Greater Species Diversity on Rocks than Soil in a Karst Old-Growth Forest

Rocks and soil are two important substrates within the karst forest ecosystem, playing a crucial role in plant growth, ecosystem services, and environmental sustainability. However, the relationship between these substrates and species diversity remains unclear. In this study, a fixed plot of 22,000 m 2 was established in an old-growth forest in Karst National Park, Southwest China, to quantify species composition and diversity [abundance (N), richness (R), Shannon-Wiener index (H'), and Pielou evenness index (E H )] on both rocks and soil. A total of 4,596 living plants, representing 62 species, were investigated and identified. The ratio of trees to shrubs was approximately 3:1, and the community similarity coefficient between the two substrates was K j = 0.66. The average species diversity of trees on rocks was significantly higher than that on soil, while the abundance of shrubs on soil was greater than that on rocks, indicating clear habitat preferences for different species. At the subplot level, differences in species diversity between the two substrates were smaller for species of the same life form, but the disparity in H' and E H between trees and shrubs on rock increased. The Moran's I index ranged from 0.038 to 0.083, suggesting that habitat heterogeneity is widespread and particularly pronounced in local areas. These results emphasize the complexity of the relationship between karst habitats and species. Rocks support higher species diversity, which can guide the setting of conservation targets and species selection for the restoration of fragile habitats and degraded vegetation. • Rocks and soil are two important substrates within karst forest ecosystem. • Subtropical karst old-growth forests have a rich species composition. • Rocks support higher species diversity than soil. • Karst species show significant habitat preferences. • A weak spatial autocorrelation of species diversity occurs in karst forests.