Agroforestry systems play an important role in the sequestration of carbon (C) to reduce atmospheric carbon dioxide (CO₂) levels. However, the extent of long-term C sequestration will depend on physical stabilization of the sequestered C. This study determined the influence of six major shelterbelt species on soil organic carbon (SOC) distribution in the light- and heavy-density fractions of bulk soil compared with adjacent agricultural fields. Soil samples were collected from the shelterbelts and adjacent agricultural fields and were separated into light and heavy fractions using sodium iodide solution (NaI, density = 1.6 g cm^-3) and analyzed for their organic C stocks. Both the light and heavy fractions to a 50 cm soil depth contained higher SOC stocks for the shelterbelts (21 and 91 Mg C ha^-1, respectively) compared with the adjacent agricultural fields (14 and 81 Mg C ha^-1, respectively). Most SOC added at the 0–10 cm soil depth was in the form of labile light fraction (92%), whereas heavy fraction contributed to 70% of the increase in the SOC stocks at the 10–30 cm soil depth. Increase in light-fraction SOC stocks was higher for coniferous species compared with hardwood species, and accounted for 48%–50% and 28%–31% of the increase in SOC stocks for coniferous and hardwood shelterbelts, respectively. This trend was attributed to the differences in the amount and quality of litter between coniferous and hardwood species.