Effects of Wollastonia biflora expansion on the soil seed bank in native forest communities on a tropical coral island.
Invasive plants and native weeds (i.e., undesirable plant species) often have negative effects on native ecosystems. However, the effects of weed expansion on soil seed banks and seedling emergence in native forests have not been well investigated. In this study, we used a seedling emergence assay to assess the effects of expansion by a native weed, the perennial C4 herb Wollastonia biflora, on the soil seed bank and above-ground vegetation in forests on Yongxing Island, a coral island in the South China Sea. We found that W. biflora expansion was associated with a reduced abundance of native species in the soil seed bank, an increased in native species richness in the soil seed bank, and a reduced similarity between the seed bank and the above-ground vegetation. W. biflora seeds were more abundant in the surface soil layer than deeper soil layer, and the number of W. biflora seeds increases in the degree of W. biflora expansion. With W. biflora expansion, more species were lost due to growth competition than from seed bank. Overall, the seed bank had more species than the above-ground vegetation regardless of the degree of W. biflora expansion. Our findings indicate a high potential for unassisted reestablishment of a species-rich plant community from the seed bank following W. biflora removal. The regenerated community could be dominated by a few native tree species or by some invasive species that could prevent subsequent recolonization by native herbs and graminoids. Continued monitoring is required to determine whether and which native species may require assisted reintroduction.