USGS and university scientists studied a 51-year fire experiment in oak savanna in Minnesota to evaluate long-term fire effects on soil carbon storage. Vegetation varied from closed-canopy forest in unburned plots to open-canopy savanna in frequently burned plots. Soil carbon peaked at intermediate fire frequency and declined in the most frequently burned plots, largely due to changes in carbon inputs from roots. Fire-induced changes in soil carbon more than doubled in measurements taken to 1-meter depth compared to the surface 0.2 meters of soil. These results highlight the important role of deep soil carbon in assessing how shifting fire regimes will alter total ecosystem carbon storage. 
 

Pellegrini, A.F., McLauchlan, K.K., Hobbie, S.E., Mack, M.C., Marcotte, A.L., Nelson, D.M., Perakis, S.S., Reich, P.B., Whittinghill, K., 2020, Frequent burning causes large losses of carbon from deep soil layers in a temperate savanna: Journal of Ecology, https://doi.org/10.1111/1365-2745.13351