Limited increases in savanna carbon stocks over decades of fire suppression

Savannas cover a fifth of the land surface and contribute a third of terrestrial net primary production, accounting for three quarters of global area burned and over half of global fire-driven carbon emissions. Fire suppression and afforestation have been proposed as tools to increase carbon sequestration in these ecosystems. A robust quantification of whole-ecosystem carbon storage in savannas is lacking, however, especially under altered fire regimes. Here, we provide the first direct estimates of whole-ecosystem carbon response to over 60 years of fire exclusion in a mesic African savanna. We found that fire suppression increased whole-ecosystem carbon storage by only 35.4 ± 12% (mean ± standard error), even though tree cover increased by 78.9 ± 29.3%, corresponding to total gains of 23.0 ± 6.1 Mg C ha-1 at an average ~0.35 ± 0.09 Mg C ha-1 yr-1, more than an order of magnitude lower than previously assumed. Frequently burned savannas had substantial belowground carbon, especially in...