Rubber plantations have long been a major cause of severe soil degradation in tropical regions, including Xishuangbanna in southwest China. In recent years, the expansion of balsa (a fast-growing lightweight wood) has raised new environmental concerns. A new study, however, suggests that the conversion from rubber to balsa may pose both risks and offer unexpected benefits.

The study, published in Agricultural Water Management, was conducted by researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences and their collaborators. It investigates how converting traditional rubber plantations to fast-growing balsa wood systems affects soil erosion dynamics.

The researchers found that balsa's large leaves and sparse canopy can intensify the initial splash of raindrops but that its root-driven soil properties dramatically increase water infiltration. This enhanced infiltration may reduce the need for soil conservation interventions compared to rubber systems.

To investigate these effects, the researchers compared splash erosion rates and their drivers across rubber monocultures, balsa monocultures of varying ages (two to four years), a mixed balsa plantation, and an open-field control. They monitored 14 rainfall events between August and October 2024, measuring throughfall, leaf drip characteristics, splash erosion, and soil infiltration across six plantation types. They used modified splash cups and bowls to quantify both potential and actual splash erosion, providing a comprehensive in-situ assessment.

The results showed that, although balsa monocultures experience significantly higher splash erosion than rubber plantations, their superior infiltration capacity effectively prevents surface runoff and large-scale soil loss. Specifically, splash erosion in balsa monocultures was 0.82 to 1.14 times higher than in rubber plots. Mixed balsa stands reduced splash erosion by 80.44% compared to monocultures. Balsa plantations also showed higher infiltration rates and higher saturated hydraulic conductivity than rubber systems. Despite high rainfall intensity, these hydrological gains decouple splash detachment from actual soil loss by minimizing runoff.

"While balsa monocultures may increase splash erosion potential, their enhanced infiltration capacity largely compensates for this risk, making soil conservation measures less critical than in rubber systems," said LIU Wenjie of XTBG. "Notably, integrating native species into balsa plantations offers a nature-based solution that balances productivity with soil protection."

The researchers noted that factors such as terrain slope and soil structure may still influence erosion risks in more complex landscapes. Nevertheless, they emphasized that the strong infiltration capacity of balsa-based systems provides an important buffer against water-driven soil loss and could inform future strategies for the sustainable management of tropical plantations.