Understory Floristic Diversity in Poplar Plantations in the Dongting Lake Wetlands, China

Large-scale poplar plantations have evoked great concern over their adverse effects on floristic diversity in understory vegetation. The aim of this study was to investigate the effects of tree density on the composition of understory vegetation in poplar (Populus deltoides) plantations in the Dongting Lake wetlands, China. Stand characteristics and soil properties had significant effects on understory plant distribution. Stand density was positively correlated with number of species, Shannon diversity index, and proportions of mesophytes and partial-shade plants but was negatively correlated with the proportions of hygrophytes and heliophytes. Understory light availability was negatively correlated with number of species, Shannon diversity index, and the proportions of mesophytes and partial-shade plants and was positively correlated with the proportions of hygrophytes and heliophytes. Soil water content was negatively correlated with species richness and the proportion of mesophytes and was positively correlated with the proportions of hygrophytes and heliophytes. Compared to low-density stands, high-density stands had a higher number of species and higher proportion of annual/biennial plants, mesophytes, and xerophytes and had lower proportions of perennial plants and hygrophytes during the one-year monitoring period. Therefore, poplar plantations should be managed at lower densities in the Dongting Lake wetlands to conserve the understory flora.