The calculation of Simpson, Shannon-Weiner, and Pielou indices
The Simpson and Shannon-Weiner indices are both comprehensive indices of richness and evenness, but the Simpson index is more sensitive to species evenness, and the Shannon-Weiner index is more sensitive to species richness (Xu et al., 2011). These indices are usually used together to comprehensively evaluate species diversity (Heip et al., 1998). The Simpson index is calculated as
\(D=1-\sum_{i=1}^{s}{P_{i}}^{2}\) (1)
where S is the number of tree species and \(P_{i}\) is the proportion of the number of individuals of species i relative to the total number of individuals in the community. The Shannon-Weiner index is calculated as
\(H=-\sum_{i=1}^{s}{P_{i}\ln P_{i}}\) (2)
where the meaning of the above parameters is the same as that of formula (1). The Pielou index describes the evenness of the individual number distribution among species in an ecosystem and is calculated as
\(J=H/\text{lnS}\) (3)
where H is the Shannon-Weiner index and S is the number of species.