Scientists have discovered that the ancient, natural forests of the Southern Western Ghats in India are far superior at locking away planet-warming carbon compared to the man-made teak plantations that often replace them. A new study published in the journal PLOS One reveals that while planting trees is often seen as a quick fix for the environment, the type of forest matters immensely for the health of our soil. 

Researchers from KSCSTE - Kerala Forest Research Institute (KFRI), Kerala, Purdue University, USA, Forest Research Institute (FRI), Uttarakhand, and Cochin University of Science and Technology (CUSAT), Kerala,  found that natural forests maintained substantially higher average soil organic carbon concentrations, about 16.61 grams per kilogram, compared to just 11.82 grams per kilogram in teak plantations. 

The team employed stratified random sampling across five ecological zones in Kerala. They collected soil samples from four distinct layers to a depth of 1 m. By analysing these samples for carbon content, acidity, and texture, they were able to build a 3D map of how carbon is stored underground. Soil is a massive carbon vault, storing three times more carbon than the atmosphere and all the world’s vegetation combined. When a diverse natural forest is cleared for a single-species plantation such as teak, the complex biological processes that sequester carbon in the soil are often disrupted.

The study found that in natural forests, the vast majority of carbon (over 70%) is stored in the top 30 centimetres of soil. However, as the researchers moved from natural wildlands to managed plantations, they noticed a significant drop in this storage capacity. One of the main reasons for this is soil acidity. The researchers observed that plantations often become more acidic over time due to the way teak trees shed their leaves and to soil management practices. This acidity makes it harder for the soil to hold onto carbon. Interestingly, the study found one exception: an older teak plantation that had been left undisturbed for over 50 years showed high carbon levels. This suggests that while natural forests are the gold standard, better management and longer growth cycles for plantations could help narrow the gap.

This study provides the first systematic, long-term comparison of soil carbon across the specific, varied landscapes of the Western Ghats. It provides a roadmap for how we should manage our land to fight climate change. It warns policymakers that simply greening an area with commercial plantations is insufficient to replace the complex carbon-storage capacity of an original, wild forest. By prioritising the protection of natural forests and improving how we manage plantations, we can ensure that the ground beneath us remains a powerful ally in stabilising the Earth's climate.