According to research published today in Science, a leading global peer-reviewed scientific journal, drought pressure may jeopardize the growth of tropical forests. The projections suggest that as climates get warmer and drier, this could impact the density of tropical rainforests.
In the global study, scientists studied tree rings from 483 tropical forests in Africa, Central and North America, and Southeast Asia to see how drought affects tree growth and how that might impact the ability for trees to store carbon long-term. The findings showed that, during the driest 10% of years since 1930, tree growth dropped by about 2.5%. In around a quarter of the cases, the drop was over 10%, especially in hotter, drier areas and for certain types of trees.
The study includes contributions from Dr. James Speer, Professor of Geography and Geology at Indiana State University’s College of Arts and Sciences, alongside an international team of researchers from North America, Africa, Europe, and Asia.
Dr. Speer has dedicated over 30 years to dendrochronology, the study of tree rings, to uncover historical climate patterns and ecological changes. His work focuses on sub-Saharan Africa, a region critical to global climate science yet vastly underrepresented in tree-ring records. Of the more than 5,000 records in the International Tree-Ring Data Bank, only five were from sub-Saharan Africa when the team began their research. Through their collaborative efforts, that number has now increased to 25.
Since 2021, Dr. Speer has helped launch and lead dendrochronology field schools in Zambia in partnership with Dr. Justine Ngoma, Lecturer and Researcher at Copperbelt University. These schools, now in their fifth year, train local students and scientists in tree-ring analysis and have played a key role in this research.
To support this research, Dr. Speer recently received a $319,165 grant from the National Science Foundation. This is part of a larger collaborative project totaling $550,000, in partnership with Dr. Matt Becker (Brigham Young University), Dr. Stockton Maxwell (Radford University), and Dr. Nicole Zampieri (Central Florida University). Together, the team is expanding their field school model and research capacity across the region.
“Sub-Saharan Africa holds vital climate records locked within its trees, yet it’s one of the least studied regions in dendrochronology,” said Dr. Speer. “Through this collaborative research, we’re not only expanding the global understanding of climate change but also building local capacity through education and collaboration. Working with such rich biodiversity is a fantastic opportunity to document ecological resilience over time.”
Dr. Melinda Roberts, Dean of Indiana State University’s College of Arts and Sciences added, “Dr. Speer’s work exemplifies the kind of globally relevant, high-impact research we are proud to support at Indiana State University. His dedication to advancing environmental science and mentoring the next generation of researchers embodies our mission to foster discovery that transcends borders and contributes meaningfully to our world.”
The study found that while drought can temporarily slow tree growth, tropical forests have typically rebounded in wetter years - showing resilience so far. But as global temperatures continue to rise, researchers caution this recovery may not last.
Looking ahead, Dr. Speer and his team aim to expand the project to other African countries, including Kenya and Botswana, to build a more complete network of climate data that can help predict future environmental change.