Yale Researchers Map How Soil Fertility Controls Tropical Forest Productivity

Tropical forests anchor the global carbon cycle by storing roughly 50% to 60% of the world’s biomass carbon. Yet understanding how these vital ecosystems drive and protect that carbon remains one of ecology’s most persistent puzzles. Because these forests typically sit on highly weathered, nutrient-poor soils, scientists have long anticipated that soil fertility would directly dictate biomass carbon accumulation.

Michelle Wong and Global Scientists Target Soil Fertility Knowledge Gaps

To untangle these complex ecological dynamics, Yale Ecology and Evolutionary Biology (EEB) Assistant Professor and Yale Center for Natural Carbon Capture (YCNCC) Faculty Affiliate Michelle Wong served as first author on the study titled Soil fertility controls on tropical forest productivity and mortality: synthesis and roadmap, which was published on June 29, 2026, in New Phytologist. The project was based on research funded by the YCNCC.

The research initiative gathered more than 20 scientists from around the world who specialize in diverse tropical regions. By bringing this collaborative network together, the core workshop organizers sought to bridge a glaring disconnect in global forest research: while past studies show that soil fertility consistently boosts plant growth, it does not reliably increase overall biomass.

The process of developing the manuscript was highly collaborative. Because of the wide range of topics involved, the core workshop organizers wrote the initial drafts and utilized a series of Zoom meetings and rounds of feedback from the remaining co-authors.

Defining Soil Fertility Challenges in Complex Forest Ecosystems

The term soil fertility comes straight from agricultural science, where it describes the capacity for soil to sustain plant growth by supplying essential resources (i.e., nutrients). Translating that metric from a managed crop field to a complex, ancient forest, however, reveals stark limitations.

Agricultural testing accurately pinpoints which fertilizers and quantities support crop yields. Forest ecosystems operate under entirely different rules, featuring many more plant species that are much longer-lived, with varying nutrient demands. Furthermore, different elemental nutrients can limit growth simultaneously, and modern methodology still struggles to measure true nutrient availability to wild plants.

As YCNCC Science Communications Fellow Samantha Tracy outlined during a recent discussion with Wong, overall soil fertility offers reliable insight into agricultural health, but proving a direct application to forest health remains intensely challenging because the effects of soil fertility on forest growth and biomass are highly complex.

The Productivity-Mortality Paradox in Tropical Research

One of the primary driving motivations behind the collaborative New Phytologist roadmap was addressing an unresolved contradiction in tropical forestry data. While soil fertility reliably drives plant growth rates upward, its relationship with structural biomass is far murkier.

Compounding this mystery, some scientific literature indicates that tree mortality rates actually climb alongside increased soil fertility. Right now, researchers lack clear, universally accepted mechanisms to explain why higher fertility correlates with higher tree mortality.

Global environmental pressures add even more urgency to these questions. Rising atmospheric carbon dioxide, intensifying climate stress, and ongoing land-use changes continue to alter both local nutrient availability and overall forest responses in unpredictable ways.

A Collaborative Roadmap for Future Carbon Cycling Studies

Before scientists can model how global climate shifts will alter tropical carbon cycling via soil fertility feedbacks, the newly published roadmap argues that the field must first establish baseline definitions for soil fertility itself. The team realized that how they measure and define soil fertility is a huge hindrance to large-scale syntheses across the tropics, noting that you can't find a clear X-Y relationship when the X isn't clearly defined.

The international working group identified several priority knowledge gaps that researchers must tackle next. These include determining how soils directly influence tree mortality mechanisms, quantifying how much carbon forests allocate above-ground versus below-ground, and mapping how plant traits and species composition shift across natural soil gradients.

Because these ecological patterns remain highly context-dependent, the authors stress that future progress requires expanded scientific networks dedicated to measuring these variables consistently across multiple international sites.