Results/Conclusions: Thinning treatments significantly (Tukey’s HSD, P < 0.1) reduced total soil C (Mg ha-1) and N (kg ha-1) compared to no treatment by 31% and 32%, respectively. Most of this loss (65% and 73%, respectively) occurred in the subsoil (below 20 cm in depth). Potential mechanisms that may explain lower soil C and N stocks due to thinning treatments, as well as differential changes in surface soil compared to deeper soil C and N, include: (1) reduced root density with thinning (fewer total trees) decreasing root turnover and root exudates; (2) reduced competition for water and nutrients with thinning allowing trees to allocate less gross productivity to underground growth; and (3) increased surface soil moisture and temperature with thinning increasing soil organic C decomposition rates. Fertilization treatments tended to reduce soil pH throughout the entire soil profile compared to both thinning treatments and no treatment, indicating the potential for nitrate leaching. Across all management regimes, the subsoil contained over 50% of total soil C and N. This study shows: (1) over a relatively short period (< 30 years), thinning treatments significantly reduced soil C and N stocks; and (2) accurately assessing soil C and N stocks requires sampling deep soil.