Nutrient enrichment threatens tropical forests: study reveals dramatic impact of human activities

Tropical forests, often referred to as the 'lungs of the earth', are under pressure from deforestation or slash-and-burn agriculture and less visible threats such as nutrient enrichment. A recent study published in “Current Forestry Reports” is the first to systematically examine how inputs of nitrogen, phosphorus and potassium from human activities such as agriculture affect the growth and composition of these fragile ecosystems.

The international team of researchers - led by RPTU Kaiserslautern-Landau, the University of Applied Sciences and Arts Göttingen (HAWK) and the HUN-REN Centre for Ecological Research in Hungary - conducted a comprehensive meta-analysis of 59 studies. The results are alarming: the addition of nutrients significantly promotes the growth of tropical tree seedlings. On average, shoot biomass increased by 26 per cent and growth rates by 14 per cent. In particular, the combination of nitrogen (N), phosphorus (P) and potassium (K) had the most pronounced effects, increasing growth rates by up to 27 per cent. The effects were particularly strong in seasonally dry regions, where growth increased by up to 70 percent.

Growing threat from human activities

"Nitrogen, phosphorus and potassium are essential nutrients for plant growth. But many tropical soils are nutrient-poor," says Daisy Cárate Tandalla, a plant ecologist at RPTU. The additional nutrient input therefore disproportionately benefits fast-growing, competitive species and can permanently alter the composition of forests and their ability to store carbon.

The researchers emphasise that nutrient inputs from agriculture and fossil fuels far exceed natural deposition and reach even remote tropical forests. "These additional nutrients favour fast-growing, competitive tree species, which can drastically reduce forest biodiversity and weaken their resilience to climate change," warns Péter Batáry of the HUN-RUN Centre.

Diverse research on a global problem

The analysis highlights how tropical trees respond differently to nutrient inputs, depending on factors such as climate, soil and experimental methodology. "Our results show the complexity of the interactions and underline the critical importance of sustainable nutrient management," says Jürgen Homeier of HAWK.

The study calls for a global view of the impact of human activities on tropical ecosystems. This is the only way to protect the functions of tropical forests as a cornerstone of the global climate system in the long term.

The study:
Cárate Tandalla, D., Homeier, J. & Batáry, P. Responses of Tropical Tree Seedlings to Nutrient Addition: A Meta-analysis to understand future changes in Tropical Forest Dynamics. Curr. For. Rep. 11, 3 (2025). https://doi.org/10.1007/s40725-024-00240-6

Contact:
iES, Institut für Umweltwissenschaften
Daisy Cárate Tandalla
E-Mail: dcarate.tandalla[at]rptu.de