if anyone wants to try their hand at making chow chow, kombucha or kimchi, that could serve as a good starting point,” says Roche.

The paper, “Cooking-Class Style Fermentation as a Context for Co-created Science and Engagement,” is published open access in the journal Microbiology Spectrum. Corresponding author of the paper is Rob Dunn, William Neal Reynolds Distinguished Professor of Applied Ecology at NC State. The paper was co-authored by Sarah Michalski of Southern Peak Brewery; Soo Hee Kwon, an unaffiliated expert in making kimchi; Elizabeth Weichel and Amanda Matson of the Piedmont Picnic Project; Lauren Nichols of Duke University; Samuel Alvarado of NC State and the University of West Florida; and Julie Horvath of the University of North Carolina at Chapel Hill, NC State, and the North Carolina Museum of Natural Sciences.

This work was done with support from the National Science Foundation under grant 1319293.

Scientists and chefs have collaborated on a new study that demonstrates how fermented foods can be used to drive participatory science projects that both engage the public and advance our understanding of microbial ecology. This photo shows several jars of kimchi produced as part of the study.

Credit

Lauren Nichols.

Journal

Microbiology Spectrum

DOI

10.1128/spectrum.02660-24 

Method of Research

Observational study

Subject of Research

Not applicable

Article Title

Cooking-Class Style Fermentation as a Context for Co-created Science and Engagement

Article Publication Date

15-Aug-2025

 

Global study warns hepatitis B care must be overhauled to meet WHO 2030 elimination targets

University of Liverpool

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The first global systematic review and meta-analysis of hepatitis B care has found critical patient losses at every step of care, calling for decentralised, integrated models to improve diagnosis, treatment, and patient retention.

Published in The Lancet Gastroenterology & Hepatology, the findings reveal that current hepatitis B service delivery models are failing to keep patients engaged in lifelong care — threatening the world’s ability to meet the World Health Organisation (WHO) 2030 hepatitis B elimination goals.

The WHO-commissioned review was conducted by researchers from the University of Liverpool and Imperial College London in collaboration with colleagues from The Gambia, India, the Philippines, the USA, and Vietnam. It analysed data from more than 1.7 million people with chronic hepatitis B across 50 countries and found significant drop-offs in diagnosis, treatment initiation, and long-term retention, even in the best-performing systems.

Key findings of the review show that:

• Specialist-led hospital care achieved the best results but still showed major gaps: fewer than 75% of patients were assessed for treatment eligibility; of those eligible, only 78% began therapy. Retention plummeted among those not receiving treatment.
• Primary care, co-managed care, and passive referral models fared worse, with lower rates of assessment, initiation of care, and retention once in care.
• Postpartum care for women diagnosed during antenatal care had particularly low follow-up rates.
• Community screening with active linkage to specialist care achieved high treatment initiation rates for eligible patients.

Lead author Dr Alexander Stockdale from the University of Liverpool, said: “This is the first global review to map our progress across the hepatitis B care pathway. Without urgent changes, millions will miss out on lifesaving treatment. Many patients are not being fully assessed or being started on antivirals when they could benefit, and far too many are lost to follow-up over time. Strengthening primary care in low- and middle-income countries is essential to prevent hepatitis B-related deaths — already estimated at 1.1 million in 2022.”

Senior author Professor Philippa Easterbrook (Imperial College London; formerly WHO Global Hepatitis Programme) added: “WHO’s 2024 guidelines were a major step forward, expanding treatment eligibility to nearly half of all people living with chronic hepatitis B. But simplifying criteria alone is not enough. Too many still lack access to services, and even where clinics exist, patients often fall through the cracks.

“We need simple, decentralised models — integrating hepatitis B into primary care or existing HIV and chronic disease services. The HIV response has proven that streamlined care can achieve over 90% diagnosis, treatment initiation, and retention. It’s time we applied those lessons to hepatitis B.”

Professor Easterbrook added: “An integrated approach is even more pressing given the recent reductions in funding through USAID and the US President’s Emergency Plan for AIDS Relief (PEPFAR) for health programmes in LMICs”

The researchers have made the following recommendations:

• Decentralise care into primary health facilities and integrate with HIV/non-communicable disease (NCD) clinics.
• Remove financial barriers by eliminating out-of-pocket costs for testing and treatment.
• Accelerate access through same-day assessment and treatment initiation.
• Improve long-term engagement using adherence and retention strategies from HIV care programmes.

