Effect of Stand Density on Understory Herb Diversity and Soil Properties in the Cornus officinalis Plantation at the Southern Foot of Funiu Mountain

Using the typical plot method, five plots were set up in each of the five stand densities (535, 715, 895, 1030 and 1250 plants·hm⁻²) at the southern foot of Funiu Mountain. The species and height of understory herb were investigated, soil physicochemical properties were measured, and differences in various indicators were tested under different densities. The results showed that the stand density had a significant impact on the composition and diversity of understory herb in the C. officinalis plantation. The dominant species rapidly transformed with the density increased. The dominant species at densities 535 and 715 plants·hm⁻² were Polygonum nepalense, while at densities 895, 1030 and 1250 plants·hm⁻² were Pilea japonica, Amphicarpaea edgeworthii, and Acalypha supera, respectively. The species similarity coefficient between different densities showed a decreasing trend with the density difference increased, with a maximum of 0.70 and a minimum of 0.47. The understory herb diversity showed a trend of first increasing and then decreasing with the increase of stand density, and reached the highest value in the density 715 plants·hm⁻². The total soil porosity, field capacity, saturated water content, organic matter, total nitrogen, alkali-hydrolyzable nitrogen, total phosphorus, available phosphorus, total potassium, and available potassium content showed a similar changing trend with the diversity of herbaceous plants according to the stand density, reaching the maximum value at the medium and low densities of 715 or 895 plants/hm. The comprehensive scoring results showed that the density of 715 plants/hm had the highest score, followed by the densities of 895, 535, 1030, and 1250 plants/hm. The study suggested that the stand density of 715 plants/hm was the optimal density for Cornus officinalis plantation, as it could better enhance the diversity of herbaceous plants under the forest and improve the soil physical and chemical properties.