Forest Strata and Abiotic Factors Primarily Regulate Understory Species Richness Rather than Forest Type in a Temperate Forest of South Korea

The understory vegetation forms an important ecosystem by providing habitat, cycling nutrients, and contributing to community diversity. However, previous studies have focused on identifying mechanisms between understory herbaceous diversity and abiotic factors. This study conducted a comprehensive analysis of the effects of abiotic factors (topography, climate, and soil) and biotic factors (species richness and individuals by forest strata), as well as stand age, on understory species richness. Also, we analyzed the effects of seven different forest types in the sampled plots. The most important factors were selected through a multimodel inference test and then applied to piecewise structural equation models on total, woody and herbaceous understory plants. In the total model, elevation-associated temperature had positive effects, respectively. In the woody model, overstory species richness has an indirect positive effect on woody understory plants through the midstory species richness. In the herbaceous model, total phosphorus and elevation-associated temperature had a positive effect on herbaceous understory plants. Therefore, this study indicates that woody species richness controlled by biotic factors and herbaceous species richness controlled by abiotic factors. Our study suggests that woody and herbaceous species richness are regulated by different mechanisms, highlighting the need for distinct management methodologies to enhance plant diversity in forest ecosystems.