Forest management practices can increase the soil organic carbon sequestration potential of Robinia pseudoacacia plantations in the Loess Plateau

Forest management practices such as thinning and understory removal can directly or indirectly affect soil organic carbon (SOC) content in plantations. However, the effects of plantation management practices in semiarid regions are unclear. The following management practices were used in Robinia pseudoacacia plantations in the Loess Plateau: control treatment (CK), understory removal (UR), thinning, and thinning–understory removal (TUR). This study aimed to determine the effects of different management practices on SOC fractions and stability in plantations. After a 3-year period, we measured soil physicochemical properties and SOC fractions. The results showed that the thinning and understory removal did not significantly change SOC content but did change soil easily oxidized organic carbon (EOC) storage and non-oxidizable organic carbon (NOC) storage, and their proportions in aggregates. Thinning and TUR significantly (p < 0.05) increased EOC in macroaggregates and microaggregates and decreased EOC in silt–clay fractions compared to CK. Soil total nitrogen was the most important factor, explaining 56.9% of the variation in SOC fractions. Soil temperature explained most of the variation in SOC stability (61.6%). Different management practices have a major indirect impact on EOC storage, NOC storage, and the carbon pool management index by affecting soil temperature, soil total nitrogen, and soil water content. Understory removal increased the carbon pool management index without increasing the carbon lability index. As an effective forest management practice, understory removal can increase the potential for SOC sequestration in R. pseudoacacia plantations. Our findings can serve as a reference for the management of plantation forests in the Loess Plateau and for promoting high-quality development.