Ecology: Assessing the carbon storage benefits of savanna conservation

Suppressing fires and planting trees in savannas may not lead to substantial increases in carbon storage over timescales of decades, according to a study published in Nature. The findings cast doubt over the benefits of increasing tree cover in savannas for climate-change mitigation.

Over half of global, fire-driven carbon emissions come from savannas. Increasing tree cover, by suppressing fires and planting trees, has been invoked as a strategy to reduce emissions by increasing carbon storage. However, long-term studies estimating carbon storage above and below the ground in this biome have been lacking.

Drawing on data from a 68-year-old burning experiment in Kruger National Park, South Africa, Yong Zhou, Carla Staver and colleagues compared plots of land burned annually with unburned plots and plots burned every three years. They estimated the amount of carbon stored in the soil and plants in each of the plots. The authors found that fire suppression increases total-ecosystem carbon storage in the study site, but only by about 0.35 tonnes of carbon per hectare per year — nearly 30 times less than the previous estimates.

In an accompanying News & Views article, Niall Hanan and Anthony Swemmer note that the experiments were conducted in a limited number of plots in the wettest part of the park, and that "similar studies in other regions are needed to further explore the role of fire suppression and tree planting in fire-prone savannahs."