Changes in Forest Soil Carbon and Nitrogen after a Thirty‐Year Interval

Abstract

Increases in atmospheric C have resulted in concerns about global warming and interest in finding the means to sequester atmospheric C through land management strategies. The purposes of this study were to: (i) compare changes in mineral soil C after a 30‐yr interval, and (ii) examine the potential roles of soil N, soil texture, and topography in these changes. The Camp Branch watershed is a second‐growth, oak‐dominated, mixed hardwood forest on the Cumberland Plateau in central Tennessee. In July 1976, soil samples were collected at permanently identified points and archived. These points were resampled in July 2006 and both the archived and new samples of the 0‐ to 10‐cm increment of the mineral soil were analyzed for C and N. Comparisons revealed that the changes in C and N were distinct to each of the eight soil series occurring on the site. Comparison of 2006 samples to 1976 samples indicated that changes in C concentration ranged from −13.1 to 12.0%. Changes in C mass ranged from −11.3 to 8.3%. Increases in C were most closely associated with increases in the C/total N ratio. The change in C was positively correlated with the change in exchangeable inorganic N ( r 2 = 0.31, P < 0.0001). An overstory inventory indicated a decline in oak domination and site‐specific changes in basal area, density, and stand age. Since regression analysis revealed that the change in C was not predicted by topographic factors or soil texture, we speculate that changes in forest cover influenced the changes in mineral soil C.