Characteristics of Typical Forest Vegetation and Their Relationship with Soil in Qianjiangyuan-Baishanzu National Park

To explore the vegetation characteristics of different forest communities and their relationships with soil, the typical plot method was used to study the species diversity and soil physical-chemical properties of three forest communities （evergreen broad-leaved forest, coniferous-broadleaved mixed forest, and coniferous forest） in Qianjiangyuan-Baishanzu National Park, with each plot area of 1200 m² per community type. The results showed that the tree layers（with DBH ≥ 5 cm）of the above forests had 28, 27, and 13 plant species, respectively; the shrub layers （including regenerating tree seedlings） had 41, 60, and 37 plant species, respectively; and the herb layers had 7, 6, and 7 plant species, respectively. For the tree layer, the species richness index, Simpson dominance index, Shannon index, and Pielou evenness index all followed the order: evergreen broad-leaved forest > coniferous-broadleaved mixed forest > coniferous forest, with the indexes of coniferous forest being significantly lower than those of the other two forest types (P < 0.05). In the shrub layer of the coniferous-broadleaved mixed forest, the indexes of four types were significantly higher than those of the evergreen broad-leaved forest and the coniferous forest (P < 0.05). DBH distribution of the tree layer in all three forest types exhibited a “Inverted-J” shape, while tree height showed a positively skewed distribution. Soil pH in the evergreen broad-leaved forest was significantly higher than those in the coniferous–broadleaved mixed forest and the coniferous forest (P < 0.05). Soil organic carbon content showed a distinct gradient, that in coniferous-broadleaved mixed forest was the highest, followed by evergreen broad-leaved forests, and then coniferous forests, with significant differences among the three types (P < 0.05). For the tree layer, the Simpson index, Shannon index, and Pielou evenness index were significantly negatively correlated with soil bulk density (P < 0.05), significantly positively correlated with total soil porosity (P < 0.05), and the Pielou evenness index was significantly positively correlated with the maximum soil water-holding capacity (P < 0.05). For the shrub layer, species richness and Shannon index were significantly positively correlated with soil organic carbon content (P < 0.05). In summary, the tree and shrub layers in the coniferous forest had relatively few plant species. Moderate thinning of the coniferous forest to reduce canopy density is recommended, which would facilitate the natural recruitment, establishment, and growth of other native tree species, thereby increasing plant diversity.