Click here to read the full review. 

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Journal

The Lancet Gastroenterology & Hepatology

Method of Research

Meta-analysis

Subject of Research

People

New antibody therapy shows promise in reducing Zika virus in reproductive tissues

University of Alabama at Birmingham

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A new study from the University of Alabama at Birmingham reveals that an antibody originally designed to fight dengue virus may also block the spread of Zika virus in vulnerable areas of the body — including the reproductive organs. The findings, published today in the Journal of Virology, offer new hope in the fight against a virus that has affected more than 80 countries since 2007 and poses serious risks to pregnant women and their babies.

What makes Zika especially dangerous is its ability to hide in protected areas of the body, including the brain, eyes and reproductive organs, where it can linger undetected. Even more troubling, Zika can be passed through sex or from a pregnant mother to her baby, potentially leading to severe birth defects.

In this new study, led by J. Victor Garcia, Ph.D., and Angela Wahl, Ph.D., in the Department of Microbiology at UAB, scientists tested the effectiveness of the C10 dengue virus antibody using a novel preclinical in vivo model. They found that a single dose of C10 administered before Zika virus exposure:

• Significantly suppressed viral replication in blood and tissues
• Prevented viral shedding in saliva and reproductive secretions
• Reduced viral levels in the brain, eyes and reproductive organs
• Improved survival rates in preclinical models

“Our work lays the foundation for deploying passive immunization strategies in high-risk populations,” Garcia said. “This could be a game-changer in outbreak response, especially in regions where Zika is endemic or resurging.”

Researchers evaluated the antiviral compound DFMA (7-deaza-2’-C-methyladenosine), which significantly reduced viremia and prolonged survival in a preclinical model.

“This study provides compelling evidence that antibody-based therapies can be used to reduce systemic infection and target the very tissues where Zika hides and causes the most damage,” Wahl said. “This is especially important for protecting pregnant individuals and preventing sexual transmission during future outbreaks.”

Currently, there are no approved treatments for Zika virus. This research marks a significant step toward developing effective countermeasures against future outbreaks.

Other collaborating institutions in this study include the University of North Carolina at Chapel Hill and Emory University.

Funding for this study was provided by the National Institutes of Health grant AI106695 (R.S.B.).

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Journal

Journal of Virology

Article Title

Envelope-dimer epitope 1 (EDE1) antibody (C10) treatment significantly reduces Zika virus replication in the male and female reproductive tracts

Article Publication Date

18-Aug-2025

Study reveals how HPV reprograms immune cells to help cancer grow

Using animal models, researchers from the USC Norris Comprehensive Cancer Center at the Keck School of Medicine of USC uncovered how cervical and throat cancers linked to the human papillomavirus evade the immune system, opening the door to new treatment

Keck School of Medicine of USC

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The most common cancer-causing strain of human papillomavirus (HPV), HPV16, undermines the body’s defenses by reprogramming immune cells surrounding the tumor, according to new research from the Keck School of Medicine of USC. In mice, blocking this process boosted the ability of experimental treatments for HPV to eliminate cancer cells. The results were just published in the Journal for ImmunoTherapy of Cancer.

HPV16 causes more than half of cervical cancer cases and roughly 90% of HPV-linked throat cancers. It can be neutralized with the preventive vaccine Gardasil-9, but only if vaccination occurs prior to HPV exposure.

Researchers are now working to develop “therapeutic vaccines,” which can be taken after HPV exposure—for instance, following an abnormal pap smear or cancer diagnosis—to trigger an immune response against infected cells by T-cells, a type of “fighter” cell that helps defend the body from disease. But these vaccines, now in clinical trials, have limited effectiveness—and the new study helps explain why.

The research, funded in part by the National Institutes of Health, focuses on a signaling protein in the immune system with inflammatory properties called Interleukin-23 or IL-23. While IL-23 was previously implicated in cervical and throat cancers, its exact role was unclear. In a series of tests in mice and cell cultures, USC researchers found that two HPV proteins, E6 and E7, prompt nearby cells to release IL-23, which in turns prevents the body’s T-cells from attacking the tumor.

“In order to eliminate the cancer, T-cells need to proliferate and destroy infected cells. But IL-23 stops them from working effectively, so the tumor keeps growing,” said the study’s senior author, W. Martin Kast, PhD, professor of molecular microbiology & immunology, obstetrics & gynecology, and otolaryngology and Walter A. Richter Cancer Research Chair at the Keck School of Medicine.

