# Pyrogenic carbon contribution to tropical savanna soil carbon storage

## TL;DR

Fire-derived carbon significantly contributes to soil carbon storage in African savannas, especially in clay-rich, drier soils.

## Contribution

The study provides new empirical evidence on the role of pyrogenic carbon in tropical savanna soil carbon storage.

## Key findings

- Pyrogenic carbon constitutes an average of 14.08% of soil organic carbon in tropical savannas.
- Clay-rich soils in drier regions accumulate more pyrogenic carbon due to better preservation conditions.
- Fire frequency and grass biomass influence pyrogenic carbon stocks in savanna soils.

## Abstract

Savannas are fire-prone ecosystems that contribute substantially to global fire emissions, but these emissions may be partly offset by deposition of fire-derived, persistent pyrogenic carbon (PyC) in soils. Although estimates of PyC contributions to soil organic carbon (SOC) storage in savanna exist, factors driving its accumulation remain unclear due to limited measurements with consistent methods. To address this, we sampled 253 sites across tropical savannas in Kruger National Park, South Africa, spanning broad gradients in fire regimes, grass biomass, rainfall, and soil texture. Here we show, PyC measured with H2O2/HNO3 digestion contributed, on average, 14.08% (se = 0.36%, n = 253) of SOC in surface soils, with values up to 40%. While fire frequency and grass biomass influenced soil PyC stocks, savannas with higher clay content and lower rainfall – conditions favoring PyC preservation – tended to accumulate more. These results demonstrate PyC’s significant contribution to SOC storage and highlight environmental factors driving its accumulation in tropical savannas, providing an empirical basis for understanding fire’s role in the savanna carbon cycle.

This study shows that fire-derived pyrogenic carbon constitutes a substantial share of soil carbon in African savannas, with clay-rich soils in drier regions storing the most, highlighting fire’s key role in shaping the savanna carbon cycle at regional scales.