Analysis of the difference and correlation between the spatial structure and understory herbaceous species diversity of typical subtropical forests

The spatial structure of a forest has a remarkable effect on the diversity of the understory herbaceous species. To clarify the dominant factors that affect the species diversity of understory herbaceous vegetation, a subtropical pure Chinese fir plantation, mixed Chinese fir plantation, and natural secondary forest were used. On the basis of the quantitative analysis of three kinds of stand spatial structure index and understory herbaceous species diversity index of different characteristics, the main spatial structure factors influencing the understory herbaceous species diversity were excavated using grey relational analysis. The results showed that: 1) In terms of the tree species isolation degree, forest layer diversity, competition situation, and forest spatial distribution pattern, the natural secondary forest was the best, followed by the mixed Chinese fir plantation and then the pure Chinese fir plantation. 2) In the five indexes of species richness (Simpson diversity, Shannon-Wiener diversity, Simpson evenness, and Pielou evenness), a regularity showed that natural secondary forest > mixed plantation > pure plantation. 3) The degree of mixing was the common key factor affecting the diversity of the understory herbaceous species in the pure Chinese fir plantation, mixed Chinese fir plantation, and natural secondary forest. Therefore, to improve the diversity of the understory herbaceous species in pure Chinese fir and mixed Chinese fir plantations, to some extent, it is acceptable to use artificial interference measures, such as regulating the tree species structure.