Soil carbon sequestration across a chronosequence of tallgrass prairie restorations in the Ozark Highlands region of northwest Arkansas

Prairie restoration studies and research conducted in native prairie systems have been mostly centered in the Great Plains region of the United States and little research has been pursued in Arkansas to further understand the soil carbon (C) sequestration potential over time of remnant prairie sites and prairie restorations. The objective of this study was to evaluate the effects of restoration age and soil moisture regime on near-surface soil C and other soil property changes over time in a chronosequence of humid-temperate tallgrass prairie restorations (i.e., 15, 16, 17, and 38 yr) in the Ozark Highlands region of northwest Arkansas. A nearby undisturbed, native prairie was also studied for comparison as a baseline. Soil samples were collected from the top 10 cm in 2005 and 2017 and the change over time was assessed for soil bulk density, pH, electrical conductivity, soil organic matter (SOM), total C (TC), total nitrogen (TN), and the fraction of TC and TN in SOM. Soil property magnitudes from the 2017 sampling only were also compared among sites to evaluate the current state of the restorations. Soil properties within the restorations generally behaved as expected, with beneficial decreases in soil BD and increases in SOM, TC, TN, and TC and TN fractions of SOM occurring over time as restoration age increased and tended towards that in the native prairie. The direct measurement of change in total C content over time differed (P = 0.03) between soil moisture regimes among ecosystems, where the greatest soil C sequestration rate of 0.6 Mg C ha(-1) yr(-1) was recorded in the native prairie in the aquic soil moisture regime, while soil C sequestration rates ranged from -0.21 to 0.12 Mg C ha(-1) yr(-1) across the four prairie restorations. Results indicate that the prairie restorations evaluated in this study are still evolving and have not yet reached the rate of C sequestration observed in the native, undisturbed prairie ecosystem and that direct measurement of soil C storage changes over time should be used whenever possible.