Joint Influence of Forest Strata Attributes and Abiotic Factors on Herbaceous Plant Abundance in South Korean Forest Restoration Sites: Native Versus Alien Species

The success of ecosystem restoration is often evaluated by the stable establishment and growth of native plants while preventing the spread of alien plants. However, research on the factors and mechanisms controlling the abundance (richness and coverage) of native and alien plants remains limited. To address this, we analyzed data from 167 plots (100 m2) in forest restoration sites in South Korea. We assessed the effects of abiotic factors (topography, climate, and soil), biotic factors, and the number of years integrally since restoration on both plant groups by using a piecewise structural equation model. Native plant abundance was influenced by shrub density (species richness: β = 0.19; coverage: β = 0.20) and available phosphorus (β = 0.19), while alien plant abundance was controlled by soil pH (species richness: β = 0.45), elevation (β = −0.15), species richness, and tree (β = −0.15) and shrub species richness (β = −0.16). The number of years since restoration has indirectly affected native and alien plants through shrub species richness and shrub coverage. Our results indicate that high resource availability, such as light, in the early stages of restoration may allow native and alien herbaceous plants to coexist. However, as vegetation and forest strata develop, reduced light availability can lead to a decline in alien species and the dominance of native plants. We also provide management strategies to suppress alien plants by promoting structural complexity within forest stands.