Absence of tree seeds impedes shrubland succession in southern China

Change in landuse in southern China has resulted in the abandonment of over 40 million ha of degraded grazing pasture and cultivated farmland, which have consequently converted to shrubland. Shrubland has low economic value and provides limited ecosystem services but is now the dominant vegetation in three provinces of southern China. Effective management of such shrubland ecosystem requires improved understanding of many ecological factors, including sources of viable seeds in the soil seed bank and the interaction between the seed bank and the current vegetation. We investigated the soil seed bank in a shrubland using a seedling germination assay, and compared the species composition in the seed bank with vegetation community using Sorensen’s coefficient. While total seed bank density in the shrubland was high, the Sorensen’s coefficient and species richness in the soil seed bank were low. The soil seed bank was mainly dominated by grass and shrub species; no pine or other indigenous tree seeds were detected. Our findings suggest that the limited seed source of tree species is one of the primary factors slowing or stopping secondary succession in southern China. Direct planting of tree seedlings may facilitate secondary succession in the severely degraded shrublands.