Assessing the Soil Carbon Storage Potential of Texas Grasslands after 20 Years of Restoration
Grasslands act as carbon sinks, converting carbon dioxide (CO2) into soil organic carbon (SOC) that can be stored underground for decades to centuries. Habitat management incorporating prescribed fires can theoretically extend the carbon sequestration longevity of grassland soils to millennia through the formation of highly recalcitrant pyrogenic carbon (PyC). To evaluate the effects of fire management on SOC and PyC, I collected 30cm depth soil cores, partitioned into 10 cm segments, from seasonal burn, frequent mow, control, and old-growth plots, and before and immediately following a summer prescribed fire (n=6 per treatment) on managed grasslands at the LBJ Wildflower Center and City of Austin Water Quality Protection Land (WQPL) sites in Central Texas. Six cores were taken along established transects from 36 one-half hectare plots for a total 252 cores. Soils were separated by depth, pooled at the plot level, and analyzed for SOC, PyC, nitrate, ammonium, macronutrients, pH, cation exchange capacity, and carbon mineralization rates. PyC and SOC increased significantly (p-value < 0.05) between pre- and post-summer burn treatments producing an average of 3.8x10-4 (g cm-3) of PyC, a 7.29% increase, in a single burn. Soil incubation tests confirmed that higher PyC concentration was associated with lower CO2 total emissions. PyC was detected in all treatments, suggesting distribution beyond the pasture scale via wind and water erosion after formation as a possible mechanism. However, PyC correlated positively with organic matter (OM) (p-value < 0.01) and relative to OM, PyC concentrations were consistently higher on burned compared to unburned treatment plots (p-value < 0.01). My findings indicate that fire management has a significant effect on soil PyC and potentially the enhancement of long-term C storage in soils.
pyrogenic carbon, grassland, prescribed fire management, Central Texas
Foulkes, T. (2023). Assessing the soil carbon storage potential of Texas grasslands after 20 years of restoration (Unpublished thesis). Texas State University, San Marcos, Texas.