Recovery in soil carbon stock but reduction in carbon stabilization after 56-year forest restoration in degraded tropical lands

Abstract

Afforestation is considered as an effective method for alleviating the rising of atmospheric carbon dioxide (CO2) concentration through the accumulation and long-term storage of carbon (C) in the vegetation and soil. However, it is still unknown whether soil C accumulation in the restored forests could eventually recover to the equivalent level of the undisturbed forests and much less is known about how afforestation will affect C stabilization. Here we conducted a field study in degraded tropical forests of south China. The aim was to evaluate the recovery of soil C stock following afforestation by comparing different C fractions in soils (0–10 cm and 10–20 cm) in two reforested forests [a restored secondary forest (RSF) and a managed Eucalyptus plantation (MEP)] to those in a bare land (BL) and a nearby undisturbed forest (UF). Results showed that after 56-year afforestation at the bare lands, C stocks in both soil layers were significantly increased with an increase greater in the RSF than the MEP, while C recalcitrant indices (RI) were reduced. Soil C stock in the RSF recovered to a similar level to the UF, but soil RI in the RSF was still lower than the UF particularly in the 10–20 cm layer. The calculated capacity of soil C sequestration with the product of soil C stock and its RI followed the order of UF > RSF > MEP > BL. Our results demonstrate that afforestation on degraded tropical lands could recover soil C stock within a few decades, but C stabilization would be reduced.