Soil Carbon Changes After 26 Years in a Cumberland Plateau Hardwood Forest

Concerns about global warming and discussions of possible mitigation measures have generated a need for information on changes in soil C over time. The objective of this study was to determine if there was a change in soil C concentration in an aggrading oak forest over a 26‐yr interval. Using permanently identified points on the Camp Branch Experimental Watershed, soil samples were first collected in July of 1976 and archived. During July of 2002, 11 points covering 6 of the 18 soil series present on the watershed were resampled. The series chosen represent a range in topographic positions and forest cover types. In both 1976 and 2002, a bucket auger was used to collect samples at depth intervals of 0 to 10, 10 to 30, and 30 to 50 cm. Both sample sets were analyzed in 2002 using a loss on combustion technique to determine organic C concentration. A bootstrapping data analysis indicated an increase (95% confidence interval) in the concentration of C in the 0‐ to 10‐cm depth. No change in C concentration occurred in the 10‐ to 30‐ or 30‐ to 50‐cm samples. Average soil C concentration in the 0‐ to 10‐cm samples increased from a mean of 20.8 g kg −1 in 1976 to 35.9 g kg −1 in 2002. Among soil series, concentrations ranged from 9.5 to 28.9 g kg −1 in 1976 and 22.1 to 64.7 g kg −1 in 2002. Although the sample numbers are limited, results indicate that average soil C concentration in the top 10 cm of the mineral soil increased by 73% at this site over a 26‐yr interval.