Kast and his colleagues found that blocking IL-23 made an HPV therapeutic vaccine more effective because it let T-cells do their job: find and kill cancer. Antibodies that inhibit IL-23 are already FDA-approved for treating psoriasis and other conditions, offering a clear and potentially quick path to use in cancer treatment when they are combined with therapeutic vaccines.

“The fact that these antibodies are already FDA-approved for something else makes this approach promising—and it also allows for rapid translation into the clinic,” said Kast, who also co-leads the Tumor Microenvironment Program at the USC Norris Comprehensive Cancer Center.

The role of IL-23

Researchers used a combination of cell cultures, mouse studies and genomic analyses to uncover IL-23’s role in cancers caused by HPV16.

First, they implanted mice with HPV16 tumors, then delivered a therapeutic vaccine that caused the mice to develop specialized T-cells for fighting the tumor. They extracted these T-cells, then combined them with IL-23. When IL-23 was present, the T-cells had reduced capacity to multiply and destroy cancerous cells.

The researchers then gave IL-23 neutralizing antibodies to mice with HPV16 tumors. Blocking IL-23 increased the number of T-cells around the tumor that could recognize and kill cancer. When combined with the HPV therapeutic vaccine, this approach triggered a stronger immune response and led to longer survival than either treatment on its own.

Researchers also analyzed the RNA and chromatin (the DNA and proteins that control gene activity) of tumor cells to reveal precisely how HPV’s E6 and E7 proteins increase IL-23 production. Understanding the biological mechanism is a key step toward better treatments for HPV-linked cancers, Kast said.

New strategies for treatment

The study offers insight into why therapeutic vaccines for HPV, now in clinical trials, have had limited success.

“Therapeutic vaccines do prompt the immune system to create HPV-specific T-cells, but they don’t work well—and now we have an idea why,” Kast said.

Combining experimental vaccines with IL-23 neutralizing antibodies could significantly increase their effectiveness, he added. He and his team are now developing their own therapeutic vaccine, which they will test in combination with antibodies that block IL-23.

The findings may have implications for cancers not related to HPV, such as testicular and bladder cancers, where IL-23 is also found at high levels. Further research is needed to clarify what role IL-23 plays in those diseases, the researchers said.

About this research

In addition to Kast, the study’s other authors are Ruben Prins, Daniel Fernandez and Omid Akbari from the Department of Molecular Microbiology and Immunology and the USC Norris Comprehensive Cancer Center, Keck School of Medicine of USC, University of Southern California; and Diane Da Silva from the Department of Obstetrics & Gynecology and the USC Norris Comprehensive Cancer Center, Keck School of Medicine of USC, University of Southern California.

This work was supported by the National Institutes of Health [R01 CA074397], the American Association of Immunologists, R.F. Brennan, S. Bloch and I.Y. Khandros.

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Journal

Journal for ImmunoTherapy of Cancer

DOI

10.1136/jitc-2025-011915 

Method of Research

Experimental study

Subject of Research

Animals

Article Title

HPV16 E6 AND E7 EXPRESSING CANCER CELLS SUPPRESS THE ANTI-TUMOR IMMUNE RESPONSE BY UPREGULATING KLF2 MEDIATED IL-23 EXPRESSION IN MACROPHAGES

Article Publication Date

19-Aug-2025

Smithsonian study reveals carbon markets undervalue shade-grown coffee farms

Existing shade trees on coffee farms store more carbon than tree-planting projects can sequester

Smithsonian

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The diversity of trees on shade-grown coffee farms makes them a haven for biodiversity.  

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Credit: Roshan Patel, Smithsonian’s National Zoo and Conservation Biology Institute.

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 Communications Earth & Environment, 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.

Tree canopy on shade-grown coffee farms helps mitigate impacts of climate change by lowering ground temperatures and maintaining moisture levels. 

Credit

Roshan Patel, Smithsonian’s National Zoo and Conservation Biology Institute.

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Journal

Communications Earth & Environment

DOI

10.1038/s43247-025-02574-w 

Method of Research

Literature review

Subject of Research

Not applicable

Article Title

Carbon payment strategies in coffee agroforests shape climate and biodiversity outcomes

Article Publication Date

19-Aug-2025